Thermo-Mechanical Treatment on Microstructure and Mechanical Properties of Mg-5.0Sn-1.0Mn-0.4Zr Alloy

Xiaoping Luo,Baosheng Liu,Daqing Fang

doi:10.4236/ampc.2018.81004

Abstract

The mechanical properties and microstructure of an as-cast Mg-5.0Sn-1.0Mn-0.4Zr alloy were investigated during thermo mechanical treatments consisting of hot extrusion, rolling, and ageing at 200°C. The results indicate that only Mg2Sn phases formed in the Mg matrix, Mn and Zr do not cause the formation of any new phases. The average grain size, tensile strength and elongation were 22 μm, 285 MPa, and 14.5%, respectively, after extrusion + rolling + ageing treatment (ERA). The mechanical properties of ERA alloys with a peak hardness of 81 HV and 6.7% are improved compared with those of EA (extrusion + ageing treatment) samples; these changes are attributed to grain refinement and solid solution strengthening, age hardening, and precipitation strengthening.

Highlights

Increasing demands to reduce the weight of automobiles and efforts to reduce the emission of greenhouse gases have accelerated the development of lightweight metallic materials
The results indicate that only Mg2Sn phases formed in the Mg matrix, Mn and Zr do not cause the formation of any new phases
In order to eliminate the non-equilibrium phase, a solid solution treatment is employed; the average grain size (AGS) increases slightly to 210 μm and most of the secondary phase on the grain boundary is dissolved into the Mg matrix (Figure 2(b))

Summary

Introduction

Increasing demands to reduce the weight of automobiles and efforts to reduce the emission of greenhouse gases have accelerated the development of lightweight metallic materials. The most common method for improving high temperature performance is via alloying elements and forming thermally stable precipitates along the grain boundaries to restrict grain boundary sliding during deformation. It has been reported that the Sn element could significantly improve the elevated temperature properties of Mg alloys via solid solution strengthening and age strengthening [8] [9]. Because of the low cost of the Sn element with a high solid solubility (14.48%) at 561 ̊C, there is the possibility of precipitating a cubic Mg2Sn phase in the Mg-rich matrix with decreasing temperature, whose formation during ageing is accompanied by strengthening [10]. The precipitation of a-Mn within a Mg matrix can form Mn-containing inter-metallic compounds to improve creep-resistance [11]. We prepared as-cast Mg-5.0Sn-1.0Mn-0.4Zr alloys to perform comparative investigations among different thermo mechanical treatments, which could provide some valuable clues towards improving the mechanical properties of the alloy in the future

Experimental

Microstructure Evolutions

Mechanical Properties

Conclusion