Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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中国有色金属学报(英文版)

Transactions of Nonferrous Metals Society of China

Vol. 21    No. 6    June 2011

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Microstructural effects in corrosion of aluminium tube alloys
WANG Guan1, JIAO Hui-sheng2

1. Institute of Mechatronics, Guangdong University of Technology, Guangzhou 510006, China;
2. Oxford Instruments (Shanghai) Ltd, Shanghai 201109, China

Abstract: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.

 

Key words: cold deformation; Mn precipitation; aluminium tube alloy

ISSN 1004-0609
CN 43-1238/TG
CODEN: ZYJXFK

ISSN 1003-6326
CN 43-1239/TG
CODEN: TNMCEW

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