Effect of Fe, Ni, and Cr on the corrosion behaviour of hyper-eutectic Al-Si automotive alloy under different pH conditions

Mohammad Salim Kaiser,Maglub Al Nur

doi:10.5599/jese.493

Abstract

Effect of Fe, Ni and Cr on the corrosion behaviour of hyper-eutectic Al-Si automotive alloy was studied. The test of corrosion behaviour at different environmental pH 1, 3, 5, 7, 9, 11 and 13 was performed using conventional gravimetric measurements and complemented by resistivity, optical micrograph, scanning electron microscopy (SEM) and X-ray analyser (EDX) investigations. The highest corrosion rate was observed at pH 13 followed by pH 1, while in the pH range of 3.0 to 11, there is a high protection of surface due to formation of stable surface oxide film. The highest corrosion rate at pH 13 is due to presence of sodium hydroxide in the solution in which the surface oxide film is soluble. At pH 1, however, high corrosion rate can be attributed to dissolution of Al due to the surface attack by aggressive chloride ions. Presence of Fe, Ni and Cr in hyper-eutectic Al-Si automotive alloy has significant effect on the corrosion rate at both environmental pH values. Resistivity of alloy surfaces initially decreases at pH 1 and pH 13 due to formation of thin films. The SEM images of corroded samples immersed in pH 1 solution clearly show pores due to uniform degradation of the alloy. In pH 13 solution, however, the corrosion layer looks more packed and impermeable.

Highlights

Al–Si alloys with more than 13 % of silicon content are termed as hyper-eutectic alloys
Since the Al-Si hypereutectic alloy should work in different atmosphere of different pH, the purpose of the present study is to find out the effect of added Fe, Ni and Cr on its corrosion characteristics under different environmental pH conditions
These findings primarily suggested that low pH 1 and high pH 13 solutions are very aggressive environmental media that induced high corrosion of the aluminium alloys

Summary

Introduction

Al–Si alloys with more than 13 % of silicon content are termed as hyper-eutectic alloys. Plots of the corrosion rates, KCorr, calculated from the weight loss tests using Eq (2), are presented in Figures 3 and 4 for all experimental Al-Si alloys exposed during 27 days in pH 1 and pH 13 solutions.

Objectives

Results

Conclusion