摘要
Fine gauge extruded aluminium alloy tubes can experience preferential corrosion and early failure when they are formed into ＂u-bend＂ via cold deformation. The relationship between the electrochemical reactivity and the microstructure of the bent vs straight parts of the tube was established. Investigations were carried out on two alloys containing 0.08% and 0.22% （mass fraction） of manganese. The corrosion morphology of bent tubes after immersion in salt water acetic acid test （SWAAT） solution showed the highest attack at the bent region of the high-Mn alloy. SEM characterisation of the alloys showed that each alloy has one main type of coarse intermetallic particle. However, TEM observation showed that there is a distinct difference in particle morphology between the bent and straight regions of the high-Mn tubes, the bent region revealed an additional population of 10 50 nm Mn-rich intermetallic particles, which increased both the anodic and cathodic reactivity. For the low-Mn alloy, no such effects were observed. The results suggested that cold deformation of the high-Mn tube allowed room temperature precipitation of fine Mn-rich particles, which increased the cathodic reactivity of that region by providing more cathodic sites, and increased the susceptibility to pitting by removing noble Mn from solid solution. Such an effect was not observed for the low-Mn alloy.
发现一些管状铝合金通过机械变形弯曲成U形时更容易在弯曲表面发生腐蚀。建立了管状铝合金的水平和弯曲表面的显微组织与腐蚀的关系。通过对含0.08%及0.22%Mn的两种铝合金弯管弯曲部分的显微组织的观察,及在酸性盐水(SWAAT)中的腐蚀形貌及微观电化学反应的研究,发现高Mn铝管在弯曲表面较易发生点蚀,有较低的击穿电压及较高的阴极电流密度。SEM及TEM观察发现此现象的产生与高Mn铝管弯曲处弥散的粒径小于100nm的富含Mn的合金二次相有关。
