Abstract

This report investigates the influence of ageing on the susceptibility to intergranular corrosion (IGC) of an Al–Mg–Si alloy. The selected AA6063 Al-alloy has been exposed to ageing treatments at a predetermine temperature of 423 K for durations of 1 to 168 h to achieve the wide range of ageing states covering under- to peak- to over-aged. The ageing behaviour of the selected alloy has been determined based on the results of hardness and tensile properties. The susceptibility to IGC has been evaluated following the British standard (BS ISO-11846) method B and assessed based on the average and maximum corrosion depths apart from in-depth surface and sub-surface characterizations of corroded specimens. It has been observed that the depths of corrosion increase monotonically with increase in ageing time. With progress of artificial ageing, the dominant mode of corrosion gradually changes in the order of minor pitting, moderate pitting, pitting plus localized IGC, localized IGC and uniform IGC. The phenomenon of preferential dissolution of Mg from the β″ (Mg₅Si₆) and β (Mg₂Si) precipitates as well as the existence of Fe-rich intermetallic particles at the grain boundaries cause the pitting and intergranular corrosion because of the formation of local galvanic cells between the lower corrosion potential of Mg-depleted precipitates or precipitate free zones and to the adjacent anodic grain boundary precipitates.

Graphic Abstract

中文翻译：

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时效对Al-Mg-Si合金晶间腐蚀的影响

摘要

本报告调查了时效对Al-Mg-Si合金的晶间腐蚀（IGC）敏感性的影响。所选的AA6063铝合金已在423 K的预定温度下进行了1至168 h的时效处理，以实现广泛的时效状态，涵盖了从过低到峰值到过时的状态。已根据硬度和拉伸性能的结果确定了所选合金的时效行为。已根据英国标准（BS ISO-11846）方法B评估了对IGC的敏感性，并根据除腐蚀样品的深入表面和亚表面特征之外的平均和最大腐蚀深度进行了评估。已经观察到，腐蚀的深度随着老化时间的增加而单调增加。随着人工老化的发展，腐蚀的主要模式按小点蚀，中点蚀，点蚀加局部IGC，局部IGC和均匀IGC的顺序逐渐变化。镁从β''（Mg₅ Si ₆）和β（Mg ₂ Si）析出，以及在晶界处富铁金属间化合物的存在会导致点蚀和晶间腐蚀，这是由于贫镁的低腐蚀电位之间形成了局部原电池析出物或析出物自由区，并向邻近的阳极晶界析出。

图形摘要