Interphase precipitation in an Ag-modified Mg-Al-La casting alloy

Abstract Intermetallic precipitates at a Mg/η-Al3La interface formed during solidification were studied using transmission electron microscopy. Two precipitates, namely e-Mg3Ag (or e-Mg26−xAg7+x) and β-Mg2(Al, Ag)3, were revealed to be semi-coherent with η-Al3La, following crystallographic orientation relationships as: (001)e//(001)η, [010]e//[010]η and (110)β//(001)η, [ 3 ¯ 32]β//[010]η, respectively. Although with a greater mismatch for (001)e//(001)η, e phase is significantly more than β phase. The underlying causes were discussed and revealed as the greater driving force of Ag segregation during solidification and the straightforward formation path of e phase.