Effect of NaCl concentration on corrosion of Al alloy during repeated wet–dry cycle tests at 323 K—comparing with corrosion in immersion tests‐

Abstract

Corrosion of 4043‐Al alloy was examined by repeated wet–dry cycle tests with NaCl solutions at 323 K, and compared with immersion test corrosion in 0.2–5.5 kmol/m3 NaCl solutions. The Al alloy specimens after the immersion tests for 86.4 ks (1 day) or 604.8 ks (7 days) showed preferential dissolution of the aluminum matrix around Si‐phase compounds, and the dissolution was more remarkable at lower NaCl concentrations. Mass loss of the specimens after the 604.8‐ks immersion was also higher at lower NaCl concentrations. In the repeated wet–dry cycle tests, a 20 mm3 droplet of 0.2–5.5 kmol/m3 NaCl solution was initially dripped on the specimens, and left for 690 s to allow the drying up of the droplet, resulting in solid NaCl precipitation. Then, the dissolution and precipitation of NaCl were repeated a further 149 times by dripping 20‐mm3 pure water at 690‐s intervals. The specimens after the 150 cycles showed different corrosion modes at the center and edge of the droplets. At the edge, 40–80 × 10−6 pits/m2 of 20–50 µm diameter had formed, showing more corrosion with higher NaCl concentration droplets, and at the droplet center, the corrosion showed preferential dissolution of the aluminum matrix around the Si‐phases, similar to the situation in the immersion tests. Copyright © 2015 John Wiley & Sons, Ltd.