Effects of homogenization treatment on microstructure and elongation of the Mg–13Gd–4Y–2Zn–0.6Zr alloy

Abstract

The microstructure and elongation of Mg–13Gd–4Y–2Zn–0.6Zr (wt%) alloy after homogenization treatment at 500 °C and 520 °C in the time range of 0–40 h were investigated by optical microscopy, x-ray diffraction, scanning electron microscopy with energy dispersive spectrometer and tensile tests. Tensile tests were performed at a temperature range of 20 °C–300 °C with different strain rates of 10−3 and 10−1 s−1. The results indicate that the as-cast alloy is composed of α-Mg matrix phase with lamellar structure, (Mg, Zn)24(Y, Gd)5 phase and Mg12(Y, Gd)Zn phase. With increasing the holding time, the lamellar structure in the as-cast alloy completely disappears first, then a new lamellar structure forms in the Mg matrix and gradually increases, finally the new lamellar structure gradually reduces during homogenization treatment. The (Mg, Zn)24(Y, Gd)5 phase completely disappears and the morphology of Mg12(Y, Gd)Zn phase transforms into strip-shaped. Especially, a large number of grain boundary precipitated particles (GBPs) generate after the homogenization treatment at 520 °C. The elongation of all specimens after homogenization treatment at 500 °C slightly decreases first, then increases rapidly, finally decreases slowly or remains stable with increasing the holding time. It is considered that volume fraction of the lamellar structure and the size of the eutectic phase at the grain boundaries are the main factors affecting the elongation. The elongation of all specimens after homogenization treatment at 520 °C is lower than that of homogenization treatment at 500 °C. It is because a large number of GBPs at the grain boundaries have an adverse effect on the elongation.