Nd:yttritium–aluminum–garnet laser welding of copper to stainless steel

Systematic laser welding experiments were conducted on dissimilar metal of copper and 300 series stainless steel using a high average power Lumonics JK 701H Nd:yttritium–aluminum–garnet laser. The laser melt penetration depth and width in copper and stainless steel were evaluated as a function of the laser parameters. The results reveal that melting of copper demands much higher average power, shorter pulse duration, and lower welding speed than melting stainless steel. If the laser beam is focused on the interface of the joint or on the stainless steel side, the weld penetration in stainless steel is much deeper than that in copper and the weld formation is poor and solidification cracks emerge. Distributing heat input by positioning the laser beam with respect to the interface of the joint was explored. Good results were achieved while positioning the laser beam 0.4 mm on the copper side. Butt weld penetration can go up to 2.4 mm and fusion zone in both copper and stainless steel is evenly distributed. By adjusting welding parameters, weld defects such as shrinkage, porosity, solidification cracks, etc., can be eliminated. Although isolated hot crack clusters exist along the austenite grain boundary in stainless steel HAZ, the strength of the weld joint is higher than copper and high vacuum tight property can be achieved.