Al-Zn-Mg-Cu合金的局部腐蚀行为与Zn、Mg含量的关系

Behavior of localized corrosion of Al-Zn-Mg-Cu alloys in relation with their Zn and Mg contents

研究了峰值时效状态下,不同Zn、Mg含量(质量分数)对高Cu含量(2.0%~2.5%)的Al-Zn-Mg-Cu合金耐局部腐蚀能力的影响,利用透射电镜和扫描电镜表征了合金局部腐蚀行为与其微观结构之间的关系。结果表明:对Mg含量不同的两组目标合金,Zn含量降低,合金的耐局部腐蚀能力变差;对应比较Mg含量不同的两组合金,初始阶段低Mg组合金的耐晶间腐蚀能力较差,但深度发展阶段低Mg组合金的耐晶间腐蚀能力较好;前期阶段高Mg组合金的耐剥蚀能力较好,但后期深度腐蚀阶段,高Mg组合金的耐剥蚀能力变得较差。

It has generally been believed that the Cu addition in Al-Zn-Mg-Cu alloys can improve the stress corrosion resistance of the alloys. Nonetheless, for such alloys with a high Cu-content, few papers have paid attention to their exfoliation corrosion（EXCO） and intergranular corrosion（IGC）（two kinds of localized corrosion） resistance in relation with their Zn and Mg contents. In the present study, peak-aged Al-Zn-Mg-Cu alloys with relatively high Cu contents（2.0%-2.5%） were studied for their localized corrosion behaviors with varying Zn and Mg contents. By scanning/transmission electron microscopy（S/TEM）, the microstructures of the alloys were characterized in relation with their properties of corrosion resistance. The alloys were classified into two groups： one with higher Mg content（high-Mg group） and another with lower Mg content（low-Mg group）. The results show the following： 1） For both the two groups of alloys, with decreasing the Zn-content, their localized corrosion resistance decreases without exception; 2） The high-Mg group of alloys are worse than the low-Mg group of alloys in IGC resistance in their initial stages of corrosion, but better in their late stages; 3） For EXCO resistance, the former group is better than the late group in their early-stages of corrosion, but worse in their late stages of in-depth corrosion.