不同热处理工艺对Al-3.8Zn-1.6Mg铝合金微结构 与腐蚀行为作用的探讨

本文针对一种经历了三级时效后获得优良力学性能的7N01铝合金,采用慢应变速率拉伸、剥落腐蚀测试,并采用透射电镜系统研究了该合金局部腐蚀行为与微观结构的关系.结果表明,三级时效状态的7N01铝合金,相比直接热处理(T4、T5、T6)的材料,其抗应力腐蚀性能和抗剥落腐蚀性能均可获得显著提高.透射电镜观察发现:T4状态合金中晶界析出相以细小的GP区以及溶质原子团簇为主,且晶界处元素分布均匀;T5状态合金中晶界析出相粗大,存在晶界无析出带(PFZ),Zn、Mg元素于晶界析出相处富集;T6状态合金中晶界析出相细小且接近连续分布,Zn、Mg元素于晶界析出相处富集;虽然三级时效工艺后Zn、Mg元素也于晶界析出相处富集,但晶界析出相粗大且断续程度加大,形成较宽的耐腐蚀的PFZ,因此有着更好的抗腐蚀性能.

Influence of different aging process on microstructure and corrosion behavior of Al-3. 8 Zn-1. 6 Mg aluminum alloy

Influence of a three-step-ageing treatment on the EXCO ( exfoliation corrosion ) and stress corrosion cracking ( SCC ) resistance of Al-3. 8Zn-1. 6Mg aluminum alloy was investigated by the slow strain rate technique ( SSRT) and EXCO test, which used TEM, EDS and SEM. It was shown that the three-step-aged alloy had better EXCO and SCC resistance, compared with the directly one-step-aged alloy. Transmission electron microscopy ( TEM) showed that the grain boundary precipitates in the T4 state alloy were mainly composed of small Guinier-Preston ( GP) zone and solute-atom-clusters, and the elements in the grain boundary were uniformly distributed. The T5 state alloy had coarse grain boundary precipitates ( GBP) and precipitated in the free zone ( PFZ) , Zn and Mg were enriched in the GBP;T6 state alloy had fine GBP, and Zn and Mg elements were enriched in the GBP. While the three-step-aged alloy could improve corrosion resistance because of the more discrete and coarser GBP and wider PFZ.