A method of surface treating an aluminum alloy base body of an heat
exchanger which method enables an etching procedure to be carried out
uniformly and quickly and a corrosion-resistant chemical conversion
coating to be formed, is effected by pretreating the Al heat exchanger
base body with an aqueous pre-treating liquid having a pH of 9.0 or less,
etching the pretreated base body with an aqueous alkaline solution having
a pH of 9.0 or more, and then subjecting the etched base body to a
chemical conversion treatment or a hydrophilicity-enhancing treatment.