Brazing method of aluminum material and brazed structure
In order to enable a satisfactory fluxless brazing without needing flux or vacuum facilities, a brazing object including an aluminum alloy material provided with an Al—Si—Mg brazing filler metal is joined by the Al—Si—Mg brazing filler metal without the use of flux by heating the aluminum alloy material, when raising the temperature in a brazing furnace, at least in a temperature range of 450° C. to before melting of the filler metal under a first inert gas atmosphere having an oxygen concentration of preferably 50 ppm and following by heating at least at or above a temperature at which the filler metal starts to melt under a second inert gas atmosphere having an oxygen concentration of preferably 25 ppm and a nitrogen gas concentration of preferably 10% by volume or less. The oxygen concentration and nitrogen concentration in the atmosphere in the course of brazing are controlled in this way, whereby the reliability of a joint is remarkably improved, compared with conventional fluxless brazing methods, while suppressing cost increases as much as possible.
1. A brazing method of aluminum material, comprising: joining a brazing object including an aluminum alloy material provided with an Al—Si—Mg brazing filler metal by the Al—Si—Mg brazing filler metal without the use of flux by heating, when raising the temperature in a brazing furnace, the aluminum alloy material to a temperature of at least 450° C. before melting of the filler metal under a first inert gas atmosphere having an oxygen concentration of a first predetermined value and followed by heating at least at or above a temperature at which the filler metal starts to melt under a second inert gas atmosphere having an oxygen concentration of a second predetermined value lower than the first predetermined value and a nitrogen gas atmosphere of a predetermined concentration.
2. The brazing method of aluminum material according to claim 1 , wherein the Al—Si—Mg brazing filler metal and the aluminum alloy material constitute a brazing sheet by cladding the brazing filler metal on the aluminum alloy material as a core material.
3. The brazing method of aluminum material according to claim 1 , wherein the first predetermined value is 50 ppm, the second predetermined value is 25 ppm, and the predetermined concentration of the nitrogen gas concentration is 10% by volume.
4. The brazing method of aluminum material according to claim 1 , wherein the second inert gas atmosphere has an inert atmosphere or a mixed inert atmosphere.
5. The brazing method of aluminum material according to claim 4 , wherein the inert gas is argon.
6. The brazing method of aluminum material according to claim 1 , wherein the first inert gas atmosphere is obtained by substituting the atmosphere of nitrogen gas, and the second inert gas atmosphere is obtained by substituting the first inert gas atmosphere by the gas or the mixed gas containing gas.
7. The brazing method of aluminum material according to claim 1 , wherein the brazing filler metal contains Si: 5.0 to 13.0% and Mg: 0.1 to 3.0%, by mass, with the balance of Al and unavoidable impurities.
8. The brazing method of aluminum material according to claim 7 , wherein the brazing filler metal further contains more than one of Be: 0.0001 to 0.1%, Bi: 0.01 to 0.3% and Ca: 0.002 to 0.3% by mass.
9. The brazing method of aluminum material according to claim 1 , wherein the aluminum alloy material has a composition containing, by mass, more than one Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0% and Si: 0.1 to 1.0% by mass, with the balance of Al and unavoidable impurities.
10. The brazing method of aluminum material according to claim 1 , wherein the aluminum alloy material has a composition containing, by mass, Mg: 0.01 to 1.0%, and further containing more than one of Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0% and Si: 0.1 to 1.0%, by mass, with the balance of Al and unavoidable impurities.