Effect of Blasting and Spraying Parameters on the Adhesion of Arc Wire Sprayed Aluminium Coatings

The application of aluminium coatings onto steel for corrosion mitigation is governed by standards specifying surface cleanliness and roughness prior to coating, and minimum coating bond strength. Controlling the surface preparation and spray parameters to achieve the specified surface condition and coating bond strength is challenging, particularly for manual on-site work. In this research, the process parameters were varied and the effect on surface quality and coating adhesion determined. It was found that blasting at angles as low as 30° from the surface, and varying stand-off distances up to 100 mm from the optimum, produced an acceptable surface; whilst spray angles of 60° to 90° and stand-off distances up to 50 mm from the optimum produced acceptable coatings with adhesion above 20 MPa. Adhesion appeared unaffected by some remaining mill scale, but was reduced to ≈15 MPa when the surface chloride content was increased from 2 to 20 µg cm^-2.