Study On The Effects Of Laser-arc Hybrid Welding Processes And Post Weld Heat Treatment On Microstructure And Properties Of The Welded Joint Of 7449 Aluminum Alloy

7449 aluminum alloy developed by the Alcan Company in French is a new kind of Al-Zn-Mg-Cu-Zr series alloys.It has high strength,fracture toughness and fatigue crack growth resistance and has been applied in the civil aircraft A350 studied by Air Bus company lately.But there are few research reports on the laser-arc hybrid welding of 7449 aluminum alloy at home and abroad.Under the background of the research project about aluminum alloys used for big aircraft making,by means of microscopic analysis methods,including Optical microscope,Scanning electron microscope,and through Vikers hardness test,tensile test,intergranular corrosion experiment and exfoliation corrosion experiment,the effects of the laser-arc hybrid processes and post weld heat treatment processes(solution treatment and single aging)on micro structure and properties of the laser-arc hybrid weld joints of 7449 aluminum alloy were studied and discussed.The main achievements were obtained as follows:(1)During the laser-arc hybrid welding processing,the laser beam deviated from the vertical direction about 10° and combined with arc welding gun,with 15 L/min high purity argon as a protective gas,and the angle between arc welding gun and base metal is 54 degrees,the distance between the laser beam and the welding stick is 3 mm.Under the condition of the above,the optimized process of laser-arc hybrid welding of 7449 aluminum alloy sheet is 2.3 KW,welding speed is 40mm/s,defocusing amount is 0 mm,the wire feeding speed is 7mm/s;In this process,the tensile strength of the welded joint is 256.73 MPa,the elongation is 2.87%,and the hardness of the welded joint is about 112.75 HV.The hardness values of each part of the joint increased gradually from the weld zone to the fusion zone and the heat affected zone.The hardness of the welded joint is equivalent to that of the base metal.(2)After solution treating at 475℃/1h,the tensile strength and elongation of the laser-arc hybrid welded joint of 7449 aluminum alloy are 430.70 MPa,3.80%respectively and hardness of welded joint is 117.38 HV.Compared with the welded joint before solution treatment,the tensile strength is increased by 36.94%,the elongation is increased about 32.40%,and the hardness is increased by 4.11%.(3)After single aging at 120 ℃/24h,the tensile strength and elongation of the laser-arc hybrid welded joint of 7449 aluminum alloy are 542.90 MPa and 3.96%,respectively,and the hardness of the welded joint is 140.65 HV.Compared with the welded joints after solution treatment,the tensile strength and elongation and hardness were increased by 26.05%,4%and 19.82%,respectively.The hardness of heat affected zone was restored to the equivalent of base metal.The ductility of welded joints is recovered to a certain extent.(4)The corrosion resistance of the laser-arc hybrid welded joint before and after solution treatment is basically the same,and the corrosion resistance of the weld zone,heat affected zone and base metal decreases in turn;After single aging,the corrosion resistance of weld zone,heat affected zone and base metal is increased in turn;The effect of post-welding heat treatment on the intergranular corrosion and exfoliation corrosion resistance of the welded joint is the same.