The Research Of Process And Joining Mechanism Of Dissimilar Materials Al/Fe Byfriction Stir Welding

In this article, the 4mm thick 5A06 aluminum alloy and 316 L stainless steel were selected as experimental materials for friction stir lap welding and modified butt welding. This article adopt a modified butt configuration which is based on the principle of “height difference- pin offset”, and take advantage of a cylindrical milling stir pin in order to adopt the welds of the aluminum/steel. This method is able to achieve a higher quality of aluminum/ steel welded joints, and avoid the incomplete root penetration defect at the root of the interface, eliminate the Hook in the welding processing, reduce the wear of the stirring head, increasing the service life of the shoulder and stir pin.The experiment results that lap welding and modified butt welding of aluminum and stainless steel were success welded by FSW under reasonable processing conditions. In the lap welding, when the speed was 60mm/min, the rotating speed was 1200r/min and the plunge depth of the pin to steel 0.3mm, the formation of the joint is the best, the maximum tensile shear force of the joint is 6.71 KN. At this time, the surface of the welds joint is smooth, and the joint have a good combination of the weld interface, and there were no defects, such as holds in the weld nugget zone. And the interlocking structure, named HOOK Hooks were sensible at the interface, which is advantageous to the joint. There are obvious cleavage and fracture morphology in the fracture, so the fracture is composite of cleavage-dimple. For the friction stir modified butt welding, when the rotating speed was 1500r/min, welding speed was 90mm/min, the pin offset was 0.3mm toward stainless steel and steel was put on advance side, the well weld was formed and obtained the best quality of welded joints. Since the modified butt joint effective control the welding heat input in the processing condition, there were no metal melting at the interface, and effectively avoid the hard and brittle metal intermetallic compounds at the interface; and there are also composition gradient formation, which the thickness is less than 3μm, that is good to the Al to Fe metal metallurgy combination. The plastic material formed a continuous material flow under the influence of the thermal-mechanical coupling effect, including the annular flow in the lower part of the welds and the horizontal flow at the top surface of the welds. Because of the micro excessive plunge into the interface, there effectively avoids the Hooks appeared at the root of the welds, which improve the properties of the welds. The fracture morphology shows typical complex ductile-cleavage fracture morphology, but the duticle fracture is dominated.