Effect Of Brazing Joint Clearance On Microstructure And Mechanical Properties Of Pure Copper Brazed Q235 Steel Joints

In this paper,pure copper is used as the brazing filler metal,and the large-area butt joint of Q235 round steel with the same specifications is realized by brazing in the furnace.Under the same conditions of other process parameters,the joint gap of the joint is 0.01mm,0.30mm,0.60 mm,1.00mm,1.20mm,1.50mm,1.80mm,and 2.10mm,respectively.The microstructure and mechanical properties of the welded joints were analyzed,and the influence of the braze gap on the microstructure and properties of the joints was investigated,exploring the mechanism of joint strengthening.The conclusions are as follows:(1)The brazed joint is well formed,the brazing material is tightly bonded to the base metal,the interface is clear,and no welding defects occur.There is a phenomenon that the solder penetrates into the base material along the grain boundary at the bonding interface,and some of the base metal breaks into the interface and enters the weld.(2)The solder in the joint diffuses with the elements of the base material,and the Fe element diffused into the solder is distributed in the weld in the form of a solid solution and an enriched state.The Cu element diffused into the base material is distributed in the form of a solid solution in the range of about 10?m adjacent to the interface.(3)In the normal temperature tensile test,the sample with a gap of not more than 0.30mm is broken in the base metal,and the tensile strength is 380MPa,the joint strength is higher than the base metal in the same welded structure.If the gap of the brazing joint exceeds 0.30mm,the specimens are ductile fractured at the center of the weld,the tensile strength of the joint decreases as the braze gap increases.(4)All samples in the impact test are ductile fractures,the joint impact toughness increases with the increase of the braze gap,the maximum value is 98.62J/cm2.In the bending experiment,as the gap of the brazing joint increases,the bending strength of the joint decreases first and then increases,and the minimum bending strength is 598MPa.None of the samples broke or cracked at the joint.The hardness of the brazing filler metal in the weld was slightly improved.The difference in the braze gap had no significant effect on the joint hardness.The hardness of the joint area increased obviously after the tensile test.(5)The results of high cycle fatigue test show that the fatigue life of brazed joint decreases with the increase of the braze gap.Under the cycle number of 2×106,the fatigue strength at the 95%survival rate of the joint with a gap of 0.30 mm is 166MPa,and the fatigue ratio is 0.43.The joint has excellent fatigue performance.