PURPOSE: To manufacture a heat exchanger-medium material excellent in fat and oil contamination resistance, by providing a phosphorus-type compound and a surface active agent to an inorganic-type film formed on the surface of a cold-rolled stock of Al or Al alloy and then carrying out temper annealing and the prescribed working.

CONSTITUTION: An inorganic-type film such as hydrating oxidation treated film is formed on the surface of a cold-rolled stock of Al or Al alloy. Subsequently, a phosphorus-type compound, such as hydrophosphite, and a cationic or anionic surface active agent are provided to the above film. As the above surface active agent, a cationic or anionic one can be used independently or further in combination with nonionic surface active agent. The sheet metal after the above film treatment is subjected to temper annealing at about 200W360°C for about 3W20hr, by which mechanical properties are regulated to the prescribed values, respectively. Then, by subjecting the sheet metal to the prescribed working, the heat-exchanger medium material excellent in contamination resistance, wettability, workability, etc., can be obtained.