微观组织演变对细晶Mg-Y-Nd合金超塑性性能的影响

Influence of Microstructure Evolution on Superplastic Properties of Fine-grained Mg-Y-Nd Alloy

在初始应变速率为2×10^-2~4×10^-4 s^-1,温度为683~758 K的条件下,对用水下搅拌摩擦加工制备的细晶Mg-Y-Nd合金进行高温拉伸实验,研究了微观组织演变对其超塑性性能的影响。结果表明:因为具有细小均匀的微观组织和良好的热稳定性,Mg-Y-Nd合金在733 K和3×10^-3 s^-1初始应变速率下表现出最大的伸长率(967%),在758 K和2×10^-2 s^-1条件下表现出最优的高应变速率超塑性(900%)。在高温下暴露时间过长导致α-Mg晶粒和第二相颗粒显著长大,使试样的伸长率明显降低;因为第二相颗粒与镁基体之间有良好的变形协调性,在相界处不会产生明显的应力集中,裂纹主要在晶界生成。

Superplastic performance of the submerged friction stir processed Mg-Y-Nd alloy was assessed by initial strain rates in range of 2×10^-2 to 4×10^-4 s-1 at temperatures in range of 683 to 758 K, aiming to reveal the correlation of the microstructure evolution and the superplastic performance of the alloy. Results show that due to the fine-grained and stable microstructure, the alloy exhibits the maximum elongation of 967% by strain rate of 3×10^-3 s^-1 at 733 K, and the excellent high strain rate superplasticity of 900% by 2×10^-2 s^-1 at 758 K respectively. The average size of α-Mg grains and secondary phase particles remarkably increased when the alloy subjected to high temperature tensile tests for long time, as a result, the elongation of the alloy significantly decreased. Cavities easily formed at grain boundaries instead of the interface of secondary particles and matrix, which may be responsible to the good deformation compatibility between particles and matrix.