Study On Friction Stir Welding Of 7B52 Aluminum Laminated Composite

Aluminum laminated composite(ALC)consists of two or more different aluminum alloys.It is produced by rolling,casting and other manufacturing processes to achieve metallurgical bonding on the interface.Compared with traditional A1 alloys,ALCs are superior in strength,ductility and impact resistance.The friction stir welding(FSW)of Al alloy can effectively avoid the defects caused by fusion welding,but the FSW of ALCs is in its infancy stage.In this paper,friction stir welding experiments of 7B52 ALC plates with the thickness of 12 mm and 16 mm were carried out.The microstructures and laminated structures of the joint were investigated by means of optical and scanning electron microscopy and material flow was further researched.The tensile properties,impact resistance and microhardness of the FSW joint were analyzed by tests and the effects of FSW on the fracture mechanisms of 7B52 ALC were studied by observing the fracture surfaces of tensile specimens and impact specimens after tests.By investigating optimal welding process parameters,a defect free weld with the thickness of 12 mm was obtained with the joint efficiency of 71.4%.The maximum hardness exceeded 90%of base metal and the impact absorbed energy was 41.1%higher than that of base metal.In addition,a weld with the thickness of 16 mm was obtained with the joint efficiency of 68.6%.FSW was proved to be an effective welding method for ALCs.A scale like morphology is discovered on the AS of the NZ.It is proved to be the superposition of onion rings and stripe shapes formed by transverse flow of materials.By analyzing the microstructures of the joint,a new conjecture on the formation of onion rings is proposed and a new theory of material flow is advanced.In the region between L2 and L3 on the AS of the NZ,L2 alloy,L3 alloy and interlamellar material were alternately distributed and innumerable interfaces were formed.It is the weakest area in the weld,where the crack initiated in tensile test.The impact toughness of 7B52 ALC was greatly increased due to the improvement of microstructure.It is of great significance for the application of this structural material.