Brazing sheet, manufacturing method thereof, and aluminum structure brazing method
A brazing sheet is provided for use in brazing performed in an inert gas atmosphere both using flux and without using flux. The brazing sheet includes an aluminum-based core, an intermediate material layered on the core and being composed of an aluminum alloy that contains Mg: 0.40-3.0 mass %, and a filler metal layered on the intermediate material and being composed of an aluminum alloy that contains Si: 6.0-13.0 mass % and Mg: less than 0.050 mass %. The brazing sheet satisfies the formula below where M [mass %] is the Mg content in the intermediate material, ti [μm] is the thickness of the intermediate material, and tf [μm] is the thickness of the filler metal: tf ≥10.15×ln( M×ti )+3.7.
1. A brazing sheet applicable to brazing performed in an inert gas atmosphere both using flux and without using flux, the brazing sheet comprising:
a core composed of aluminum or an aluminum alloy;
an intermediate material layered on the core and being composed of an aluminum alloy that contains Mg: 0.40-3.0 mass %; and
a filler metal layered on the intermediate material and being composed of an aluminum alloy that contains Si: 6.0-13.0 mass %, and Mg: less than 0.050 mass %,
wherein the brazing sheet satisfies the relation of below formula (1) where M [mass %] is the Mg content in the intermediate material, ti [μm] is the thickness of the intermediate material, and tf [μm] is the thickness of the filler metal:
tf≥ 10.15×ln( M×ti )+3.7 (1)
2. The brazing sheet according to claim 1 , wherein the filler metal further contains Bi: 0.004-0.20 mass %.
3. The brazing sheet according to claim 1 , wherein the intermediate material further contains Si: 3.0-12.0 mass %.
4. The brazing sheet according to claim 1 , wherein the intermediate material further contains Zn: 0.90-6.0 mass %.
5. The brazing sheet according to claim 1 , wherein the intermediate material further contains at least one of Be: 0.050-0.20 mass % and Bi: 0.050-0.30 mass %.
6. The brazing sheet according to claim 1 , wherein the core is composed of an aluminum alloy that contains Mg: 0.20-0.80 mass %.
7. The brazing sheet according to claim 1 , further comprising an Mg diffusion inhibiting layer disposed between the intermediate material and the filler metal and/or on an outermost surface of the brazing sheet,
wherein the Mg diffusion inhibiting layer is composed of aluminum or an aluminum alloy, in which Mg is less than 0.050 mass % and Si is less than 0.050 mass %, and
the total thickness of the Mg diffusion inhibiting layer(s) is 15% or less with the thickness of the filler metal being 100%.
8. A method for manufacturing the brazing sheet according to claim 1 , comprising:
preparing the brazing sheet by clad bonding the core, the intermediate material and the filler metal according to claim 1 ; and
etching the brazing sheet with acid or alkali.
9. A brazing method, comprising:
preparing an object to be brazed that includes an aluminum structure having at least one brazing sheet according to claim 1 such that the object to be brazed has at least one part where a brazed joint will be formed after brazing,
applying a fluoride-based flux to a portion, but not all, of the at least one part where the brazed joint will be formed, and
brazing the object in an inert gas atmosphere to form the brazed joint.
10. The brazing method according to claim 9 , wherein the aluminum structure before being subjected to the brazing includes a hollow member constituted from the brazing sheet and having a contact portion at which the filler metals are in contact with each other, the contact portion being said at least one part where the brazed joint will be formed after brazing.
11. The brazing method according to claim 9 , wherein prior to preparing the object to be brazed using the brazing sheet, the brazing sheet is etched with acid or alkali.
12. The brazing method according to claim 11 , wherein the aluminum structure includes a hollow member at least partially constituted by the brazing sheet and having a contact portion at which the filler metals are in contact with each other, the contact portion being said which the filler metals are in contact with each other, the contact portion being said at least one part where the brazed joint will be formed after brazing.
13. The brazing method according to claim 12 , wherein:
the contain portion includes at least one first contact portion, at which a first brazed joint will form on an exterior surface of the hollow member after brazing, and at least one second contact portion, at which a second brazed joint will form on an interior surface of the hollow member after brazing; and
the fluoride-based flux applied is applied to only the exterior surface of the at least one first contact portion and no fluoride-based flux applied is applied either to: (a) an interior surface of the at least one first contact portion or (b) the at least one second contact portion.
14. The brazing sheet according to claim 2 , wherein the core is composed of an aluminum alloy that contains Mg: 0.20-0.80 mass %.
15. The brazing sheet according to claim 2 , wherein the intermediate material further contains Zn: 0.90-6.0 mass %.
16. The brazing sheet according to claim 2 , further comprising an Mg diffusion inhibiting layer disposed between the intermediate material and the filler metal,
wherein the Mg diffusion inhibiting layer is composed of an aluminum alloy, in which Mg is less than 0.050 mass % and Si is less than 0.050 mass %, and
the Mg diffusion inhibiting layer has a thickness that is 15% or less of the thickness of the filler metal.
17. The brazing sheet according to claim 2 , further comprising an Mg diffusion inhibiting layer disposed on an outermost surface of the brazing sheet,
wherein the Mg diffusion inhibiting layer is composed of an aluminum alloy, in which Mg is less than 0.050 mass % and Si is less than 0.050 mass %, and
the Mg diffusion inhibiting layer has a thickness that is 15% or less of the thickness of the filler metal.