The Influence of Zinc Content, Strain Rate, and Deformation Temperature on the Thermomechanical Compression of Magnesium-Zinc-Cerium Alloys

A recent focus on environmental preservation has led to a call for increasing in fuel efficiency and the reduction of vehicle emissions. One approach that U.S. automakers intend to take to address this issue is increasing vehicle efficiency through weight reduction. Additionally, a redistribution of the vehicle center of gravity can increase safety through enhanced handling and control. Magnesium is an attractive material due to having the lowest density among engineering materials however its use to date has been hindered by its relatively low ductility, strength, and tendency to exhibit galvanic corrosion. A Mg-Zn-Ce alloy has been developed which greatly reduces these shortcomings and presents itself as an acceptable candidate to lower vehicle front-end weight. Though this alloy system has shown drastic formability increases over pure magnesium and other Mg-based alloy systems, relatively little is understood about the behavior of this system. This study examined the compression behavior of this alloy at different zinc contents, deformation temperatures, and strain rates. It was observed that the lowest zinc content (2 wt.%) was the most formable as it was able to be compressed over the largest range of strain rates and temperatures. Through a metallurgical examination of the raw material and deformed samples it was seen that at low temperatures samples were able to accommodate imposed stress via twinning. High deformation temperatures showed evidence of dynamic recrystallization. An electron microscopy examination showed that there was a large amount of zinc segregation at the grain boundaries, and showed intergranular fracture modes suggesting that detrimental zinc increases were detrimental. An EBSD analysis showed randomized as-cast grain orientation, as well as randomly oriented grains in recrystallized regions suggesting heterogeneous texture played a large role in increasing ductility.