热浸镀55%Al-43.4%Zn-1.6%Si合金镀层表面锌花尺寸不均原因及腐蚀特征

Study on the Inhomogeneous Defect and Corrosion Resistance Characteristic of 55%Al-43. 4%Zn-1.6%Si Alloy Coating on the Steel Substrate

利用OM、SEM、EDS、XRD等研究55%Al-43.4%Zn-1.6%Si合金镀层表面锌花特征、合金元素分布规律;通过极化曲线研究镀层不同区域耐腐蚀行为,并探讨热浸镀形成过程及在腐蚀过程中组织演变规律。结果表明:不同尺寸特征的锌花其金相组织均是由垂直网格状树枝晶构成,且晶臂间距大小一致;不同尺寸锌花表面成分均是由Al、Zn组成,且含微量Si元素,Al、Zn元素约为2∶1;大小尺寸锌花的金属化合物层中α-{Fe,Al,Si}相数量不同是造成锌花尺寸不均的主要原因,锌花尺寸数值越小,IMC层中τ5相数量越多,凝固过程中形核点就会越多,形成的锌花尺寸就越细小;采用多点采集统计,不同尺寸特征的锌花其耐蚀性几乎相当。

Spangle characteristic and distribution of alloying elements coating on the steel substrate of 55%Al-43.4%Zn-1.6%Si alloy are carried out by using OM,SEM and EDS testing means.Coating corro- sion resistance behavior of different areas was studied by polarization curve, and the formation process of hot dip and evolution of microstructures in the process of corrosion has been discussed.The results show that the different sizes of spangle microstructures consist of vertical grid dendrites arms with same spacing and and the composition of the different size of spangle surface ement where the ratio of Al/Zn is about 2 ： 1.It is found out size is mainly caused by the different number of α- { Fe, A1, Si spangle contains Al, Zn and trace amounts of Si elthat inhomogeneous distribution of spangle } in the metal compounds layer.The smaller size generates more T5 phase in the IMC layerand hence more shape nucleolinus in the solidifica- tion process,and the resulting spangle is much more fine. Multi-point statistical collection indicates that the different sizes of spangle have the same corrosion resistance behavior.