Loctite epoxy plastic bonder, though made primarily to bind together plastic surfaces, can work just as well on aluminum and steel. Though it's a two-component system, the adhesive comes in an easy-to-use syringe that dispenses exactly the amount of epoxy you need, in the ratios needed, ready for mixing and application. With the proper surface preparation, a thin layer of the epoxy will hold the metals tightly together, creating a bonding layer that won't crack even when drilled, won't shrink after drying and that's water resistant, making it usable in most situations where you require a secure bond between the disparate materials.
Things You'll Need
Mild liquid soap
Wooden stirring stick
Clean both the aluminum and stainless steel surfaces with a mild liquid soap and water mix, using a sponge or scrub brush to remove any dirt present. Use a degreaser to remove any grease stains from the surfaces. Rinse with clean water then allow the surfaces to dry.
Put on a pair of safety goggles, work gloves and a facemask. Attach a sheet of 220-grit sandpaper to a sanding block and then use the sandpaper to sand away any finish placed onto the surfaces such as a polyurethane coating, wax or paint. Sand the surfaces in small circles, to avoid creating grooves in metal. If no finish is present, then sand the surface until you create a series of scratches that can serve as texture for the adhesive.
Wipe the surfaces clean of sanding residue with a cloth dipped in rubbing alcohol.
Prepare the adhesive applicator by removing the plug located between the piston handle, and then use a utility knife to cut the tips from the two-chamber syringe.
Turn the syringe containing the Loctite adhesive upside down, so that the tips points straight up. Pull the plunger back about a 1/4 inch to bring any air in the syringe to the tips, and then press the plunger slightly to empty the air from the syringe chambers. Clean the tips of the syringe with an alcohol-dampened cloth then replace the plug to prevent the components from drying out.
Place the syringe against a disposable surface and press the plunger to dispense the amount of adhesive you need to join the aluminum with the steel. You only need spread a thin layer on each surface. Mix the materials dispensed from the syringe tips together with a wooden stirring stick.
Brush the mixed adhesive onto both the aluminum and the steel where you wish to create the bond. Press the aluminum and stainless steel together with the adhesive applied and hold firmly for about 30 seconds to allow the bond to begin to form. Wipe any excess adhesive from the metal's surfaces with the alcohol-dampened cloth. Wait about 25 minutes for the adhesive to set fully.
Check the fit of the surfaces you with to bind together to make sure they can lie flat together. Make any adjustments needed before applying the epoxy.
Use Loctite in well-ventilated rooms only to avoid breathing in the fumes from the adhesive.