| Welding technology is one of the important processing methods in manufacturing industry.With the continuous advancement of the?Made in China 2025?strategy,green,high-efficiency and energy-saving have become the development direction of welding technology.Aluminum alloy is widely used in aerospace,petrochemical,rail transportation,energy engineering and other fields due to its high specific strength,corrosion resistance and good cutting performance.In this paper,laser-arc hybrid welding and aluminum alloy multi-stranded welding wire were combined,and laser-MIG hybrid welding process of with aluminum alloy laser-multi-stranded welding wire is proposed.Firstly,the arc characteristics,the droplet transfer forms and the welding process of MIG welding with multi-stranded wire were studied.The results show that when the welding current is greater than 130 A,the arc changes from the oblique column state to the bell cover state.When the welding voltage increases from 22 V to 30 V,the arc length increases from 2 mm to 8 mm.The main forms of droplet transfer are short-circuit transfer,sub-jet transfer and droplet transfer;MIG welding with multi-stranded wire has a narrow process range,poor short-circuit transfer formation,and is difficult to remove splashes on both sides of the droplet transfer weld.A comparative test of aluminum alloy multi-stranded wire MIG welding and aluminum alloy solid wire MIG welding was carried out,and the differences in weld morphology and deposition characteristics between the two welding wires were studied.The results show that multi-stranded wire has shallow melting depth and wide melting width,and the deposition efficiency is not significantly improved.By applying the welding resistance heat theory and electromagnetic pressure theory,the reasons of deposition characteristics and weld morphology differences were analyzed.The influence of laser introduction on MIG welding of multi-stranded wire was studied.The influence of laser introduction on arc morphology,droplet transfer form and weld morphology was studied.The results show that the introduction of laser improves the stability of welding process and weld penetration.In addition,it helps reduce the short-circuit transition frequency,shorten the sub-jet transition droplet falling path,and improve the splash on both sides of the droplet transfer weld.The introduction of laser enables MIG welding with multi strands of twisted wire to obtain good weld formation under short-circuit transfer and droplet transfer,and expands the process range of MIG welding with multi strands of twisted wire.The MIG hybrid welding process of aluminum alloy laser multi-stranded welding wire was studied.The effects of laser power,welding current,fiber spacing,defocus and welding speed on weld morphology and porosity were studied.The results show that increasing the welding current,defocusing amount,and reducing the welding speed have a good inhibitory effect on the porosity of laser-MIG hybrid welding with multi-stranded wire.When the welding current is 200?220 A,the defocus is+10?+20 mm,and the welding speed is 0.5?1 m/min,the porosity of the weld is less than 2%.The optimized welding process range is laser power of 3?6 kW,welding current of 160?220 A,defocus of-5?+20 mm,fiber spacing of 4?6 mm,and welding speed of 0.5?3 m/min.20 mm thick aluminum alloy welding was realized through the groove design.The quality evaluation and microstructure analysis of 20 mm thick aluminum alloy welded joints were carried out.The results show that the weld zone is mainly equiaxed grains,and the average size of the grains is 34.83 ?m.The grains in heat-affected zone lose the directionality of rolling growth,and the average size of the grains is 10.21 ?m.The average tensile strength of the joint is 291 Mpa,reaching 84.2%of the tensile strength of the base metal.The tensile fracture position is the fusion line,and the fracture is ductile fracture.The fusion zone is relatively weak,and the hardness is 74.7 HV,which is about 84.6%of the hardness of the base metal. |
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