The Continued Quest for Low-Temperature Formability in Mg Alloys: Historical Developments and Future Opportunities

摘要

It is well-known that opportunities for the application of wrought magnesium alloys have been limited by the limited low-temperature formability. The roots of this problem lie in the limited number of active slip mechanisms and strong basal textures, which result in strong deformation aniso-tropy, and thus brittle behavior. Historically, there have been many studies on approaches that aim at activation of non-basal deformation mechanisms and weakened or randomized texture to lend magnesium allows more formability. On the processing side, these approaches include rolling variants such as cross-rolling, twin-cast rolling, and differential speed rolling. On the alloying side, it has been shown that the addition of rare-earth elements (REs) activates non-basal slip modes and simultaneously weakens texture, therefore improving the plasticity, however the cost and availability or REs has encouraged the search for similar, yet cheaper alternatives. In this regard, Ca has emerged as a strong candidate replacement element, with Mg-Ca alloys showing many similar behaviors to Mg-RE alloys. Another less-common approach to enhanced formability is grain refinement. It is commonly believed that fine grained Mg-alloys will not behave in a uniform plastic manner due to the suppression of the twinning mechanisms that are critical to c-axis deformation. New studies, however, indicate that reduction of grain sizes to the sub-micrometer, and even nanoscale, can alter plasticity mechanisms and promote more uniform material flow. Other novel approaches to enhancing formability, including nanoparticle dispersions and tension-twin promotion will be presented. The scientific opportunities and challenges for each mechanism will be deliberated, and future research and development opportunities will be considered.