低温慢速挤压和电脉冲处理制备具有优异力学性能的AZ91双峰合金

Exceptional mechanical properties of a bimodal AZ91 alloy prepared by low-temperature slow rate extrusion and electrical pulse treatment

摘要:

通过低温慢速挤压(LTSRE)和电脉冲处理(EPT)获得具有双峰结构的AZ91镁合金,这种结构由粗大的尺寸约为20-60μm 的未再结晶晶粒和细小的尺寸约为200nm的再结晶晶粒组成。双峰晶粒结构的形成原因主要是LTSRE过程中的不均匀变形以及EPT对于变形AZ91镁合金静态再结晶的加速效应。与常规热处理时的静态再结晶过程相比,EPT过程的再结晶温度显著降低,处理时间明显缩短,有效抑制了再结晶晶粒的生长。同时在EPT过程中析出了大量形状规则的Mg₁₇Al₁₂相,平均尺寸约为200nm。因此,本研究获得了屈服强度为463MPa和极限抗拉强度为527MPa的AZ91双峰合金,这主要归功于双峰组织以及细晶强化、析出强化和加工硬化的共同作用。

Abstract:

Low-temperature slow rate extrusion (LTSRE) and electrical pulse treatment (EPT) were carried out to obtain a bimodal microstructure in AZ91 Mg alloy, which consisted of coarse un-recrystallized grains of about 20-60μm and fine recrystallized grains of around 200nm. The bimodal grains can be contributed to the inhomogeneous deformation under LTSRE and the acceleration effect of the static recrystallization of the deformed AZ91 magnesium alloy under EPT. In addition, the growth of the recrystallized grains was effectively restrained due to the notably lower recrystallization temperature and shorter processing time compared with the conventional static recrystallization by heat treatment. Meanwhile, abundant Mg₁₇Al₁₂ phase with an average size of 200nm and regular shapes precipitated during EPT. Consequently, the exceptional yield strength of 463MPa and ultimate tensile strength of 527MPa were acquired in the bimodal AZ91 alloy, which can be primarily attributed to the bimodal microstructure as well as the combined effect of fine grain strengthening, precipitation strengthening and work hardening.