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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.

Many process design factors effect the outcome of a sheet stamping operation. Particularly inner panel structures of hang-on panels are difficult to produce in aluminium. This paper deals with material behaviour issues related to formability and friction. Formability is characterized by the mechanical properties while friction is related to surface topography. Formability is evaluated by means of laboratory tests and stamping trials on actual inner panels. Optimum results are obtained with materials with high n value and isotropic r value. An improved AA5182 alloy has been developed to meet these demands on mechanical properties. This alloy creates the best condition for downgauging and cost saving targets.

An extended test program has been carried out at Volvo to determine the implications of the application of pretreated aluminium with dry lubrication. This should replace the standard route which is pressing with oil and subsequent pickling and passivation of panels. The separate results from each individual step in the production route are acceptable. However when a part is put through the whole route from pressing to assembly to paint line then it fails due to cratering after the e-coat. This is a result of incomplete removal of the dry-lubricant. To guarantee complete removal the pre-curing of the adhesives, the degreasing before phosphating and the composition of the dry-lube have to be optimized. Although pretreated aluminium with dry-lube offers great possibilities the application is at present not qualified at Volvo.

This paper focuses on the development and performance of an aluminium prototype bonnet for the Saab 9-3. The first part describes how the bonnet was re-engineered in order to meet the functional demands. The study reveals that when considering these criteria the aluminium bonnet behaves equally well as the steel version and the target, to gain a 50% weight reduction, is met. The second part deals with the results of the performance tests by Saab. These tests give a good indication of the behavior which can be expected for the aluminium bonnets during service of the vehicle.