Research On Structure ?Property And Metal Migration Of Al/Cu Lap Joint By Friction Stir Welding

The 1060 aluminum alloy and the T2 copper have been widely used in the industry for their good physical and mechanical property.The connection of the dissimilar copper and aluminum metal has been one of the research focuses all over the world.As a method for solid-phase connection,FSW was usually used in connecting the nonferrous metals like aluminum,magnesium,copper,etc.The lap FSW of copper and aluminum is now still in the experimental phase.And it is rear of the report concerning the metal migration behavior in copper-aluminum lap welds.So,there is a foundational meaning for the promotion of1060 aluminum alloy and T2 copper to study and reform the process of Al-Cu lap FSW.In this paper,6mm 1060 aluminum alloy plates and the 2mm T2 copper plates were lap welded by FSW process.Effects of the FSW process on morphology,properties and the metal migration of the joints were studied by changing the FSW parameter,lap material group and the length of the pin.It formed a weld with good surface morphology when n=800rpm,v=90mm/min.The shear strength of the weld reached 96.5% of the aluminum base metal and 43.4% of the copper base metal when n=1100rpm,v=80mm/min.The intermetallics of CuAl2 and Cu9Al4 were generated in the weld.In the three layer Cu-Al-Cu joint,the second weld widened the high-hardness zone,and increased the peak value of the microhardness.There were more macro-defects in the second weld than the first weld.And the shear strength of the second weld was lower than that of the first weld.The formability and strength of the welds produced by the shorter pin was better than that produced by the longer pin.The macro-migration of the metal in the cross-section,vertical-section,shoulder friction plane and Al-Cu interface plane of the joint were studied in this paper.It was founded that,the metal migration in the thickness direction can be divided into three areas.The plastic metal moved in the horizontal circle motion in shoulder affected zone and moved in convection vertically in the turbulent flow area.In nugget area,it moved in an ellipsoid circulation.In the shoulder plane,the plastic metal on the one hand migrated along radial direction in the advancing side,on the other hand,it moved along the welding direction pushed by the shoulder.On the edge of the shoulder,the metal in the advancing side moved forward and the metal in the retreating side was rolled into shoulder area,migrated along radius and bypassed the pin then moved forward.In the interface plane,large amount of copper and aluminum migrated in opposite direction and formed the mixture structure,which then moved in a short distance along radius.The second welding reduced the amount of mixture in the turbulent flow area in section,shortened the migration distance in the downward direction,shortened the distance in radial direction in interface plane,and increased the amount of granular copper migrated into the base metal.In the weld section,the longer the pin,the shorter the move distance in vertical direction.In the shoulder plane,the longer pin increased the migration distance in radial direction.In the interface plane,the longer pin worsened the liquidity of metal and resulted in the shorter and uneven migration distance in radial direction.