Laser Welding On Dissimilar Metals Of Brass/Copper And Brass/Low-Carbon-Steel

Laser beam welding of dissimilar metals between copper and brass as well as brass and low carbon steel was studied using a high power Nd:YAG laser in this thesis. Firstly, the laser weldability and the threshold for laser deep penetration welding of brass HPb59 were explored in the experiments. The influences of some parameters, welding speed, defocusing distance and shielding gas, to the weld formation, the depth and the width, were investigated too. Secondly, the laser welding process of the lap joint between copper and brass was studied. Finally, the behavior of the butt joint between brass and low carbon steel by laser penetration brazing was tested.In the laser welding experiment of copper and brass, the process of the lap joint was adopted. The focused laser beam was irradiated at the brass side to form the weld with the deep penetration character and the approving intensity of the joint.For satisfying the engineering requirements, it was done in the studies that the effects of different welding speed and the combination parts with different thickness to the weld forming, weld microstructure and weld mechanical properties. By adjusting the parameters, the welds with good appearance and metallurgical bonding are achieved. The data of bursting test shows that the fracture strength of the joint is up to 264 bar under the optimizing parameters of speed at 20mm/s and thickness of brass with 1.1mm.In the welding experiment of brass and steel, a new method, namely laser penetration brazing, was adopted and the focused laser beam was irradiated at the brass side of the butt joint. Thus the brass was penetratingly melted while the steel side remained solid state, and the melted brass interacted with the solid steel to form a brazing bonding. The interfacial characterizations of the joint were investigated by metallographic microscope, SEM and EDS. The results show that the element diffusion and solution at the interface occur and the metallurgical bonding between brass weld and steel is gotten. The width of the interaction layer is about 3μm. The hardness of the brass weld is higher than that of the brass substrate. The failure occurs at the part of the brass substrate in the bursting test. Consequentially, the weld joint of brass and steel is suitable for engineering application.