Q. I am the manager of manufacturing for my company. We produce sheet metal cabinets and enclosures. We are essentially sheet metal benders and most of our expertise is with joining steel panels by fasteners and weldments. We anticipate a rather large order involving aluminum and fiberglass enclosures. We will need to bond aluminum to itself and fiberglass using a moisture-resistant, room-temperature curing adhesive. Only a low bond strength is required, because the finished structure is a cabinet. However, the joint must be able to withstand long-term exposure to an 80ºF, 100% relative humidity environment. What is the best pretreatment for the aluminum surface for maximum corrosion resistance and adhesion, recognizing that specific primers are recommended by adhesive suppliers for their systems? S.P.
A. In general, metal pretreatments that enhance paint adhesion are also suitable for use with adhesives. Adhesive primers are really specialty paints, and in most cases, the resins used in paints are also used in adhesives. To maximize corrosion resistance, and to provide an excellent substrate for paints and adhesives, anodizing would be the pretreatment of choice. Adhesives and adhesive primers will have excellent adhesion to anodized aluminum. After pretreatment, the primers, if required, and the adhesives can be applied according to the supplier’s recommendations.
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Although you didn’t ask, you must also clean or otherwise pretreat the surface of the fiberglass to remove contaminants such as molding compounds, oily soils, and others that may act as interference coatings. The choice of pretreatment will depend on the nature of the fiberglass and its contaminant. Since all fiberglass is not created equal, I suggest contacting the supplier for pretreatment recommendations.