The effect of Al-Mg substrate preparation on the adhesion strength of plasma sprayed Ni-Al coatings

Abstract

In the present work, the adhesion strength of the atmospheric plasma sprayed Ni\\Al coating deposited on differently pretreated Al\\Mg alloy substrate was measured in order to evaluate the effectiveness of the substrate surface cathodic cleaning in comparison with conventional mechanical and chemical substrate preparation methods. The study includes brief characterization of the deposited coatings, microscopic examination of the interface zones, and coating adhesion measurements by a pull-off test. Cathodic cleaning enabled a significant increase in adhesion strength: compared with the best result obtained on conventionally pretreated specimens (22.8MPa), adhesion strengthwasimprovedby 9.6MPa (or 42%) andwas equal to32.4MPa.The results obtained showed strong correlation with surface free energy and hydroxides' concentration at the surface. Statistical analysis of the experimental data has been performed in order to relate adhesion strength to the main surface parameters.