Microstructures And Properties Of Inertia Friction Welded Joints Of Aluminum Alloy To Stainless Steel

The composite structure of aluminum alloy and stainless steel(short for Al/steel)can take full advantages of the properties of metals,and has some advantages suc as saving materials,reduction of weight,and flexible design,which has wide application prospects in industru such as aerospace industry,automobile industry and metallurgy industry.In high thrust liquid rocket engine,feeding pipeline of liquid propellent is the lightweight Al/steel pipes,which need to be joined by welding process.While both the corrosion resitance of the brazed joint and brazed-fusion welded joint can not meet the requirements,so the inertia friction welding of Al alloy to stainless steel was proposed to perpare the lightweight Al/steel feeding pipeline of liquid propellent for high thrust liquid rocket engine.As a solid-phase joining technology,inertia friction welding is widely applied to joining the dissimilar metals with large differences in mechanical and thermophysical propertiws such as Al/steel because of its advantages of low energy input,energy concentration and precision heat input.By using small size test bar 2Al4 aluminum alloy/0Cr18Ni9Ti stainless steel in this paper,the microstructures and properties of Al/steel dissimilar metal inertia friction welded joints were studied.The effects of welding parameters such as initial rotation speed(n),axial friction pressure(P),flywheel moment of inertia(I)and the state of friction interface before welding on the microstructures and properties of Al/steel inertia friction welded joint were studied.The research results will provide basic theoretical guidance and data support for Al/steel pipes in aerospace engine.The results of inertia friction welding of Al/steel show that the highest tensile strength can reach up to 321.5 MPa,which is equal to that of 75%of Al base metal at the welding parameters of n=1100 rpm,P=180 MPa and I=0.16 kg,m2.The tensile fracture of the joint is a typical brittle fracture.The formation of Fe2Al5 and FeAl3 phase at the joint interface indicates that the metallurgical bonding forms between Al and stainless steel in inertia friction welding.Tensile strength of joints can easily reach the maximum at low speed matches high pressure,or the opposite.Variations in temperature of characteristic points in the friction interface show that the temperature in 2/3 radius region of the friction interface is the highest,which can reach up to 412.9℃;then that in 1/3 radius region,the temperatures in the boundary and the center region are the lowest.Friction pressure has few effects on the peak temperature of the friction interface.However,with the increase of the initial rotation speed,the peak temperature of the friction interface tends to rise,and the time to peak temperature is gradually extended.The diffusion of different regions is different,and the diffusion behavior at the radius of 2/3 is the most intense.With the increase of process parameters,the diffusion degree of elements increases,the thickness of element diffusion layer increases,even the IMCs layer appears obviously.The interface roughness before welding also affects the frictional heat flux.For rough interface,the friction interface after welding is still zigzag,and IMCs is formed in the groove in steel surface,but uneven interface diffusion layer is formed;And smooth surfaces,the diffusion layer is relatively uniform.To ensure the safe application of Al/steel pipes under the working environment of liquid medium,the corrosion resistance of Al/steel inertia friction welded joints was studied.The steady-state polarization test and EXCO test results show that the corrosion resistance of the joints is improved relatively with the increase of energy input power.The corrosion microstructures of joints show cracking and peeling of the oxide film from Al side,as well as the pitting near interface which is in the stable growth stage.