Mechanism of weld formation in variable polarity plasma arc-MIG hybrid welding of high strength aluminium alloy

VPPA-MIG hybrid welding integrates the advantages of strong arc penetrability of VPPA and high deposition efficiency in MIG welding. It can overcome the disadvantages of narrow range of stable technological parameters in vertical position in VPPA welding and shallow penetration in MIG welding. The weld pool images on 2A12 aluminum alloy with thickness of 6 mm in VPPA-MIG hybrid welding were obtained by Red Lake Y4 high-speed camera acquisition system. The force model of weld pool was established. The influence of different energy ratio of the hybrid heat source on the weld formation and the weld pool was analyzed. The weld formation in VPPA-MIG hybrid welding and MIG welding were investigated. The results show that VPPA-MIG hybrid heat source is easier to maintain weld formation stability than single VPPA heat source. When the VPPA current is close to the perforation threshold, a low-power MIG heat source can be used to achieve the weld formation on 2A12 aluminum alloy with thickness of 6 mm; When the VPPA energy ratio is too low, the keyhole is shallower, the melting efficiency is lower, and the effect of increasing the penetration depth can not be achieved; When the VPPA energy ratio is too large, it can damage the stability of weld pool and the weld formation. Under the same heat input power, the weld formation in VPPA-MIG hybrid welding was narrower and deeper when comparing with conventional MIG welding． The welding productivity was improved dramatically