Title:
METHOD FOR MAKING HIGH STRENGTH ALUMINUM ALLOY SHEET AND PRODUCTS MADE BY SAME
Kind Code:
A1


Abstract:
Disclosed is a method for producing a non-heat-treatable high strength aluminum sheet from aluminum scraps using a continuous caster. The method includes providing a molten aluminum non-heat-treatable alloy including Si about 0.7% max., Fe about 0.8% max., Cu about 0.3% max., Mn about 0.5-1.2%, Mg about 1.3-2.8%, Zn about 0.20% max., Cr about 0.2% max., Zr about 0.30% max., Sr about 0.30 max., the remainder aluminum, incidental elements and impurities; and continuously casting the molten aluminum alloy into a slab and rolling the slab into a sheet product with high strength and reasonable formability. Typically, the sheet product is used for the products, such as truck trailer siding panel or electrical conduits for the building industry.



Inventors:
Platek, Paul (Massillon, OH, US)
Keller, Christopher (Coshocton, OH, US)
Ding, Shixi (Canton, OH, US)
Thompson, David O. (Dennison, OH, US)
Li, Zhong (Lexington, KY, US)
Application Number:
11/960928
Publication Date:
06/25/2009
Filing Date:
12/20/2007
Assignee:
Commonwealth Industries, Inc. (Beachwood, OH, US)
Primary Class:
International Classes:
C22F1/047
View Patent Images:



Primary Examiner:
LEE, REBECCA Y
Attorney, Agent or Firm:
Vorys, Sater, Seymour and Pease LLP (Washington, DC, US)
Claims:
What is claimed is:

1. A method for making an aluminum sheet product of non-heat-treatable alloy comprising the steps of: providing a molten non-heat-treatable aluminum alloy comprising: Si about 0.7% max., Fe about 0.8% max., Cu about 0.3% max., Mn about 0.5-1.2%, Mg about 1.3-2.8%, Zn about 0.20% max., Cr about 0.20% max., Zr about 0.30% max., Sr about 0.30% max., the remainder aluminum, incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total; continuously casting the alloy in a continuous caster into a slab having a thickness of about 0.1 to 2 inches; rolling the slab to form the aluminum sheet product of non-heat-treatable alloy, wherein the rolling comprises hot rolling; wherein the aluminum sheet product has a yield strength of about 20 to 45 and an ultimate tensile strength of about 30 to 60 ksi, and elongation of about 4 to 16% and wherein the product is made in the absence of solution heat treatment.

2. The method of claim 1, wherein the hot rolling starts in a temperature range of about 700° to 1050° F. and ends in a temperature of about 350° to 700° F. and reduces the thickness of the slab about 60 to 98% of the original thickness of the slab.

3. The method of claim 1, wherein the total YTS increase from slab condition to the exit of the hot rolling is in the range of about 165% to 435%.

4. The method of claim 1, wherein hot rolling occurs in a three stand hot rolling mill wherein the yield tensile strength (YTS) increase after the first rolling stand should be in the range of about 70 to 110%, the YTS increase after the second rolling stand should be about 30 to 70% greater than the strength from the first rolling stand and the YTS increase after third hot rolling stand should be about 20 to 50% greater than the strength from the second rolling stand.

5. The method of claim 1, wherein the method forms the aluminum sheet product in the absence of annealing.

6. The method of claim 1, wherein the cold rolling provides about a 20 to 90% gauge reduction.

7. The method of claim 1, wherein the hot rolled sheet is annealed in a temperature range of about 600° to 1100° F. prior to cold rolling.

8. The method of claim 1, wherein the cold rolled sheet is annealed in a temperature range of about 300° F. to 750° F.

9. The method of claim 1, wherein the hot rolled sheet is annealed in a first annealing step to form an annealed sheet, the annealed sheet of the first annealing step is cold rolled, and the cold rolled sheet is annealed in a second annealing step to form the aluminum sheet product.

10. The method of claim 1, wherein the high strength sheet product is strain hardened to an H1x temper.

11. The method of claim 1, wherein the high strength sheet product is strain hardened and partial annealed to H2x or stabilized to H3x tempers.

12. The method of claim 1, wherein the sheet product has a yield strength >about 36 ksi and ultimate strength >about 40 ksi.

13. The method of claim 1, wherein the sheet product has a yield strength of >about 38 ksi, ultimate strength >about 42 ksi.

14. The method of claim 1, wherein the aluminum sheet product has a thickness of about 0.01 to 0.08 inches, UTS about 30-45 ksi, and YTS about 25-40 ksi %.

15. The method of claim 1, wherein the continuous caster is a belt caster or a block caster.

16. The method of claim 1, wherein the hot rolled sheet product is cold rolled to a thickness in the range of about 0.01 inch to 0.1 inch.

17. The method of claim 1, further comprising forming the aluminum sheet product into a truck trailer panel having a thickness of about 0.01 to 0.19 inches, yield strength >about 36 ksi, and ultimate strength >about 40 ksi and elongation of 4 to 10%.

18. The method of claim 1, further comprising forming the aluminum sheet product into a truck trailer panel having a thickness of about 0.01 to 0.19 inches, yield strength >about 38 ksi, and ultimate strength >about 42 ksi and elongation of 4 to 10%.

19. The method of claim 1, further comprising forming the aluminum sheet product into an electrical conduit having a thickness of about 0.01 to 0.08 inches, having UTS about 30-45 ksi, and YTS about 25-40 ksi and elongation of 6 to 16%.

20. The method of claim 1, wherein, the alloy has the following composition: Si about 0.25-0.7%, Fe about 0.35-0.8%, Cu about 0.05-0.28%, Mn about 0.5-1.0%, Mg about 1.3-2.5%, Zn about 0.20% max., Cr about 0.20% max., Zr about 0.25% max., Sr about 0.25% max., the remainder aluminum, incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total.

21. A method for making an aluminum sheet product of non-heat-treatable alloy comprising the steps of: providing a molten aluminum alloy comprising: Si about 0.7% max., Fe about 0.8% max., Cu about 0.3% max., Mn about 0.5-1.2%, Mg about 1.3-2.8%, Zn about 0.20% max., Cr about 0.20% max., Zr about 0.30% max., Sr about 0.30% max., the remainder aluminum, incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total; continuously casting the alloy in a continuous caster into a slab having a thickness of about 0.1 to 1 inch, cold rolling the continuously cast slab to form the aluminum sheet product, wherein the method has an absence of hot rolling; wherein the aluminum sheet product has a yield strength of about 20 to 45 ksi, an ultimate tensile strength of about 30 to 60 ksi, and elongation of 4 to 16%.

22. The method of claim 21, wherein the continuous caster is a roll caster or belt caster.

23. The method of claim 21, wherein the cold rolling provides about a 60 to 98% gauge reduction.

24. The method of claim 21, wherein, the alloy has the following composition: Si about 0.25-0.7%, Fe about 0.35-0.8%, Cu about 0.05-0.28%, Mn about 0.5-1.0%, Mg about 1.3-2.5%, Zn about 0.15% max., Cr about 0.15% max., Zr about 0.25% max., Sr about 0.25% max. the remainder aluminum, incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total.

25. A truck trailer siding made from a non-heat-treatable aluminum alloy sheet in an H temper comprising: Si about 0.7% max., Fe about 0.8% max., Cu about 0.3% max., Mn about 0.5-1.2%, Mg about 1.3-2.8%, Zn about 0.20% max., Cr about 0.20% max., Zr about 0.30% max., Sr about 0.30% max., the remainder aluminum, incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total; having a thickness of about 0.01 to 0.19 inches, a yield strength >about 36 ksi, ultimate strength >40 ksi and elongation about 4 to 10% as measured.

26. An electrical conduit made from a non-heat-treatable aluminum alloy sheet in an H temper comprising: Si about 0.7% max., Fe about 0.8% max., Cu about 0.3% max., Mn about 0.5-1.2%, Mg about 1.3-2.8%, Zn about 0.20% max., Cr about 0.20% max., Zr about 0.30% max., Sr about 0.30% max., the remainder aluminum, incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total; having a thickness of about 0.01 to 0.07 inches, ultimate strength at least about 30 ksi and elongation about 6 to 16%.

Description:

FIELD OF THE INVENTION

The present invention provides a method to use continuous casting to make flat rolled aluminum sheet for vehicular components, for example, truck trailer siding, or for other uses, such as building and electrical products, where the combination of high strength and formability are required. The invention also simplifies processing steps for making high strength sheets. Further, the invention provides a non-heat-treatable aluminum alloy utilizing most types of non-heat-treatable and some types of heat-treatable wrought aluminum scraps as charge materials.

BACKGROUND OF THE INVENTION

As will be appreciated herein below, except as otherwise indicated, alloy designations and temper designations refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records, as published by the Aluminum Association in 2007.

For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated.

It is well known that for a non-heat-treatable aluminum alloy, as the strength increases, the formability of the aluminum alloy decreases. For certain applications, it is very important to have a good combination of strength and formability to meet the product requirements. For example, the most popular aluminum alloy used for truck trailer siding is AA 3004, H291 temper. The mechanical property requirements for the currently used AA 3004 after painting are: yield strength >34 ksi, ultimate strength >38 ksi and elongation >4%. To meet the toughness requirement, the material needs to have high strength with reasonable elongation.

In other uses for aluminum sheet, such as flexible aluminum conduits for electrical conductors, both higher strength and higher formability are required to meet the product requirements. There is also a desire to continually reduce the thickness of the aluminum sheet to lower the final product material cost.

In many instances, continuous casting (CC) of molten aluminum into slab utilizing twin belt, block or twin roll casters is favored over DC (direct chill) casting because continuous casting can result in substantial energy savings and total conversion cost savings compared to the DC cast method. In the continuous casting process, molten metal is continuously introduced to an advancing mold and a slab or strip is produced which may be continuously formed into a sheet product which is collected or wound into a coil.

However, continuous casting has unique processing constraints. For example, the alloy composition and the processing steps must be carefully controlled to have the formability level to avoid cracking during forming and yet have the requisite strength properties in the final product. That is, the alloy derived from scrap and the processing thereof must be carefully controlled to provide sheet having the formability suited to the fabricating steps necessary to form the final product or part. If the alloy and processing steps are not controlled, then in the forming steps, fracture can occur and the formed parts have to be scrapped.

There are many uses where it would be desirable to down-gauge to reduce material costs; for example, products in the building and construction, consumer durable, electrical and transportation markets, etc. However, the ability to do this is limited by the combination of strength and formability of the sheets, which are manufactured using aluminum scraps and continuous cast technology, from which these products are made.

U.S. Pat. No. 4,411,707 to Brennecke et al., incorporated herein by reference, discloses an aluminum container scrap alloy that is processed by a modified chill roll cast process into a highly formable sheet material suitable for use as a container end stock, by employing at least a 60% cold reduction followed by an anneal for about two hours at a temperature of from about 825° F. to about 900° F., followed by cold reduction to final gauge.

U.S. Pat. No. 5,976,279 to Selepack et al., incorporated herein by reference, discloses a process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the steps of continuously annealing the cold rolled strip in an intermediate anneal using an induction heater and/or continuously annealing the hot rolled strip in an induction heater. The alloy composition has mechanical properties that can be varied selectively by varying the time and temperature of a stabilizing anneal.

U.S. Pat. No. 5,985,058 to Selepack et al., incorporated herein by reference, discloses a process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the step of heating the cast strip before, during or after hot rolling to a temperature in excess of the output temperature of the cast strip from the chill blocks.

U.S. Pat. No. 5,993,573 to Selepack et al., incorporated herein by reference, discloses a process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the steps of

(a) heating the cast strip before, during or after hot rolling to a temperature in excess of the output temperature of the cast strip from the chill blocks and
(b) stabilization or back annealing in an induction heater of cold rolled strip produced from the cast strip.

U.S. Pat. No. 6,193,818 to Legresy et al., incorporated herein by reference, discloses a process for forming an aluminum alloy strip, including the steps of a) obtaining an aluminum alloy consisting essentially of, by weight, 0.5 to 13% Si, 0 to 2% Mg, 0 to 2% Cu, 0 to 1% Mn, 0 to 2% Fe, other elements less than 0.5% each and less than 2% total, and remainder Al; and b) continuously casting the aluminum alloy between twin cooled rolls having a force applied thereto, to obtain a cast strip of thickness between 1.5 and 5 mm, and optionally cold rolling the cast strip.

U.S. Pat. No. 6,264,765 to Bryant et al., incorporated herein by reference, discloses a method and apparatus for casting, hot rolling and annealing non-heat treatment aluminum alloys. The method and apparatus comprises continuous casting, hot rolling and in-line inductively heating the aluminum sheet to obtain the mechanical properties within the specification tolerance of the hot rolled product.

U.S. Pat. No. 6,280,543 to Zonker et al., incorporated herein by reference, discloses continuous casting of flat rolled sheets selected from automotive sheet, can body sheet, and endstock which exhibits properties comparable to the same products made from World Class Ingot. A preferable embodiment for the continuous caster is a vertical continuous caster.

U.S. Pat. Nos. 5,772,802 and 6,045,632 describes producing solution heat treated sheets. These patents describe a process for producing a solution heat treated sheet which requires the aluminum alloy to be cast and run through a hot mill. During hot milling, the strip or sheet is cooled by a combination of water sprays and thermal transfer to the hot rolls, but the temperature is maintained above the solvus temperature. Once the cast alloy exits the hot mill as a sheet, the sheet is quenched to below the solvus temperature and cold rolled into a coil. Following the cold roll, the sheet is annealed at or reheated to a high temperature to accomplish the solution heat treatment of the sheet. The solution heat treated sheet is then quenched again and cold rolled to its final gauge and aged before use in its final application.

US Patent Application Publication No. 2004/0011438 to Lorentzen et al., incorporated herein by reference, discloses a method and apparatus for making a solution heat-treated sheet. The method comprises continuously casting an aluminum alloy to produce a cast strip. Once the cast strip is formed, it is hot rolled and quenched during hot rolling to form the solution heat treated sheet. The process of Patent Application Publication No. 2004/0011438 to Lorentzen et al. operates on heat-treatable alloys.

In contrast to the alloys operated on by the process of Patent Application Publication No. 2004/0011438 to Lorentzen et al., a large number of other wrought compositions rely instead on work hardening through mechanical reduction, typically in combination with various annealing procedures for property development. As explained in the ASM Specialty Handbook, Aluminum and Aluminum Alloys, ASM International, page 5 (1993), these alloys are referred to as non-heat-treatable or work-hardening alloys. Non-heat-treatable aluminum alloys are hardenable by cold working, but not by heat treatment. Strengthening can be created by cold working-deformation which induces strain-hardening denoted by the H-tempers. For example, AA 1xxx, 3xxx and 5xxx aluminum alloys are non-heat-treatable.

There is a need for the development of an improved aluminum alloy and thermal mechanical processing utilizing a continuous caster to meet the demands of improved material performance and to lower the product cost; particularly from non-heat-treatable alloys.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved, low cost method utilizing continuous casting, followed by rolling, to produce a high strength sheet product with sufficient formability.

It is another object of the invention to provide a method including continuously casting a slab from a melt derived from aluminum scrap and rolling the slab into a high strength sheet product with sufficient formability.

It is yet another object of the invention to provide a high strength sheet product, suitable for being formed into final products.

These and other objects and further advantages may be met or exceeded by the present invention.

The present invention provides a method for making an aluminum sheet product of non-heat-treatable alloy comprising the steps of:

providing a molten aluminum alloy comprising:

    • Si about 0.7% max., preferably about 0.25-0.7%, more preferably about 0.3-0.7%,
    • Fe about 0.8% max., preferably about 0.35-0.8%, more preferably about 0.4-0.8%,
    • Cu about 0.3% max., preferably about 0.05-0.28%,
    • Mn about 0.5-1.2%, preferably about 0.5-1.0%, more preferably about 0.5-0.8%,
    • Mg about 1.3-2.8%, preferably about 1.3-2.5%, more preferably about 1.4-1.8%,
    • Zn about 0.20% max., preferably about 0.15% max.,
    • Cr about 0.20% max., preferably about 0.15% max.,
    • Zr about 0.30% max. preferably about 0.2% max.,
    • Sr about 0.30% Max, preferably about 0.2% max.

the remainder aluminum, incidental elements and impurities (the incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total);

continuously casting the alloy in a continuous caster into a slab having a thickness of about 0.1 to 2 inches, typically about 0.2 to 1.5 inches or about 0.2 to 1 inch;

rolling the slab to form the aluminum sheet product, wherein the rolling comprises hot rolling;

wherein the aluminum sheet product has a yield strength of about 20 to 45 ksi and an ultimate tensile strength of about 30 to 60 ksi, or about 30 to 55 ksi and elongation of about 4 to 16% as measured according to ASTM E 8-04, year 2004, and wherein the product is made in the absence of solution heat treatment, quenching and aging.

In continuous casting, molten metal is continuously introduced to an advancing mold and a slab is produced which may be continuously formed into a sheet product which is collected or wound into a coil. In many instances, continuous casting of molten aluminum into slab utilizes twin belt, twin roll or block casters. Typically a HAZELETT twin belt caster may be employed in embodiments having hot rolling after casting before cold rolling.

The rolling step may be accomplished by a number of embodiments.

For example, the rolling step may comprise hot rolling the slab into a hot rolled sheet and cold rolling the hot rolled sheet, to form the aluminum sheet product. If desired, the sheet may be annealed before and/or after cold rolling.

In another embodiment the rolling step may comprise hot rolling the slab and, optionally back annealing the hot rolled sheet, to directly form aluminum sheet product without cold rolling.

In the embodiments for the production of high strength aluminum sheet employing hot rolling, the control of the thickness reduction and the amount of strain hardening of the aluminum sheet through each stand of the hot rolling mill is important in achieving the required hot rolled temper. The total yield tensile strength (YTS) increase from slab condition to the exit of the hot mill, independent of the number of the rolling stands, is in the range of 165% to 435%. The preferred strain hardening, for instance, in a three stand hot rolling mills is listed as follows; the yield tensile strength (YTS) increase after the first rolling stand should be in the range of 70 to 110% with a gauge reduction in the range of 50 to 75%, the YTS increase after the second rolling stand should be 30 to 70% greater than the strength from the first rolling stand with a gauge reduction of 40 to 70% and the YTS increase after third hot rolling stand should be 20 to 50% greater than the strength from the second rolling stand with a gauge reduction in the range of 30 to 65%.

The temperature in each mill will have an influence on strength. The strength range can be achieved with the stated temperature range later in this patent.

The present invention avoids solution heat treating. The method controls the reduction and the amount of strain hardening of the aluminum sheet through each mill stand to achieve the desired hot band temper.

In another embodiment, the present invention provides a method comprising cold rolling a continuously cast strip without hot rolling. This method for making an aluminum sheet product of non-heat-treatable alloy comprises the steps of:

providing a molten aluminum alloy comprising:

    • about Si 0.7% max., preferably about 0.25-0.7%, more preferably about 0.3-0.7%,
    • about Fe 0.8% max., preferably about 0.35-0.8%, more preferably about 0.4-0.8%,
    • about Cu 0.3% max., preferably about 0.05-0.28%,
    • about Mn 0.5-1.2%, preferably about 0.5-1.0%, more preferably about 0.5-0.8%,
    • about Mg 1.3-2.8%, preferably about 1.3-2.5%, more preferably about 1.4-1.8%,
    • about Zn 0.20% max., preferably about 0.15% max.,
    • about Cr 0.20% max., preferably, about 0.15% max.,
    • about Zr 0.30% max. preferably about 0.2% max,
    • about Sr 0.30% max., preferably about 0.2% max.

the remainder aluminum, incidental elements and impurities (the incidental elements and impurities present, if any, in amounts of 0.05 wt. % max. each, 0.15 wt. % max. total);

continuously casting the alloy in a continuous caster into a strip having a thickness of about 0.1 to 1.0 inch, typically about 0.15 to 0.8 inches or about 0.15 to 0.6 inch;

cold rolling the continuously cast slab to form the aluminum sheet product, wherein the method has an absence of hot rolling;

wherein the aluminum sheet product has a yield strength of about 20 to 45 ksi, an ultimate tensile strength of about 30 to 60 ksi, or about 30 to 55 ksi as, and elongation of about 4 to about 16%. Yield strength, ultimate tensile strength and elongation are measured according to ASTM E 8-04 (2004).

Typically a twin roll caster may be employed in embodiments which do not have hot rolling after casting. If desired, the sheet may be annealed before and/or after cold rolling.

Thus, for example, processing the slab to form the sheet product may be according to any of the following embodiments:

    • 1. hot rolling the slab to form a hot rolled sheet, annealing the hot rolled sheet, cold rolling the annealed sheet, and annealing the cold rolled sheet to form the product sheet (cold rolling and annealing may be performed one or more times, depending on the capability of the equipment);
    • 2. hot rolling the slab to form a hot rolled sheet, annealing the hot rolled sheet, and cold rolling the annealed sheet to form the product sheet;
    • 3. hot rolling the slab to form a hot rolled sheet, cold rolling the hot rolled sheet to form a cold rolled sheet, and annealing the cold rolled sheet to form the product sheet (cold rolling and annealing may be performed one or more times, depending on the capability of the equipment);
    • 4. hot rolling the slab to form a hot rolled sheet and cold rolling the hot rolled sheet to form the product sheet;
    • 5. hot rolling the slab to directly form the product sheet;
    • 6. hot rolling the slab to a hot rolled sheet and annealing the hot rolled sheet to form the product sheet;
    • 7. cold rolling the cast strip to directly form the product sheet with optional annealing before cold rolling; or
    • 8. cold rolling the cast strip to a cold rolled sheet and annealing the cold rolled sheet to form the product sheet (cold rolling and annealing may be performed one or more times, depending on the capability of the equipment) with optional annealing before cold rolling.

The present invention manufactures a rolled aluminum alloy sheet of non-heat-treatable alloy comprising:

    • about Si 0.7% max., preferably about 0.25-0.7%, more preferably about 0.3-0.7%,
    • Fe about 0.8% max., preferably about 0.35-0.8%, more preferably about 0.4-0.8%,
    • Cu about 0.3% max., preferably about 0.05-0.28%,
    • Mn about 0.5-1.2%, preferably about 0.5-1.0%, more preferably about 0.5-0.8%,
    • Mg about 1.3-2.8%, preferably about 1.3-2.5%, more preferably about 1.4-1.8%,
    • Zn about 0.20% max., preferably about 0.15% max.,
    • Cr about 0.20% max., preferably about 0.15% max.,
    • Zr about 0.30% max., preferably about 0.20% max.,
    • Sr about 0.30% max., preferably about 0.2% max.;

the remainder aluminum, incidental elements and impurities (the incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total);

wherein the aluminum sheet product has a yield strength of about 20 to 45 ksi and an ultimate tensile strength of about 30 to 60 ksi, or about 30 to 55 ksi and an elongation of about 4 to 16% as measured according to ASTM E 8-04, wherein the sheet is about 0.01 to 0.19 inches thick.

The present method is sufficiently flexible that it can process almost all post consumer and manufacturing aluminum scraps, including but not limited to building and construction scraps, used beverage cans, food containers, truck trailer siding and auto scraps.

Thus, the process for making the high strength sheet product tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be strain hardened to H1x, or annealed to H2x or stabilized to H3x temper.

The high strength sheet product of the present invention may be formed into a variety of high strength products.

A typical product made from the sheet product of the present invention is truck trailer body panel (siding). AA 3004 alloy is currently used for the majority of aluminum truck trailer siding. As mentioned previously, the mechanical property requirements for the currently used AA 3004 after painting and curing of the paint are: yield strength >about 34 ksi, ultimate tensile strength >about 38 ksi and elongation of about 4 to 10%. However, it would be desirable to produce thinner sheets to down gauge to further reduce weight and cost of truck trailers while still meeting mechanical property requirements for truck trailer siding. But this means the alloy must be stronger than currently used AA 3004. To meet the toughness requirement, the material needs to have proportionally higher strength with equivalent elongation. However, it is impossible to use AA 3004 to make sufficiently strong material to produce these thinner sheets with sufficient mechanical properties. For the currently used gauge, AA 3004 is suitable, but for the desired reduced gauge products of the present invention AA 3004 is not strong enough.

The alloy of the product sheet is selected such that it is non-heat-treatable alloy and, when used for truck trailer siding, after painting and paint curing it will have a yield strength of >about 36 ksi (248 MPa) (this is 5 to 10% higher than AA3004 sheet), ultimate tensile strength >about 40 ksi (276 MPa), and elongation about 4 to 10% as measured by ASTM E 8-04. Thus, to support the same load, at least about 5 to 10% thickness reduction (or 5 to 10% weight reduction) can be made by using the proposed alloy when compared to the commercially used AA3004 alloy. Typical truck trailer siding panels have a thickness of about 0.03 to 0.06 inches. (0.76 to 1.5 mm), depending on the trailer design and application.

To use an alloy of the above composition derived from aluminum scrap in the process of the invention to form truck trailer panels having the requisite strength and formability properties requires careful control and selection of the elements in the alloy and the processing steps. The present process achieves the difficult task of balancing the constituents in the alloy and processing steps to form a sheet product having desirable strength properties while avoiding undesirable properties which lead to fracture or cracking, for example, during the manufacturing process or during service.

Another typical product which can be made from sheets of the present invention is electrical conduits, in particular flexible metal conduits for the building industry. Such electrical conduits typically meet Standard UL 1569 (current revision through and including May 25, 2005) of the Underwriter's Laboratory. Typical electrical conduits have a thickness of about 0.01 to 0.08 inches (0.25-2.0 mm). Typical electrical conduit properties range as follows: UTS about 30-45 ksi, YTS about 25-40 ksi and % elongation about 6-16%. The mechanical property ranges may vary for specific applications. For example, metal clad cable requires UTS of about 40 to 44 ksi with elongation of about 6 to 10%. Conversely, flexible conduit applications permit UTS as low as about 30 ksi, e.g., about 30 to 38 ksi, with elongations of about 10 to 16%. The current invention can satisfy these requirements.

For some other applications, an equivalent strength but high elongation may be needed to facilitate the forming process.

It is important to have alloying elements and impurities in the controlled amounts as herein described. The alloy is typically designed to use the maximum amount of scrap aluminum alloy without significantly affecting the microstructure and mechanical properties.

All ranges provided herein are meant to include all the numbers within the range as if specifically set forth, e.g., 1 to 5 would include 1.1, 1.2, 1.3, etc., or e.g., 2, 3, 4.

The term “aluminum” when used herein is meant to include aluminum and its alloys. The term “strength” means the maximum stress a material can sustain. In tension testing, the ratio of maximum load to original cross-sectional area is known as ultimate tensile strength. The stress at an offset of 0.2% of gauge length is known as tensile yield strength for aluminum. The term “formability” when used herein is used to describe the ease with which a sheet of metal can be shaped through plastic deformation. In particular, formability of a material is the extent to which it can be deformed in a particular process before the onset of failure. Formability of a metal can be evaluated by measuring strength, ductility, and the amount of deformation to cause failure. In the present description, the term “hot rolling” means any process to reduce the thickness of the strip at a temperature above about 350° F. (177° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing method steps of various embodiments of the present invention.

FIG. 2 is a flow diagram of a first embodiment of the present invention comprising a continuous caster, hot rolling mill, post hot rolling annealer, cold rolling mill, post cold rolling annealer and rolls (coils) of sheet material for performing the method of the present invention.

FIG. 3 shows an apparatus for performing the method of FIG. 2, comprising a continuous caster, hot rolling mill, intermediate collection rolls (coils), post hot rolling annealing station, cold rolling mill, post cold rolling annealing station and rolls (coils) of product sheet material, wherein the product of hot rolling is coiled before being annealed and cold rolled. As shown in FIG. 3, the post hot rolling annealing station, cold rolling mill, post cold rolling annealing station may be drawn separate boxes from the cast-hot rolling line.

FIG. 4 is a flow diagram of an apparatus for performing a second embodiment of a method of the present invention comprising a continuous caster, hot rolling mill, post hot rolling annealing station, cold rolling mill and coils of sheet material for performing the method of the present invention.

FIG. 5 is a flow diagram of a third embodiment of an apparatus comprising a continuous caster, hot rolling mill, cold rolling mill, post cold rolling annealing station and coils of sheet material for performing the method of the present invention.

FIG. 6 is a flow diagram of a fourth embodiment of an apparatus comprising a continuous caster, hot rolling mill and cold rolling mill and coils of sheet material for performing the method of the present invention.

FIG. 7 is a flow diagram of a fifth embodiment of an apparatus comprising a continuous caster, hot rolling mill and coils of sheet material for performing the method of the present invention.

FIG. 8 is a flow diagram of a sixth embodiment of an apparatus comprising a continuous caster, hot rolling mill, post hot rolling annealing station and coils of sheet material for performing the method of the present invention.

FIG. 9 is a flow diagram of a seventh embodiment of an apparatus comprising a continuous caster and cold rolling mill to directly form the product sheet while performing the method of the present invention.

FIG. 10 is a flow diagram of an eighth embodiment of an apparatus comprising a continuous caster, cold rolling mill and annealer to form the product sheet while performing the method of the present invention.

FIG. 11 is a drawing of a truck having a trailer with panels.

FIG. 12 is a drawing of a metal clad cable.

FIG. 13 is a cross-sectional drawing of the metal clad cable of FIG. 12 along view 13-13 of FIG. 12.

FIG. 14 is a drawing of a hollow electrical conduit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A. Methods of the Present Invention Employing Hot Rolling

The present invention provides a method for making an aluminum sheet product comprising the steps of:

providing a molten non-heat-treatable aluminum alloy comprising:

    • Si about 0.7% max., preferably about 0.25-0.7%, more preferably about 0.3-0.7%,
    • Fe about 0.8% max., preferably about 0.35-0.8%, more preferably about 0.4-0.8%,
    • Cu about 0.3% max., preferably about 0.05-0.28%,
    • Mn about 0.5-1.2%, preferably about 0.5-1.0%, more preferably about 0.5-0.8%,
    • Mg about 1.3-2.8%, preferably about 1.3-2.5%, more preferably about 1.4-1.8%,
    • Zn about 0.20% max., preferably about 0.15% max.,
    • Cr about 0.20% max., preferably about 0.15% max.,
    • Zr about 0.30% max., preferably about 0.25% max.,
    • Sr about 0.30% max., preferably about 0.25% max.

the remainder aluminum, incidental elements and impurities (the incidental elements and impurities present, if any, in amounts of 0.05 wt. % max. each, 0.15 wt. % max. total);

continuously casting the alloy in a continuous caster into a slab having a thickness of about 0.1 to 2 inches, typically about 0.2 to 1.5 inches or about 0.2 to 1 inch;

rolling the slab to form the aluminum sheet product, wherein the rolling comprises hot rolling;

wherein the aluminum sheet product has a yield strength of about 20 to 45 ksi and an ultimate tensile strength of about 30 to 60 ksi, or about 30 to 55 ksi, and an elongation of about 4 to 16% as measured according to ASTM E 8-04, and wherein the product is made in the absence of solution heat treatment.

Preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 36 ksi, ultimate strength >about 40 ksi and elongation >about 4%. More preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 38 ksi, ultimate strength >about 42 ksi and elongation >about 4%.

Preferably if used for electrical conduit, the aluminum sheet product typically meets Standard UL 1569 of the Underwriters Laboratory (current revision through and including May 25, 2005). Typical electrical conduits have a thickness of about 0.01 to 0.07 inches (0.25-1.8 mm), elongation of about 6 to 16% and UTS at least about 30 ksi, for example UTS of 40 to 44 ksi.

FIG. 1 is a flow diagram showing manufacturing steps of a number of embodiments of the present invention. FIG. 1 shows preparing molten aluminum alloy 14 from aluminum scrap. With reference to FIG. 1, the method and apparatus of the present invention begins by melting the chosen alloy in a furnace (not shown) to produce molten aluminum alloy 14. The molten aluminum alloy is then degassed and filtered in degassing and filtering devices to reduce dissolved gases and particulate matter in the molten aluminum alloy.

The aluminum scrap can be almost all types of non-heat-treatable and 6xxx series heat-treatable aluminum scrap such as aluminum building and construction materials, used beverage containers, food containers, truck trailer siding, and auto parts. Minor adjustments may be made to the alloy composition by adding prime aluminum when necessary. However, it is preferred not to use any prime aluminum or small amounts of prime aluminum to favor economics of the method. The aluminum scrap may include non-heat-treatable alloys and heat-treatable aluminum alloys such as, for example, Aluminum Association (AA) alloys 1xxx, 3xxx, 5xxx, 8xxx and 6xxx, whose compositions are included herein as if specifically set forth. However, the overall alloy feed from blending these alloys is a non-heat-treatable alloy.

By “scrap derived” as used herein is meant that most of the alloy used in the process comes from scrap, and primary aluminum is used when necessary to adjust the alloy within the composition ranges provided herein.

The molten aluminum alloy 14 is continuously cast to form a slab 15. The slab 15 can be prepared by any of a number of continuous casting techniques well known to those skilled in the art. The term “continuous caster” is meant to include the twin belt, block, twin roll casters or other continuous casters.

For example, a HAZELETT twin belt continuous caster could be employed. In some applications, it may be advantageous to employ the method and apparatus described in the following U.S. Pat. Nos. 3,937,270 3,864,973; 3,921,697; 4,648,438; 4,940,076 and 4,972,900, 5,363,902; 5,515,908; 5,564,491 and 6,102,102, incorporated herein by reference in their entirety. Improved nozzles for a belt caster are set forth in U.S. Pat. No. 5,452,827, incorporated herein by reference in its entirety.

A twin roll caster has two rolls which rotate to provide the continuously advancing mold. As in the belt caster, a tundish and nozzle are used to transfer molten aluminum to the mold defined by the two rolls. Again, the rolls are normally chilled to aid in solidification of the molten metal into a strip or slab. U.S. Pat. No. 4,411,707, incorporated herein by reference, describes using the roll caster.

A block caster has blocks connected to function as belts. When using a block caster, a tundish and nozzle transfer molten metal to the blocks of the block caster wherein solidification occurs to provide a solidified slab 15 and the blocks are chilled to aid in solidification of the molten metal.

Various casters are described in U.S. Pat. No. 5,452,827 incorporated herein by reference in its entirety.

Molten aluminum alloy 14 is introduced to the caster 3 in a temperature range of about 1230 ° to 1350° F. (666 to 732° C.), typically about 1250° to 1300° F. (677 to 704° C.), and exits the caster 3 as slab 15 at a temperature in the range of about 750° to 1150° F. (399 to 621° C.), typically about 860° to 1050° F. (460 to 566° C.). In addition, typically the continuous slab 15 exiting the continuous caster 3 has a thickness in the range of about 0.1 to 2 inches (0.25 to 5.1 cm), for example, about 0.20 to 1.5 inch (0.5 to 3.8 cm) or about 0.20 to 1 inch (0.5 to 2.54 cm). A typical slab thickness for the belt caster 3 is about 0.4 to 1 inch (1.02 to 2.54 cm) or about 0.50 to 0.90 inches (1.27 to 2.29 cm). These gauge ranges are suitable for embodiments making hot rolled and/or cold rolled products. These gauge ranges include thicknesses available from a roll caster (usually at lower thickness and only cold rolling is applied downstream of the caster) and HAZELETT twin belt caster (usually at thicker gauge and hot rolling is applied downstream of the caster).

The slab 15 is processed by hot rolling to form a hot rolled sheet 34 to make the high strength sheet product 42. In the production of high strength aluminum sheet, the control of the thickness reduction and the amount of strain hardening of the aluminum sheet through each stand of the hot rolling mill is very important in achieving the required hot rolled temper.

The total YTS increase from slab condition to the exit of the hot mill, independent of the number of the rolling stands, is in the range of 165% to 435%.

The preferred strain hardening, for instance, in a three stand hot rolling mill is listed as follows; the yield tensile strength (YTS) increase after the first rolling stand should be in the range of about 70 to 110%, the YTS increase after the second rolling stand should be about 30 to 70% greater than the strength from the first rolling stand and the YTS increase after third hot rolling stand should be about 20 to 50% greater than the strength from the second rolling stand.

Optionally, the hot rolled sheet 34 is cold rolled. For example, the cold rolling may provide about a 20 to 90% gauge reduction.

Also, optionally the hot rolled sheet 34 is annealed before cold rolling and/or the cold rolled sheet is annealed after cold rolling. If desired the cold rolled product sheet 42 may be sent back to the annealer 40 and then cold rolled again.

For example, the slab may be formed into the high strength sheet product 42 according to any of the following methods of the present invention:

    • 1. hot rolling the slab to form a hot rolled sheet, annealing the hot rolled sheet, cold rolling the annealed sheet, and annealing the cold rolled sheet to form the product sheet;
    • 2. hot rolling the slab to form a hot rolled sheet, annealing the hot rolled sheet, and cold rolling the optionally annealed sheet to form the product sheet;
    • 3. hot rolling the slab to form a hot rolled sheet, cold rolling the hot rolled sheet to form a cold rolled sheet, and annealing the cold rolled sheet to form the product sheet;
    • 4. hot rolling the slab to form a hot rolled sheet and cold rolling the hot rolled sheet to form the product sheet;
    • 5. hot rolling the slab to directly form the product sheet;
    • 6. hot rolling the slab to a hot rolled sheet and annealing the sheet to form the product sheet;

These embodiments are further described below.

1. Hot Rolling With Post-Hot Rolling Annealing Cold Rolling and Post-Cold Rolling Annealing

FIG. 2 is a flow diagram of a first embodiment of an apparatus to perform the present invention. This comprises a continuous caster 3, hot rolling mill 30, intermediate collection rolls (coils) 23, 25, post hot rolling annealer 40, cold rolling mill 50, a coiler to form rolls (coils) 48, 49, and post cold rolling annealer 44 to form annealed rolls (coils) 48, 49 of product sheet material 42. Optionally cold rolled sheet can be returned to the annealer 40 for additional annealing prior to additional cold rolling.

FIG. 3 shows details of the apparatus of FIG. 2. In FIG. 3, molten aluminum 10 obtained from aluminum scrap (or other sources) is provided in a furnace or reservoir 12. Molten aluminum 14 from reservoir 12 is typically passed through a filter and degasser (not shown) and is then directed along a line to a tundish 16 from where it is metered through a nozzle 18 into an advancing mold created by revolving belts 20 and 22 and side dam blocks (not shown). Belts 20 and 22 are turned by means of rolls 24. Molten metal, e.g., molten aluminum, is solidified to form a continuous slab 15 between belts 20 and 22 which are chilled using coolant spray 26. Although the continuous caster 3 is shown as a belt caster, another continuous caster could be substituted for the belt caster if desired.

Molten aluminum alloy 14 is introduced to the caster 3 in a temperature range of about 1230° to 1350° F. (666 to 732° C.), typically about 1250° to 1300° F. (677 to 704° C.), and exits the caster 3 at a temperature in the range of about 750° to 1150° F. (399 to 621° C.), typically about 860° to 1050° F. (460 to 566° C.). In addition, typically the continuous slab 15 exiting the continuous caster 3 has a thickness in the range of about 0.1 to 2 inches (0.25 to 5.1 cm), for example, about 0.20 to 1.5 inch (0.5 to 3.8 cm) or about 0.20 to 1 inch (0.5 to 2.54 cm) or about 0.25 to 1 inch (0.64 to 2.54 cm). A typical slab thickness for the belt caster 3 is about 0.4 to 1 inch (1.02 to 2.54 cm) or about 0.50 to 0.90 inches (1.27 to 2.29 cm). Belt casting speed can range from about 10 to 40 ft/min (3 to 12 m/m in), depending on the thickness of the slab. It is important to adhere to these casting conditions to achieve the volume and quality required for the end product. Thus, the present invention provides continuous cast slab 15 for forming into sheet material with high cost savings and yet retains the desirable properties such as strength and formability.

After exiting the caster 3, the slab 15 is directed to hot rolling mill 30 where it is rolled to form a rolled strip or flat product (sheet) 34. Hot rolling mill 30 includes one or more pairs of oppositely opposed rolls 32 which reduce the thickness of the slab 15 a controlled amount as it passes between each stand of rolls. Three sets of hot mill stands or rolls are illustrated in FIG. 3.

The temperature of the slab 15 entering hot rolling mill 30 would typically be in the range of about 700° to 1050° F. (371 to 566° C.). Typically, temperature of sheet product 34 exiting the hot rolling mill 30 would be in the range of about 350° to 700° F. (177 to 371° C.).

Hot rolling mill 30 can reduce the thickness of the slab 15 about 60 to 98% of its original thickness, with a typical reduction being about 75 to 95%. For example, slab 15 having a thickness of about 0.2 to 1 inch (0.5 to 2.54 cm) could be reduced to a sheet product having a thickness of about 0.03 to 0.25 inch (0.76 to 6.3 mm) or about 0.01 to 0.1 inch (0.25 to 2.5 mm).

In the production of high strength aluminum sheet, the control of the thickness reduction and the amount of strain hardening of the aluminum sheet through each stand of the hot rolling mill is important in achieving the required hot rolled temper. The preferred strain hardening, for instance, in a three stand hot rolling mill is listed as follows; the yield tensile strength (YTS) increase after the first rolling stand should be in the range of about 70 to 110%, the YTS increase after the second rolling stand should be about 30 to 70% greater than the strength from the first rolling stand and the YTS increase after third hot rolling stand should be about 20 to 50% greater than the strength from the second rolling stand.

The total YTS increase from slab condition to the exit of the hot mill, independent of the number of the rolling stands, is in the range of about 165% to 435%.

After hot rolling the hot rolled strip (hot rolled sheet) 34 may be annealed to promote recrystallization of the deformed structures in an annealer 40. If desired the hot rolled strip may be annealed to a fully annealed or O-temper condition. Typically, as shown in FIG. 3, annealer 40 is a batch annealing furnace and the hot rolled sheet 34 is coiled on intermediate coils 23, 25 and afterwards is statically annealed in the batch annealing furnace. Thus, the hot rolled strip 34 may be batch annealed in annealer 40 at a temperature range of about 600° to 1000° F. (316° to 538° C.) for about 2 to 10 hours to provide the rolled sheet in a fully annealed or O-temper condition.

However, in an alternative (not shown), the hot rolled strip 34 may be continuously annealed in a temperature range of about 600° to 1100° F. (316 to 593° C.) in time periods from about 0.3 to 60 seconds, to provide the rolled sheet in a fully annealed or O-temper condition in a continuous annealer. A typical continuous annealer could be an infrared, solenoidal or transverse flux induction heater after hot rolling but upstream of forming coils 23, 25. A flash tunnel annealing furnace may also be used.

After annealing, the resulting strip is cold worked by cold rolling in a cold rolling mill 50 to give sheet product 42 a final gauge. The cold rolling may be performed by passing strip 42 through several pairs or stands of the cold rolling mill 50 to provide the cold rolling to produce the final gauge. Cold rolling can reduce the thickness of strip (sheet) 42 by about 20% to 80% or about 20% to 90%. Final gauge can range from about 0.01 to 0.16 inch (0.25 to 4.1 mm), typically about 0.015 to 0.08 inches (0.038 to 0.20 cm). It will be appreciated that the cold rolling, which is rolling at lower than about 350° F. (177° C.), can be performed in a cold rolling line separate from the subject continuous casting and hot rolling line.

After cold rolling, the material can be coiled to form coils 48, 49 and then annealed in annealer 44 to an H2x temper or stabilized to an H3x temper. FIG. 3 shows the annealer 44 as a batch annealing furnace for statically annealing coils 48, 49 to form product 42. For batch annealing, the temperature range can be from about 300° F. to 700° F. for 2 to 10 hours. In an alternative (not shown) the material is processed in a continuous annealer prior to forming coils 48, 49. For continuous annealing the temperature range can be from about 350° F. to 750° F. for 0.3 to 100 seconds. The actual annealing time and temperature will depend on the material temper required.

2. Hot Rolling and Post Hot-Rolling Annealing With Cold Rolling

FIG. 4 shows a flow diagram of a second embodiment of an apparatus for performing the method of the present invention. This employs a continuous caster 3, hot rolling mill 30, coiler to form intermediate collection coils 23, 25, post hot rolling annealing station (annealer) 40, and cold rolling mill 50 to make rolls (coils) 48, 49 of sheet material. Thus, the method is the same as that of FIG. 2 but the post cold rolling annealer 44 of FIG. 2 is omitted.

The product sheet 42 discharged from cold rolling mill 50 has along the rolling direction a yield tensile strength of about 20 to 45 ksi (138 to 310 MPa) and an ultimate tensile strength of about 30 to 60 ksi (207 to 414 MPa) as measured according to ASTM E 8-04. Thus, the process tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be strain hardened to an H1x temper.

3. Hot Rolling With Cold Rolling and Post-Cold Rolling Annealing

FIG. 5 is a flow diagram of an apparatus for performing a third embodiment of the method of the present invention having a continuous caster 3, hot rolling mill 30, coiler to form intermediate collection coils 23, 25, cold rolling mill 50, and post cold rolling annealing station (annealer) 44 to make rolls (coils) 48, 49 of product sheet material 42. Thus, the method is the same as that of FIG. 2 but the post hot rolling annealer 40 is omitted. After cold rolling to final gauge, the sheet product 42 is subject to annealing or stabilization in the post cold rolling annealing station 44 to ensure the desired crystallographic texture and grain structure for forming into the final sheet product.

The sheet 42 discharged from annealer 44 has along the rolling direction a yield tensile strength of about 20 to 45 ksi (138 to 310 MPa) and an ultimate tensile strength of about 30 to 60 ksi (207 to 414 MPa) and elongation of about 4 to 16% as measured according to ASTM E 8-04. Thus, the process tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be annealed or stabilized to H2x or H3x tempers,

4. Hot Rolling With Cold Rolling and Without Annealing

FIG. 6 is a flow chart of an apparatus for performing a fourth embodiment of the method of the present invention having a continuous caster 3, hot rolling mill 30, and cold rolling mill 50 to make rolls (coils) 48, 49 of sheet material 42. Thus, the method is the same as that of FIG. 2 but the annealer 40 and annealer 44 are omitted. Typically the hot rolled material is coiled before cold rolling.

The cold rolled product sheet material 42 discharged from cold rolling mill 50 has along the rolling direction a yield tensile strength of 20 to 45 ksi and an ultimate tensile strength of 30 to 60 ksi (207 to 414 MPa) as measured according to ASTM E 8-04. Thus, the process tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be strain hardened to an H-temper, e.g. H1x temper.

5. Hot Rolling Without Cold Rolling and Without Annealing

FIG. 7 is a flow diagram of a fifth embodiment of an apparatus for performing the method of the present invention having a continuous caster 3 and hot rolling mill 30 to make rolls (coils) 48, 49 of sheet material 42. Thus, the method is the same as that of FIG. 2 but the annealer 40, cold rolling mill 50 and annealer 44 of FIG. 2 are omitted.

The product sheet material 42 discharged from hot rolling mill 30 has along the rolling direction a yield tensile strength of 20 to 45 ksi and an ultimate tensile strength of 30 to 60 ksi (207 to 414 MPa) as measured according to ASTM E 8-04. Thus, the process tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be strain hardened to an H1x-temper.

6. Hot Rolling Without Cold Rolling and With Post-Hot Rolling Annealing

FIG. 8 is a flow chart of a sixth embodiment of an apparatus for performing the method of the present invention comprising a continuous caster 3, hot rolling mill 30, and annealer 40 to make rolls (coils) 48, 49 of sheet material. Thus, the method is the same as that of FIG. 2 but the cold rolling mill 50 and annealer 44 of FIG. 2 are omitted.

The product sheet material 42 discharged from annealer 40 has along the rolling direction a yield tensile strength of 20 to 45 ksi and an ultimate tensile strength of 30 to 55 ksi as measured according to ASTM E 8-04. Thus, the process tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be annealed or stabilized to H2x or H3x tempers.

B. Embodiments Without Hot Rolling

The present invention also provides a method for making an aluminum sheet product comprising cold rolling a continuously cast sheet of non-heat-treatable aluminum alloy without hot rolling and with or without anneal after cold rolling. This method comprises the steps of:

providing a molten aluminum alloy comprising:

    • Si about 0.7% max., preferably about 0.25-0.7%, more preferably about 0.3-0.7%,
    • Fe about 0.8% max., preferably about 0.35-0.8%, more preferably about 0.4-0.8%,
    • Cu about 0.3% max., preferably about 0.05-0.28%,
    • Mn about 0.5-1.2%, preferably about 0.5-1.0%, more preferably about 0.5-0.8%,
    • Mg about 1.3-2.8%, preferably about 1.3-2.5%, more preferably about 1.4-1.8%,
    • Zn about 0.20% max., preferably about 0.15%,
    • Cr about 0.20% max., preferably about 0.15%,
    • Zr about 0.30% max. preferably about 0.25% max.,
    • Sr. about 0.30% max, preferably about 0.25% max.

the remainder aluminum, incidental elements and impurities (the incidental elements and impurities present, if any, in amounts of about 0.05 wt. % max. each, about 0.15 wt. % max. total);

continuously casting the alloy in a continuous caster into a strip having a thickness of about 0.1 to 1 inch, typically about 0.15 to 0.6 inches or about 0.2 to 0.4 inch;

cold rolling the continuously cast strip coil to form the aluminum sheet product, wherein the process has an absence of hot rolling;

wherein the aluminum sheet product has a yield strength of 20 to 45 ksi and an ultimate tensile strength of 30 to 60 ksi, or 30 to 55 ksi, and elongation of about 4 to 16% as measured according to ASTM E 8-04.

Preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 36 ksi, ultimate strength >about 40 ksi and elongation >about 4%. More preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 38 ksi, ultimate strength >about 42 ksi and elongation >about 4%.

Preferably if used for electrical conduit, the aluminum sheet product typically meets Standard UL 1569 of the Underwriters Laboratory (current revision through and including May 25, 2005). Typical electrical conduits have a thickness of about 0.01 to 0.07 inches (0.25-1.8 mm), elongation of about 6 to 16% and UTS at least about 30 ksi, for example UTS of 40 to 44 ksi.

Thus, for example, the product may be made by:

    • 1. cold rolling the strip to directly form the product sheet (with optional annealing before cold rolling); or
    • 2. cold rolling the strip to a cold rolled sheet and annealing the cold rolled sheet to form the product sheet (with optional annealing before cold rolling).

In the production of high strength aluminum sheet, the thickness reduction and the amount of strain hardening of the aluminum sheet through each pass of the cold rolling mill is performed to achieve the desired cold rolled temper.

The method tends to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets may be strain hardened to an H1x-temper, or annealed to H2x or stabilized to H3x tempers. The sheets are not hardened by solution heat treating and/or artificial aging.

1. Cold Rolling Without Hot Rolling and Without Post Cold Rolling Annealing

FIG. 9 is a flow chart of a seventh embodiment of an apparatus for performing the method of the present invention having a continuous caster 3, coiler to form intermediate collection coils 23, 25, an optional annealer 40A to anneal the material before cold rolling, and cold rolling mill 50 to directly form the product sheet 42. Thus, the method and equipment for the various unit operations for embodiments without hot rolling could be the same as that of FIG. 2 but the hot rolling mill 30, annealer 40 and annealer 44 of FIG. 2 are omitted. The conditions of casting and cold rolling are adjusted to compensate for the lack of hot rolling. Molten aluminum alloy is introduced to the caster 3 and exits from the caster at a temperature in the ranges described above regarding for FIG. 1. Typically the continuous strip 15 exiting the continuous caster 3 has a thickness in the range of about 0.1 to 1 inch (0.25 to 2.54 cm), typically about 0.15 to 0.6 inches (0.38 to 1.52 cm) or about 0.2 to 0.4 inch (0.5 to 1.0 cm). Although various continuous casters may be employed, a belt caster or a roll caster could be employed in the embodiments of the method of the present invention employing continuous casting followed by cold rolling in the absence of hot rolling. (For instance, FIG. 3 shows a belt caster employed with an embodiment including hot rolling). Typically when employing a roll caster the cast sheet is directly coiled after casting to form intermediate coils 23, 25, allowed to cool, and then cold rolled and coiled to make the sheet product 42.

In using the roll caster, the molten aluminum alloy within the above-composition ranges is initially chill cast between the water cooled rolls of the caster to a thickness between about 0.15 inches to about 0.5 inches. The temperature of the aluminum alloy on introduction between the rolls is preferably in the temperature range of about 1230° F. (666° C.) to 1300° F. (704° C.). As the aluminum alloy solidifies between the rolls, there will be a reduction by the force of the rolls of up to about 30%. After the solid aluminum sheet leaves the chill roll continuous caster it is coiled continuously and the coils are allowed to cool to below 200° F. (93° C.) prior to subsequent cold working. It will be appreciated that the cold rolling, which is rolling at lower than 350° F. (177° C.), can be performed in a cold rolling line separate from the continuous casting line.

Optionally, a batch anneal furnace 40A, or a heater such as an infrared, solenoidal or transverse flux induction heater can be used upstream of cold rolling mill 50 to optimize the microstructure of the material for further cold rolling, for example, annealing to 0 temper. For batch annealing, the temperature range can be from 600° F. to 1100° F. for 2 to 10 hours. However, if desired, a continuous annealer (not shown) can be used. The actual annealing time and temperature will depend on the material temper required. At the end of the annealing step the sheet stock is allowed to cool and cold worked to the final gauge.

The cooled, coiled sheet material is cold rolled with at least a 60% reduction in thickness to an H temper.

Cold rolling mill 50 includes one or more pairs of opposed rolls which reduce the thickness of the slab 15 a controlled amount as it passes between each stand of rolls. The cold rolling may be performed by passing strip 42 through several pairs or stands of the cold rolling mill 50 to provide the cold rolling to produce the final gauge. Cold rolling can reduce the thickness of slab 15 by about 60 to 98% of its original thickness, with a typical reduction being about 75 to 95%. For example, slab 15 having a thickness of about 0.2 to 0.6 inch (0.5 to 1.5 cm) would be reduced to a sheet product having a final gauge which can range from about 0.01 to 0.16 inch (0.25 to 4.1 mm), typically about 0.015 to 0.08 inch (0.038 to 2.0 cm).

The cold rolled sheet 42 is discharged from cold rolling mill 50. The method is operated such that product sheet 42 has along the rolling direction a yield tensile strength of about 20 to 45 ksi (138 to 310 MPa) and an ultimate tensile strength of about 30 to 60 ksi (207 to 414 MPa) or about 30 to 55 ksi (207 to 379 MPa) and an elongation range from about 4% to 16% as measured according to ASTM E 8-04.

Preferably if used for truck trailer siding the aluminum sheet product 42 has a yield strength >about 36 ksi, ultimate strength >about 40 ksi and elongation about 4 to 10%. More preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 38 ksi, ultimate strength >about 42 ksi and elongation about 4 to 10% as measured according to ASTM E 8-04.

Preferably if used for electrical conduit, the aluminum sheet product 42 typically meets Standard UL 1569 of the Underwriters Laboratory (current revision through and including May 25, 2005). Typical electrical conduits have a thickness of about 0.01 to 0.07 inches (0.25-1.8 mm), UTS at least about 30 ksi, for example UTS of about 40 to 44 ksi, and elongation of about 6 to 16% as measured according to ASTM E 8-04.

2. Cold Rolling Without Hot Rolling and With Annealing

FIG. 10 is a flow chart of an apparatus for performing an eighth embodiment of the method of the present invention having a continuous caster 3, cold rolling mill 50 and annealer 44 to form the product sheet 42. Optionally this embodiment may also have an annealer 40A to anneal the material before cold rolling. Thus, the method is the same as that of FIG. 10 but the annealer 44 of FIG. 2 has been added.

After cold rolling, the material is annealed to H2x temper or stabilized to H3x temper for final applications. The annealing can be done either using a batch annealing furnace or a continuous heater. Typically, a batch anneal furnace 44, or a heater such as an infrared, solenoidal or transverse flux induction heater or a flash tunnel anneal furnace can be used. For batch annealing, the temperature range can be from 300° F. to 700° F. for 2 to 10 hours. However, if desired, a continuous annealer (not shown) can be used. For continuous annealing the temperature range can be from 350° F. to 750° F. for 0.3 to 600 seconds. The actual annealing time and temperature will depend on the material temper required. At the end of the annealing step the sheet stock is allowed to cool and may again be cold worked to the final gauge.

The method is operated such that aluminum sheet product 42 has along the rolling direction a yield tensile strength of about 20 to 45 ksi (138 to 310 MPa) and an ultimate tensile strength of about 30 to 60 ksi (207 to 414 MPa) or about 30 to 55 ksi (207 to 379 MPa) and elongation of about 4% to 16% as measured according to ASTM E 8-04.

Preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 36 ksi, ultimate strength >about 40 ksi and elongation about 4 to 10%. More preferably if used for truck trailer siding the aluminum sheet product has a yield strength >about 38 ksi, ultimate strength >about 42 ksi and elongation about 4 to 10%.

Preferably if used for electrical conduit, the aluminum sheet product 42 typically meets Standard UL 1569 of the Underwriters Laboratory (current revision through and including May 25, 2005). Typical electrical conduits have a thickness of about 0.01 to 0.07 inches (0.25-1.8 mm), UTS at least about 30 ksi, for example UTS of about 40 to 44 ksi, and elongation of about 6 to 16% as measured according to ASTM E 8-04.

Typical Uses For the Sheet Material of the Present Invention

The present invention desires high strength products. The methods of the present invention are operated such that sheet product 42 has along the rolling direction a yield tensile strength of about 20 to 45 ksi (138 to 310 MPa) and an ultimate tensile strength of about 30 to 60 ksi (207 to 414 MPa) or about 30 to 55 ksi (207 to 379 MPa) and an elongation range from about 4% to 16% as measured according to ASTM E 8-04.

For example, for truck trailer siding panels the sheet product preferably has a yield strength of >about 36 ksi (248 MPa), ultimate strength >about 40 ksi (276 MPa) and elongation of about 4 to 10% as measured according to ASTM E 8-04. More preferably, the sheet product has along the rolling direction a yield strength of >about 38 ksi (262 MPa), ultimate strength >about 42 ksi (290 MPa) measured according to, and elongation of about 4 to 10% as measured by ASTM E 8-04.

Thus, the methods of the present invention for making the high strength sheet product tend to make the high strength sheet product in tempers selected to assist in attaining the desired high strength. For example, the sheets 42 may be strain hardened to an H1x-temper, or annealed to H2x temper or stabilized to H3x temper. The alloy is not hardened by solution heat treatment and/or artificial aging.

When used for truck trailer siding, after painting and paint curing it will have a yield strength of >about 36 ksi (248 MPa), ultimate strength >about 40 ksi (276 MPa) and elongation about 4 to 10% as measured according to ASTM E 8-04. Thus, to support the same load, about 5 to 10% thickness reduction (or 5 to 10% weight reduction) can be made by using the cited alloy as compared to commercially used 3004 alloy. More preferably, when used for truck trailer siding, after painting and paint curing the truck trailer siding sheet has a yield strength of >about 38 ksi (262 MPa), ultimate strength >about 42 ksi (290 MPa) measured according to, and elongation about 4 to 10% as measured by ASTM E 8-04. Typically according to the present invention sheet for truck trailer sidewall YTS will be about 36 to 45 ksi, UTS will be about 40 to 50 ksi and elongation will be about 4 to 10%. Typical truck trailer siding panels of the present invention have a thickness of about 0.01 to 0.19 inches, for example about 0.03 to 0.06 inches (0.076 to 0.152 cm).

FIG. 11 is a schematic showing a truck 60 having a front cab 62 and a trailer 64 with panels 66. The panels may be made from sheet made according to the present method.

The invented alloy can provide greater resistance to the property loss incurred in a customer's further thermal processing of the material. For example, different paint systems can require a curing temperature range from about 350° F. to 500° F. With existing alloys, many times, such processing will lower the mechanical properties. The invented method and alloy after such a curing temperature may not negatively affect the mechanical properties. If desired the method includes a back anneal in the production of truck trailer siding sheet so the further decrease of the strength may not occur during the paint curing.

Another typical product which can be made from sheets of the present invention is electrical conduits, in particular flexible metal conduits for the building industry.

Such electrical conduits typically meet Standard UL 1569 of the Underwriters Laboratory (current revision through and including May 25, 2005). Typical electrical conduits have a thickness of about 0.01 to 0.07 inches. (0.25-1.8 mm) and elongation of about 6 to 16%. There is a range of mechanical property requirement based on specific applications.

For example, metal clad cable has UTS of about 40 to 44 ksi with elongation about of 6 to 10%. FIG. 12 is a drawing of a typical electrical conduit (metal clad cable) 70. FIG. 13 shows a cross-section of a metal clad cable 70 along view 13-13 of FIG. 13 showing an aluminum interlocked armor or cladding 72 made from sheet according to the present invention, a bare aluminum grounding/bonding conductor wire 73, and insulated conductor wires 74, 76.

Conversely flexible conduit applications have UTS at least about 30 ksi with elongations about 10 to 16%. The current invention can satisfy both requirements. FIG. 14 is a drawing of a hollow flexible electrical conduit 80 showing aluminum interlocked armor.

EXAMPLES

Example 1

One example is for making truck trailer siding. An aluminum alloy with chemistry in the weight percentage of 0.229% Si, 0.467% Fe, 0.055% Cu, 0.626% Mn, 1.583% Mg, 0.040% Zn and 0.014% Cr was cast using a twin belt caster. The cast slab of 0.875 inches was directly fed into a three stand hot rolling mill with an entry temperature of 1,000 F. The material was hot rolled to 0.110 inches with a total plastic reduction of 87%. The total YTS increase from slab condition to the exit of the hot mill, independent of the number of the rolling stands, was about 222%. The 0.110 inches hot band was further cold rolled to 0.040 inches and annealed to an H291 temper with a yield strength of 39.5 ksi, an ultimate strength of 43.2 ksi and an elongation of 4.7%.

Example 2

As a comparison to Example 1, currently used AA3004 alloy having the following composition 0.30% Si, 0.59% Fe, 0.16% Cu, 1.02% Mn, 0.91% Mg, 0.08% Zn, 0.02% Ti, 0.03% Cr, balance Al and inevitable impurities was tested. The AA3004 alloy was made into a 0.875 inch slab using a belt caster and hot rolled to 0.10 inch then cold rolled to 0.04 inch thickness and then annealed to H291 temper. The H291 temper material had a yield strength of 36.4 ksi and an ultimate strength of 40.3 ksi with an elongation of 4.0%. Yield strength of the invented alloy is 3.1 ksi (or 8.5%) higher than that of the currently used AA3004 alloy for the truck trailer siding application.

Example 3

Another example is for making electrical conduits. An aluminum alloy with chemistry in the weight percentage of 0.233% Si, 0.567% Fe, 0.119% Cu, 0.614% Mn, 1.585% Mg, 0.064% Zn and 0.030% Cr was cast using a twin belt caster. The cast slab was directly fed into a three stand hot rolling mill and rolled from 0.875 inches to 0.055 inches with a total plastic deformation of 93.7%. The total YTS increase from slab condition to the exit of the hot mill, independent of the number of the rolling stands, was about 200%.

The 0.055 inches hot band was further cold rolled to 0.016 inches and then annealed to have a yield strength of 36.6 ksi, an ultimate strength of 41.3 ksi and an elongation of 9.5%. The material was formed into metal clad cable (similar to that of FIGS. 12 and 13) without forming failure. The formed metal clad cable was tested and pass the UL test standard UL 1569-Metal-Clad Cables (current revision through and including May 25, 2005).

Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied within the scope of the appended claims.