Effect Of Plastic Flow And Deformation On IMCs Formation In Inertia Friction Welded Joints Of Aluminum Alloy To Stainless Steel

Composite structure of aluminum/steel dissimilar metal has been widely used because of its light weight and good performance.However,the traditional fusion welding methods cause excessive brittle Fe-Al intermetallic compounds(IMCs)in the Al/steel joints,which will increase the brittleness and decrease the strength of the joints.As a kind of solid state welding method with lower heat input,inertial friction welding(IFW)has been widely concerned by scholars because it can effectively control the formation of IMCs in joints and obtain welded joint with excellent mechanical properties.Unlike other welding methods,IFW has the characteristics of high efficiency welding speed,low temperature and strong plastic flow deformation.This paper focuses on the influence of plastic flow and deformation on IMCs of the Al/steel inertia friction welding process.Through this study,the formation mechanism of IMCs was revealed,which has important guiding significance for the control of the properties of Al/steel friction welded joints and the acquisition of efficient joints.The inertia friction welding of 2A14 Al alloy to 304 stainless steel was taken as the research object.Based on the deformation characteristics and thermal conditions in the inertia friction welding process,a thermal compression welding-thermal simulation device with external heat source was designed,and the friction welding process can be simulated physically.Thermal compression welding was used to simulate the friction welding process,and the heat was generated by external induction heating equipment instead of interface friction,so it was convenient to obtain thermal simulation samples without plastic flow and with different deformation.Comparing the joints by hot pressure welding with inertia friction welded joints,the influences of plastic deformation and flow conditions on IMCs during friction welding were studied.The experimental results show that the friction flow behavior of Al/steel during inertia friction welding can significantly promote the formation of IMCs at the interface.Under the similar thermal conditions,the Fe-Al IMCs layer at friction welding interface was obviously thicker than that in hot pressure welded joint.The existence of submicron spherical IMCs near the side interface of friction welded Al alloy was observed by TEM,which indicates that the peeling effect of plastic flowing Al on steel surface.At the same time,the flow of Al alloy will also have a stirring effect on the IMCs in the joint,resulting in the uneven shape of the IMCs at the interface.The promoting mechanism of friction and flow behavior of metal on Al side on IMCs formation was discussed.It was considered that one-dimensional and two-dimensional crystal defects caused by severe friction and deformation during friction promote the diffusion of elements and the formation of IMCs.The influence of plastic deformation conditions on IMCs formation at bonding interface in inertia friction welding of Al/steel was studied by combining thermal simulation with friction welding,and its mechanism was discussed.It was found that the plastic deformation of Al alloy can slightly promote the formation of IMCs during welding,and the change of deformation rate will also change the formation of IMCs.The plastic deformation at lower rate will lead to the thicker IMCs layer.The inhomogeneity of thermal conditions of friction welded joints results in the inhomogeneity of microstructure and mechanical properties of joints.A multilayer tensile test was designed to quantitatively characterize the nonuniformity of bonding strength of friction welded joints at different radius positions.At the same time,combined with the morphology of IMCs at different positions,the influence of IMCs formation with different morphology on bonding strength was summarized.It was found that there was no obvious IMCs layer in the central area of the bonding interface,while the tensile strength was the highest.There was a negative correlation between IMCs layer thickness and tensile strength of Al/steel friction welded joints.Thin,uniform,dense IMCs layer in crack-free joints usually means high tensile strength.If the IMCs layer was too thick,the shape was uneven or cracks and holes appear,the tensile strength at the interface will be significantly reduced.By designing annealing heat treatment,the growth rule of IMCs layer of friction welding and thermal simulation samples was observed and compared.