Experimental investigation of temperature field and fusion zone microstructure in dissimilar pulsed laser welding of austenitic stainless steel and copper

Abstract

Laser dissimilar welding of copper/ stainless steel was experimentally conducted to investigate the process parameters influence on the temperature field and formation mechanism of melt pool microstructures. The experimental approach is to estimate the influence of the Nd:YAG pulsed laser process parameters (e.g welding speed, laser power, focal length and laser beam deviation) on the temperature gradient and the resultant metallurgical aspects of the melt pool such as Solidification cracking, copper particle diffusion and microstructure of the fusion zone. Creating the appropriate temperature gradient during welding plays a crucial role to effectively control solidification cracking at the fusion zone in order to reduce heat conduction effect of the copper. Increasing welding speed from 2 to 6 mm/s not only reduces the temperature about 50 °C but also decreased the fusion zone cracking significantly. Evidently, increasing the laser power from 240 to 260 W transmitted the fusion zone cracks toward the stainless steel base due to creating higher temperature about 230 °C and 150 °C for steel and copper respectively. Therefore, higher discrepancy of the temperature field between copper and steel clearly changed the place and pattern of cracks propagation. The EDS analysis of the fusion zone confirms diffusion of copper particles inside the weld pool. The temperature measured near the molten pool region showed that clear discrepancy at the temperature gradient of the melt pool at the copper and stainless steel side has increased the possibility of cracking the stainless steel fusion zone. Also, high temperature gradient for compensating copper high rate of cooling could lead to excessive copper ablation or even diffusion of copper elements into the stainless steel fusion zone.