Effect of velocity on the corrosion behavior of hyper-eutectic Al-Si automotive alloy in 3.5% NaCl heated solution

Abstract

The corrosion behavior of hyper-eutectic Al-Si automotive alloy in 3.5% NaCl solution was studied. The samples were rotated at different velocity at 94°C heated solution for 8 hours per day. The work was carried out using conventional gravimetric measurements and complemented by resistivity, optical micrograph, scanning electron microscopy (SEM) and X-ray analyzer investigations. Gravimetric analysis authenticates that with varying exposure periods the weight of the alloy increases and the negative corrosion rate profile of an initial steep rise followed by a nearly constant value of corrosion rate are observed. Aluminum forms a very thin film of aluminum oxide and hydroxide and it has a bond to its surface which increases the weight of the alloy. The rate of negative corrosion at higher velocity of the alloy is found to be lower than that at lower velocity due to gradual breakdown of the passive films. The creation of the thin film also changes the resistivity. Optical micrographs of the alloy show the higher corroded surface for higher exposer time. The SEM and EDX analysis confirm that the percent of oxygen means the corrosion of the alloy and the presence of aluminum oxide layer on the surface of the alloy, which in turn leads to the decreasing corrosion of the alloy.