Research On Continuous Drive Friction Welding Of Magnesium/aluminum Dissimilar Alloys

For the magnesium/aluminum dissimilar alloys joints welded by traditional fusion welding method have low strength,and the rod structure limitations of magnesium/aluminum dissimilar metals welded by other solid-state welding methods,as well as few domestic and foreign research on magnesium/aluminum continuous driven friction welding,this paper studied on process optimization,the design of the end surface structure and the research of the middle layer of continuous drive friction welding of AZ31B magnesium alloy bar and 6061 aluminum alloy bar.And the macrostructure,microstructure,SEM,EDS,XRD and tensile properties of the joints were analyzed.The results of parameter experiments of magnesium/aluminum welding showed that the orthogonal test factors reasonable range of values were speed 1200-2300r/min,friction time 4-8s,upset pressure 85-130MPa.Orthogonal experiments' results showed that the optimal combination of process parameters was A₃B₂C₂,namely the speed 2000r/min,friction time 6s,upset pressure 105MPa.The order of influence degree of the process parameters on the strength of the joint was A?speed?>B?friction time?>C?forging pressure?.The results of the typical sample analysis of the parameter experiments showed that the difference of the heat-force coupling at different positions of the joint interface led to the obvious division of the microstructure and hardness on both sides of the Mg-Al joint.There were fine-grained hardening zone near the Mg interface and the softening zone formed by Mg₂Si dissolution on the Al side.The maximum tensile strength of the joint was 96MPa,and the fracture morphology was brittle fracture.The intermetallic compounds Al₃Mg₂ and Al₁2Mg₁7 were found in the joints by fracture EDS and interface XRD.The diffusion layer and the intermetallic compound layer at the interface of joint as a whole were relatively thin and uniform,and the type and thickness of the intermetallic compounds were different due to the difference in the properties of heat generation and intermetallic compound at the center and edges of the interface.The experiment results of different end structure aluminum rods showed that the strength of the screw joint increases with the increase of pore size.When the diameter of the screw hole was 3mm,the tensile strength came to 129MPa,which increased by 37.7%and reaches 57.3%tensile strength of the base material magnesium,and the fracture morphology was brittle fracture.The conical surface of the tapered cone and frustum structure were easy to form a plastic metal plug,reducing joint performance.Screw hole structure can change the material flow,achieving the dual effect of riveting and welding.With the aperture increased,the discontinuous area offset to the hole,the reduction effect of aperture was weakened and the shape of "hook-shaped" near the orifice tends to be reasonable,which improving the joint strength.The intermetallic compounds layer near the screw hole underwent uniform orientation bending along the orifice under the action of extrusion.The experiment results of adding middle zinc layer showed that the joint strength increased with the increase of the thickness of zinc layer,the maximum increase of 19.8%.The fracture of the joint was brittle fracture and the joining of zinc made the joint fracture in the residual Zn or Mg-Zn brittle phase.The whole diffusion layer consisted of residual zinc layer,Mg-Zn diffusion layer and a thin Al-Zn diffusion layer.The thickness of the diffusion layer was reduced from 150?m to 64?m from the center to the edge of the interface.In the Mg-Zn diffusion layer,magnesium-zinc intermetallic compound Mg₂Zn₁1 with high hardness and Mg-Zn-Al ternary compound Mg₃2?AlZn?₄9 were the weakest points in the joint,and the thickness of the residual zinc layer can not be precisely controlled,which limits the improvement of joint strength.