ABSTRACT

In the drive toward light transportation vehicles for ground and aerospace magnesium and its alloys are attractive candidate structural materials due to their low density and good mechanical properties. Powder metallurgy (P/M) offers additional advantages of alleviating formability problems through near-net-shape processing and also allows unique chemical compositions that can lead to new alloys with novel properties. The present era of additive manufacturing in part relies on consolidating of powders, and it is important to review the history of metal sintering. For reactive metals, and particularly Mg, the surface layer formed on powders during processing acts as a barrier to diffusion, and sintering is problematic. During the process to develop magnesium alloys via powder metallurgy it was found that the layer contains oxides, hydroxides, hydrates, and carbonates of magnesium formed by reactions with the atmosphere. Each of these compounds are decomposed at different temperatures and the study of sintering contained plenty of surprises and pitfalls. In the present study the global view of the research towards structurally acceptable magnesium alloys is discussed. Results relevant to the fundamental sintering studies obtained by FIB-TMS, XPS, DSC, and mechanical post processing are discussed along with the results of strategies such as creating cracks on the surface layer and reducing the layer by additions of Ca, Li, Sn, and Y are presented. In addition, a thermochemical analysis of the magnesium sintering process is presented.