Effect of heat treatment on microstructure, mechanical properties and corrosion behavior of Mg–Sm–Zn–Zr–xNd alloys

Simultaneously improving the strength and corrosion properties of Mg alloys remains a significant challenge for biomedical applications. Towards this end, the high-performance Mg-2.0Sm-0.4Zn-0.4Zr-xNd alloys were achieved by alloy design and heat treatment. The microstructure of the as-cast alloy mainly consists of α -Mg grains and β eutectic phase. After the solution treatment at 515 °C for 8 h, most of the β phases decomposed, and the α -Mg grains significantly coarsened. The nanoscale β ′, β 1 and γ ′ phases precipitated from the α -Mg matrix following an aging treatment at 200 °C for 18 h. As the Nd content increased, the precipitates increased gradually, and grains were refined significantly. The aged 2.5Nd alloy had a maximum ultimate tensile strength of 260 MPa, 73 % better than the as-cast Nd-free alloy. The improved mechanical properties were primarily attributed to the effect of precipitation strengthening and fine grain strengthening. The corrosion rate of the aged 2.5Nd alloy was 0.48 mm/year, 28.3 % lower than the as-cast 2.5Nd alloy. The as-cast alloys exhibited poor corrosion properties due to severe micro-galvanic corrosion caused by the uneven distribution of coarse β phases. The heat treatment reduced micro-galvanic corrosion by regulating the quantity and size of nano-precipitates. These findings provide a deeper comprehension of how the mixed light RE elements and heat treatment might improve the overall performance of Mg alloys.