Study On Microstructure And Properties Of Zn-Al-Ni Hot-dip Galvanized Alloy Coatings

Hot-dip galvanizing has been widely used in steel corrosion resistance as a kind ofsurface treatment technology. Along with the development of science and technology andmodern industry, a growing demand has been applied to hot-dip galvanized quality, and it isinvolved not only the proper coating thickness and excellent corrosion resistance, but alsolustrous and smooth appearance.In view of the above requirements, the hot-dipped Zn-0.01%Al-（0.02～0.12）%Ni andZn-0.05%Al（-0.02～0.12）%Ni alloy coatings were gained by adding a small amount of Ni inthe Zn-0.01%Al bath and Zn-0.05%Al bath.The study on the microstructure of Zn-Al-Ni alloy coatings in different componentproportions reveals that, for Zn-0.01%Al-xNi alloy coatings, the thickness of coatings reducesgradually with the increasing of Ni content; the extra thick ζ phase appears when the Nicontent is0.02%; the growth of fragile ζ phase in the coating is restrained to some extent withthe increasing of Ni content; both ζ phase and δ phase in the coating are thickest when the Nicontent is0.05%, so the mechanical property and the corrosion resistance are preferable. ForZn-0.05%Al-xNi alloy coatings, the thickness of pure zinc coating reduces gradually, thesurface condition becomes worse, and the thickness of the coatings decreases firstly and thenincreases with the increasing of Ni content; the thickness of the coating is minimum and thepure zinc coating is densest when the Ni content is0.05%; the bad resistance of the thick andloose ζ phase in the coating makes the corrosion resistance worse when the Ni content is0.12%.The study on the hardness, surface appearance and abrasive resistance of Zn-Al-Ni alloycoatings in different component proportions show that, the grain size decreases firstly andthen increases, and the hardness increases firstly and then decreases for Zn-0.01%Al-xNialloy coatings along with the increase of Ni content. The grain size decreases firstly and thenincreases and then decreases and the hardness increases firstly and then decreases forZn-0.05%Al-xNi alloy coatings along with the increase of Ni content. The grain size is smallest, the hardness is maximal and the wear proof time is longer for Zn-0.01%Al-0.05%Nialloy coating. The wear proof time of Zn-0.05%Al-0.09%Ni alloy coating is longest, but thefriction coefficient for this coating is larger. When the Ni content is constant, the increase ofAl content increases the friction coefficient of the coatings and decreases the surface hardnesssignificantly.The study on the corrosion resistance of Zn-Al-Ni alloy coatings in different componentproportions reveals that, when the Al content is constant, the corrosion rate decreases firstlyand then increases for Zn-Al-Ni alloy coatings along with the increase of Ni content, thecorrosion rate is the minimum and the corrosion resistance is the best for the coatings whenthe Ni content is0.05%. When the Ni content is constant, the corrosion rate decreases with theincrease of Al as a whole. The corrosion resistance of Zn-0.05%Al-0.05%Ni alloy coating isthe best.