Microstructural characterizations on Mn-containing intermetallic phases in a high-pressure die-casting Mg-4Al-4RE-0.3Mn alloy

The types and the detailed structures of the Mn-containing phases in the high-pressure die-casting Mg-4Al-4RE-0.3Mn alloy were thoroughly investigated using transmission electron microscopy (TEM). The results reveal five Mn-containing intermetallic phases with different morphologies, namely the regular blocky phase, the irregular blocky phase, the interlaced lath-shaped phase, the nano-scale phase on the surface of or embedded in the Al11RE3 particles, and the nano-scale precipitate in the α-Mg matrix. The former twos belong to Al10RE2Mn5 but the latter one contains numerous normal (11.1) twins and orientation twins. In addition, the third one simultaneously contains Al10RE2Mn5 and Al8REMn4, of which both are coherent with each other and contain normal twins. Finally, the last two nano-scale Mn-containing phases on the surface of or embedded in Al11RE3 and precipitated in α-Mg grains are Al10RE2Mn7 and Al8Mn5, respectively.