Microstructure of Hot-Dip Galvanized Zn-Al-Mg Alloy Coating

The microstructure of hot-dip galvanized Zn-11%Al-3%Mg-0.2%Si alloy coating was studied in this article.X-ray diffraction analysis revealed the coating is composed by Zn,Al and MgZn;phase.Optical microscope （OM） and scanning electron microscope（SEM） observations showed the coating is occupied by snowflake-like dendrite,double hexagonal organization and eutectic.The coating backbone was the dendrite considered to be a phase of hexagonal close-packed（HCP） structure judging form its morphology according to the crystal growth way in the coating.Transmission electron microscopy（TEM） and energy dispersive spectroscopy（EDS） researches on the dendrite suggested that an intermediate Zn-Al phase was formed at high temperature,then decomposed into a type of Zn-Al granular eutectoid after cooling down to room temperature,while the eutectoid Zn and Al had a certain crystallographic relationship.The coating solidification process and the grain crystal structure were discussed.