With the acceleration of the development of lightweight vehicles in recent years, more and more automobile manufacturers have begun to use aluminum alloy panels as the main material for automobile manufacturing, which also benefits from the excellent performance of aluminum alloy panels and meets the needs of enterprises. What performance requirements does the company have for aluminum alloy panels?
1. Need to have good formability
The formability of a sheet refers to its ability to withstand shape changes during the stamping process. Formability can be evaluated by a formability test. At present, a large number of test results have been obtained for the formability of the steel sheet, but the test results of the formability of the aluminum alloy sheet can fully satisfy the performance requirements of the automobile.
2. Certain anti-aging stability
The characteristic that the aluminum alloy sheet does not age when stored at room temperature is called anti-aging stability. Because aging will cause the yield point elongation of the alloy during tensile deformation, that is, the Lüder ribbon, which will cause uneven surface deformation and wrinkling during stamping, which will affect the appearance of the stamping parts; the sheet is often required from the time of production to the stamping of parts. Transport and storage for some time, usually requires the board to be stored at room temperature for 6 months without aging.
3. Good bake hardenability
Automotive stampings are also aged when they are painted and baked, so that the characteristic of increasing the yield strength is called bake hardenability. High bake hardenability will impart high dent resistance to the part. Since the paint baking process of most automobile companies is currently designed for steel plates, and the bake hardenability of aluminum alloys is significantly different from that of steel, it is desirable that the bake hardenability of aluminum alloy plates is best compatible with the paint process of steel plates; The bake hardenability of the material can be assessed according to relevant standards.
4. Good flanging ductility
When the outer cover of the automobile is punched and flanged, the characteristic of the sheet against cracking is called the flanging ductility. Therefore, aluminum alloy sheets are required to have good flanging ductility to ensure that cracking does not occur when flanging. The flanging ductility of the sheet is related to the overall elongation of the sheet and also to the internal organization of the material. Flange ductility can be detected by the cold bend test, but the usual cold bend does not take into account the strain rate sensitivity, and the stamping flange is deformed faster and the strain rate is larger, which has higher requirements for the flanging ductility.
5. Better surface glare
Unlike aluminum alloy sheets, the grain size is much larger than that of steel. Under coarser grains, if the grain size is uneven, the surface of the stamping part will appear unevenly like the rope ring in the rolling direction. This kind of surface defect is also called Luoping line, which leads to inconsistency of the surface of the paint. Therefore, the aluminum alloy plate for automobile needs to have good surface glazing.
6. Surface treatment and coating performance
Before the steel material is painted, the surface should be pickled and phosphated to improve the adhesion of the stamping surface to the paint and improve its corrosion resistance. Since the aluminum alloy surface has a tightly bonded oxide film, the surface before the paint The treatment method is different from the steel material. Instead of the general acid phosphating method, it can be treated by chromizing. Considering the toxicity of hexavalent chromium to the human body, in recent years, the chrome-free or low-chromium treatment technology has been developed to meet the requirements. Business needs.
