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Weight reduction is the key argument for the application of aluminium in cars. However, the extra costs and its limited formability compared to steel slow down the increase in volume. Application of dry lubricants improves the forming behavior as well as reduce the sensitivity to surface damage. A pre-treatment of the surface before assembly is necessary in order to guarantee a good durability of the joints. Cost optimization can be realized when downgauging possibilities of pre-aged material (Superlite®) having an improved bake-hardening response are utilized. A further possibility for cost optimization at the car manufacturer is created when the supplier performs all three processing steps (pre-ageing, pre-treatment and dry-lubricant) in one continuous annealing and surface pre-treatment line.

The choice of alloys for closures is dependent on the functional requirements such as dent resistance, torsional rigidity, feasibility of the panel and corrosion resistance. Based on its good hemming performance, low FFC susceptibility and high formability AA6016 is the preferred alloy choice for outer panels in Europe. With the newly developed pre-bake qualities 6016 T4P having an improved Bake-Hardening-Response for conventional paint lines the requirement for dent resistance is no longer a limiting factor for downgauging. When torsional rigidity is the most critical demand for closures the 6016/5182 as outer/inner combination provides the best weight saving solution.