Friction Stir Welding Of AM60B And 5083 Dissimilar Alloys

AM60B magnesium alloy and 5083 aluminum alloy have the advantages of low density,high specific strength and high specific stiffness,which can be used to replace some high-strength steels to achieve weight reduction.Now,aluminum-magnesium composite components are widely used in automobile manufacturing,rail transportation equipment manufacturing,aerospace industry,shipbuilding industry and other fields.Friction stir welding(FSW)is a solid phase connection method that can effectively achieve welding of dissimilar metals.It's an ideal welding method for aluminum-magnesium dissimilar alloy welding.It is not easy to produce welding defects such as pores and hot cracks during the welding process.It does not need shielding gas and solder,and does not generate soot and arc radiation.In this paper,the friction stir welding of dissimilar alloys of 3 mm thick AM60 B magnesium alloy and 5083 aluminum alloy sheet was studied.The macroscopic morphology and micro-structure of the welded joints under different process parameters were observed.The micro-hardness and pull of different joints were measured.The effects of various process parameters(rotation speed of the stirring head,welding speed,offset of the stirring head)on the weld quality,micro-structure and mechanical properties of the joint were studied,and the specific reasons were analyzed.The temperature field of AM60 B and 5083 dissimilar alloy friction stir welding process was numerically simulated.By analyzing the distribution of temperature field and the influence of process parameters on temperature field distribution,it explains how the process parameters affect the joint quality.Finally,the residual stress in the joint was measured,and the residual stressdistribution law of friction stir welding were obtained.Sound defect-free AM60B/5083 dissimilar alloy FSW joints with good mechanical properties could be obtained with proper welding process parameters.The best tensile strength obtain with the combination of rotation rate of 1000 rpm,traverse speed of 100mm/min and no tool offset by place AM60 B Mg alloy on advancing side could reach up76% of that of the Mg base metal and 94% of that of AM60 B similar alloy FSW joints.The ratio ?/v of the rotational speed ? to the traverse speed v affects the shape of the weld,where the effect of the rotational speed on the weld profile is more pronounced than the traverse speed.Grains in the agitation zone will undergo dynamic recrystallization,grain refinement,and grain coarsening will occur in both the thermo-mechanically affected zone(TMAZ)and the heat affected zone(HAZ).Because of the mechanical action of the shoulder and the stirring pin,a layered,vortex-like Al-Mg mixed belt can be observed in the cross section of the advancing side weld.The intermetallic compounds(IMCs)consisted of Al3Mg2 and Mg17Al12 are present in the joint weld by EDS elemental analysis and XRD phase analysis.The hardness distribution of the weld cross section is "W" type,the distribution curve of hardness is asymmetrically distributed along the center line of the weld,and the hardness value of the advancing side edge is smaller than the hardness value of the retreating side edge.The fractures of dissimilar alloy FSW joints can observe cleavage characteristics such as river patterns and tearing edges,and are brittle fractures.The distribution of the temperature field during the FSW process is asymmetrical.The peak temperature on the side of the 5083 aluminum alloy is higher than that on the side of the AM60 B magnesium alloy,and the peaks on both sides appear between the thermo-mechanically affected zone(TMAZ)and the heat affected zone(HAZ).The temperature field change during FSW numerical simulation is positively correlated with the rotation rate of the stirring head and negatively correlated with the traverse speed.The distribution trend of the longitudinal and transversal residual stress of the weld is “M” type,and the distribution is asymmetrical.The residual stress on the aluminum side(advancing side)is higher than that on the magnesium side(retreating side).Compared to the thermo-mechanically affected zone(TMAZ),the lower residual stress of the stirring zone(SZ)may be attributed to the higher hardness caused by natural aging,so the stress relaxation in the stirring zone(SZ)is greater than the thermo-mechanically affected zone(TMAZ).