This paper describes a new composite coating technology developed for hot dip galvanizing rolls used in automotive manufacturing. The multilayer coating consists of HVOF sprayed WC and electroless Ni-P plating. Coating surfaces and cross-sections are examined and adhesion strength, friction, and wear resistance are measured. In addition, changes in surface roughness are recorded on galvanizing rolls after three months of service.

In this study, MoB-CoCr composite coatings are deposited on low-carbon steel substrates by HVOF spraying and salt spray tests are conducted to qualitatively evaluate coating density. Test samples with optimized dense coatings showed no rust after 300 hours in a salt spray. Samples with porous coatings, on the other hand, showed signs of rust after just 24-48 hours. Test samples protected by the dense composite coatings, as confirmed by salt spray testing, were undamaged after 90 days of immersion in a Zn-0.2%Al galvanizing bath at 460 °C.

Zinc coatings are widely adopted for cathodic corrosion protection. Mostly the process of choice is hot-dip galvanizing but due to limitations regarding component size and composition of the galvanizing bath it is not always practicable. In the present paper zinc coatings alloyed with Al, Sn, Mg and Cr are applied by twin wire arc spraying to enhance the corrosion protection ability of zinc thermal sprayed coatings. The alloys were characterized and investigated using salt spray test and by means of electrochemical corrosion. Corrosion damage and products were investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and electron probe microanalysis (EPMA).