The effect of roughness and pre-heating of the substrate on the morphology of aluminium coatings deposited by thermal spraying

Thermal spraying is a technique to deposit on previously treated surfaces metallic or non-metallic materials whose main adhesion mechanisms are mechanical and chemical–metallurgical anchorage. The preparation of the substrate comprises cleaning, development of a rough surface and sometimes preheating to guarantee mechanical anchorage at microwelding sites. To evaluate splat morphologies, test samples with aluminium coatings deposited by different thermal spray processes, namely, flame spraying, high-velocity oxy-fuel and electric arc spraying, were carried out on substrates with different roughness, with and without preheating. Coating adhesion to the substrate was also evaluated. Different splat morphologies were obtained; the results indicated that coatings on preheated substrates may have lower roughness than that recommended in the literature. Besides, although preheating was essential for the flame spray process, it may be eliminated for the electric arc and high-velocity spraying processes.