Research on friction stir welded joints of Copper to Magnesium alloy

Dissimilar magnesium alloy AZ31 and pure copper sheets with a thickness of 5mm were successfully friction stir welded. Microstructure and mechanical properties of the butt joints were investigated. Complicated microstructure was formed in the nugget zone, in which vortex-like pattern and lamella structure could be found. CuMg2 intermetallic compounds were found in the nugget zone. The hardness of the stir zone was much higher than that of the base material. The maximum value of hardness existing in the middle of the stir zone. Hardness values near the Mg side were relatively higher than that of near the Cu side in the weld zone. The ultimate tensile strength (UTS) of the joint was 86MPa and the joint failed with a brittle fracture mode. Introduction Aiming to reduce the vehicle weight and in turn cut down fuel consumption, magenisum alloys, the lightest structure metallic material with high specific strength and high specific stiffness, are widely used in the atuomotive and aerospace industries in recent years. They also have attractive electromagnetic and thermal conductive properties and therefor have been increasingly used in the electronic industry [1, 2]. Copper and its alloys also have a wide application in electronic and electrical power industry, electrical appliances and automobiles [3]. It has been reported that Cu-Mg bimetals are widely used in the electronic and electrical industries, electrical appliances, machinery and automobile industries [4]. Welding processing is essential to make the Cu-Mg bimetals. However, the joining of Cu-to-Mg alloy through conventional fusion welding processes remains a major challenge due to the huge difference in the melting point, formation of intermetallic compounds (IMCs), and severe thermal cracking. Liming Liu investigated the TIG welding of Mg to Cu [5], he found that metallic oxide and intermetallic compounds are the main reason that weak the joints strength. Moreover, Caiwang Tan joined these two metals by fiber laser-TIG hybrid welding [6], the different morphologies including Mg–Cu eutectic structure, Mg–Cu intermetallic compound and Mg-Al-Cu ternary intermetallic compound were identied at the Mg-Cu interface. R. Cao obtained Mg-Cu welding-brazing joint via cold metal transfer welding processing by using AZ61A magensium alloy wire as filler metal [7], the interfacial reaction layers of the brazing joint consisted of Mg2Cu, Al6Cu4Mg5, MgCu2 and Mg17Al12 IMCs. As a result, alternative solid-state joining techniques like friction stir welding (FSW), ultrasonic spot welding (USW), and diffusion bonding are of special interest due to their potential of obtaining superior joint properties compared with the fusion welding techniques. G. Mahendran studied diffusion bonding of AZ31B magnesium and copper alloys [8], they found that The principal difficulty when joining Mg-Cu lies in the existence of hard-to-remove oxide films on the magnesium surfaces and the formation of brittle metallic interlayers and oxide inclusions in the bond region, the optium lap shear test strength of the joint is 66MPa. Many researchers have concluded that friction stir welding can over come the problems that occur during fusion welding process [9], while the joining of Mg to Cu by FSW was not reported until nowadays. In the present study, the AZ31 magnesium alloy and pure copper are butt welded via FSW. After welding, the weld surface and cross-section appearances were investigated. Further, the microstructure, interfacial structure and mechanical properties of the joints were researched. International Symposium on Mechanical Engineering and Material Science (ISMEMS 2016) Copyright © 2016, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Engineering Research, volume 93