Observations of the Relative Performance of Magnesium and Aluminum Steering Wheel Skeletons with Identical Geometry

Automotive steering wheels depend on a structural skeleton made of steel, aluminum, or magnesium to be the basis for the mechanical properties of the finished part. The mechanical properties of concern are the fatigue properties and the crash performance. The purpose of this study was to evaluate the crash and the fatigue performance of a steering wheel skeleton fabricated by high pressure die casting. Two materials were used to produce two groups of wheels with identical geometry. The production part was designed, optimized and fabricated with AM50A magnesium. The production magnesium component met all of the regulatory design and performance requirements. A small sample run was made in a proprietary aluminum - magnesium alloy. The fatigue and crash properties were evaluated empirically.

In fatigue testing, the aluminum skeletons displayed a significant improvement, with respect to the magnesium skeletons, in the number of cycles to failure at the loads tested. Droptower impact tests were used to simulate a crash environment. The crash performance was described by an Energy Absorption Factor (E.A.F) and the Coefficient of Restitution. The results indicated that the aluminum skeletons absorbed more energy than the magnesium skeletons. The aluminum skeletons performed well under severe impact loading, while some cracking and fracture was observed in the magnesium parts. Further testing was performed to compare the crash performance of the two skeletons after fatigue cycling. There was no evidence of decay in crash performance after fatigue in the test conditions used.