Microstructure and phase analysis on Zn-Al-Mg alloy coatings

Zn-Al-Mg coated steels have excellent cut edge protection and atmospheric corrosion resistance, but the phase composition of Zn-Al-Mg coating is still controversial. In order to better control the coating structure, the formability and corrosion resistance of the coated steel sheet, the microstructure and phase structure of the Zn-Al-Mg coated steel sheet were analyzed in detail with scanning electron microscopy (SEM), X-ray diffraction (XRD), glow discharge spectrum(GDS) and transmission electron microscopy (TEM). It was determined that the Zn-Al-Mg coatings consisted of three phases such as Zn, Al and MgZn₂. TEM analysis showed that there was an Al-Fe alloy layer with a thickness of 0.01 μm and a Zn-Mg alloy layer with a thickness of 0.1 μm at the interface between the coating and the steel plate.