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Most of the applications of magnesium in lightweighting commercial cars and trucks are die castings rather than sheet metal, and automotive applications of magnesium sheet have typically been experimental or low-volume serial production. The overarching objective of this collaborative research project organized by the United States Automotive Materials Partnership (USAMP) was to develop new low-cost magnesium alloys, and demonstrate warm-stamping of magnesium sheet inner and outer door panels for a 2013 MY Ford Fusion at a fully accounted integrated component cost increase over conventional steel stamped components of no more than $2.50/lb. saved ($5.50/kg saved). The project demonstrated the computational design of new magnesium (Mg) alloys from atomistic levels, cast new experimental alloy ingots and explored thermomechanical rolling processes to produce thin Mg sheet of desired textures.

Magnesium and aluminum alloys offer lightweighting opportunities in automotive applications. Joining of dissimilar materials, however, generally requires methods that do not involve fusion. This paper explores the use of self-pierce riveting (SPR) to join magnesium to aluminum alloys for structural and closure applications. The preliminary results indicate that SPR is a viable option for joining aluminum extrusions to magnesium die castings, as well as stamped sheet aluminum to quick-plastic-formed (QPF) sheet magnesium.

Experimental decklids for the Cadillac STS sedan were made with Al AA5083 sheet outer panels and Mg AZ31B sheet inner panels using regular-production forming processes and hardware. Joining and coating processes were developed to accommodate the unique properties of Mg. Assembled decklids were evaluated for dimensional accuracy, slam durability, and impact response. The assemblies performed very well in these tests. Explicit and implicit finite element simulations of decklids were conducted, and showed that the Al/Mg decklids have good stiffness and strength characteristics. These results suggest the feasibility of using Mg sheet closure panels from a structural perspective.

This study details preliminary results of hot rolling trials of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400 and 450°C and two rolling speeds, 20 and 50 RPM. A total thickness reduction of 67% was obtained using multiple passes with reductions of either 15% or 30% per pass. The entry temperature of each rolling schedule was kept constant, by reheating the strip between passes. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e. strain) per pass and the rolling speed (i.e. strain rate). A combination of a rolling temperature of 400°C, reduction per pass of 15%, and rolling speed of 50 RPM produced the finest and most homogeneous microstructure.

Experimental quick plastic forming (QPF) of commercially available magnesium alloy AZ31B sheet into Cadillac STS decklid inner panels was done successfully with existing QPF tools and processes developed for forming QPF-grade AA5083 aluminum sheet. This demonstrates that QPF parts designed for aluminum can be made with magnesium. The post-formed properties of the formed panel were investigated. Thinning of the magnesium alloy sheet in the successfully formed panel was limited to just under 50%, which is normally considered acceptable in QPF aluminum panels. The basal crystallographic texture of the sheet material was essentially maintained through the forming process. Tensile properties of samples cut from the formed panels exceed the specified minimums for the O-temper AZ31 sheet. Significant reduction in cycle time is expected based on the results of this work.