| Cu-Cr-Zr alloy is a kind of precipitation-strengthened alloy,which is widely used in aerospace,military,electronic and mechanical fields due to its high electrical conductivity and mechanical properties.For the Cu-Cr-Zr alloy,the defects such as non-bonding of pore cracks and serious degradation of grain coarseness and mechanical properties are easy to occur in the welded joints by traditional melt welding,plasma arc welding and brazing methods,which seriously affect the application of high strength and high conductivity Cu-Cr-Zr alloy.Therefore,in this paper,friction stir welding is used to solve the problems of traditional welding methods.In this paper,friction stir welding of 3 mm thick Cu-Cr-Zr alloy plate in aging state and solid solution state was carried out with welding parameters of 750 and 1500 rpm and 23.5 mm/min,aging treatment was applied to the joints after welding.The effects of the initial state of the base material at different welding speeds and aging treatment on the microstructure(grain size,precipitation phase)and mechanical properties(hardness,tensile properties at room temperature)of the welded joints were studied,and the tensile properties of the welded joints were quantitatively analyzed by modeling.The main research results are as follows.When base metal(BM)is aged initially,the grain size of nugget zone(NZ)refined from BM 40 μm to 3.7 and 33.3μm respectively after FSW at 750 rpm and 1500 rpm.At the same time,part of the precipitate phase Cr particles of the aging 750 rpmNZ joint were dissolved in the matrix,while all the precipitate phase Cr particles of the aging1500 rpmNZ joint were dissolved.After FSW,compared with BM,the mechanical andelectrical properties of the joints with aging 750 rpmand 1500 rpm are seriously reduced.Meanwhile,the mechanical and electrical properties of aging 750 rpmjoint were higher than that of aging 1500 rpm joint.After AT,NZ grain size did not change much,and Cr particles precipitated in the solid solution in the matrix were precipitated again.The mechanical properties and conductivity of the joints of aging 750 rpm and aging 1500 rpm were significantly improved.Precipitation strengthening was the main strengthening mechanism,followed by grain boundary strengthening.When the initial state of BM is solid solution,after FSW,the grain size of NZ of solid solution 750 rpm and solid solution 1500 rpm joints decreases from 25 μm to 10 and 21 μm.BM itself has no precipitation phase,and the connection with solid solution750 rpm and solid solution 1500 rpmNZ still has no precipitation phase.Compared with BM,mechanical and electrical properties of the solid solution 750 rpm and 1500 rpm connector NZ are improved.The mechanical and electrical properties of solid solution750 rpm joints were higher than that of solid solution 1500 rpm joints.After AT,NZ grain size did not change much,and Cr particles precipitated in the solid solution in the matrix were precipitated again.The mechanical properties and conductivity of the joints of solid solution 750 rpm and solid solution 1500 rpm were significantly improved.Precipitation strengthening and grain boundary strengthening were the main strengthening mechanisms.When the aging temperature was 525℃ and the insulation time was 3 h,the microhardness conductivity and tensile properties of the 750 rpm and 1500 rpm joints were well matched.After AT,the microhardness of the 750 rpm and 1500 rpm joints NZ was 96.54 and 108.55 HV,the conductivity was 56 and 53 MS/m,the tensile strength was 311 and 324 MPa,and the fracture location of the joints was NZ zone.The microhardness of the solid solution at 750 rpm and 1500 rpm reached 98.5 and 99.8 HV,and the conductivity increased to 54 and 55 MS/m.The tensile strength was 303 and333 MPa,and the fracture location of the joint was BM zone.It was found by comparing the tensile strength of four samples aged750 rpm after AT,aged 1500 rpm after AT,solid solution 750 rpm after AT and solid solution 1500 rpm after AT,the tensile strength of the sample solid solution 1500 rpm after AT was the highest and the fracture was in BM zone,indicating that the tensile strength of the solid solution 1500 rpmNZ joint after AT would be higher and the connection performance would be better.Therefore,in this study,the base material was solid solution material,with welding speed of 1500 rpm,aging temperature of 525℃and insulation time of 3h,the performance of FSW joint would be better. |
PDF Full Text Request