Effect of Solidification Cooling Rate on Microstructure and Mechanical Properties of 55Al-Zn-1.6Si Alloy Coating

55Al-Zn-1.6Si alloy ingot was obtained at solidification cooling rates of 0-0.5 ℃·s^-1, and the samples were taken from conventional cooling and rapid cooling (solidification cooling rates of 5-10, 15-30 ℃·s^-1, respectively) DC51D+AZ coated steel plates. The effect of solidification cooling rate on the microstructure, phase composition and mechanical properties of them were comparatively studied. The results show that the 55Al-Zn-1.6Si alloy at different cooling rates all consisted of α(Al), β(Zn) and small amount of needle-like silicon phase precipitated along α(Al) grain boundaries. With increasing cooling rate, the microstructure was gradually refined, and the dendrites transformed from space growth in near equilibrium state to non-equilibrium plane growth. Hexagonal zinc spangles were formed in the coating, and the zinc spangles in the rapid cooling coating were the smallest. The hardnesses of the ingot, conventional cooling coating and rapid cooling coating were 123, 106, 125 HV, respectively. The yield strength of rapid cooling coating (287 MPa) was higher than that of conventional cooling coating (273 MPa), but lower than that of ingot (330 MPa). The total extension proof strengths of conventional cooling coating and rapid cooling coating were 389, 406 MPa, respectively. The tensile properties of the coated steel plates under conventional cooling and rapid cooling process had little difference.