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Automotive manufacturers are continually pushing for reduced cost, increased fuel economy, lower emissions and improved performance. Magnesium is the lightest structural metal and has therefore enjoyed a double-digit annual growth in automotive applications since 1990, aimed at reducing vehicle platform weights to increase fuel economy. Nevertheless the progress of magnesium as an alternative lightweight structural material (compared to aluminum, engineered plastics and high alloy steels) is being impeded by the lack of published alloy properties and general knowledge of the material. Thixomat, Inc. is conducting independent fundamental studies to measure the influence of Thixomolding® process parameters on a variety of physical and mechanical properties for injection molded magnesium alloys. Determination of conventional mechanical properties are being complemented with fatigue behavior studies using new ultrasonic fatigue instrumentation at the University of Michigan.

Thixomolding® produces net-shape parts from Magnesium alloys in a single step process involving high speed injection molding of semi-solid thixotropic alloys. A description of the process and status of commercial developments will be presented.. The mechanical properties and microstructures of Thixomolded® AZ-91D magnesium materials will be presented. Tensile strengths of semi-solid AZ-91D at both room temperature and elevated temperatures ( 373K, 423K) are compared with die cast AZ-91D. Data on enhanced creep properties of Thixomolded® AZ91-D alloy relative to die cast AZ-91D will be examined with respect to relative changes in microstructural features. Controlling the percent solids in the semi-solid state prior to injection molding can lead to improved creep performance for use in net-shape automotive components.