Effects of SiC ceramic particles on microstructures and mechanical properties of gas tungsten arc welded AZ31magnesium alloy with Cr 2 O 3 flux coating J. Shen* 1 , K. Liu 1 , D. J. Zhai 1 , D. Wang 1 , N. Xu 1 and C. J. Jiang 2 The effects of SiC ceramic particles on the macromorphologies, microstructures and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints with Cr 2 O 3 flux coating were investigated. The results showed that an increase in the amount of SiC ceramic particles contained in the Cr 2 O 3 flux coating led to the gradual decrease in weld penetrations. The weld penetrations of all welded seams with flux coatings were obviously higher than those without flux coating. Grain refinement was obtained in the welded seams when SiC ceramic particles were added in the Cr 2 O 3 flux coating. With an increase in the amount of SiC ceramic particles, the ultimate tensile strength value of the welded joints increased at first and then decreased. Moreover, the microhardness of the fusion zone increased gradually with an increase in the addition of SiC ceramic particles in the Cr 2 O 3 flux coating. Keywords: AZ31 magnesium alloy, Tungsten inert gas welding, Cr 2 O 3 flux coating, SiC ceramic particles, Microstructure, Mechanical property Introduction Magnesium alloys are attractive for applications in transportation, electronics, aircraft, etc. due to their characteristics of low density, excellent castability, high strength and damping capability. 1–3 Recently, welding technologies of magnesium alloys mainly focus on tungsten inert gas (TIG) welding, resistance spot welding, friction stir welding, laser beam welding and electron beam welding. 4–8 Tungsten inert gas welding technology is adopted widely for magnesium alloys because of its advantages of economy and utility, whereas the relatively shallow penetration in single pass welding and poor productivity restrict the application of TIG welding on magnesium alloys. In order to improve the TIG welding penetration of magnesium alloys, an activating flux TIG (A-TIG) welding technology has been adopted. This technology is characterised by the application of a fine layer of an activating flux on the top surface of the base material (BM) before TIG welding to get a greatly increased weld penetration. Some researchers considered that the increase in the weld penetration is caused by the constriction of the electric arc. 9,10 Others believed that the greater penetration is due to the change in the liquid flow of molten metal in the weld pool. 11,12 Zhang et al. 13 reported that the Cr 2 O 3 flux increased the weld penetra- tion of TIG welded magnesium alloy joints with good bead cosmetics. Liu et al. 14 studied the mechanism and microstructure of oxide fluxes for gas tungsten arc welding of magnesium alloy. They found that the Cr 2 O 3 flux increased the weld penetration effectively. However, the grains in the welded seams were coarsened seriously, which resulted in the decline of the mechanical properties of the A-TIG welded AZ31 magnesium alloy joints. Dispersion strengthening is an important way to improve the mechanical properties of magnesium alloys. Hence, hard ceramic particles that immerged in the welded metal may improve the mechanical properties of the welded joints. Gu ¨ nther et al. 15 researched the grain refinement of AZ31 magnesium alloy by SiC ceramic particles through theoretical calculation and experiment. They reported that SiC ceramic particles remained stable in magnesium alloys due to their high thermodynamic stability. Above investigations reported the mechanisms of the weld penetration increase in the A-TIG welded magne- sium alloy joints. Relatively few investigations have been carried out to improve the mechanical properties of A- TIG welded magnesium alloy joints by distributing ceramic particles in them. Therefore, in this study, SiC ceramic particles were added to Cr 2 O 3 to form a flux mixture for a magnesium alloy A-TIG welding test [since the SiC ceramic particles will not melt during the welding process and they can distribute in the welded seams due to the change in the liquid flow of molten metal in weld pool, this welding method may be named as strengthening activating flux TIG (SA-TIG) welding 1 College of Material Science and Engineering, Chongqing University, Chongqing 400044, China 2 Fabrication Workshop, Dong Feng Turbine Co., Ltd, Deyang 618000, China *Corresponding author, email shenjun@cqu.edu.cn ß 2013 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 20 June 2012; accepted 14 August 2012 DOI 10.1179/1362171812Y.0000000063 Science and Technology of Welding and Joining 2013 VOL 18 NO 1 11