Main alloy and production process of aluminum automobile body panel

Compared with steel, aluminum has many advantages, such as high specific strength, good corrosion resistance, high recovery rate, but higher price. Since the 1940s, aluminum automobile body panels have been developed and produced. However, due to process and cost reasons, the application of aluminum in automobiles was still mostly limited to cast parts until the 1990s.

In order to meet these stringent standards, various vehicles, including family cars, must lose weight, which forces automakers to consider new materials, and the process development and production application of aluminum body panels have developed rapidly. The aluminum used for automobile body panels are mainly 5 and 6 series alloys. Among them, the 5 series have higher strength and are mostly used as inner panels and internal structural panels, and the 6 series are mostly used as outer panels. Since the 1940s, some well-known aluminum processing companies have cooperated with many automobile companies successively, and have done a lot of work in the research and development of aluminum body panels, and developed a set of detailed parameters for each production process. The purpose is to being tied to the customers it supplies makes it difficult for other vendors to supply them. For example, AA6016A products have very strict requirements in different ranges, and require additional surface treatment, such as electric spark texturing (EDT) surface and stable passivation layer, which leads to the need for at least 5 years to pass the certification, which caused great resistance for other aluminum processing enterprises to enter the European and American aluminum automotive sheet market.

The production process of automotive sheet is as follows: semi-continuous casting, milling, hot rolling, cold rolling, continuous solution heat treatment, finishing and surface treatment (cleaning, passivation, wet or dry oiling, straightening). Among them, the casting, hot rolling and cold rolling stages are similar to many cases of production. The bottleneck of the processing process lies in the continuous solution heat treatment stage (6-series and a few 5-series alloys require solution heat treatment), so the production capacity of automobile sheets depends on these production lines. A typical continuous solution treatment line includes: an uncoiler (possibly with an in-line roll leveler), a looper (which can store a sufficient amount of coil material when unloading or changing coils). The strip is then heated in a furnace, typically at a temperature of 550-600°C, followed by rapid quenching and coiling. Coiling is carried out in a controlled state to achieve stable pre-aging, eventually reaching the T4 state, at which point the material becomes stable, soft, and has good formability. The heat treatment is followed by a series of surface finishing processes. The strip is chemically or electrolytically cleaned, rinsed, and then stabilized with fluozirconic acid and fluotitanic acid to prevent further oxidation, giving the sheet a stable surface for at least 6 months prior to use by the manufacturer. After passivation treatment, the sheet is rolled or sprayed with a dry lubricating film to increase the formability when stamping the panel, then dried and coiled. The supply form may be cut sheets or coils according to the requirements of different manufacturers.