Even though aluminium does not rust, corrosion can still form between aluminium and a non-aluminium bolt. This is especially true of aluminium parts and stainless steel bolts subjected to saltwater. The saltwater causes electrolysis between the metals. This will corrode the two unlike metals and create a bond nearly as strong as welding the pieces together. To break this bond, you need to expand the aluminium with heat. Since aluminium is an excellent heat sink, you need a lot of heat to free the corroded bolt.
Put on safety glasses.
Inspect the oxyacetylene torch to ensure that parts are not damaged. Pay special attention to the oxygen and acetylene gas lines as both gases are highly flammable and a leak can quickly lead to a fire.
Put on welding gloves. Turn on the acetylene valve of the oxyacetylene torch and ignite the acetylene with the striker.
Open the oxygen valve of the oxyacetylene torch and adjust the valve until you have a blue neutral outer flame and a bright blue inner flame that is between 3/8 and 1/2 inch in length.
Heat the corroded bolt by placing the neutral flame of the oxyacetylene torch 3 to 4 inches away from the head of the bolt. Aluminium will draw heat from the bolt, so you will need to heat the bolt longer than a standard carbon bolt.
Stop heating the bolt when the bolt head glows a dull orange. Allow the bolt to cool naturally back to room temperature.
Place the wrench on the head of the bolt and attempt to loosen the corroded bolt. If the bolt does not move, repeat Steps 5 and 6 until the bolt works free of the aluminium part.