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The development of commercial magnesium die casting alloys has progressed over the past several decades. The most commonly used die casting alloy, AZ91D, with 9% aluminum content, has been and still is used in the majority of structural automotive applications. New magnesium alloys have been developed in the past several years to meet the needs of structural applications that require an appreciable amount of creep resistance and improved stress relaxation performance during service. Typical applications would include powertrain components. This paper provides further mechanical property data on the “AE-Type” magnesium alloys. These alloys consist primarily of aluminum and rare-earth additions to magnesium to increase creep resistance and stress relaxation performance attributes of the base metal. However, changes in tensile strength, elongation, etc. may also be realized.

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.