Microstructures and mechanical properties in a Gd-modified high-pressure die casting Mg-4Al-3La-0.3Mn alloy

Effects of 2 wt% Gd addition on microstructures and tensile properties of a high-pressure die casting (HPDC) Mg-4Al-3La-0.3Mn (wt.%) alloy were studied. The newly developed alloy owns much finer grains than commercial/experimental HPDC Mg alloys. Furthermore, it contains various intermetallic phases, namely eta-Al-3(La, Gd), Al-2(Gd,La) or Al-2(La,Gd), Al-7(La,Gd)(3) and Al-2.12(La,Gd)(0.88), among which Al-7(La,Gd)(2) was experimentally observed in Mg-Al-RE-based alloys for the first time. Moreover, both eta-Al-3(La,Gd) and Al-2(Gd,La) present two or more morphologies due to different chemical compositions. Finally, the studied alloy exhibits more excellent tensile properties than commercial/experimental HPDC Mg-Al-based alloys. The underlying causes for grain refinement, variety of intermetallic phases, as well as excellent tensile properties were discussed and revealed.