Nd: YAG laser welding of copper to stainless steel

Systematic laser welding experiments were conducted on dissimilar metal of copper and 300 series stainless steel by using high average power Lumonics JK 701H Nd: YAG laser. The laser melting penetration depth and width in copper and stainless steel were evaluated as a function of laser parameters and the results reveal that melting copper demands much higher average power, shorter pulse duration and lower welding speed than melting stainless steel. If laser beam is focused exactly on the interface of the joint of stainless steel and copper, the weld penetration in stainless steel is much deeper than that in copper and the weld formation is of poor quality. Distributing heat input by positioning the laser beam with respect to the interface of the joint was explored. Good results were achieved while positioning laser beam 0.4mm on copper side. Butt weld penetration can go up to 2.4mm and fusion zone in both copper and stainless steel is evenly distributed. By adjusting welding parameters, weld defects such as shrinkage, porosity and solidification cracks etc can be well controlled or eliminated and the only welding defect comes to be hot cracks along austenite grain boundary in stainless steel HAZ. The property tests reveal no obvious effect of the hot cracks on strength and vacuum seal of the joint.