Two types of corrosion here. Surface or oxide and galvanic corrosion. Steel screws used to hold down aluminum sheets to aluminum ribs causes galvanic corrosion between steel and aluminum while oxide corrosion is caused by oxygen and water reacting to the aluminum (basically). Not all of this is corrosion. Some is just fabric glue and zinc chromate. Surface oxydation shows up as white powder Surface corrosion removedCorrosion inhibitor added
Stinson Station Wagon, NC9391K Restoration 