Published by Maney Publishing (c) IOM Communications Ltd Corrosive wear of aluminium alloy in presence of phosphate V. I. Pokhmurskii, I. M. Zin*, V. A. Vynar, O. P. Khlopyk and L. M. Bily The effect of phosphate on the tribocorrosion of aluminium D16T (AA 2024 equivalent) alloy in synthetic acid rain was studied. It was established that an extract of modified zinc phosphate increases the resistance of aluminium alloy to corrosion and mechanical wear, which is confirmed by the reductions in its polarisation current, friction coefficient against a ceramic counter body and erosion track dimensions. Electrochemical impedance results confirm the decrease in the corrosion rate of the rubbing surface of the aluminium alloy in the presence of phosphate. The charge transfer resistance of aluminium in the track area was found to be 1?65 times higher due to the formation of a conversion film in the phosphate containing solution. Precipitation of the phosphate film on the wear track area is accelerated due to the mechanical activation of aluminium alloy and its anodic polarisation at places of local destruction of oxide film. Keywords: Tribocorrosion, Phosphate, Impedance spectroscopy, Friction coefficient Introduction Aluminium alloys are widely used in different industries due to their low specific gravity and high strength. 1 However, they are predisposed to localised corrosion due to the presence in their structure of intermetallic phases. 1,2 In some applications, aluminium is subject to simultaneous corrosion and mechanical wear. 3 The oxide film on the surface of aluminium alloy under such conditions is more rapidly destroyed due to the influence of mechanical abrasion and consequently the metal corrosion is significantly accelerated. The synergy between these two processes has been described in Ref. 4, which is known as tribocorrosion, and can cause significant economic losses due to early failure of process equipment and structures. The use of inhibitors, conver- sion coatings and organic coatings is a necessary condition to provide corrosion protection of aluminium alloys 1,5–7 and phosphate inhibiting compounds play an important role. They may be added to working solutions as metal corrosion inhibitors, used in phosphatising compositions for obtaining conversion coatings and in anticorrosion paints. Not enough data are present in the scientific literature concerning the effect of inhibitors on the tribocorrosion of aluminium alloys. It has been established 8 that the presence of strontium chromate in slightly acidic corro- sion solution promotes the formation of the passive film on aluminium alloy, consisting of hydrated oxides of Cr(III) and Al(III), which slows down the electrochemical corrosion during wear of the metal in the environment, mainly by controlling the anodic reaction. However, the addition of the inhibitor to the working environment in general speeds up the destruction of the alloy under conditions of corrosive sliding wear, as a result of insufficient wear resistance of the chromate passive film. 8 A tribocorrosion study of 6082 aluminium alloy in contact with stainless steel in 0?01M NaCl solution has revealed 9 that the addition of sodium molybdate to the environment reduces the friction coefficient of the pair. This effect is explained by adsorption of MoO {2 4 from corrosive solution onto the oxidised surface of the alloy and by formation of a film composed ofMoO 3 (H 2 O) 2 . Konno et al. 10 concluded on the basis of their own and literature data that the oxide film, formed at the anodic areas of the aluminium, degrades in aqueous solutions, and its dielectric and mechanical properties deteriorate. This can be explained by transformation of amorphous alumina to the hydrated oxide Al 2 O 3 .3H 2 O. The presence in the aqueous solution of even small concentrations of ions PO 3{ 4 significantly reduces the rate of hydration due to the formation on the aluminium oxide surface of insoluble phosphate compounds. 10,11 Since the coordi- nate interaction of phosphate ions with Al 3z are stronger, they will tend to prevail over H 2 O, OH { and other ligands. Leivo et al. 12 found that treatment of plasma deposited aluminium oxide by a solution of Al(OH) 3 –H 3 PO 4 increases its wear resistance and antic- orrosive properties. Therefore, phosphate compounds may be promising for protection of aluminium alloys from tribocorrosion. The aim of this research is to study the effect of zinc phosphate on the corrosive wear of aluminium alloy. Experimental Corrosive wear tests of 2000 series aluminium alloy D16T 13 (the Russian analogue of AA 2024-T3) were performed on a special self-made tribometer using linear Karpenko Physico-Mechanical Institute of National Academy of Sciences of Ukraine, 5, Naukova Str., Lviv 79601, Ukraine *Corresponding author, email Zin@ipm.lviv.ua ß 2012 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 2 September 2011; accepted 3 September 2011 182 Corrosion Engineering, Science and Technology 2012 VOL 47 NO 3 DOI 10.1179/1743278211Y.0000000022