Corrosion Resistance of AA2036 and AA7075-T651 in Contaminated Acid Chloride Environments

Abstract

In the present study, an assessment on corrosion resistance of aluminium alloys type AA2036 and AA7075-T651 in varying solution consisting of acidic, saline and in contaminated acid-chloride environments was investigated using weight loss and electrochemical techniques. The as-received samples were sectioned into corrosion coupons polished, degreased and weight taken. Solutions containing 3.5 % NaCl, 0.5 M HCl, 0.5 M H₂SO₄ were prepared as corrosion media and combination of these solutions were used as contaminated environment for the samples. In the weight loss method, the samples were exposed separately in each solution and it combinations for period of 3 to 60 days (72 to 1440 h). While in the electrochemical method, a potentiostat corrosion kit was used. The scanning electron microscope and X-ray diffractometry were used to characterize the as-corroded samples. The corrosion rate of the alloy decreases with increase in exposure time. The corrosion rate of AA2036 in NaCl solution was observed to be the lowest (0.058253 mm/yr) as compare with AA7075-T651 (0.14273 mm/yr) in the same environmental conditions indicating a 59 % improvement. From the SEM surface morphology, the evidence of pitting corrosion attack was found when the samples are used in a various contaminated acid-chloride environments. The XRD spectra of the samples immersed in contaminated 0.5 M H₂SO₄ with NaCl for AA2xxx and AA7xxx comprised of Al (FCC structure), while H₂SO₄ (H₂O) with an unknown peak found at 2q = 82° detected on the corroded AA7xxx series. It was observed that the corrosion potentials of the alloy were practically reduced when in any of the contaminated environments.