Mechanical Properties and Microstructure of AZ31 Magnesium Alloy Processed by Intermittent Ultrasonic-Assisted Equal Channel Angular Pressing

An intermittent ultrasonic-assisted equal channel angular pressing (IU-ECAP) technique for grain refinement is proposed in this study. AZ31 Mg alloy samples were divided into two groups (IU-ECAP and ECAP) and processed using four passes along route BC, and the effects of ultrasonic vibration on the mechanical properties and microstructure were examined. Mechanical testing revealed that IU-ECAP significantly reduced the extrusion force relative to that for ECAP, whereas the microhardness and ultimate tensile strength were strengthened. The maximum true ultimate tensile strength and microhardness of the IU-ECAPed specimens were achieved using ultrasonic vibration with an amplitude of 35 μm and intermittent time of 2 s. In addition, the microstructures were the most homogeneous for the smallest grain sizes. The IU-ECAPed specimens also possessed less high-angle grain boundaries because of the lower temperature of the IU-ECAP die. Texture analysis revealed that after the 4th pass, the texture of the IU-ECAPed specimens along the (0001) crystal plane exhibited maximum reduction; furthermore, the textures along the (0001), ( $$01\bar{1}0$$ ), and ( $$\bar{1}2\bar{1}0$$ ) crystal planes were scattered homogeneously. These findings may be related to ultrasonic-induced grain boundary rotation.