Contribution of the Guinier-Preston zones to the hardening of Al-5%Ag alloy and its photo-electrochemical protection in seawater using n-CdS

The contributions of the GP zones and the matrix to the alloy hardening have been studied in the alloy Al-5% at. Ag aging at 150 °C. They were determined separately using a method based on the hardness measurement which obeys the relation ΔHv_SS = 19.72x^2/3 + 0.218 (Gpa), where x is the means atomic concentration of the matrix. The GP zones follows the relationship (ΔHv _GP = 18.4 f_v^0.94 kg/mm²), f_v is the volume fraction of GP zones. In a second part, the photo-electrochemical properties of n-CdS were exploited for the cathodic protection of the alloy Al-5% at.Ag in one of the most corrosive environments namely seawater. The corroded surface was rough and the corrosion product contains divided particles. However, the corrosion was significantly hindered by contacting the alloy to n-CdS (E_g = 2.40 eV) irradiated by visible light with different intensities (42–103 mW cm^-2). Under illumination, the electrode potential of the alloy is cathodically shifted when short-circuited to n-CdS, indicating a photo cathodic protection while the corrosion current falls from 2.67 (in the dark) down to 1.73 mA cm^-2 under a light flux of 103 mW cm^-2. Conversely, when the alloy is short-circuited to p-type CuO (E_g = 1.46 eV), the corrosion current increased by 26% under illumination, due to the activated dissolution by photoholes.