Preliminary study of friction stir overlap welding on variable polarity plasma arc weld

The friction stir overlap welding on variable polarity plasma arc (FSOW-VPPA) weld was first proposed for a complete girth weld in 2219 aluminium alloy. The mechanical properties, microstructures, and metallurgical processes of FSOW-VPPA in comparison to single-FSW and VPPA welded joints were studied in this paper. The FSOW-VPPA welded joint was characterized by the modified nugget zone (NZ), thermo-mechanically affected weld zone (WZ), heat affected fusion zone (FZ), and double heat affected zone (HAZ). The modified NZ was characterized by “onion-rings” without the porosity that appeared in the VPPA weld. The grains in the thermo-mechanically affected WZ were finer than that of the VPPA weld. In the second thermal cycle, the angle of the direction of crystal growth from the horizontal decreased from 38 degrees in the VPPA weld to 22 degrees. In contrast with the single-FSW weld, there was no serious deformation on the advancing side (AS). In general, the second thermal cycle did not degrade the quality of the weld. The elimination of pores and grain refinement improved both the tensile strength and elongation of the FSOW-VPPA weld compared to the VPPA and single-FSW welds. The tensile strength increased to 84.0% compared to 79.8% for the VPPA weld. In addition, the metallurgical processes were analysed and compared.