At present, the aluminum alloy sheets used for automotive body panels are 5000 series and 6000 series. The common grades are 5052, 5754, 5182, 6016, 6014 and 6181. The 5000 series alloy is an aluminum alloy that cannot be strengthened by heat treatment. It has medium yield strength and tensile strength, good corrosion resistance, processability and good weldability.
Mg dissolves in the Al matrix to form solid solution strengthening, which makes the alloy have the characteristics of general steel in terms of yield strength, tensile strength, formability and corrosion resistance. Therefore, 5000 series aluminum alloys like 5182 aluminum coil is usually used as the automotive inner panel material.
The main alloy grades of 6xxx series aluminum alloy automotive sheets include 6014, 6022, 6016 aluminum sheet etc., which are the main aluminum alloys currently used in body outer panels. Automobile sheets have high requirements on comprehensive performance, surface quality and quality stability. The current mainstream automotive aluminum sheet production process is relatively complex, including several major processes: melting and casting, soaking, machining, hot rolling, cold rolling, and continuous heat treatment.
Aluminum alloys have extremely high performance requirements when used in automotive panels, so key links must be controlled during the production process. In the raw material production stage, it is necessary to design the composition. After homogenization heat treatment, the material is prepared into aluminum plates with different thickness specifications through cold and hot rolling processes, and finally the structure and second phase are controlled by heat treatment to achieve products that meet production requirements. During the entire production process, reasonable composition design and heat treatment process formulation are the necessary prerequisites to ensure high-quality aluminum plates.
The 6000 series aluminum automotive sheets like 6016 t4 need to have good stamping and flanging performance, natural aging resistance stability, good strength increase of baking paint, and no Luoping line on the surface of the material after stamping. To meet the special performance requirements of automobile sheets, not only qualified cold-rolled billets are required, but also special heat treatment technology and production equipment are required.
This is the mainstream automotive aluminum sheet production process: semi-continuous casting to produce large-size slabs- sawing head and tail- sharpening surface- heating- high-temperature rolling in large wide-width hot rolling mills- coil- cold rolling processed to the thickness of the finished product- heat treatment with an air-cushion continuous heat treatment furnace of special heat treatment equipment for automotive panels. If it is necessary to control the microstructure and grain size of the material, an intermediate annealing process can be added in the cold rolling pass.
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