Synergistic effect of an organic hydrophobic film deposited on MAO containing NaH2PO4 for enhanced corrosion resistance of 6063 aluminum alloy

Abstract

Aluminum alloys play a significant role in aviation, medical equipment, electronic device and automotive industry. Nevertheless, the corrosion is a critical problem that must be solved before applications. In this work, synergistic effect of an organic hydrophobic film (2-mercaptobenzothiazole (MBT), sodium stearate (SS) or 8-hydroxyquinoline (8-HQ)) deposited on micro-arc oxidation (MAO) which was post-sealing treated by NaH2PO4 was investigated on corrosion resistance. The morphology and composition of the resulting organic hydrophobic films were analyzed by FESEM, EDS and FTIR. The results revealed that the organic hydrophobic films were successfully deposited on the MAO coating with NaH2PO4 (MAO-NaH2PO4), and the pores and cracks of the MAO layer were effectively sealed. Moreover, the contact angle of the sample with 8-HQ treating reached the hydrophobic level (136.8°), which was much higher than that of the MAO-NaH2PO4 (58.06°). The PDP and EIS measurements showed that the sample with 8-HQ treating possessed superior corrosion resistance with a low corrosion current (1.924 × 10−8 A cm−2) and the decreased corrosion rate (1.8 × 10−4 mm·a−1), which was two order of magnitude higher than that of the MAO-NaH2PO4 sample (3.8 × 10−2 mm·a−1). This facile and low-cost strategy to form organic-inorganic composite coatings could have promising application in the corrosion protection for the light alloys.

Keywords

• Aluminum alloy
• Micro-arc oxidation
• Corrosion resistance
• 8-Hydroxyquinoline
• Hydrophobic property