Solidification pathways and hot tearing susceptibility of MgZnxY4Zr0.5 alloys

Abstract

Hot tearing is known as one of the most serious solidification defects commonly encountered during solidification. It is very important to study the solidification path of alloys. In the work, thermal analysis with cooling curve was used for the investigation of microstructure evolution with different Zn contents during solidification process of MgZnxY4Zr0.5 alloys. Thermal analysis results of MgY4Zr0.5 alloys revealed one distinct phase precipitation: a-Mg. Three different phase peaks were detected in the Zn-containing alloys: a-Mg, Z-phase (Mg12YZn) and W-phase (Mg3Y2Zn3). In addition, for the present MgZnxY4Zr0.5 alloys, the freezing ranges of these alloys from large to small were: MgZn1.5Y4Zr0.5>MgZn3.0Y4Zr0.5>MgZn0.5Y4Zr0.5>MgY4Zr0.5. The effect of different contents of Zn (0, 0.5, 1.5, 3.0wt.%) on hot tearing behavior of MgY4Zr0.5 alloy was investigated using a constrained rod casting (CRC) apparatus equipped with a load cell and data acquisition system. The experimental results show that the addition of Zn element significantly increases hot tearing susceptibility (HTS) of the MgY4Zr0.5 alloy due to its extended freezing range. Some free dendrite-like bumps and ruptured liquid films on the fracture surfaces were observed in all the fracture surfaces. These phenomena proved the fact that the hot tearing formation was caused by interdendritic separation due to lack of feeding at the end of solidification.