Mg对Zn-6%Al镀层凝固组织的影响及耐腐蚀性的研究

Effect of Mg Addition on Solidification Structure and Corrosion Resistance of Zn-6%Al Alloy Coating

研究了Mg含量对Zn-6%Al合金镀层凝固组织及其耐腐蚀性能的影响。结果表明,Mg对合金镀层凝固组织和耐腐蚀性的影响明显,当Mg含量在3%以内时,随着Mg含量的增加,镀层凝固组织中出现了耐腐蚀相MgZn2,晶粒不断细化,形成了Zn/Al/MgZn2三元共晶,并且随着Mg含量升高更加均匀致密,镀层的耐腐蚀性不断增强;当Mg含量达到3%时,镀层的耐腐蚀性能最好;Mg添加量超过4%后,镀层耐蚀性有所下降,进一步添加Mg镀层会出现漏镀等质量缺陷。XRD分析表明,含Mg镀层表面经过盐雾腐蚀后主要形成具有优良耐腐蚀性的腐蚀产物Zn5(OH)8Cl2.H2O,Mg促进了腐蚀产物Zn(OH)2向Zn5(OH)8Cl2.H2O的转变,有利于镀层耐腐蚀性的提高。

The effects of Mg addition on solidification structure and corrosion resistance of hot-dip Zn-6% A1 alloy coating were investigated. The experiment results show that the addition of Mg evidently effects the structure and morphology of the coating, with the additive quantities of Mg in the alloy coating from 0. lwt% to 3wt%, hard and brittle MgZn2 phase and the Zn/AI/MgZn2 ternary eutectic present in the coating. As the addition of Mg refines the grains and makes the eutectic more regular and denser, the corrosion resistance of the alloy coating enhances with the increase of the Mg in coating. The Zn-6% A1-3% Mg has excellent corrosion resistance in all samples. As the content of the Mg is more than 4% in the alloy, the corrosion resistance and the surface quality decreases. The results of the XRD show that corrosion product of Zn-6%A1-3%Mg alloy coating is mainly Zn5 （OH）8Cl.H2O. The characteristic of Zn5 （OH）8Cl2. H2O is dense, insoluble and short of electric conductivity. Since the addition of Mg can promote the formation of Zn5 （OH）8C12. H20, Mg in the coating can improve the corrosion resistance of Zn-Al alloy coating.