THE EFFECT OF RuO2 CONCENTRATION ON CORROSION TOPOGRAPHIC OF ALUMINIUM ALLOY IN TROPICAL SEA WATER MEDIUM

M. S. Din Yati*, M. N. Derman, M. Che Isa, S. R. Sayd Bakar and N. H. Nik Yussoff

Abstract

THE EFFECT OF RuO₂ CONCENTRATION ON CORROSION TOPOGRAPHIC OF ALUMINIUM ALLOY IN TROPICAL SEA WATER MEDIUM

1. S. Din Yati^1*, M. N. Derman¹, M. Che Isa², S. R. Sayd Bakar² and N. H. Nik Yussoff.

1*School of Materials Engineering,

Kompleks Pusat Pengajian Jejawi 2, Universiti Malaysia Perlis, 02600 Jejawi, Perlis, MALAYSIA

2 Maritime Technology Division,

Science & Technology Research Institute for Defense (STRIDE),

c/o KD MALAYA, Pangkalan TLDM, 32100 Lumut, Perak, MALAYSIA

ABSTRACT

The electrochemical properties of aluminium sacrificial anode such as open circuit potential, corrosion potential, impedance behaviour, and current capacity have been studied by many researchers since 1960s. However, the correlation between surface topography and dissolution rates of aluminium alloy in marine environment was less highlighted in the literature. In this study, the surface morphology and topography of aluminium alloy coated with different concentration of ruthenium dioxide (RuO₂) has been characterised by using electron microscopy and confocal techniques respectively. Confocal laser scanning microscope (CLSM) will collect all height information and allows for a quantitative 3 dimension (3D) evaluation of topographic surface parameters such as average surface roughness (R_Sa), surface skewness (R_Ssk) and surface kurtosis (R_Sku). 3D topographic image and surface topography parameters were then correlated with corrosion rate value extracted from Tafel plot. Results showed that Al-Zn-Mg-Sn alloy coated with 12,000 ppm RuO₂ gave highest corrosion rate (456.18 μm/year). Base on CLSM study, the corroded surface of the alloy with same RuO₂ concentration gave 3D surface parameters with positive skewness which indicate topographic with high peaks of filled valleys (R_ssk > 0) and also high peaks and low valleys (R_sku >3). Qualitative observation by scanning electron microscope (SEM) showed the presence of porous mud-crack corrosion product on the aluminium alloy surface that has facilitated an aggressive electrolyte adsorption and penetration that lead to better dissolution process of the alloy. It was found that CLSM was very useful and recommended to be selected as a tool for quantitative surface measurement to study the effect of RuO₂ concentration on the topographic characteristics of corroded aluminium alloy surface.

Keywords: Confocal microscopy, Ruthenium dioxide, Surface topography, Polarisation