LASER FUSION WELDING OF CU TO AL WITH SPIRAL TRAJECTORY AND MONITORING OF PROCESS SIGNALS

Welding of Aluminium (Al) and Copper (Cu) in a dissimilar fashion is required for the manufacturing of solar thermal absorbers, battery modules and refrigeration applications. The high strength, thermal and electrical conductivity of Cu combined with the lightweight property of Al material enable the high performance of the product. A laser is a precise tool, which can increase the productivity and quality of the welding process. Welding Al and Cu is considered difficult because of the formation of complex intermetallic phases which reduce the strength of the joint. Laser brazing from low melting Al sheet to Cu sheet is the traditional technique to reduce the intermetallic phases. This thesis focuses on irradiation of laser beam from copper sheet to aluminium sheet in overlapped configuration. The approach is to form a large amount of intermixing to obtain (Cu) solid solution and Al-rich phase Al+Al2Cu in the interface. By this approach, it was found that a fusion zone with a large number of good phases was formed. The intermetallic compounds Al2Cu,Al3Cu4,Al4Cu9 are intermixed and small. Such a microstructure is beneficial for joint strength. The characterization was done by light optical microscopy and scanning electron microscope. EDS analysis was used to estimate the composition and identify the phases. It was found that a beneficial Cu solid solution phase is present in the joint.
To qualify the joint and identify the weld status, melting characteristics during laser welding by observation of the optical emission in Ultraviolet-visible wavelength was studied. The Al melting peak at 396 nm and Cu melting peak at 578 nm was found to correlate to the welding process parameters. The signals correlate to the actual melting of Cu and Al sheets, which was investigated by the cross-sectional images and the weld images on the top of the Cu-Al weld. Therefore, the possibility for real-time analysis to identify different welding conditions is shown.