Effects of treatment situations on the microstructure and mechanical properties of ZTM630 magnesium alloys

In this work, Mg-6Zn-3Sn-0.5Mn (ZTM630) alloy was prepared with different heat treatment states including as-cast, homogenization, hot extrusion and double-age. The microstructure and tensile mechanical properties of the alloy with four states were investigated. The very high cycle fatigue (VHCF) tests have been performed to evaluate long-term service properties of the extruded and double-aged alloys. Fatigue strength and fatigue crack initiation mechanism were analyzed. After double-aging, the secondary phase in size of dozens nanometers distributes evenly in the matrix, α-Mn phase distributed at the grain boundary effectively inhibits the grain growth, and the double-aged alloys has the highest tensile mechanical strength. The fatigue ratios σ−1/σb of the extruded and double-aged alloys are 0.44 and 0.37, respectively, which means that ZTM630 alloys in the two states possess an excellent fatigue performance. As the activity of slipping is limited in the double-aged ZTM630 alloy, twinning behavior induces fatigue crack initiation during the VHCF test, while slip-dominated fatigue crack initiation of the extruded ZTM630 alloy.