Formation mechanism of aluminum and its carbides under wobbling laser melting injection with carbon nanotubes-SiC hybrid particles

The softening problem of fusion zone (FZ) impede the widespread application of wobbling laser welding (WLW) which plays an essential role in aluminum alloy welding. The introduction of carbon nano tubes (CNTs) and SiC particles (SiCp) has the potential to alleviate this problem, whereas the mechanism of aluminum solidification and carbides synthesis under wobbling laser with multiple reinforcers is still unknown. Accordingly, CNTs-SiCp reinforced aluminum FZ is fabricated by wobbling laser melting injection (WLMI) for the first time. The numerical simulation of WLW and WLMI is incorporated in microstructure characterization, kineticthermodynamic calculation is innovatively carried out to determine the critical synthesis condition of carbides. The new insights into the nucleation/growth and orientations principle of aluminum with its carbides are demonstrated comprehensively. Firstly, the process of WLMI makes preferred growth of Al in FZ more diversified than that under WLW due to the undulate liquid-mushy interface. Secondly, carbides of Al4C3 and Al4SiC4 can exhibit a coupled growth in FZ edge due to high frequency and large amplitude of temperature fluctuation, rather than that have an independent growth in FZ center with relatively stable temperature. Thirdly, the coherent orientation relationships (ORs) that <0001>Al4C3//<0001>Al4SiC4 and <0001>Al4C3//<100>Al is preferred to be formed under oscillating heat-flow field of WLMI. Finally, the desired orientation of Al, Al4C3 and Al(4)SiC(4 )with fine grain can be gained in FZ, its strength has even exceeded base metal by more than 10 %. This paper can be regarded as a breakthrough in strengthening FZ under WLW, by WLMI with CNTs-SiCp hybrid particles, and provide a theoretical guidance of microstructure and property optimization.