Microstructure and Corrosion Behavior of Friction Stir-Welded 6061 Al/AZ31 Mg Joints with a Zr Interlayer.

Yang Zheng,Shuming Liu,Libin Zang,Yinglei Ma,Xiaomeng Pan,Yong Chen

doi:10.3390/ma12071115

Abstract

Friction stir welding (FSW) with a Zr interlayer was employed to join dissimilar alloys of 6061 Al and AZ31 Mg. The microstructures of Al/Mg and Al/Zr/Mg joints were investigated by optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometer (EDS). The results showed that the central part of the Zr interlayer was smashed and intermixed with the base materials in the stir zone, whereas the undamaged part remained stable at the Al/Mg interface. The formation of Al–Mg intermetallic compounds (IMCs) was suppressed by the Zr interlayer due to its synergetic effects of chemical modification and thermal barrier. The electrochemical measurements revealed a differentiated corrosion behavior for each joint, where the corrosion rate of representative regions increased in the order of Al alloy < Mg alloy < heat-affected zone < stir zone. The immersion tests indicated an enhancement in corrosion resistance for the Al/Zr/Mg joint compared with the Al/Mg joint, which is owing to the mitigated galvanic corrosion between the base materials by the Zr interlayer.

Highlights

Vehicle weight reduction is attracting unprecedented attention under increasingly strict emission regulations in recent years
Intermixed with the base materials, while the undamaged part remained stable at the Al/Mg interface
Dissimilar alloys of 6061 Al and AZ31 Mg were successfully joined by Friction stir welding (FSW) with a Zr interlayer

Summary

Introduction

Vehicle weight reduction is attracting unprecedented attention under increasingly strict emission regulations in recent years. Al and Mg alloys have been extensively studied to substitute steel parts to realize an obvious lightweight effect. The development of suitable welding techniques for these two alloys is vital and has become a hot research topic [1,2]. The undesirable Al–Mg intermetallic compounds (IMCs) with hard and brittle properties formed by the conventional fusion welding techniques seriously deteriorate the joint quality, which is the main obstacle for the dissimilar joining of Al and Mg alloys [3,4]. Friction stir welding (FSW), a solid-state welding technique developed by the Welding Institute (Cambridge, UK) in 1991, exhibits great potential to join Al and Mg dissimilar alloys [5,6,7,8]. Rao et al [5]

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Conclusion