Development of a new magnesium alloy ZW21

A new magnesium alloy named ZW21 has been developed through orthogonal experiment method and the effects of heat treatment on the alloy’s tensile properties have also been investigated. The results indicate that the alloy only has one Mg–Zn–Y(Nd) phase of Mg3Zn3(Y, Nd)2 (named W phase) and has higher mechanical properties, lower cost and lighter weight compared with the other congeneric alloys. Its microstructure is composed of small equiaxed dendrites and interdendritic discontinuous net-like eutectic structures. The eutectic structures appear in divorced W phase laths in the thin regions between the dendrites and in regular W + α-Mg lamellar structures in the triangle regions. The eutectic structures, especially the W phase, with such distribution are harmful to the tensile properties and thus proper heat treatment can improve its properties through changing the W phase distribution. Solution treatment at 525 °C for 4 h (T4 treatment) increases the elongation from 17.75% to 26.5%. Subsequent ageing treatment at 250 °C for 24 h (T6 treatment) improves the ultimate tensile strength from 210 MPa to 243 MPa. The fracture modes of the as-cast, T4- and T6-treated alloys all obey the quasi-cleavage regime. The fracture of the as-cast alloy belongs to a mixed mode of intergranular and transgranular forms, but those of the T4- and T6-treated alloys follow the transgranular mode due to the relatively high bonding strength between the grains.