Question: What is the best way to prepare my aluminum surfaces for bonding with epoxy or acrylic adhesives?

Answer: This is a complex subject. Aluminum has been widely used in the aerospace industry for many years. Most recently, it has become a very important metal in vehicle body manufacturing. The metal and its alloys can be bonded successfully with a range of adhesives; epoxies and acrylics are very suitable. It is quite common for adhesive manufacturers to quote technical data on both steel and aluminum substrates.

Many pretreatments are available for aluminum; most promote maximizing the adhesive strength and maximizing the durability of the assembled joints. This generally involves cleaning the surface to remove contaminants or modifying the existing surface by chemical treatment. The simplest treatment involves solvent wiping or vapor degreasing for cleaning, often followed by abrasion. Chemical conversion can also protect the base metal from corrosion and enhance the durability of the bonded joint in various service environments. The well-established Forest Products Laboratory process involves alkaline cleaning and then chemical immersion. The other major process designed for maximum adhesion and bond durability is the method developed for aerospace bonding involving phosphate anodizing. I recommend that you consult the ASTM D3933-98(2010) standard for phosphoric acid anodizing.

A recent process for treating aluminum surfaces is the sol-gel process. This consists of a ceramic inorganic coating to establish an aluminum-oxide based coating. The ingredients are alumina and organosilane.  

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