Study On Mg And RE In The Modification Of Zn-23Al-0.3Si Coating

Steel as an important structure material of national production, has been widely used in construction, automotive industry and household appliances. In order to protect the steel materials, hot galvanizing technology is widely used in modern industrial production, it has the advantage of good protective property and low production cost. Many research results showed that, adding the alloy elements such as Al, Mg, Si and RE to the galvanizing liquid can improve the corrosion resistance and mechanical properties.Zn-23%Al-0.3% Si coating as a new excellent coating was developed by the company of Comico in Canada. This coating is a kind of high hardness, good toughness, and corrosion resistant. This alloy coating with high corrosion resistance is better than Galfan coating, it is 5-6 times of conventional hot dip galvanized layer.In order to improve the corrosion resistance and mechanical properties of it, in this syudy, we added the alloy elements Mg and RE to the coating, and then we used the neutral salt spray test, electrochemical test, mechanical drawing experiment and SEM, XRD, OM detection method to study the effects of Mg and RE on the corrosion resistance, formability, microstructure and corrosion mechanism of Zn-23%Al-0.3%Si coating.Neutral salt spray test and electrochemical test showes that, Mg and RE can significantly improve the corrosion resistance of the coating.The corrosion rate of Zn-23%Al-0.3%Si, Zn-23%Al-0.3%Si-2.0Mg and Zn-23%Al-0.3%Si-2.0Mg-0.15RE coatings are 0.0672g · m'2 · h'1,0.0245 g · m"2 · h-1 and 0.0133 g · m"2 · h-1, The corrosion rate decreased significantly. Mechanical drawing experiment showed that, Mg and RE can improve the formability of Zn-23Al-0.3Si coating; the crack of this coating was reduced and narrowing after adding Mg, RE can refine microstructure and there is no crack on this coating. Mg and RE can improve the surface quality, reduce the thickness of this coating.The microscopic detection of coating surface shows that:the addition of Mg (2.0%wt.%) and RE (0.15 %wt.%) can significantly improve the uniformity of the structure of the coating, Zn-23Al-0.3Si coating in the interdendritic region generated MgZn2 when the Mg added to the coating. RE has the role of grain refinement, the Zn-23Al-0.3Si-2.0Mg-0.15RE coating become the uniaxial uniform after the RE joined in. The section detection shows that:Mg and RE can make the alloy of internal layer become thinner and more uniform and can reduce the thickness of coating. The morphology of corrosion products shows that:Mg and RE can improve the stability of the corrosion product, it can make the corrosion product of Zns (OH) 8Cl2 · H2O become more compact, and the internal crack completely disappeared. The corrosion types analysis shows that:Mg and RE can change the corrosion types of this coating, the surface corrosion of Zn-23Al-0.3Si-2.0Mg coating is not serious and the surface of Zn-23Al-0.3Si-2.0Mg-0.15RE coating remained flat, the corrosion pits is shallow and small, so we basically think that such corrosion was uniform corrosion.Based on the above results, whether in corrosion resistance, microstructure or formability, the Zn-23Al-0.3Si-2.0Mg-0.15RE coating is better than Zn-23Al-0.3Si. This alloy coating shows more broad application prospects.