Research On Microstructure And Mechanical Properties And Welding Porisity Of The2219Aluminum Alloy Cross-weld Joint By FSW And VPPAW

In order to adapt to the technological development of rocket tank production, someindustries use the2219aluminum alloy cylinder tank as the main structural material, whichis welded by friction stir welding on the cylinder longitudinal seam and welded by variablepolarity plasma welding on girth. However, in the actual production and related research,some researcher found that cross-connectors of both the process exist porosity defects,which are affecting the joint performance. Therefore, this article will be FSW/VPPA crosswelded joints of aluminum alloy2219for further research, analysis of the microstructureof the cross connector. Cross joints were observed pore distribution, density and the type ofporosity, and the analysis of the causes of holes in the cross, the research of the effects ofdifferent welding parameters on mechanical properties and number of stomata will bepresented.The2219aluminum alloy cross-weld joint’s microstructure is changed in positioncompared with VPPA seam, especially in the heat affected zone. The microstructure ofCross joint weld and VPPA weld are both equiaxed dendrite and dendritic equiaxedalternating tissue. The microstructure of cross-weld joint and VPPA joint are bothessentially comprised with α (Al) matrix, the (α-Al+Al2Cu) eutectic structure and crystalprecipitation θ (Al2Cu) and other enhanced phase. However, the number and the size ofcross-weld tissue strips eutectic phase is more and larger than VPPAweld’s, which reducesthe mechanical properties of joints.Cross-weld joint’s pores are mainly located in the vicinity of the fusion line. You cansee from the walls of the pores by SEM scanning images, the surface is clean and smooth,no oxidation, according to the relevant data analysis, it can be concluded that the type ofcross-weld joint’s pores is hydrogen vent holes. The hydrogen source is from material, itcan be inferred that the oxide film on friction stir weld joint is the main reason for theformation of cross-pores.The study of the retention time before FSW, friction stir welding heat input andvariable polarity plasma line energy input which impact on cross-weld joint found:(1) TheFSW/VPPA cross-weld joint which the oxide film is not removed before FSW caused thedegree of seriousness of the pores;(2) with the friction stir welding heat input increased, the degree of porosity defects and mechanical properties of cross-weld joint decreased. Inthe friction stir welding, the plastic flowed metal filled continuously the transient cavity.When lower heat input, instantaneous cavity contact with air longer, the greater the extentof the instantaneous high temperature metal oxide within the cavity, the more the metalabsorb air moisture. This provided more hydrogen source for the variable polarity plasmacross welding, resulting in more severe degree of porosity within the joints;(3) the degreeof porosity defects of cross-joints increased with variable plasma welding welding speedincreasing. This is because of the speed of the welding speed impacts on the weld metalcrystallization rate, the faster the crystallization rate, the shorter the time the air bubbles.