Hot Dipped Zn-Al-Mg-Cu Coating with Improved Mechanical and Anticorrosion Properties

摘要

Three types of coatings: Zn-0.1 wt.%Cu (G), Zn-5 wt.%Al-0.1 wt.%Cu (ZA) and Zn-5 wt.%Al-1wt.%Mg-0.1 wt.%Cu (ZAM) were deposited by hot dipping method on mild steel substrates. Thephase structure, cross section microstructure, composition, microhardness and corrosion property ofthe coatings were characterized by X-ray diffraction (XRD), environmental scanning electronmicroscopy (ESEM-EDS), microhardness test, and electrochemical analysis. Continues salt spray testswere performed to access the corrosion behaviour of coatings. The microhardness of ZAM coating wasimproved to 178 HV comparing with 43 HV of G coating and 89 HV of ZA coating. The improvedmicrohardness of ZAM coating is due to the strengthening effect of grain boundary at whichintermetallic compounds of Al5Fe2Zn0.4, MgZn2 and Mg2Zn11 has precipitated. ZAM coating alsoshowed the highest impedance and the extended exposure during the salt spray test. Simonkolleite wasidentified as the main corrosion product on three tested coatings. The slow corrosion mechanism ofZAM coating was discussed.