Microstructural Evolution and Mechanical Properties of As-Cast Mg-12Zn Alloys with Different Al Additions

Yu Zhang,Zong-Gang Wang,Ming Li,Xue-Zhi Wang,Wen-Long Yang

doi:10.1590/1980-5373-mr-2019-0582

Abstract

Abstract In this study, Mg-12Zn magnesium alloys alloyed with Al additions (0, 2, 4, 6, 8 and 10, wt.%) were fabricated by permanent mould casting. The Al content on their microstructure and mechanical properties were systematically examined with an optical microscope (OM), a scanning electron microscope (SEM), an X-ray diffractometer (XRD) and mechanical tests at room temperature. The experimental results indicate that the microstructure of the alloys is mainly composed of α-Mg and semi-continuous or continuous eutectic phases. A higher addition of Al (≥6%) causes the generation of the Mg17Al12 phases. Notably, the grain sizes of the alloys gradually decrease, whilst the partial morphology of some eutectic phases is modified into lamellar structure with increasing of Al addition. Mechanical properties characterization manifested that, the alloys with different Al additions reveal distinguishing tensile properties. Among them, the alloy with 4% Al provides an excellent mechanical properties, i.e., a UTS of 206 MPa and an EL of 7.92%, which is respectively higher 28 MPa and 1.08% than that of ZA120 alloy. The deterioration in the tensile properties for the higher Al-bearing alloys is possibly related to the lamellar structure, coarse and continuous net-work morphology and β-Mg17Al12 phases, respectively.

Highlights

Magnesium and its alloys are considered to be the lightest metallic structural materials at present
When the liquid melt temperature was slowly rised to approximately 750 °C, and was held at 750 °C for 20 min to guarantee the homogeneity of alloying elements
It can be summarized that the Zn/Al mass ratio has a significant influence on the phase composition of the investigated alloys

Summary

Introduction

Magnesium and its alloys are considered to be the lightest metallic structural materials at present. The existence of many β-Mg17Al12 phases in these alloys seriously affects the properties of the alloys mentioned As a result, their widespread applications in engineering are severely restricted. The main precipitated phases of the alloys include Mg32(Al, Zn)[49] and/or MgZn, which have a good strengthening effect It is further reported[10] that the ZA series alloys show mechanical properties superior to that of the AZ series alloy in both room temperature and high temperature, and have a broad commercial application prospect comparable to that of the AZ system alloys. Based on the reports of ZA series alloys and previous studies, Mg-12Zn-xAl alloys (0, 2, 4, 6, 8 and 10, wt.%) alloyed with different additions of Al were designed and investigated systematically, so as to provide a reference for the research and development of new type ZA alloys

Experimental procedure

As-cast microstructure

As-cast mechanical properties

Conclusion