Effect of Cooling Rate on Microstructure and Mechanical Property of Mg-4.4Zn-0.3Zr-0.4Y Wrought Magnesium Alloy

Abstract

The Mg-4.4Zn-0.3Zr-0.4Y (mass fraction/%) alloy ingots were prepared by two casting processes namely air cooling and water cooling. These two types of Mg-4.4Zn-0.3Zr-0.4Y alloy ingots were extruded and then ageing treated under the same conditions, and the effect of ageing treatment on the microstructure and mechanical properties of the alloys was studied. The results show that the lamellar eutectic structure and dendrite cell size are significantly refined under water cooling, which restrain the formation of W phase (Mg3Y2Zn3) and promote the increase of volume fraction of I phase (Mg3YZn6) in the as-cast alloy. For the different original microstructure and second phase, the ultimate tensile strengths of the extruded Mg-4.4Zn-0.3Zr-0.4Y alloy under water cooling and air cooling reach 327MPa and 306MPa respectively, and the elongations of the alloy reach 14.8% and 10.0% respectively. After ageing treatment, the grain size and texture intensity change slightly. Thus, the contents of precipitated phases (MgZn and MgZn2) mainly affect the mechanical properties of the extruded alloy. The aged as-extruded alloy exhibits a tensile yield strength, an ultimate tensile strength and an elongation of 330, 348MPa and 14.4% respectively under water cooling, and 344, 359MPa and 8.6% respectively under air cooling.

Keywords

• wrought magnesium alloy
• cooling rate
• quasicrystal
• microstructure
• mechanical property