Research On Diffusion Welding Of Extruded AZ61Magnesium Alloy/7075Aluminum Alloy Dissimilar Material

As a kind of metal structure material, Magnesium alloy is currently the most widely used material and have superior performances such as high specific strength, high specific stiffness, low melting point and low density. In various industrial fields, especially the aerospace industrial, magnesium alloys all occupy an important position. However, the low melting point, higher linear expansion coefficient and thermal conductivity of magnesium makes it easy to form welding defects, which makes the limitations of welding performance, using general fusion welding method can not get a satisfactory weld joint. As a state-of-the-art solid-phase connection technology, diffusion welding can effectively avoid fusion welding cracks, holes and other defects. And with diffusion welding process, weldments have small deformation, high precision, and no longer need to be machined. So the research on diffusion welding of magnesium alloy has the extremely important practical value and theoretical significance. In order to promote the application of magnesium alloys, this paper study the vacuum diffusion welding connections of AZ61magnesium alloy and7075aluminum alloy. This paper mainly analysis of the microstructure of the diffusion layer, the joint strength and hardness, and make a useful exploration of magnesium/aluminum alloy dissimilar metal diffusion bonding.In order to get better performance of welded joints, this test use recrystallization annealing process for the grain refinement of AZ61magnesium alloy. Then the best annealing treatment is done on the condition of temperature of300℃and holding time of30min to obtain the average grain size of11.31μm from20.14μm, and grain refinement proportion reached43.8%.The vacuum diffusion welding results showed that on the condition of fixed pressure of10MPa, vacuum of18Pa, diffusion welding temperature, holding time and the welding interface surface treatment are the main factors which affect the organizational structure and joint performance. The best diffusion welding process parameter is temperature470℃and holding time60min. The maximum shear strength was up to46.39MPa, which was about46.7%of the base metal. The results of microhardness measurement of diffusion bonding diffusion transition zone show that the hardness of the aluminum alloy side of the highest, up to287.3HVo.of, magnesium side of the buffer layer and the intermediate diffusion layer also significantly higher than the base metal substrate, the direction of the base metal by the diffusion region, microhardness decreases gradually. The test found that post-welding heat treatment can improve the interfacial bonding, carried out the recrystallization heat treatment at temperature of300℃, holding time30min for the sample of diffusion welding, it was found that the width of the diffusion layer increases, and the joint shear strength improved.