热处理过程中纯锌镀层的组织转变和表面氧化

采用FE-SEM,EPMA和XRD等分析了纯锌镀层在加热过程中的组织转变和表面氧化。试验结果表明:GI镀层在较低温度加热后,厚度相对原始镀层没有改变,镀层与基板界面明显,高于800℃加热后,镀层厚度大幅增加,镀层/基体界面并不清晰;500℃加热后镀层组织为ζ相和δ相;随着加热温度升高,镀层组织转变为含铁量更高的Γ1相、Γ相和α-Fe(Zn);900℃加热后镀层几乎全为α-Fe(Zn),只在表面存在少量的Γ相;镀层中的铝随着加热温度升高逐渐向镀层表面迁移,900℃加热后铝完全迁移至镀层表面,形成连续的氧化铝层;低温加热后镀层表面只有很少的Fe-Zn相和氧化物。随着加热温度升高,表面的氧和铝含量增加,锌含量降低。900℃加热后,镀层表面存在Γ相、Al2O3和ZnO。

Microstructure Transformation and Surface Oxidation of GI Coating During Heat Treatment

Microstructure transformation and surface oxidation of GI coating during heat-treatment were investigated by FE-SEM, EPMA and XRD. These were observed that thickness of GI coating did not change after heated at lower temperature, and the interface between coating and substrate was clear. After heated at higher than 800℃, thickness of coating increased and the interface was not easy to identify. The microstructures of coating after heated at 500℃ were ζ and δ. With the heating temperature increasing, the microstructures of coating transformed to Fe-rich phases, such as Γ1, Γ and α-Fe(Zn). The coating was almost made of α-Fe(Zn) after heated at 900℃, there was only a little of Γ phase near the surface of coating. Al in coating gradually migrated to the surface of coating with heating temperature increasing. After heated at 900℃, Al completely migrated to the surface of coating and a continuous alumina layer was formed. Only a little of Fe-Zn phase and oxide were found on the surface of coating after heated at low temperature. The contents of O and Al increased and the content of Zn decreased on the surface with heating temperature increasing. The surface of coating was consisted of Γ, Al2O3 and ZnO after heated at 900℃.