搅拌摩擦加工低镁Al-Mg-Sc-Zr合金组织及高应变速率超塑性

Microstructure and High-Strain-Rate Superplasticity of Friction Stir Processed Al-Mg-Sc-Zr Alloy with Low Magnesium Content

摘要:

研究了搅拌摩擦加工速比因子对Al-3Mg-0.1Sc-0.1Zr合金显微组织、显微硬度和超塑性能的影响。结果表明，随着速比因子和热输入的增加，搅拌区面积增大，晶粒尺寸变大，动态再结晶更加充分，而搅拌区硬度峰值降低。不同速比因子加工的合金在温度为475 ℃、应变速率为10^–2 s^–1的条件下进行拉伸实验时均发生高应变速率超塑性，并观察到3种类型的真应力-真应变曲线。其中速比因子为4的合金延伸率最高，达到2500%，且在拉伸断裂前产生明显的应变硬化，这将改善常见的超塑性成形后期应力软化流失现象，表现出较高的工程应用价值。优异的超塑性主要归因于热稳定性好的等轴细晶以及高比例的大角度晶界组织，基于晶粒长宽比、孔洞演变以及断口侧面形貌分析，各速比因子下合金超塑性变形的主要机制为晶界滑移。

Abstract:

The effect of speed ratio factor of friction stir processing on microstructure, microhardness and superplasticity of Al-3Mg-0.1Sc-0.1Zr alloy was investigated. The results show that with the increase in speed ratio factor and heat input, the area of stir zone and the grain size are increased, the dynamic recrystallization is more complete, while the peak hardness in stir zone is decreased. All alloys processed at different speed ratio factors show high-strain-rate superplasticity when they are tensile-tested at 475 ℃ with strain rate of 10^–2 s^–1. Three types of true stress-true strain curves are observed during tensile tests. The optimal elongation of 2500% is achieved in the alloy processed with a speed ratio factor of 4, and significant strain hardening occurs before tensile fracture, which improves the common softening loss of stress at the later stage of superplastic forming, implying high engineering application value. The outstanding superplasticity is mainly attributed to equiaxed fine grains with excellent thermal stability and a high proportion of high angle grain boundaries. Based on the analysis of grain aspect ratio, cavity evolution, and morphology of fracture profile, the dominant mechanism of superplastic deformation under all speed ratio factors is grain boundary sliding.