Improving mechanical properties of ZK60 magnesium alloy by cryogenic treatment before hot extrusion

Tao Lin,Ji-Xue Zhou,Xiang-Bin Meng,Yun-Teng Liu,Lin-Lin Zhang,Cai-Nian Jing

doi:10.1515/htmp-2020-0054

Abstract

AbstractFew studies of cryogenic treatment were focused on nonferrous alloys, such as magnesium alloy. In this work, the effect of cryogenic treatment (77 K) before extrusion on microstructure and mechanical properties of ZK60 alloy was investigated. The results showed that many fine G.P. zones were formed during the cryogenic treatment and then grew to short fine {\beta }_{1}^{^{\prime} } precipitates when heating before extrusion. These precipitates pinned dynamic recrystallized grain boundaries in the subsequent extrusion, resulting in fine gains and dispersed spherical precipitates. By the cryogenic treatment before extrusion, the extruded ZK60 alloy showed good tensile strength and elongation balance. Especially, elongation was improved by 29%.

Highlights

Magnesium (Mg) alloys are the light metallic materials with low density and high specific strength
It was reported that the grain size in the as-cast ZK60 alloy was significantly reduced from 70–100 to 30–50 μm after the cryogenic treatment, due to the sub-grain generated by internal stress [31]
It was demonstrated that, in the paper [38,39], the grains in the Mg–1.5Zn–0.15Gd alloy and AZ91 alloy were refined little by the cryogenic treating

Summary

Introduction

Magnesium (Mg) alloys are the light metallic materials with low density and high specific strength. Many works have been done to further enhance their mechanical properties by adding rare earth (RE) or free-RE elements [12,13,14,15,16], using the aging treatment by which Mg–Zn agehardening precipitates were formed [17,18,19,20,21]. The main idea was that fine precipitates were expected to be formed by the APE before hot extrusion. These precipitates could pin the dynamically recrystallized grain boundaries and hinder the growth of them during the subsequent hot deformation [23,24,25]. The extrude magnesium alloy had fine microstructures and a resultant increase in strength and ductility

Methods

Results

Conclusion