Effect of Temper on Seawater Corrosion of an Aluminum-Silicon Carbide Composite Alloy

The corrosion behavior of annealed (O), as-fabricated (F), and naturally age-hardened (T4) aluminum alloy Al 6013 (UNS A96013) with 20 vol% silicon carbide in particulate form (SiC[P]) was investigated in 3.5 wt% sodium chloride (NaCl) and in Arabian Gulf water. Of the three tempers, T4 showed the lowest corrosion rate (0.04 mpy and 2.61 mpy) in deaerated and aerated NaCl, respectively. The corrosion rate in seawater was slightly higher. Predominant forms of corrosion were pitting and intergranular corrosion. Formation of corrosion chimneys was observed. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and energy dispersive spectroscopy (EDS) showed intermetallic formation and the presence of a gelatinous film of aluminum hydroxide (Al[OH]₃) of bayrite type. The higher corrosion resistance of the T4 temper resulted from finer and more homogeneously distributed precipitates compared to tempers F and O. In view of the the alloy's good corrosion resistance and outstanding ultimate tensile strength (UTS), yield strength (σ_y), and specific modulus (E), it can be considered a strong competitor to Al 2024 (UNS A92024), Al 2014 (UNS A92014), and Al 6061 (UNS A96061), which are used mainly for structural applications.