| Magnesium has some excellent performances such as lower density, higher intensity and recycling utilization, which gradually become the focus on engineering and structure materials. These defects, such as brittleness phases, cracks, air hole, wider heat affected zone (HAZ) and welding distortion, can be formed during welded Mg alloys. So the welding problem of Mg and Mg alloys is the key to block their wide application.In order to improve the application of Mg alloys, the dissimilar metals of Mg and Al were welded by means of the solid-state and fusion welding in this paper. According to the results of microstructure observed and performance test for Mg/Al welded joint, the relation between microstructure and performance of welded joint was analyzed. The microstructure and diffusion behavior of element near the interface for Mg/Al diffusion bonding was analyzed, which helpful seek the relation between interfacial transition zone formed and element diffusion.The microstructure and performance in the welding zone of Mg/Al dissimilar metals was analyzed by metalloscope and scanning electron microscope (SEM). The interfacial transition zone of diffusion bonded-joint included Al transition layer, middle diffusion layer and Mg transition layer. The microhardness of two transition layers is location at HM200-350, and middle diffusion layer is location at HM125-150. The test results indicated that the Mg/Al diffusion bonded-joints combined well can be obtained by controlling heating temperature 470-490℃, holding time 60-120min and welding pressure less than 0.1 MPa. When the heating temperature is at 475 ℃, the maximal shear strength for diffusion bonding interface is 18.94MPa, which is about 40% of Al base metal. The fusion zone of TIG welded joint included melting crystal region and half-melting crystal region. The melting crystal was composed of bulk column crystal and equiaxed dendrite, but half-melting crystal region was composed of non-crystal structure and column dendrite.
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