Research On Laser Welding Process And Properties Of A6082 Aluminum Alloy Body-in-White

This thesis aims at new energy car body-in-white 2mm thick A6082 aluminum alloy thin-walled structural parts,by using laser self-fusion welding,laser welding with filling wire and laser-arc hybrid welding process to study formability,microstructure and properties of thin-walled aluminum alloys.Control variables method was used to analyze effects of laser power,welding speed,defocus amount,wire feeding speed,welding direction,laser-wire distance,assembly gap of laser self-fusion welding,laser welding filling wire and laser-arc hybrid welding on welds formation,microstructure and joints quality,determined the best process parameters for the three laser welding methods.Weld formation,microstructure,phase composition and micro-domain ingredient of welds were studied by metallographic microscope?OM?,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?and X-ray diffraction?XRD?.Hardness distribution of welding joint was measured by micro vickers hardness tester,tensile properties of welding joint was measured by universal tensile testing.The results showed that the best parameters for laser self-welding was laser power 2100W,welding speed 3m/min,defocus amount+2mm,protective gas flow 15L/min;The best parameters for laser welding with filling wire was laser power 4200W,welding speed4.2m/min,wire feeding speed 6m/min,defocus amount+10mm,protective gas flow 20L/min;The best parameters for laser-arc hybrid welding was laser power 1900W,welding speed0.6m/min,wire feeding speed 1.5m/min,defocus amount 0mm,laser-wire distance 0mm,electric current 23A,assembly gap 0mm,protective gas flow 20L/min.Microstructure of A6082 aluminum alloy laser filling wire welds and laser-arc hybrid welds was mainly composed of??Al?solid solution and small amount of??Al₈Mg₅?phase,content of Al₈Mg₅ phase in laser-arc hybrid welds was lower than that of laser filling wire welds.Base metal,laser self-welds and HAZ were composed of??Al?solid solution and small amount of Mg₂Si phase,content of Mg₂Si phase in laser self-welds was lower than that of base metal.Welding heat input from small to large successively was laser self-fusion welding?1.05J/cm²?,laserweldingfillingwire?1.5J/cm²?andlaser-archybrid welding?4.8J/cm²?,HAZ of weld gradually increases,at the same time,grain size of weld metal gradually increases;Under the best process parameters,weld metal hardness of laser self-fusion welds was 75.89-79.08HV,tensile strength was 224.5MPa,and elongation was18%;Weld metal hardness of laser with filling wire welds was 79.23-84.95HV,tensile strength was 238MPa,and elongation was 21.5%;Weld metal hardness of laser-arc hybrid welds was63.4-69.88HV,tensile strength was 194MPa,and elongation was 41%.Weld metal hardness,tensile strength and elongation of above three laser welding methods were compared with hardness?89.49-94.26HV?,tensile strength?276.75MPa?and elongation?50.25%?of base metal,weld metal hardness of laser self-fusion welds was 84%of base metal,tensile strength more than 81%of base metal,and elongation was 36%of base metal,weld metal hardness of laser filling wire welds was 89%of base metal,tensile strength more than 86%of base metal,and elongation was 43%of base metal,weld metal hardness of laser-arc hybrid welds was 72%of base metal,tensile strength more than 70%of base metal,and elongation was 82%of base metal.Fracture location of tensile specimen was weld zone or HAZ,according to fracture morphology analysis,fracture morphology of laser self-fusion welding,laser welding with filling wire and laser-arc hybrid welding all were ductile fracture.