| From single-wire,double-wire to three-wire,high efficiency has always been the focus of welding research.At present,the research and application of three-wire Metal inert gas arc welding(MIG)mainly focused on steel welding.There are few reports on three-wire welding of aluminum alloy.6082-T6 aluminium alloy has excellent corrosion resistance compared with other aluminium alloys and is widely used in rail transit.In this experiment,low-frequency modulation pulse was added to the three-wire MIG,which can effectively reduce the porosity.At the same time,this paper also studied the electrical signals and droplet transfer characteristics of the welding process,weld formation and the property of weld joint.First of all,Compared with three-wire single-pulse MIG and double-pulse MIG,there are some differences in droplet transfer and weld formation between the two welding processes.As for three-wire single-pulse MIG,The peak value,base value,peak time and base value time of a single pulse are the same,and the droplet transfer is mainly one pulse and one drop,with very few two pulses and one drop.As for double pulse MIG,The electrical signal change regularly between strong pulse groups and weak pulse groups;When the pulse changes from strong pulse to weak pulse,The pulse base value and pulse peak value decrease gradually,and the base value time increases gradually.The pulse peak value time of both is the same.At the same time,double-pulse MIG can get fish-scale weld,and Melting width and Melting depth of weld are larger than those of single-pulse weld.Importantly,compared with three-wire single-pulse welding,three-wire double-pulse welding has a great improvement on the porosity-problem of aluminum alloy welding.Then,The double-pulse frequency,preset voltage and arc length correction of strong pulse group have obvious effects on droplet transfer,electrical signal and weld formation.With the increase of double-pulse frequency,the fish-scale pattern becomes more and more dense;when the double-pulse frequency is 3 Hz,the preset voltage is18 V,and the arc length of the strong pulse group is-2%,electrical signal and droplet transfer are stable,the fish-scale pattern of the weld is uniform and the shape is the best;under other parameters,the droplet transfer and the electric signal welding process are unstable and the weld formation is bad.Lastly,Three-wire double-pulse MIG was used to the butt welding of 6082-T6 aluminum alloy.The property and EBSD of the welded joint of different double-pulsefrequency were studied.The hardness distribution of the welds under three double pulse frequencies is the same,there are two weak hardness zones(weld and low hardness zones in heat-affected zone);when the frequency is 1Hz and 3Hz,the lowest hardness value appears in heat-affected zones,and the welded joint break in heat-affected zones,which are ductile fracture and dimples are uniform;when the frequency is 5Hz,The lowest hardness value appears in the weld zone and break.Cracks and pores can be observed through the fracture morphology.Base metal,weld and heat affected zone are mainly large angle grain boundaries,and the texture and grain of three regions are different.The grain of base metal is lath,the weld is columnar,The grain size and shape of HAZ are different,and the double pulse frequency has a certain effect on the grain size and texture of weld metal,and the grain size is relatively small when the frequency is 3 Hz. |
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