Volvo Laboratory Study of Zinc-Coated Steel Surface Treatment Properties and Outdoor Behavior 890704

An investigation of 14 different precoated sheet steels with an uncoated sheet material as a reference was carried out. The materials used represent a broad spectrum of hot dip, electrogalvanized and prepainted materials. The sheet materials are commercially available and intended both for car and for truck production.
The phosphated surfaces were characterized from the point of view of coating weight, shape and size of the crystals formed. Both spray and dip phosphated panels, with the phosphatization made in car production lines, were examined.
The painted sheets were examined with a cathodic electrophoretic primer (EC-coat) only and with a full paint system (4 coats). The paint adhesion was shown to be lower for zinc-nickel and for zinc-iron compared with the reference, but for prepainted panels an increase was observed. The rest of the materials did not show any significant difference compared with the reference. As regards stone-chip resistance, no significant differences were observed for the different materials.
A prolonged outdoor exposure test showed that the corrosion measured as creep from scribe was approximately linear with the coating thickness of the metallic zinc or zinc alloy layer. Deviation forwards higher creep values was found for the materials containing aluminum and nickel as alloy elements.


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