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Aluminium Automotive Body Construction Seminar Report



Weight reduction is considered as a primary key to improvements in fuel economy. One area of considerable development has been through materials substitution. Thirty years ago, automotive structural elements were made almost exclusively from relatively low-strength steels. Today, however, a variety of materials can be found within the vehicle structure. This includes a range of steels, magnesium alloys, plastic composites, and of course, aluminum. Aluminum has been of particular interest for these applications for a number of reasons. First and foremost, the aluminum alloys under consideration today offer strength-to-weight ratio improvements over mild steel on the order of 3:1. This suggests that for an equivalent design, body-in-white weight reductions on the order of 70% could be achieved simply by this direct substitution. Even given strength and stiffness between aluminum and steel, weight reductions of 40 to 60% can still be realized. Additionally, aluminum sheets typically offer considerable corrosion benefits over even galvanized steels. This is of considerable advantage when addressing increased reliability requirements on newer generations of vehicles. A recent survey assessing trends in the automotive industry clearly showed an increase in aluminum usage. This has also been reflected in the numbers of aluminum-intensive vehicles that have been either developed or are under evaluation. These include the Mercedes-Benz CL Coupe, the Audi A-2, Audi A-8, and the just to name a few. The welding aluminum alloys offer unique challenges different than those seen on steels. As a result, research and development associated with welding these materials goes on to this day.

USE OF ALUMINUM ALLOY SHEET IN VEHICLE CONSTRUCTION

Aluminum alloys for automotive construction are largely dominated by three classes of materials. These include both sheet and casting grades. Sheet materials include both 5XXX and 6XXX alloy classes. 5XXX materials are nominally solid solution strengthened /work hardenable grades. These materials are typically alloyed with magnesium (2–5%), and are also applied where corrosion resistance is required. These materials are primarily used in under-body applications. Most common alloys here are 5754, 5182, and more recently 5083. 5XXX alloys are largely used for underbody applications. 6XXX materials are precipitation hardening type alloys, containing additions of both Mg (0.5 to 1%) and Si (0.5 to 1.5%). Specific variants under consideration include 6111 and 6022 alloys. Materials are generally supplied in the T4 (natural aged) condition, and then subjected to forming and subsequent welding. Peak strengths are then obtained as part of the paint bake aging cycle. This class of alloys is attractive for dent resistance applications (skin panels) due to the high-tensile strengths obtainable ( < 300 MPa) after aging. Aluminum casting alloys used in automotive construction are typically of the A3XX grade. These are aluminum-magnesium -silicon alloys using the high silicon content to promote castability. Another material aspect almost universal for automotive-grade aluminum alloys is surface pretreatment. Aluminum is a reactive metal and well known to form an instantaneous oxide on contact with air. This surface is also known to hydroxylate on exposure to humid conditions. Generally, instabilities in surface conditions are known to lead to quality variations in a range of joining technologies. As a result, considerable work has been done to develop specific surface treatments for automotive aluminum alloys. The majority of the treatments used in the automotive industry include a bonding agent and a lubricant.







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