Method for anticorrosion treatment of outer surface of heat exchange tube made of aluminum extrusion and method for producing heat exchanger

A method for producing a heat exchanger, comprising

• providing an aluminum extruded heat exchange tube which is formed of an alloy comprising Mn 0.2 to 0.3 mass %, Cu 0.05 mass % or less, and Fe 0.2 mass % or less, the balance being Al, and unavoidable impurities, and which has a wall thickness of 200 μm or less, and fins formed from a brazing sheet composed of an aluminum core and a cladding made of an aluminum braze and covering both surfaces of the core;
• applying a dispersion of a flux powder and a Zn powder having a mean particle size of 3 to 5 μm and a maximum particle size less than 10 μm in a binder onto the outer surface of the heat exchange tube, and vaporizing a liquid component of the dispersion, to thereby deposit the Zn powder and the flux powder on the outer surface of the heat exchange tube, such that a Zn powder deposition amount is adjusted to 1 to 3 g/m2, a flux powder deposition amount is adjusted to 15 g/m2 or less, and a ratio of the flux powder deposition amount to the Zn powder deposition amount (flux powder deposition amount/Zn powder deposition amount) is adjusted to 1 or more;
• and
• combining and heating the heat exchange tube and the fins, to thereby braze the heat exchange tube to the fins by use of the flux powder deposited on the outer surface of the heat exchange tube and the braze of the fins, and melting the Zn powder deposited on the outer surface of the heat exchange tube, and then diffusing Zn to an outer surface portion of the heat exchange tube, to thereby form a Zn diffusion layer in the outer surface portion of the heat exchange tube.