EVOLUTION OF RAPIDLY SOLIDIFIED MICROSTRUCTURE IN SiC_P/A356 COMPOSITES WITH LASER RADIATION

The presenTinvestigation is aimed to understand the microstructure evolution of SiC P/Al Si composites, i.e. , particle distribution and matrix microstructure in rapid solidification. Microstructures of SiC P/A356 composite and the monolithic alloy were comparatively studied through laser re melting process. ITis observed that the particle remains its original distribution after re solidification, indicating that rejection of particles by rapid solidification interface does not occur. The presence of particles does not lead to any change in the phase constitution in the matrix, but has a great effect on crystal growth of primary phase. For the monolithic alloy, primary phase dendrites arrange themselves closer to the heat flux direction. Raising the scanning velocity, the dendrites become finer but remain the characteristic of regular columnar epitaxial re growth. However, the arrangement of primary α Al in laser treated composite is somewhat chaotic. These results, in addition to some evidence of unstable branching dendritic structure and dendrites terminating at a particle, indicate that the particle with a size larger than the length scale of the sub grain structure forms a complete barrier to the crystal growth.