Solidification Microstructures in Laser Welding of Dissimilar Metals

摘要

In this paper, salient features of the microstructure development during laser welding of binary couples of copper and nickel in butt-welding geometry is discussed. The two metals have very different physical properties and a simple phase diagram, thus providing a model system to study dissimilar metal welding. The process simulates high solidification rates. The microstructures are characterized to determine the size and shape of weld region, scale of microstructure and composition segregation profiles as a function of welding speed. The results highlight asymmetry of weld region, cellular microstructure, banding and an asymmetry in the mode of growth of base metal into weld region. The process is also modeled using a control volume approach to simulate heat transfer, buoyancy and marangoni convection and mixing of species to obtain temperature gradients, cooling rates and composition distribution in the weld pool. An attempt is made to correlate the experimental segregation profiles and microstructure with the computational results. The results will be compared with that obtained with other metal pairs on which we have initiated work.