Method of pretreating aluminum assemblies for improved adhesive bonding and corrosion resistance

#This disclosure relates to a method of manufacturing and preparing aluminum body panels and other parts that use adhesives and sealants that are painted after application of a conversion coating.

#Corrosion of aluminum alloys on vehicles is a complex and costly issue for vehicle manufacturers. Aluminum corrosion is generally associated with joints between parts, hem flanges and trimmed edges. As more aluminum is used in vehicle designs the potential for greater aluminum corrosion is an increasingly important issue. The root cause of aluminum corrosion is complex but is believed to relate to five key elements: surface finishing, paint shop-applied pretreatment, aluminum alloy chemistry, the presence or absence of a sealer, and craftsmanship (placement of adhesive, inner/outer overlap, inner/outer gap, burr size and orientation). All of the above elements must be addressed to achieve superior aluminum corrosion performance.

#Manufacturing materials and processes are not solely optimized to provide the best aluminum corrosion performance. New vehicle designs are trending towards deeper draws and stronger alloys that necessitate the need for improved forming manufacturing methods and materials. Aluminum vehicles depend on substantial amounts of structural adhesive that is applied to parts being joined to provide the vehicle with the necessary strength and rigidity to improve noise, vibration and harshness (NVH) performance. The interaction between the aluminum surface, the forming lubes, and the adhesive must be balanced to provide an effective manufacturing process.

#FIG. 1 is a diagrammatic view of a coil of aluminum that is diagrammatically shown as being spray coated with an thin film pretreatment layer and a dry lubricant coating, however, the coating may be applied in a bath or other well-known coating process.

#FIG. 2 is a cross-sectional view of a part of the coil with the thin film pretreatment layer and the dry lubricant coating.

#FIG. 3 is a diagrammatic cross-sectional view of a two sheet metal parts that are joined by a structural adhesive.

#The disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts. The thickness of the thin film pretreatment layer, dry lubricant coating layer, adhesive deposits and sealant deposits are greatly exaggerated to be visible in the drawings.

#Referring to FIG. 1, a coil 10 of aluminum sheet metal is illustrated diagrammatically that is coated by a thin film pretreatment layer application system 12 and by a dry lubricant coating application system 14 that applies a dry lubricant coating to the thin film pretreatment layer before the coil is shipped. The coating application systems 12 and 14 are diagrammatically illustrated as spray application systems, however, other application systems such as an immersion system or a multi-step immersion and spray application system could be used to apply the coatings.

#Referring to FIG. 2, two aluminum sheets 16 are shown with a thin film pretreatment coating 18 and a dry lubricant layer 20. The thin film pretreatment coating 18 and the dry lubricant layer 20 are thin film layers that are enlarged for better visibility in FIG. 2. The thin film pretreatment coating 18 and the dry lubricant layer 20 are applied to two sides of the sheet 16 in the illustrated embodiment. The thin film pretreatment coating 18 provides a functionalized surface that improves adhesion of adhesives and sealants. The dry lubricant layer 20 provides lubrication and yields superior formability for forming a part 26 from the blank 24.