Friction Welding Process Of Dissimilar Metals Between Aluminum Alloy And Stainless Steel

The main object focus on the R&D of lightweight composite drill pipe of aluminum alloy/steel,the aluminum alloy bar was joined to stainless steel bar by friction welding process based on the characteristics of welding metallurgy of aluminum alloy/stainless steel.The effects of welding parameters on the microstructures and mechanical properties of dissimilar friction welding of aluminum alloy to stainless steel were investigated.The experimental results of continuous drive friction welding process that a sound aluminum/steel welded joint can be obtained at the spindle rotation speed of 2200 rpm,friction pressure of 40 MPa,friction time of 1 s,and upsetting pressure of 220 MPa.In tensile tests,the fracture occurs at the friction interface,and the highest tensile strength reaches up to 304 MPa,which is about 88%of that of 6061 aluminum alloy base metal.The fractured appearance is smooth,which belongs to the typical brittle fracture mode.The joint strength and axial shortening increase with increasing friction pressure,upsetting pressure,friction time.The analyses of joint microstructure show that the microstructures of near friction interface in the Al side are small equiaxed grains,and the grains appear in the thermo-mechanical affected zone of the Al base metal.A layer of intermetallic compounds(IMCs)with non-uniform thickness forms on the friction interface of aluminum/steel joints indicate that the metallurgical bonding forms at the friction interface.The IMCs layer near 1/2 radius is the thickest,while that at the edge zone and the center zone are the thinnest.In order to further improve the properties of joints,inertia friction welding process was used to join A1 alloy bar to stainless steel bar.In interia frcition welding process,the kinetic energy stored in the flywheel can be transferred to the heat energy by the friction motion quickly and concentrically,and reduces the heat lossthrough the aluminum alloy side comparing with continuous drive friction welding process,which provides the themo-mechanical conditions for the formation of IMCs and promotes the metallurgical bonding between Al alloy and stainless steel.The tensile strength of the inertia friction welded joint reaches up to 323 MPa,at the initial speed n=1100 rpm and the friction pressure Pf=180 MPa,which is about 94%of that of 6061 aluminum alloy base metal.The joint fractured at the friction interface and TMAZ with rough appearace,and there are a large number of small dimples in fracture surface of the steel side.The impact strength of the joint is 82%of that of the aluminum base metal.No macroscopic cracks were found at the friction interface at the bending angle of 90° in bending test.The number of fatigue cycles of the aluminum/steel materials inertia friction welded joints reaches 1.25×105.