Effect of pre-treatment and cryorolling on microstructure and corrosion behaviour of Al 5052 alloy

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Date
2016-06
Authors
Chan Ji Kit
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Aluminium 5052 alloy (Al 5052 alloy) is commonly used in marine environment due to its good corrosion resistance. However, when Al 5052 alloy keep contact with chloride (Cl-) ions for a longer period, corrosion behaviour of the Al 5052 alloy is affected. Hence, this project was initiated to study the effect of Cl- ions concentration on the corrosion behaviour of pre-heat treated and cryorolled Al 5052 alloy. Four different NaCl concentration solution of 0 wt.%, 0.5 wt.%, 3.5 wt.% and 5.5 wt.% were investigated. Before corrosion test, the samples were subjected to pre-heat treatment; annealing at 300 °C and solution treatment at 540 °C then followed by cryorolling process up to 30% reduction. After that, the corrosion behaviour of the samples was investigated by using potentiodynamic polarization technique. Microstructural studies of corroded samples were observed under optical microscope and the percentage of pits on the surface was calculated. The pitting percentage of raw Al 5052 alloy in 3.5 wt.% NaCl was 24.5% and then dropped to 18.3% after cryorolling. The result revealed that with the increase of NaCl concentration, the Al 5052 alloy was more susceptible to pitting corrosion and it shifted corrosion potential (Ecorr) to more negative values. In general, corrosion rate of cryorolled sample was lowered compare to sample without cryorolled at all the NaCl concentration. Cryorolled sample underwent pre-treatment solution treated showed the best corrosion resistance with recorded value of 0.002235 mm/year, 0.026315 mm/year, 0.090998 mm/year and 0.14089 mm/year in 0 wt.%, 0.5 wt.%, 3.5 wt.% and 5.5 wt.% NaCl concentration respectively.
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