The Preparation And The Anti-corrosion Mechanisms Of Zinc-aluminium-magnesium-rare Earths Alloy Coating

Hot-dipped process is one of the methods to treat surface of the steel materials. Theadvantages of the process are the simple machining technology and excellentanti-corrosion performance of the products, so it is widely used in building, homeappliances and other industries. However, with the rapid development of modernindustry and scientific technology, the traditional hot-dipping coating has been unable tomeet the needs of the anti-corrosion performance.Based on the study of Zn, Zn-Al, Zn-Al-Mg alloy coating, three kinds of rare earth（Re=La, Ce, Pr）and the different content of elements were used in the Zn-Al-Mg melt.Study of hot-dipping technology of zinc based alloy coating, the best content of rareearths and adding method. On this basis, the Zn-Al-Mg-Re alloy coatings were prepared,the anti-corrosion performance was tested, and the anti-corrosion mechanisms wereanalyzed.All the coatings were tested by the neutral salt spray and the weight loss rate per500h and total of3000h were measured. The results show that the weight loss rate of theZn-4.5Al-0.05Mg alloy coating is lower than of the Zn and Zn-4.5Al coating, theweight loss rate of the coatings is reduced after the rare earth elements were added.The results of the polarization curves show that the corrosion current of theZn-4.5Al-0.05Mg alloy coating is lower than that of the Zn coating and Zn-4.5Alcoating, which indicated the Zn-4.5Al-0.05Mg alloy coating have better anti-corrosionperformance. When the content of La and Ce is0.09%and Pr is0.12%, the corrosioncurrent density is lowest and anti-corrosion performance is best. XRD analysis on the corrosion products show that the coating corrosion productsof the coating contain Al, Mg and Re are mainly Zn5Cl2(OH)8H2O. The products canform a dense protective film with a strong adhesion on the coating surface and preventthe steel from corrosion.The micro morphologies of coating after corrosion test were observed by SEM. Itcan be found that the Zn-Al-Mg coating is evener and no pitting corrosion. With theaddition of rare earths in the Zn-Al-Mg coating, the anti-corrosion performance of thecoating is improved. The better anti-corrosion performance of the Zn-Al-Mg-Re is dueto the corrosion products.