Hot Tearing Behavior of Mg-Gd-Y-X Alloys

Mg-Gd-Y-Zr alloy castings are widely used in the aerospace field owing to their high strength and excellent creep resistance. The castability of these alloys is also an important consideration for engineering application.Thus,the hot tearing susceptibilities(HTSs)of Mg-10Gd-1Y-1Zn-0.5Zr(VW91)alloy and Mg-10Gd-2Y-1Zn-0.5Zr(VW92)alloy are investigated with a constrained rod casting(CRC)mold. The microstructures and fracture surface are characterized by optical microscope and scanning electron microscope. The results unveil that the HTS of VW92alloy is lower than that of VW91 alloy. The microstructures indicate that obvious tears can be observed in VW91 alloy,while the tears in VW92 alloy are tiny. The tear feeding and healing by eutectic are also observed in VW91 and VW92alloys. Therefore,the lower hot tearing susceptibility of VW92 alloy is mainly attributed to the high amount of eutectic which feeds and heals tears. Besides,the effects of the coefficient of thermal expansion(CTE)and the fluidity of VW91 and VW92 alloys on their HTSs are discussed.