Microstructure and mechanical properties of NZ30K magnesium alloy processed by repetitive upsetting

A Mg-3.03Nd-0.24Zn-0.49Zr (wt.%, NZ30K) magnesium alloy was subjected to repetitive upsetting (RU) at 400 °C for 0, 1, 4 and 8 passes, respectively. The influence of RU on the microstructure evolution and mechanical properties was investigated. Results show that with the increase of RU passes, the grains of the alloy are significantly refined and the microstructure homogeneity all over the sample is greatly enhanced. The alloy exhibits a homogenous equiaxed microstructure with an average grain size of 4 μm after RU for 8 passes, compared with the initial 90 μm. Both the strength and ductility are notably improved with RU passes. The yield strength, ultimate tensile strength and elongation of the 8-passes alloy are 208.16 MPa, 248.50 MPa and 30.10%, compared with the 153.28 MPa, 213.99 MPa and 8.43% prior to RU, respectively. Yield phenomenon is observed on the tensile stress-strain curves and it becomes more pronounced with grain refinement.