Study of keyhole closure and analysis of microstructure and mechanical performance of weld joints for variable polarity vertical up plasma arc welding process

Abstract

Two technical approaches for keyhole closure were conducted. Workpieces of aluminium alloy 2219 were welded using variable polarity vertical up plasma arc welding technology. Effects of welding process parameters on keyhole closure were analysed. Appropriate technical criteria for keyhole closure in the welding of aluminium alloys (3 or 6 mm in thickness) via the variable polarity vertical up plasma arc welding technique were obtained. Experimental simulation of girth welding (overlap welding) was conducted using the appropriate process parameters for the keyhole closure stage of plate butt welding, and the feasibility of circumferential welding was verified. Accordingly, girth welding of the external tank of a carrier rocket was achieved using the appropriate parameters for the keyhole closure technique. In addition, the metallurgical process and mechanical performance for the single pass and overlap welds were analysed and compared.

Horizontal welding of aluminium alloys by soft plasma arc

“…13 In vertical-up position which is the best welding position for VPPAW, single-pass weld with few pores and little angular distortion can be made in material thickness up to 16 mm. 14 The situation becomes bad in 2G position.…”

“…As a low defect welding process, variable polarity plasma arc welding (VPPAW) has advantages in welding aluminium alloy plates with medium thickness and has been realized for a number of critical applications, such as American international space station and space shuttle tank. 13 In vertical-up position which is the best welding position for VPPAW, single-pass weld with few pores and little angular distortion can be made in material thickness up to 16 mm. 14…”

Nanomechanical, mechanical and microstructural characterization of electron beam welded Al2219-T6 tempered aerospace grade alloy: A comprehensive study

“…A notable presence of porosity in the FZ was observed as a result of air entrapment and alloy shrinkage during the solidification process. Wang et al [ 18 ] employed the variable polarity vertical plasma arc welding (VPPAW) technique to weld Al 2219 and documented the occurrence of hot cracks, owing to the high heat input during the welding process, which resulted in the melting of low melting point phases situated at the boundaries of the crystalline structure. Consequently, these molten phases prolonged the liquid state of the crystal boundaries, leading to the formation of hot cracks.…”

Variable polarity plasma arc welding of magnesium alloys

“…Moreover, VP-PAW is especially suitable to weld the structural components that are relatively thick and difficult to be welded on the back side. 3,4 The VP-PAW is the use of PAW as a source of heat, and its principle is presented in Fig. 13.1.…”