TABLE OF CONTENTS The methods described for surface preparation of metals in Ch. 6 are generally applicable, but the processes required for specific metals are different from the general techniques. The specific preparation and treatment techniques described in this chapter have been reported to provide strong reproducible bonds and fit easily into the bonding operation. It must be noted that the methods for preparing metal surfaces are generally much older than those of plastics because of the length of time that metals have been in use. This is not to say that improvements have not been made in the recent decades, but the pace of upgrades has been slow in recent years. Improvements have often been driven by environmental rules promulgated by governments to reduce emissions and toxic waste generated by the surface preparation methods of metals. An important example is chromate-free etching of aluminum.
Chemical treatments are usually most effective with aluminum alloys, especially where long-term environmental exposure is required. The sulfuric acid-dichromate etch ( FPL etch, named after Forest Products Laboratory, US Dept. Agriculture) has been used successfully for many decades. The more recently developed techniques are often modifications of the FPL procedure. Other important methods include chromate conversion coating and anodizing. Corrosion-resistant adhesive primer (CRAP), as well as anodic and chromate conversion coatings, help prevent corrosive failure of adhesion.[1]
This method is specified in ASTM D2651-01.[2]
Remove ink markings and stamped identification by wiping with commercial solvents such...
