Microstructure and mechanical properties of Mg-Zn-Dy-Zr alloy with long-period stacking ordered phases by heat treatments and ECAP process

A high-strength and good-ductility Mg93.83Zn1.5Dy4.5Zr0.17 (at%) alloy containing long-period stacking ordered (LPSO) phases was prepared by conventional casting, heat treatments and an equal channel angular pressing (ECAP) process. The microstructure evolution, especially the second phases (LPSO phases), and the mechanical properties of Mg93.83Zn1.5Dy4.5Zr0.17 alloy tailored by different treatments were investigated. The results showed that the microstructure of the as-cast alloy was composed of α-Mg matrix, block LPSO phases and eutectic phases. And, the latter two phases formed a continuous network structure in the vicinity of grain boundaries. After heat treatments, the eutectic phases in the vicinity of the grain boundaries all dissolved, while large amounts of block LPSO phases and lamellar phases were precipitated. The LPSO phases were refined obviously and a large number of kinks emerged after the ECAP treatment. The as-cast alloy exhibited ultimate tensile strength and elongation of 152 MPa and 3.58% at room temperature, respectively. After a series of treatments, the ultimate tensile strength of the alloy was increased to 322 MPa with elongation of 23.6%.