Brazing method for aluminum alloy material

[0012] A brazing method for aluminum alloy materials. A non-corrosive fluoride flux is used for brazing in an inert gas atmosphere. When the starting temperature of the solder is set to Tf, the starting temperature of the flux is set to At Ts, the Tf is less than Ts, and the difference is no more than 5 degrees; the solder and the flux flow at the same time.

[0013] The weight percentage of magnesium in the aluminum alloy is 1.15% to 1.35%. This is because when the Mg content is small, the reaction with the flux is small, and it is possible to braze even using the existing brazing method. In addition, this is because when the magnesium content is too large, it reacts rapidly with fluorine in the flux during brazing heating to form high melting point compounds such as magnesium fluoride, which hinders brazing properties.

[0014] The difference between the solidus temperature and the liquidus temperature of the solder is within 30°C.

[0015] The difference between the solidus temperature and the liquidus temperature of the flux is within 30°C.

[0016] In the soldering method of the present invention, the most important condition for solderability is the temperature at which the flux and the solder begin to flow. The temperature at which the flux and the solder begin to flow is defined as the temperature at which the flux and the solder begin to wet and expand during the brazing heating process. Many fluxes and brazing materials have different solidus temperature and liquidus temperature. They become a solid-liquid mixed state during the temperature increase, and start to flow when the ratio of the liquid phase is about 70%. Therefore, the temperature at which the flow starts is between the solidus temperature and the liquidus temperature. When this temperature difference is set to 100, it is defined as a temperature that is about 70 higher than the solidus temperature.

[0017] When the solder flows before the flux, the solder covers the aluminum surface before the flux spreads on the aluminum surface and removes the oxide film.

[0018] The flux uses at least one of components composed of KA1F4, K2A1F5, K2A1F5·H20, and K3A1F6 as a main component, but it may also be other fluxes such as CsA1F or KZnF3. Preferred is a mixture of KA1F4 and K2A1F5·H20 or a mixture of KA1F4 and K3A1F6. The adjustment of the starting temperature, the solidus temperature, and the liquidus temperature can be adjusted by the ratio of the mixture of the above-mentioned components in the flux.

[0019] The starting temperature, solidus temperature and liquidus temperature can be adjusted appropriately by the composition of silicon, zinc, and copper in the solder. The composition of the aluminum alloy in the brazing filler metal is 8-9% silicon, 1.0-2.0% magnesium, 1.5-2.5% zinc, 1.5-3.5% copper, 0.01-0.1% zirconium, 0.005- 0.03% iron and the balance aluminum.

[0020] The preferred composition is 8.5% silicon, 1.22% magnesium, 2.1% zinc, 2.4% copper, 0.03% zirconium, 0.012% iron and the balance aluminum.

[0021] Since the method for manufacturing an aluminum alloy heat exchanger of the present invention uses the above-mentioned brazing method, it is a method of manufacturing the heat exchanger by a non-corrosive brazing method using an aluminum alloy material containing magnesium.