Pore formation and melt pool analysis of laser welded Al-Cu joints using synchrotron radiation

Abstract

Known as challenging material combination, the welding of aluminium and copper, both with strongly different thermophysical properties, causes joining failures such as pores, cracks or intermetallic phases in the solidified welding area. To investigate the mixing of the materials and the occurrence of pores, the laser welding process is observed with synchrotron radiation which visualizes the phase boundaries between solid, liquid and gaseous material phases. This allows the visualization of pore formation and density differences of the materials inside the melt pool. In this investigation, pore formation in front and bottom of the keyhole is observed. The movement of the bubbles in the melt pool can be tracked until solidification at the material transition. Regarding the intermixing of the materials, the high-speed images show a fluctuating copper flow towards the keyhole and a material mixing over the entire aluminium melt pool depth. By understanding the mechanisms, compensatory measures for an improved process can be developed to enable the usability of aluminium and copper connections, for example in electromobility applications.