Erosion–corrosion of candidate HVOF aluminium-based marine coatings

This paper describes gravimetric results of HVOF sprayed commercially pure Al and Al/12% Si eutectic alloy coatings obtained under erosion–corrosion conditions. The performance of these coatings are compared to a hot-dipped zinc coating. These coatings have been applied to AISI 1020 carbon steel substrates and tested in a free jet impingement rig with a variety of fluids and slurries to enable the erosion and corrosion contributions to the total erosion–corrosion removal of the surface to be determined. Tests have been conducted at 30° and 90° jet impingement angles at jet velocities of 3.5 m/s. Erosion damage mechanisms are identified and the erosion–corrosion mass loss results discussed in terms of the contributions made by erosion and corrosion. Zinc was found to suffer severely from flow corrosion, while the other targets did not. All target materials under sand erosion lose mass in a way directly proportional to kinetic energy, and inversely related to hardness. Corrosion losses are relatively small while the generation of solid products sometimes results in net weight gains. There are greater mass losses at nominally normal incidence than at nominally oblique incidence, due to particle interference effects. Synergy is found to be both positive and negative and appears to be angle dependent, but is difficult to determine precisely.