Study on Diffusion Welding (Report 3)

Effect of Surface Roughness on Welding Process

Abstract

Roughness of the surface to be welded is one of the important factors affecting the weld characteristics on the diffusion welding. The purpose of this study is to investigate the influences of the surface roughness upon the welding process and the weldability of diffusion welds, using copper bars treated by various surface polishings. The following results were obtained.
1. Size and shape of void on welded interface depend upon roughness and shape of welded surface. The rougher surface promotes the decrease in size of void and the increase in the number of void.
2. The welding process may be considered in terms of the four stages. A clearly defined demarcation between stages does not exist, and the stages overlap.
the first stage: the growth of the welded area depends upon the plastic deformation.
the second stage: the growth of the welded area depends upon the creep deformation.
the third stage: the shrinkage and the elimination of voids on the weld interface occur due to the mechanism of sintering.
the fourth stage: all voids shrink, and the original weld interface disappears or migrates.
3. The second stage of the welding process is due to welding pressure, temperature and time. And the finer surface roughness is, the shorter this stage is.
4. The third stage is closely related to surface roughness. The shrinkage of voids in diffusion welding is similar to one in sintering, and begins to be promoted when the radius of void decreases to 2μ.
5. Welding pressure is effective to promote the third stage.