Tham khảo tài liệu 'new trends and developments in automotive industry part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Materials in Automotive Application State of the Art and Prospects 379 For skin sheet material the emphasis is on achieving a good balance of formability strength after the paint-bake and a high surface quality after pressing and paint finish. Consequently the bake hardening 6xxx alloys are the primary choice for these applications. For structural sheet materials strength may be a limiting factor in certain areas impact energy absorption and good deep drawing behaviour are often the most important. To meet these requirements 5xxx alloys are mostly used in North America. In Europe 6xxx-T4 materials are still widely used. One obvious and significant difference between aluminium and steel is the outstanding bare metal corrosion of the 5xxx and 6xxx aluminium materials. Increasingly large amounts of steel are supplied zinccoated to achieve acceptable paint durability this is not necessary for aluminium. However the aluminium coil or sheet can be supplied with a range of pre-treatment and primer layers which can improve formability surface quality and may eliminate the need for E-coating. There is a wide range of aluminium materials and surface qualities which can be chosen and the growing design and process experience is enabling the aluminium industry to help the customer specifying the right material for the application. There is a clear difference Bottema et al 1998 in the alloy choice and treatments for these applications between Europe and North America. Aluminium alloys for brazing sheet applications As mentioned earlier brazed aluminium components are used extensively in modern vehicles for engine and transmission cooling charge air coolers and climate control. It consists of a core alloy which provides the strength and life cycle requirements of the heat exchanger and a clad layer which is of a low melting point aluminium silicon alloy. During the brazing process the Al-Si alloy melts and seals joints in the heat exchanger between the different sheet .
