人工时效7055铝合金晶间腐蚀形貌与微观机理的关系

Intergranular corrosion morphologies in relation with their microscopic mechanisms in the artificially-aged 7055 aluminum alloy

摘要:

通过浸泡腐蚀实验、SEM、TEM和元素面扫描,研究了人工时效对7055铝合金晶间腐蚀行为的影响。结果表明：合金在120 ℃时效时,晶界析出相优先发生腐蚀；而在400 ℃时效时,晶界析出相周围铝基体优先发生腐蚀。TEM及元素面扫描结果显示,合金在120 ℃时效时,随着时效时间的改变,由于晶界析出相粗化、析出相间距加宽以及晶界析出相Cu含量的提升,导致合金腐蚀形貌由典型晶间腐蚀形貌向点蚀形貌转变。合金在400 ℃时效时,Cu元素几乎都偏聚于晶界析出相中,周边基体贫Cu,晶界析出相腐蚀电位反而高于基体,导致晶界周边基体腐蚀为主导的晶间腐蚀形貌。

关键词:7055铝合金;典型晶间腐蚀形貌;点蚀形貌;元素面扫描

Abstract:

The effect of artificial ageing on the intergranular corrosion behavior of 7055 aluminum alloy were investigated by accelerated corrosion test, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental mapping of X-ray energy dispersive spectra (EDS). The results show that when the alloy is aged at 120 ℃, the grain boundary precipitates (GBPs) are the preferential corrosion sites; however, when the alloy is aged at 400 ℃, the Al-matrix near the GBPs is the preferential corrosion site compared rather than the GBPs. According to the TEM and EDS results, when the alloy is aged at 120 ℃, extended ageing leads to the coarsening and discontinuous distribution of GBPs as well as increased Cu content in the GBPs. These factors result in the evolution of corrosion morphology from a typical intergranular corrosion morphology to pitting morphology. When the alloy is aged at 400 ℃, Cu element atoms will concentrate in the precipitates, especially in the GBPs, and the Al-matrix deplete Cu element. As such, the corrosion potential of GBPs becomes higher than the Al-matrix nearby, causing intergranular corrosion guided by the Al-matrix dissolution along the grain boundary.

Key words:7055 aluminum alloy; typical intergranular corrosion morphology; pitting morphology; EDS-mapping