Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments

Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments were investigated. As-cast alloy was composed of alpha(Mg) matrix, interdendritic alpha(Mg) + W(Mg3Zn3Gd2) eutectic, icosahedral quasicrystalline I(Mg3Zn6Gd) phase and Mg3Gd particles within alpha(Mg) matrix. After solution treatment at 505 degrees C for 16 h, most of alpha(Mg) + W(Mg3Zn3Gd2) eutectic dissolved into alpha(Mg) matrix, but a new phase, Zn2Zr3, precipitated within alpha(Mg) matrix. The appropriate aging treatment was done at 220 degrees C for 16 h, after which some dispersive fine eutectics re-precipitated along the grain boundary. Furthermore, rod-like beta(1)' and plate-like beta(2)' formed within alpha(Mg) matrix. The ultimate tensile strength, yield strength and elongation of the experimental alloy in the T6 state at room temperature were 280 MPa, 175 MPa and 7.5%, respectively. According to strengthening contribution calculation, it is revealed that both the second phase strengthening and the solid solution strengthening played important roles in improving the mechanical properties after T6 treatment. (C) 2015 Elsevier B.V. All rights reserved.