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JMEPEG https://doi.org/10.1007/s11665-019-04067-2

Microstructure, Texture, and Mechanical Properties of AM60 Magnesium Alloy Processed by Extrusion and Multidirectional Forging M.A. Salevati, F. Akbaripanah

, and R. Mahmudi

(Submitted October 15, 2018; in revised form February 13, 2019) In the present paper, multidirectional forging (MDF), as a severe plastic deformation process, was carried out on an extruded AM60 magnesium alloy. The microstructure, texture, and mechanical properties of the MDFed samples were examined. Microstructural findings indicated that the grain size of the alloy decreased from 10.2 to 3.7 lm after six MDF passes, carried out at a constant temperature of 220 °C. Textural studies revealed that after six MDF passes, the fiber texture of the extruded material was transformed to another texture, in which the basal planes tend to rotate toward 45o to the transverse direction. Shear punch testing (SPT) was employed to assess the shear yield stress (SYS) and ultimate shear strength (USS) at room temperature. Both SYS and USS were enhanced after two MDF passes, but decreased in the next pressing stages, despite developing finer grains at higher levels of imposed strain. The observed drop in strength is ascribed to texture softening that counterbalances the grain refinement strengthening effects. The variation in average microhardness values after different passes of MDF showed the trend that was in concurrence with the rise and fall of the SPT results. Finally, the changes in mechanical properties were discussed, based on the microstructural and textural findings. Keywords

magnesium alloy, mechanical properties, multidirectional forging, texture

1. Introduction Nowadays, lightweight alloys have gained a more vital role due to the energy crisis, environmental issues, and the need for building lighter structures for less fuel consumption in the transportation industry. Because of their low density, good castability, high strength-to-density ratio, ease of recyclability and rational cost, magnesium alloys have attracted considerable attention (Ref 1, 2). However, Mg alloys tend to develop coarse grains during high-temperature processing, and their microstructure becomes inhomogeneous, affecting their mechanical properties. Grain refinement is a proper way of enhancing mechanical properties of Mg alloys. Different severe plastic deformation (SPD) processes, such as equal channel angular extrusion (ECAE), accumulative roll-bonding (ARB), high-pressure torsion (HPT) and multi-directional forging (MDF, are well-established techniques for refining grains to submicron levels and improving mechanical properties (Ref 37). With the increase in deformation severity, materials undergo considerable refinement in such a way that they finally reach an ultrafine grained (UFG) microstructure. Among all SPD M.A. Salevati and F. Akbaripanah, Department of Mechanical Engineering, Faculty of Engineering, Malayer University, Malayer, Iran; and R. Mahmudi, School of Metallurgical and Materials Engineering, College of Engineerin