The present invention relates to a process for producing an aluminum sheet. In particular, the present invention relates to a sheet material suitable for forming from a production point in a non-heat treated alloy by a rolling method. For example, the 5000 series aluminum alloy in the manufacture of automotive panels.
5000 series aluminum alloys (ie magnesium as the main alloying element) are commonly used in automotive panels (guards, door panels, covers, etc.). For such applications, it is desirable to provide high yield points and high ductility for alloy sheets. To be achieved. Aluminum alloy sheets of suitable specifications and yield strength can be obtained by rolling after continuous casting. In the conventional continuous casting process, the metal obtained from the casting is hot rolled and warmed, then coiled (at a temperature of about 300 degrees Celsius) and then sent to another rolling mill for final cold rolling at a temperature not exceeding 160 degrees Celsius. .
For refining, it is mentioned here that what is commonly referred to as "hot rolling" is carried out at temperatures above the recrystallization temperature of the alloy. In order for the alloy to self-anneal and recrystallize between the roll slits or in the coil after rolling. The term "cold rolling" generally means a work roll having a large amount of work hardening rate so that the alloy does not recrystallize or recover during or after rolling. "Medium temperature rolling" is performed between the two so as to have no recrystallization, but the yield strength is greatly reduced due to the recovery process. For aluminum alloys, the hot rolling temperature exceeds 350 degrees Celsius, the cold rolling temperature is less than 150 degrees Celsius, and the medium temperature rolling is performed between 150 and 350 degrees Celsius.
Unfortunately, the intermediate winding of the conventional method described above is cumbersome and expensive, and storage requires a product having a suitable microcrystalline structure to produce the desired yield strength.
In U.S. Patent No. 5,514,228, a coaxial continuous casting process is disclosed on May 7, 1996, in which the sheets are rolled through the intermediate windings to the final desired specifications. However, further solution treatment is required prior to the final rolling so that the sheets are continuously completely annealed before the final winding. However, the 5000 series alloys are not strengthened after solution treatment.
It is an object of the present invention to produce an aluminum alloy sheet that is not heat treated in a convenient and economical manner for use in the manufacture of automotive panels.
Another object of the present invention is to provide a process for producing 5000 series aluminum alloy sheets in a continuous step without intermediate secondary rolling to obtain a high yield point aluminum alloy product.
In one aspect of the invention, a process for producing an aluminum alloy sheet is provided, comprising: casting a non-heat treated aluminum alloy to form a flat steel ingot, and then passing the flat steel ingot through a series of rolling steps to produce a final specification product . The rolling step comprises: hot rolling and medium temperature rolling of the slab, forming a medium-sized intermediate plate, cooling the inter-plate; and then performing intermediate-temperature rolling and cold rolling on the intermediate plate at a temperature ranging from room temperature to 340 ° C; The continuous rolling step has no winding or complete annealing of the intermediate sheet.
The above process is an alloy in the so-called H2 tempering. Further annealing and recrystallization production sites are suitable for the panels used in automobiles.
In another aspect of the present invention, an aluminum alloy sheet is provided from an aluminum alloy that is not heat-treated, and the process includes: casting an aluminum alloy without heat treatment to form a flat steel ingot; the flat steel ingot passes through a series of Rolling to produce the final specification of the product; the rolling step includes: hot rolling and medium temperature rolling of the slab, forming an intermediate-sized intermediate sheet, cooling the intermediate sheet, and then performing the intermediate sheet at a temperature ranging from room temperature to 340 ° C. Medium temperature rolling and cold rolling; a series of continuous rolling steps without winding or full annealing of the intermediate sheet.
As described above, the present invention requires hot rolling and medium temperature rolling and then performing intermediate temperature rolling and cold rolling without intermediate winding or complete retraction. When the flat ingot is continuously rolled, the hot slab loses heat to the air and the rolls so that the hot rolling ends in the intermediate temperature rolling (i.e., below the crystallization temperature).
This is the method of rolling by hot rolling and medium temperature. During hot rolling, the metal is completely recrystallized to release any strain energy generated during casting. The temperature during this period depends on the amount of simultaneous cold working and the composition of the alloy. During medium temperature rolling, the strain energy is established by gradual rolling, which is what the metal calls "recovery." As with recrystallization, the degree of external temperature recovery depends on the amount of cold work and the composition of the alloy. An important difference between recrystallization and recovery is that recrystallization causes a rapid decrease in internal tension and occurs during hot rolling, however recovery occurs throughout the entire period of medium temperature rolling and cold rolling, and the internal tension is smooth. Reduced, but most of the pressure is released during "warm" rolling.
The process of the present invention is beneficial for any aluminum alloy that is not heat treated, and the final treatment of these aluminum alloys is a fully annealed condition. However, the enhanced grain size is of the utmost importance in the 5000 series of alloys for automotive applications. The process can be used for all 5000 series alloys to be shipped in a fully annealed condition, but is especially useful for AA5754 alloys, which contain a limited amount of Mg. To avoid stress corrosion cracking, strengthening the grain size is especially important for this alloy. of. Alloys such as AA5182, which have higher Mg content, are sensitive to stress corrosion cracking, but they have higher strength. Of course it is beneficial for such alloys, but not so obvious.
The process of the present invention, at least in its preferred form, provides a 5000 series of aluminum sheets for making automotive body structures that are continuously rolled on a continuous casting machine to provide good mechanical properties.
An advantage of the present invention is that although self-annealing does not produce preferred microstructures and properties, recrystallization after subsequent rolling at lower temperatures and subsequent annealing does produce the desired fine grain size, high strength, and advantageous Crystal texture.
1. A process for producing an aluminum alloy sheet comprising: casting a non-heat treated aluminum alloy to form a flat steel ingot, and then passing the flat steel ingot through a series of rolling steps to produce a final specification product. The rolling step comprises: hot rolling and medium temperature rolling of the slab, forming a medium-sized intermediate plate, cooling the inter-plate; and then performing intermediate-temperature rolling and cold rolling on the intermediate plate at a temperature ranging from room temperature to 340 ° C; The continuous rolling step has no winding or complete annealing of the intermediate sheet.
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