Research On Friction Stir Welding Of Copper/Aluminum Dissimilar Materials

Friction stir welding(FSW)is a solid-phase joining technology,which has been widely used in the welding of aluminum alloy and other non-ferrous metal materials,and solves the problem that universal welding(MIG,etc.)cannot guarantee the weld quality of these materials.Copper(Cu)and aluminum(Al)are two kinds of metal engineering materials commonly used in power,transportation and aerospace industries.Cu/Al dissimilar joints have attracted great attention in electrical contact.Studying the efficient welding method of aluminum/copper dissimilar materials and obtaining high-quality copper/aluminum joint are beneficial to application in engineering.Friction stir welding(FSW)is a highly complex process,which includes a variety of highly coupled physical phenomena.There are few reports on numerical analysis of copper/aluminum dissimilar metal butt welding,and the FSW process of copper/aluminum dissimilar metal is still in the experimental research stage.Research on numerical analysis of friction stir welding is of guiding significance to the selection of welding process parameters.Eulerian heat flow model for friction stir welding of dissimilar materials of pure aluminum and T2 copper was established to study the maximum permeability of metal.Thermal and material flow analysis is carried out on the assumed velocity field in the weld nugget region,and heat sources obtained from Coulomb friction and loss of shear stress in viscous behavior of non-Newtonian metal flow are considered.The model is used for temperature gradient and material penetration under different offsets of stirring needles,and is compared with experimental results.The model shows that the penetration of metal is closely related to the offset of the stirring pin.In all cases,Cu is fixed on the advancing side.When the stirring pin is offset to the copper side and the aluminum side,the penetrated metal is copper and aluminum respectively.In addition,the model also shows that the highest temperature reached in metal depends to a large extent on tool compensation.When friction stir welding(FSW)is used to butt weld pure aluminum and T2 copper,the welding process parameters have great influence on the weld surface morphology,mechanical properties,microstructure and weld quality.When the Cu plate is fixed on the advancing side,the welding speed of the stirring head is 1,000 r/min,the feeding speed is 50 mm/min,and the technological parameters are 2 mm to the aluminum side,a high quality weld can be obtained.In this paper,the types and distribution of intermetallic compound phases of different Al/Cu materials and their effects on the mechanical properties of dissimilar Al/Cu friction stir welded joints were studied under different welding processes such as welding speed 800 ~1400 r/min and feeding speed 50 ~80mm/min respectively.The results show that the microstructure in the weld nugget region is greatly affected by the welding speed,and a complex layered structure containing intermetallic compound phase is formed in the weld nugget region.The microstructure analysis shows that the grains in the weld nugget region undergo dynamic recrystallization and obtain refined equiaxed structure.The heat engine affected region is twisted and deformed by the action of the stirring head,and the grains are fiberized along the flow direction of the plastic material.The grain in the heat affected region is coarser under the influence of the temperature gradient than that in the base metal region.Under the action of rotation and extrusion of the stirring head,the red copper on the forward side flows backward,causing mutual diffusion and migration,causing a small amount of Cu to enter the Al matrix.The pure aluminum on the backward side has poor fluidity and does not bypass the stirring needle to enter the copper matrix,thus increasing the possibility of intermetallic compound formation.