过时效与添加Zr对Al-Zn-Mg合金耐腐蚀性能影响的对比

Comparative Study on the Effect of Over-aging and Addition of Zr on the Corrosion Resistance of Al-Zn-Mg Alloy

以中高强Al-Zn-Mg合金为研究对象,通过慢应变速率拉伸、晶间腐蚀以及剥落腐蚀等实验,对比研究过时效处理和添加Zr对Al-Zn-Mg合金耐腐蚀性能的影响。结果表明,T76过时效处理较T6峰时效能更明显地提升合金的抗应力腐蚀、晶间腐蚀及剥落腐蚀性能;添加0.15%的Zr使合金强度得到显著提高,抗腐蚀性能也能得到不同程度的改善,其中抗应力腐蚀和晶间腐蚀性能提升最为明显,而其对抗剥落腐蚀性能的提升效果则略逊于T76过时效处理。采用SEM、EBSD及TEM等手段分析了T76过时效处理和添加微量Zr影响Al-Zn-Mg合金耐腐蚀性能的机理。结果发现:过时效处理使得合金的晶界析出相粗化且断续分布,晶界无沉淀析出带(PFZ)变宽;添加Zr则抑制了合金的再结晶,大角度晶界分数的降低提升了合金的耐腐蚀性能。

Taking Al-Zn-Mg alloy as research object,a comparative study about the effect of over-aging treatment and adding Zr on the corrosion resis-tance of Al-Zn-Mg alloy was carried out by means of slow strain rate test(SSRT),intergranular corrosion(ICG)and exfoliation corrosion tests(EXCO).In light of the results,over-aging treatment(T76)was superior to peak-aging treatment(T6)because of its significant effect in enhancing the stress corrosion cracking(SCC),intergranular corrosion and exfoliation corrosion resistance of Al-Zn-Mg alloy.A remarkable improvement in the strength of Al-Zn-Mg alloy could be observed by adding 0.15%Zr.In addition,amelioration of corrosion resistance of the alloy in different extents was achieved,in which the stress corrosion cracking and intergranular corrosion resistance showed the most obvious amelioration.However,adding Zr was less effective in improving exfoliation corrosion resistance of the alloy than over-aging treatment.The mechanism for the influence of over-aging treatment and adding Zr on the corrosion resistance of the alloy was analyzed by means of scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).It was found that over-aging treatment made the grain boundary precipitates(GBPs)of the alloy turn coarse and intermittently distributed,and widened the precipitate free zone(PFZ).While the addition of Zr inhibited the recrystallization of the alloy,and the reduction of large-angle grain boundary fraction contributed to enhancing the corrosion resistance of the alloy.