MIG-Variable Polarity Plasma Archybrid Welding Technology Of High Strength Aluminium Alloy

Owing to low density,high specific strength,and goodmachining property,high strength aluminum alloy density is widely used in aviation,aerospace and military industry.However,the weldability of high strength aluminum alloy is poor due to its physical characteristics.Modern industry has made stringent requirements for high efficiency,high quality welding methods for aluminum alloys.MIG-VPPA hybird welding hass the advantages of high penetration depth and high welding quality in VPPA welding,and those of high welding efficiency in MIG welding process.It can overcome the disadvantages of narrow range of stable technological parameters and complexity of vertical welding tooling VPPA welding,and those of small preparation depth in MIG welding.MIG-VPPA hybird welding has obvious advantages in thick plate high strength aluminum alloy welding.According to the characteristics of MIG-VPPA hybird welding,the welding process detection and analysis system were established.MIG-VPPA hybird welding process of high strength aluminum alloy has been carried out.The welding process information were collected,such as the arc shape,the flow of the molten pool and the current and voltage of two arcs with different energy ratios.Hybird welding arc coupling mechanism was analysed.The study found that the MIG arc is compressed by the combination of the minimum voltage principle and the electromagnetic coupling characteristics of the MIG-VPPA hybird arc.In the case of VPPA positive polarity,the MIG arc is compressed perpendicular to the axis of the weld line.In the case of VPPA reverse polarity,The MIG arc is affected by the ampere force of the hybird arc field and the reaction force of the coupling region,and the arc contraction is more remarkable.The increase of VPPA current increases the compression effect of MIG arc.The coupling effect of VPPA and MIG arc is weake in positive polarity period.When the MIG current increases,the arc stability and arc force of VPPA decrease.The coupling effect of VPPA and MIG arc is weake in negative polarity period.When the MIG current increases,the arc stability and the arc force of VPPA are almost constant.The behavior of MIG-VPPA hybird welding pool was discussed.The study found that VPPA and keyhole pool can change the gradient of the surface tension of the MIG weld pool,and the liquid metal flows easily to the center of the molten pool.Compared with the single VPPA welding,the MIG-VPPA hybird welding has the advantages of easy to maintain the stability of the molten pool.Compared with the single MIG welding,the MIG-VPPA hybird welding has the advantages of energy concentration and high welding efficiency.The hybird welding is easy to obtain good weld formation.When the VPPA current is close to the perforation threshold,the hybird heat source can avoid the defects of single VPPA welding,which is easy to form cutting,and can also play an important role in the energy concentration of VPPA,and also can effectively play the advantages of VPPA energy concentration,a low-power MIG heat source can be used to obtain a good weld formation.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;VPPA energy ratio is too large,easy to make the weld pool instability,can not get the good weld formation.The MIG-VPPA hybird welding and MIG Wlding of 11mm7A52 aluminum alloy were compared and analyzed.The study found that in MIG process,two passes are needed to weld 11 mm aluminum alloys.In contrast,the weld of VPPA-MIG only needs one pass by depositing from one side on 11 mm aluminum alloys.Compared with MIG welding,the heat affected zone of MIG-VPPA hybird welding joint is narrow,and the grain size of weld center is smaller.MIG welded joint coefficient is 55.2%,the hardness of weld center is 84.5HV,MIG-VPPA hybird welding joint coefficient is 64.4%,the hardness of weld center is 104.3 HV.MIG-VPPA hybird welding has higher welding efficiency and smaller degree of joint softening.It is more suitable for welding of thick plate high strength aluminum alloy.