The electrochemical behaviour of sol–gel hybrid coatings applied on AA2024-T3 alloy: Effect of the metallic surface treatment

The effect of surface pre-treatments on the electrochemical behaviour of sol–gel coated AA2024-T3 alloys was studied in this work. Three different cleaning procedures were employed: degreasing, mechanical polishing, and chemical etching. The surface morphology was different depending on the pre-treatment. The smoothest surface corresponded to polished samples while the chemically etched ones had the highest roughness, even though the sol–gel film covered all the cavities. The hybrid sol–gel film was prepared by copolymerisation of two different sols, tetra-n-propoxyzirconium (TPOZ) as inorganic precursor and 3-glycydoxypropyltrimethoxysilane (GPTMS) as organic precursor. The corrosion resistance was evaluated using accelerated test (salt spray) and electrochemical measurements under continuous immersion. Both experiments indicated that degreased samples had better anticorrosive properties.The adhesion strength was evaluated by tracking the current evolution with time under applied cathodic potential. Chemically etched and polished samples exhibited better adherence according to that test.