Study On Arc Brazing Of Nickel-Based Alloy And Stainless Steel

The rocket nozzle extension is welded together with more than 300 thin square tubes which are made of nickel-based alloy. After the fabrication process, it needs to be binded with the stainless steel hoop. Arc brazing can strictly control the residual deformations with the low heat input, prevents the thin tubes from melting through and has energy-conservation and high-efficiency feature. Arc brazing of nickel-based alloy and stainless steel was carried out in this paper.Five kinds of filler metals were tested by the optimization experiment and the weld surface appearances and joint mechanical properties were analyzed. The results show that CuSiMn has the best wettability, but there are a lot of pits and slags on the weld surface. Both CuSi3 and Copper have good wettability, the weld surface appearances are good and the joints have high shear strength. CuAl8 weld has poor surface formation and the joint is apt to appear no-bonding pad. CuFeMn has the poorest wettabilty, the weld surface appearance is very poor and the stability in welding process is bad. After all, both CuSi3 and Copper are selected as the final filler metals.TIG brazing of nickel-based alloy and stainless steel using CuSi3 and Copper is carried out and the welding torch position and process parameters were studied. The results show that when the vertical welding torch is 0.8~1.0mm far from the stainless steel and the filler metal sticks to the base material to form the continuous droplet transfer, the weld surface formation is good and the shear strength is high. The suitable parameters are that welding currents 30~35A, arc lengths 3.0~4.0mm, welding speeds 100~150mm/min, wire feed speeds 200~300mm/min. The maximum shear strength of the CuSi3 joint reaches 195.0MPa. The copper joint has higher tenacity than the CuSi3 joint and the shear strength reaches 183.3MPa.The microstructures and components of TIG brazd joints were studied. The results show that there are the interface reaction layers in both sides of the joint. The thickness of melted nicked-base alloy is 0.0348, which is 10.55% of base material, and the interface reaction layer is made of Ni-Cu-based fir-tree crystal microstructure. The stainless steel interface reaction layer is made of Fe-based matix andα-copper. The weld is made ofα-copper matrix and iron-based solid solution.In order to improve the welding efficiency, CMT MIG brazing were preliminarily studied. The results show that the suitable parameters are that welding current 85A, arc voltage 12.6V, welding speed 0.9~1.2m/min, wire feed speed 5.0m/min. The joint shear strength reaches 184.9MPa. The thickness of melted nicked-base alloy is 0.0143, which is only 4.33% of base material. The weld is made up ofα-copper matrix and iron-based solid solution which is precipitated from theα-copper grain boundary.