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MG alloys with their unique properties such as high specific strength, electromagnetic shielding, and damping capability[1] have great potential for application in the electronics, aerospace, and automotive industries. Dissimilar material welding can join different metals together to achieve versatile properties of one part, which has attracted great attention in recent years.[2] The welding of dissimilar Mg alloys is also attracting much attention. Kolodziejczak[3] used the CO2 laser welding technique to butt weld AZ91 and AM50 Mg alloys with both thicknesses of 4.5 mm. It is concluded that the joints were free of pores and cracks, and the joint strength was as high as 95 pct of the base materials. The welding of Mg to Al alloys has also been studied using various methods such as friction stir welding (FSW),[4] diffusion welding,[5,6] and laser welding.[7] Steel is one of the dominant materials in industry, and it is considered irreplaceable. Joining Mg alloys and the steel together will reduce the weight of components greatly. However, it will be challenging to weld the two materials as a result of great differences in their physical and chemical properties. The hardness, melting, and boiling points of the steel are much higher than those of the Mg alloys. For instance, the melting temperature of the steel is greater than 1773 K (1500 C), which is much LIMING LIU, Professor, XIAODONG QI, PhD Candidate, and ZHAODONG ZHANG, Lecturer, are with the Key Laboratory of Liaoning Advanced Welding and Joining Technology & School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, P.R. China. Contact e-mail: [email protected] Manuscript submitted January 21, 2011. Article published online February 8, 2012 1976—VOLUME 43A, JUNE 2012

higher than the boiling temperature of Mg 1363 K (1090 C); the crystal structure of Fe is body-centered cubic at room temperature, whereas that of Mg is closepacked hexagonal; in addition, no interaction occurs between Mg and Fe elements according to the Mg-Fe binary phase diagram. Nevertheless, many researchers have attempted to use FSW, diffusion, or braze welding techniques to join them together. Jana et al.[8] inspected the interface of the lap joint between AZ31 Mg alloy and galvanized steels. The results showed that few Zn-Mg intermetallics at the interface did not affect the joint bonding state, and that the joint strength could reach 80 pct of the Mg alloy. Chen and Nakata[9] reported that no intermediate phase formed at the Mg alloy/steel interface using the FSW technique. The joints were still nonmetallurgical bonding, although Zn-Mg phases were observed. With the addition of the Ni interlayer, AZ31 Mg alloy and 316L steel were lap joined by the diffusion-brazed technique.[10] The results showed that the joint was metallurgical bonding with shear strength 56 MPa, and that diffusion times of more than 20 minutes were detrimental to joint strength. AZ31 Mg alloy and Q235 steel were butt joined together by the laser penetration brazing technique.[11] It is sugg