Method for surface treating a heat exchanger, surface treatment agent, and aluminum heat exchanger
A method for surface treating a heat exchanger and an aluminum heat exchanger obtained from this method are provided that can effectively suppress the foul odor characteristic to flux that emanates following degradation of a hydrophilic coating film and a chemical conversion coating film in a non-corrosive flux brazed heat exchanger on which flux easily remains. The method for surface treating a non-corrosive flux brazed heat exchanger made of an aluminum material conducts a pickling treatment step, a chemical conversion treatment step, and a deodorizing treatment step on the heat exchanger, in which the acidic cleaning agent contains nitric acid and sulfuric acid as well as a predetermined amount of ferric salt, and the surface treatment agent contains silica grains coated by a vinyl alcohol polymer and polyallylamine resin such that the total content of the silica grains and the vinyl alcohol polymer is a predetermined amount.
1. A method for surface treating a heat exchanger, comprising:
(1) a pickling treatment step of causing an acidic cleaning agent to come into contact with a non-corrosive flux brazed heat exchanger made of an aluminum material;
(2) a chemical conversion treatment step of causing a zirconium-based chemical conversion treatment agent to come into contact with the aluminum material after the pickling treatment step; and
(3) a deodorizing treatment step of causing a surface treatment agent to come into contact with the aluminum material after the chemical conversion treatment step,
wherein the acidic cleaning agent contains nitric acid and sulfuric acid, and contains 0.01 to 0.05% by mass of a ferric salt, and
wherein the surface treatment agent contains silica grains coated by a vinyl alcohol polymer, and a polyallylamine resin, a total content of the silica grains and the vinyl alcohol polymer contained in the surface treatment agent being in the range of 0.2% by mass to 25% by mass, a mass ratio of the silica grains to the vinyl alcohol polymer being in the range of 30:70 to 70:30, and a content of the polyallylamine resin being the range of 100 ppm to 5000 ppm.
2. The method according to claim 1 , wherein the ferric salt is at least one selected from the group consisting of iron sulfate, iron nitrate, iron acetate, and iron chloride.
3. The method according to claim 1 , wherein the non-corrosive flux brazed heat exchanger is an evaporator for a vehicle air-conditioner.