High Efficient Fusion-Brazing Joining Technology For Dissimilar Metals Between Steel And Aluminium Alloy By Large Spot Nd:YAG Laser-Plused MIG Hybrid Process

The current welding methods which enable to weld aluminiumto steel can not satisfy with the development of automobilemanufacture. Aim at this status, large spot laser-arc hybridwelding was brought forward in this paper. Fusion-brazingjoining between 5A02 aluminium alloy sheet and zinc-coatedsteel sheet as well as aluminium-coated steel sheet weresuccessfully achieved with this method, i special type brazingflux which can achieve the fusion-brazing joining betweenaluminum sheet and non-metal-coated cold rolled steel sheetby large spot laser-arc hybrid welding was successfullydeveloped. Influences of welding parameters on bead appearance,mechanical property of the joints, microstructure of thejoints and the thickness of the A1-Fe intermetallic compoundslayer were studied in detaile. The influence of thickness ofthe il-Fe intermetallic compounds layer on shear stregth ofthe joints was also studied. The mechanism on partialincomplete brazing at the root of bond line of thefushion-brazing joint between aluminium and steel werestudied, and the relevant measures were developed to restrainor avoid the defect. And the mechanism on laser-arc hybridfusion-brazing joining between almuninum and steel was alsostudied.The results indicated that high efficiency and qualityfusion-brazing joining between aluminium alloy sheet and metals-coated steel sheet was.achieved by large spot Nd: YAGlaser-plused MIG hybrid welding and the highest welding speedcould be up to 5m/min. The tensile strength of the joint wasup to 72％～75.7ï¼…of that of the aluminium base metal. Thetensile strength of the joint used KAlF₄+Sn+Zn brazing flux wasup to 83.6ï¼…of that of the aluminium base metal. And the tensilestrength of the jiont was equivalent to that of fusion jointby conventional arc welding. When the A1-Fe intermetalliccompounds layer was within 1.5～4μm, the influences of thelayer on mechanical property of the joint were not serious.Insufficiency heat input is the essential cause of the partialincomplete brazing defect. But the temperature of the moltenpool and the steel sheet at the the root of the bond line cannot reach the critical brazing temperature which is needed toachieve a brazing joint using Al-Si brazing filler metal.Effective function of laser, accurate control of the energy,rationalization of the structure of the joints and bothactivity and alloyability of the coated metals or the metalsin brazing flux are the necessary additions of laser-arc hybridfusion-brazing joining between aluminimu and steel.