Corrosion behaviour of aircraft materials in acetate and formate based antiskid chemicals

Corrosion behaviour of four commercial aircraft materials, Al alloy 7075-T6, high strength steel AISI 4340, Ti alloy 9046 and Mg alloy RZ5, was studied in six commercial antiskid chemicals, one sodium acetate based, three potassium acetate based, one sodium formate based and one potassium formate based, using potentiodynamic polarisation measurements (polarisation curves) and chemical exposure tests (weight change data), combined with microstructural examinations (appearance of surfaces). The results show that among the four materials, the Ti alloy experiences least corrosion, showing pitting corrosion during the polarisation measurements and significant weight gains and discoloration in the exposure tests only in Safeway SF. In contrast to this, the Mg alloy and the high strength steel underwent corrosion in all chemicals, with severe pitting corrosion (polarisation measurements), significant weight changes and discoloration (exposure tests) being observed for the Mg alloy and discoloration (exposure tests) for the high strength steel. Accordingly, sodium formate based Safeway SF is the most corrosive of the chemicals, introducing some indications of corrosion on all materials, and potassium acetate based Safeway KA HOT and potassium formate based Meltium are the least corrosive chemicals: no signs of corrosion could be observed on the Al and Ti alloys. The results also show that based only on the salt, pH value and conductivity, corrosivity of the antiskid chemicals cannot be reliably evaluated. In this paper, explanations for these observations are presented and the similarities and differences between the results from the two types of corrosion tests are discussed.