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Designing for fatigue performance requires extensive knowledge of material properties, component geometry and dynamic loading conditions. These topics are addressed in an ongoing cohesive research program on fatigue behavior of magnesium die castings. The current phase of the program includes effects of alloy type, mean stress level, surface condition, and level of tensile properties. The results, presented as S-N curves and Goodman diagrams, show a significant difference in the fatigue life between AZ91D and the AM alloys. Fatigue behavior of AM60B was strongly dependent on the mean stress level, but was not significantly influenced by a minor difference in casting quality. The fatigue behavior of AM50A was not noticeably changed by the addition of vibratory polishing.

The qualification process leading to the utilization of refined recycled, high ductility magnesium alloys for automotive components at Chrysler Corporation is described. This process encompassed the steps from demonstrated process control during ingot production through the parallel performance testing of components produced from both electrolytic and refined recycled AM50A and AM60B alloys. The results of chemical analysis, optical and electron metallography, image analysis and corrosion testing of the ingot materials showed the electrolytic and refined recycled forms of the alloys to be indistinguishable. Mechanical property and salt spray corrosion tests of die cast specimens from the materials demonstrated their equivalence as well. Finally, the results of specified vehicle performance tests for three production components indicated that castings made from refined recycled AM50A and AM60B performed equally to their counterparts from electrolytic alloy materials.

The phenomenon of stress relaxation in a solid corresponds to a time-dependent decrease in stress under given constraint conditions. An apparatus for stress relaxation compression testing was constructed and utilized to evaluate a series of die cast magnesium alloys. The behavior of the alloys was determined over a 100 hour test period. In general, the percentage of stress remaining after this time decreased with increased initial stress and with increased test temperature. Of the materials tested, magnesium alloy AE21 showed the best relaxation resistance relative to 383 aluminum alloy.