表面喷丸处理对SSM319s铝合金耐盐雾腐蚀性能的影响

Salt Spray Corrosion Resistance of SSM319s Aluminum Alloy with Surface Blast Treatment

采用标准中性盐雾腐蚀实验对表面喷丸处理前后两种状态的半固态触变压铸成形(semi-solid molding,SSM)319s铝合金片状试样在中性Na Cl盐雾介质中的耐腐蚀性能进行了测试。采用微距数码相机记录了盐雾腐蚀不同时间后的表面颜色变化和宏观腐蚀产物形貌,通过称重法监测了腐蚀增(减)重和去除腐蚀产物后的平均腐蚀失重随时间的变化规律,并利用扫描电镜(SEM)和能谱仪(EDS)对腐蚀表面微观形貌、腐蚀产物种类和去除表面腐蚀产物后的表面形态和点蚀程度进行了表征和分析。测试研究表明,表面喷丸处理能够明显降低SSM319s铝合金在盐雾气氛中的平均腐蚀失重,经过表面喷丸处理的样品平均腐蚀失重减小50%以上。能谱分析证实表面均匀腐蚀产物主要以Al2O3为主,而点蚀坑内的腐蚀产物为Al2O3和Mg Cl2的混合物。喷丸处理能强烈抑制点蚀坑缺陷的发生和扩展,其原因是喷丸表面形变效应对试样表层疏松、刮痕缺陷的弥合作用以及残余压应力对抗腐蚀性能的有益影响。

The corrosion resistance for two kinds of surface processing state of semi-solid die casting（ semi-solid molding,SSM） 319 s aluminum alloy sheet specimens was tested in neutral Na Cl salt spray medium. During the whole course of corrosion,the change in surface color and the corrosion products morphology at different time were recorded by digital camera. The average corrosion weight gain or loss of specimens before and after the removal of corrosion products at different corrosion periods was also measured by analytical balance. In addition,the surface appearance,composition of corrosion products and dot corrosion state were characterized by scanning electron microscope（ SEM）and energy dispersive spectrometer（ EDS）. The results showed that the blast treatment could significantly improve the uniform corrosion rate of SSM319 s aluminum alloy in salt spray atmosphere,decreasing by 50% averagely. The EDS analysis confirmed that the surface corrosion product was Al2O3 and the inner pitting corrosion product was a mixture of Al2O3 and Mg Cl2. The blast treatment could strongly inhibit the occurrence and the spread of pitting defects,especially strongly inhibited the occurrence of pit corrosion. The reason could be attributed to the surface deformation effects,which could make the defects closed and bring about residual compressive stress at surface layer.