Potentiality of Thixocasting Associated with Shot Peening for Manufacturing Automobile Wheel Discs

The subject of this communication is the study of weight reduction applied to an automobile wheel disc with the aim of modifying the “weight reduction-freedom of style-cost” asymptote. The performance levels of thixoformed parts are compared with the manufacturers' specifications and with the performance levels of parts with identical references which are low-pressure cast or forged. The average fatigue resistance of thixoformed discs (Lf = 120 MPa at 6×10⁶ cycles), due to insufficient control of the surface quality, does not enable the weight-reduction performance sought to be achieved. To get closer to the target, surface impact prestressing treatments implemented with an appropriate Almen intensity give the parts significantly higher resistance to fatigue than expected, leading to potential weight reduction, confirmed by experience, which may exceed 40%. These initial results point out that several certifiable and industrializable solutions which are well positioned in terms of “Cost-Weight Reduction-Freedom of Style” target can be envisaged thanks to prestressing treatments. Thixocasting and, even more, rheocasting, have the greatest potential, providing surface quality is under control and complies with specification.