<p>Solidified microstructures with 15-μm and 25-μm coating thicknesses of 55%Al-Zn-1.6%Si alloy coating were investigated by means of multiple experimental approaches, and CALPHAD (CALculation of PHAse Diagram) calculations were carried out to analyze the solidification mechanism in consideration of cooling rate and coating thickness. From the scanning electron microscopy, electron probe micro-analyzer, and glow discharge spectrometer methods, it was discovered very little Si concentrated on the coated steel with 25-μm coating thickness. Focused ion beam and transmission electron microscopes were used to determine the microstructure of the 55%Al-Zn-1.6%Si alloy coating, and large Zn-rich particles were observed in the coating with 25-μm coating thickness. Electrochemical experiments showed that the incompact microstructure without enough Si leads to a decrease of surface corrosion resistance. From the CALPHAD calculation results, the enrichment of large Zn-rich particles on the coating surface was reasonably explained by thermodynamic calculations. Also, it was discovered that the back diffusion controlled solidification process influences the distribution state of Si, which agrees well with the experimental results. The calculated cracking susceptibility index takes on a decreasing trend with the increase of cooling rate, which means that suitable enhancement of incompact cooling rate benefits the solidified microstructure of the 55%Al-Zn-1.6%Si coated products.</p>