Corrosion performance of Al-Si-Cu hypereutectic alloys in a synthetic condensed automotive solution

Abstract

In this investigation the corrosion resistance of four Al-Si hypereutectic alloys in a solution typical of condensate from automotive fuel combustion products, and referred to here as synthetic condensed automotive solution, has been studied. Three commercial alloys that are used for cylinder liners, and a laboratory made alloy, were studied by electrochemical impedance spectroscopy and measurements were taken after increasing times of immersion in this solution. Comparison of the electrochemical response of the four alloys in the corrosive solution was carried out. Although the mechanisms by which the four alloys corroded were similar, the results indicated differences in corrosion resistances of these alloys, and these differences could be related to their microstructures. The laboratory prepared alloy showed increased susceptibility to pitting corrosion compared to the commercial alloys. The surfaces of the alloys were examined, before and after the corrosion test, by scanning electron microscopy and analyzed by energy dispersive spectroscopy. The results indicated preferential attack of the aluminium matrix phase in all the alloys. The alloy with higher copper content and prepared by spray forming was more susceptible to pitting compared to the other alloys. The EIS response at low frequencies indicated a diffusion-controlled process, probably that of oxygen to the alloy interface.

Effect of Peak-Aged Heat Treatment on Corrosion Behavior of the AA6063 Alloy Containing Al3Ti

“…Previous corrosion studies conducted on Al alloys [2,[4][5][6][7][8][9][10][11][12][13][14][15] have focused on the corrosion susceptibly in corrosion solution e.g. Sodium chloride.…”

“…Sodium chloride. Researchers [7][8][9]13] reported that pits initiate around secondary particles within the matrix. However, Kiourtsidis and Skalianos [29] explained that the progress of corrosion using two anodic reactions; namely corrosion of the matrix adjacent to intermetallic regions, and pitting of dendrite cores, instead of galvanic corrosion, developed between the intermetallic and matrix.…”

“…Over the years, a number of studies have been carried out to assess the effect specific intermetallic particles and individual alloying additions have on corrosion damage in Al alloys, which arises from pitting and inter-granular type corrosion [4][5][6][7][8][9][10][11][12][13][14][15]. In situations where the corrosion characteristics of constituent intermetallics have been rigorously characterised, intermetallics have been found to exhibit a complex behaviour such as active and/or noble.…”

“…In situations where the corrosion characteristics of constituent intermetallics have been rigorously characterised, intermetallics have been found to exhibit a complex behaviour such as active and/or noble. Until now the intermetallics confirmed to exist within Al alloys are [4][5][6]8,[10][11][12][13][14] 3 Zr). The sizes of precipitates range from Angstroms to fractions of a micrometer; formed by nucleation and growth in a supersaturated solid solution during natural or low temperature artificial aging.…”

“…These particles form at high temperatures and are present to control the grain size and re-crystallisation behaviour. Both constituent particles and dispersoids are susceptible to pitting corrosion because of their galvanic interaction with the Al matrix [7][8][9]13].…”