Repair Of Cast Aluminum Defects By Active And Passive Filling Friction Stir Welding

Friction stir welding repair(FSWR)as a novel defect-repair technology,compared with the traditional welding,dose not produce secondary defects such as cracks,pores,etc.during repair process.With advantages of high strength and toughness,cast aluminum alloy is widely used in aerospace and transportation fields.However,shrinkage pore,shrinkage cavity,inclusions and other casting defects will occur in the casting process.These defects seriously affect the mechanical properties of casting parts and result in casting rejection.In this paper,the active filling friction stir welding(AFFSW)and the active-passive filling friction stir welding(A-PFFSW)repair technology are adopted.The non-volume and volume defects in ZL210 cast aluminum alloy were repaired.The microstructure and mechanical properties were investigated by optimizing process parameters and pinless tool.The results show that heat is generated by friction between tool and materials during the AFFSW and A-PFFSW process,thereby resulting in metal softening and plastic deformation.Afterwards plastic material was forged and extruded by the shoulder of tools,finally,the material undergone atom diffusion and metal bond reconstruction process,realizing the repair of shrinkage pore and volume defects.In addition,excellent surface appearance and defect-free repair zone was obtained.Meanwhile,in the AFFSW repair process,elongation reached the maximum value of 12.65%,equivalent to 92.7% of defect-free BM,when the rotation speed is constant and the welding speed is 150mm/min.Tensile strength reached the maximum of 324.1MPa,equivalent to 92.4% of defect-free BM,when the welding speed is constant and the rotating speed is 1100 rpm.Furthermore,the repair zone of A-PFFSW can be divided into four areas: BM,TMAZ,HAZ and FZ.According to the different filling materials,FZ can be divided into first AFZ,Second AFZ and PFZ.Thereinto,the grain size of second AFZ is maximum,the grain size of first AFZ is minimum,and the grain size of PFZ smaller than second AFZ.Besides,the microhardness distributions of repair zone are also close to W shape,and the distribution of SZ(FZ)hardness is relatively uniform.Moreover,the microhardness of FZ is more uniform and the softening degree of HAZ is relatively minimum,when the shoulder is concave six spiral,and the rotation speed,dwell time and plunge speed is 1600 rpm,20 s and 2 mm/min,respectively.