This study is a life cycle assessment (LCA) comparing two types of a powertrain structural component: one made of diecast primary aluminum and another hypothetical part made of semi-solid injection molded primary magnesium (Thixomolded(r)). The LCA provides an indication of the potential environmental burdens throughout the life cycles of both parts, ranging from raw material acquisition to product end-of-life. Preliminary results show high sensitivity to selection of primary vs. secondary metals, and to the SF6 emission factor used in the model. Opportunities exist for reducing energy consumption using secondary instead of primary metals for both parts, although the use of such is influenced by market supply and demand.