Plasma-sprayed coatings as surface treatments of aluminum and titanium adherends

Abstract

Plasma-sprayed coatings have been evaluated as surface treatments for aluminum and titanium adherends. The best aluminum treatment is found to be a 50-μm thick blend of an aluminum-12% silicon alloy and polyester with 20-40% polyester. For FM-300M film adhesive, this coating gives a wedge test performance equivalent to phosphoric acid anodization (PAA). For FM-123 film adhesive, its performance is between that of the Forest Products Laboratory (FPL) etch and PAA. The aluminum in the composite coating provides structural strength and adhesion to the substrate; the polyester serves to toughen the coating and perhaps supplement the physical bonding (mechanical interlocking) provided by the microscopically rough morphology with chemical bonding to the adhesive. For titanium, a 50-μm plasma-sprayed Ti-6Al-4V coating provides an identical performance to the best chemical treatment with crack propagation entirely within the adhesive. These plasma-sprayed coatings avoid the disposal and environmental costs of conventional chemical treatments using chromates and strong acids or bases. They are also well suited to repair or refurbishment of existing components.

Keywords:

• Surface treatment
• aluminum
• titanium
• plasma spray
• wedge test
• durability
• adherend