Aluminium multi-layered brazing sheet product and fluxless brazing method

1. A method of manufacturing an assembly of joined components, joined by brazing in a controlled atmosphere brazing process, the method comprising the steps of:

(a) providing of components to be brazed together of which at least one is made from a multi-layered brazing sheet product having an aluminium core alloy layer provided on one side with a brazing clad layer material and an inter-layer positioned between the aluminium core alloy layer and said brazing clad layer material, and is provided with a corrosion protective layer on the other side, wherein the brazing clad layer material is made from a 4xxx-series aluminium alloy having, in weight percent, 5% to 15% Si and greater than 0.05% to 0.5% Mg, and wherein the inter-layer is made from a 1xxx-series aluminium alloy having, in weight percent, a purposive addition of Mg of 0.10 to 1.5%, wherein Mg is purposively present in the brazing clad layer material and wherein the Mg-content in the inter-layer is higher than the Mg-content in the brazing clad layer material;

wherein the corrosion protective layer is made from a 3xxx-series aluminium alloy consisting of, in weight percent: Mn 1.0% to 1.8%, Zn 1% to 3.5%, Ti 0.01% to <0.25%, remainder aluminium and unavoidable impurities each <0.05%, total <0.2%,

(b) assembling of the components into an assembly;

(c) brazing the assembly without applying brazing flux onto the assembly components, and brazing the whole assembly in a dry inert gas atmosphere at a brazing temperature, and wherein an oxygen content of the dry inert gas atmosphere is less than 35 ppm, wherein the Mg in the inter-layer diffuses into the brazing clad layer material; and

(d) cooling of the brazed assembly.

2. The method according to claim 1 , wherein the brazing clad layer material has been pre-treated by means of etching with an alkaline or acidic etchant.

3. The method according to claim 1 , wherein a dwell time at brazing temperature is in a range of 1 to 10 minutes.

4. The method according to claim 1 , wherein the oxygen content of the dry inert gas atmosphere is less than 25 ppm.

5. The method according to claim 1 , wherein the oxygen content of the dry inert gas atmosphere is controlled to be at least 5 ppm.

6. The method according to claim 1 , wherein the assembly of joined components form a charge-air-cooler or oil cooler.

7. The method according to claim 3 , wherein the dwell time at brazing temperature is in a range of 1 to 6 minutes.

8. The method according to claim 4 , wherein the oxygen content of the dry inert gas atmosphere is less than 20 ppm.

9. The method according to claim 1 , wherein the brazing clad layer material has a composition, consisting of, in weight percent:

Si

5% to 15%,

Mg

0.1% to 0.5%,

Fe

up to 0.8%,

Cu

up to 0.3%,

Mn

up to 0.8%,

Zn

up to 0.25%,

Ti

up to 0.3%,

balance aluminium and unavoidable impurities each <0.05%, total <0.2%,

wherein Mg is purposively present in the brazing clad layer material.

10. The method according to claim 1 , wherein the brazing clad layer material has a composition, consisting of, in weight percent: Si 5% to 15%, Mg 0.1% to 0.5%, Fe up to 0.8%, Cu up to 0.3%, Mn up to 0.8%, Zn up to 0.25%, Ti up to 0.3%, balance aluminium and unavoidable impurities each <0.05%, total <0.2%, wherein Mg is purposively present in the brazing clad layer material.

11. The method according to claim 1 , wherein the aluminium core alloy layer is made from an 3-series alloy having a composition consisting of, in weight percent:

Mn

0.8% to 1.5%,

Si

0.25% to 0.75%,

Cu

0.5% to 1.1%,

Fe

up to 0.45%,

Mg

up to 0.35%,

Cr

up to 0.25%,

Zr

up to 0.25%,

Ti

up to 0.20%,

Zn

up to 0.15%,

unavoidable impurities each <0.05%, total <0.2%, and balance aluminium.

12. The method according to claim 1 , wherein the inter-layer is made from 1xxx-series aluminium alloy having purposive addition of Mg of 0.10 wt. % to 1.0 wt. %.

13. The method according to claim 1 , wherein the inter-layer is made from 1xxx-series aluminium alloy having purposive addition of Mg of 0.10 wt. % to 0.7 wt. %.