Effects of variable-cavity liquid forging on microstructure and mechanical properties of Mg-Zn-Y-Zr alloy

The effects of a variable-cavity liquid forging process on the microstructure and mechanical properties of an Mg-5Zn-1Y-0.6Zr magnesium alloy are described based on the results and analysis. The results indicate that the microstructure of the alloy changed clearly during the deformation process. After variable-cavity liquid forging, the dendrites are elongated along the deformation direction. The alloys with different deformation temperatures consist of alpha-Mg, the Mg-Zn phase, the I-phase (Mg3YZn6) and the W-phase (Mg3Y2Zn3). The I- and W-phases are mainly distributed in the grain boundaries, and the Mg-Zn phase is mainly dispersed in the grains. Most of second phase is broken into fine particles during the variable-cavity forging process. There is high dislocation density in the elongated grains at a deformation temperature of 350 degrees C, especially near the grain boundaries. Due to the dislocations, there are some tiny subgrain structures (less than 1 mu m) formed near the second phase. After the variable-cavity liquid forging process, the subgrain structures did not recrystallize. The mechanical properties are significantly affected by the second phase and size of the grains. The highest tensile strength is 351.5 MPa at a deformation temperature of 350 degrees C, which is due to retained eutectic pockets. The best elongation is 7.15% at a deformation temperature of 450 degrees C, which is due to the tiny second phase particles and fine grains.