流变轧制AZ91合金的热处理和组织性能调控

Tailoring the microstructure and mechanical properties of AZ91 alloy by rheo-rolling and heat treatment

摘要:

本文对连续流变轧制AZ91合金在热处理过程中的组织和力学性能演化进行了研究。热处理后两种析出相在基体中出现：一种是晶界处的非连续析出相,另一种是从过饱和基体中析出的小尺寸连续析出相。随着时效温度升高,原子扩散速度也随之提高,导致更多的析出相生成和长大。合金的维氏硬度和拉伸强度峰值在16小时时效后出现,而合金的延伸率随着时效时间的延长和时效温度的提高呈下降趋势。经过对实验结果的分析,适合提升合金综合力学性能的热处理制度为415°C固溶20小时加220°C时效16小时。经热处理后得到的维氏硬度、拉伸强度和延伸率分别为：99 HV,251 MPa和4.5%,各项性能均显著优于流变轧制态合金。相对于传统成型手段,流变轧制加热处理方法成型的AZ91合金展现了优异且均衡的综合力学性能。

Abstract:

The evolution of microstructure and mechanical properties of the continuous rheo-rolled AZ91 magnesium alloy during heat treatment was revealed in the present study. Two kinds of Mg17Al12 phases precipitated from the supersaturated magnesium matrix were observed: most of which distributed discretely at grain boundary while the rest precipitated in alloy matrix in small size. With higher aging temperature, atom diffusion velocity increased and more precipitates formed. As a result, the hardness and the tensile strength peaked at 16h, whilst the elongation decreased with increasing time and temperature. The optimal comprehensive mechanical properties were obtained after solution treatment at 415 °C for 20 h and aging treatment at 220 °C for 16 h. The tailored hardness, tensile strength and elongation of the rheo-rolled alloy after heat treatment reached 99 HV, 251 MPa and 4.5%, respectively, which were significantly higher than that of the untreated alloy. Compared with traditional processing methods, rheo-rolling followed by heat treatment demonstrates its effectiveness on tailoring and obtaining balanced mechanical properties of AZ91 alloy.