Laser Beam Welding of Semi-Solid Rheocast Aluminium Alloy 2139

Abstract

NASA developed aluminium alloy 2139 for use in airframe structural applications as the requirement for higher strength, corrosion resistant, aluminium alloys is increasing, however the need to weld ‘unweldable alloys’ is also becoming apparent. 2139 is seen to be in this class. Semi-solid rheocast aluminium plates (Al-Cu-Mg-Ag) were cast in high pressure die casts. In total 27 welds were fabricated in experimentation, 3 on each plate to avoid distortion by using a continuous wave Nd:YAG. The weldability of this Al-Cu alloy was assessed by optical microscopy to indicate the quality and geometry of the passes. Comparisons were made with As-Cast (F) tempers. Laser power parameters ranged from 3 kW to 4 kW and weld speeds from 4 m/min to 6 m/min. Welds were allowed to cool naturally. The results show that by varying speed and power, when combined with heat treatments, produce diverse results for this unweldable alloy.