Effect of heat treatment on microstructure, mechanical properties and corrosion behavior of Mg–Sm–Zn–Zr–xNd alloys
So Young Yi, Sicong Zhao, Yicheng Feng, Lei Wang, Erjun Guo, Qingya Sun
Abstract
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.