Aluminium alloy multi-layered brazing sheet material for flux-free brazing
Described herein is an aluminium alloy multi-layered brazing sheet product for brazing in an inert-gas atmosphere without a flux that includes a core layer made of a 3xxx alloy that includes <0.2 wt. % Mg, and that provides a covering clad layer that includes 2-6 wt. % Si on one or both sides of said 3xxx alloy core layer and a Al—Si brazing clad layer that includes 7-13 wt. % Si positioned between the 3xxx alloy core layer and the covering clad layer, wherein the covering clad layer has a thickness X 1 and the Al—Si brazing clad layer has a thickness X 2 and wherein X 2 ≥2X 1 . Also described herein is the use of an aluminium alloy multi-layered brazing sheet product in a flux-free controlled atmosphere brazing (CAB) operation to produce a heat exchanger apparatus.
1 . An aluminium alloy multi-layered brazing sheet product for brazing in an inert-gas atmosphere without a flux, comprising:
a core layer made of a 3xxx alloy comprising less than 0.20 wt. % Mg and 0.15 wt. % to 1.1 wt. % Cu, and provided with a covering clad layer comprising 2 wt. % to 6 wt. % Si and 0.06 wt. % to 0.20 wt. % Mn positioned on a first side of the 3xxx alloy core layer; and
a Al—Si brazing clad layer comprising 7 wt. % to 13 wt. % Si positioned between the 3xxx alloy core layer and the covering clad layer,
wherein the covering clad layer has a thickness X 1 and the Al—Si brazing clad layer has a thickness X 2 and wherein X 2 ≥2X 1 , wherein at least one of the core layer or the covering clad layer comprises at least 0.05 wt. % Ti.
2 . The multi-layered brazing sheet product according to claim 1 , wherein the 3xxx alloy core layer comprises up to 0.1 wt. % Mg.
3 . The multi-layered brazing sheet product according to claim 1 , wherein the covering clad layer is Bi-free and Li-free, wherein Bi-free means below 0.005 wt. % Bi and Li-free means below 0.005 wt. % Li.
4 . The multi-layered brazing sheet product according to claim 1 , wherein the covering clad layer comprises, in wt. %,
Si 2% to 6%;
Fe up to 0.5%;
Mn 0.06 to 0.20%;
Cu up to 0.1%;
Zn up to 0.4%;
Ti up to 0.1%;
inevitable impurities, each up to 0.05% and total up to 0.15%; and balance aluminium.
5 . The multi-layered brazing sheet product according to claim 4 , wherein the covering clad layer has a Si content in the range of 2.5% to 5%.
6 . The multi-layered brazing sheet product according to claim 1 , wherein the 3xxx alloy core layer comprises, in wt. %,
0.5% to 1.8% Mn;
less than 0.20% Mg;
up to 1.1% Cu;
up to 0.7% Si;
up to 0.7% Fe;
up to 0.3% Cr;
up to 0.3% Sc;
up to 0.3% Zr;
up to 0.3% V;
up to 0.25% Ti;
up to 1.7% Zn;
unavoidable impurities each up to 0.05% and total up to 0.2%; and balance aluminium.
7 . The multi-layered brazing sheet product according to claim 6 , wherein the 3xxx alloy core layer has a Cu content in the range of 0.20% to 0.9%.
8 . The multi-layered brazing sheet product according to claim 1 , wherein the Al—Si brazing clad layer comprises, in wt. %,
Si 7%-13%;
Mg up to 0.5%;
Fe up to 0.7%;
Cu up to 0.3%;
Mn up to 0.8%;
Zn up to 2%;
Bi up to 0.3%;
Ti up to 0.25%; and
balance aluminium and unavoidable impurities each up to 0.05% at total up to 0.2%.
9 . The multi-layered brazing sheet product according to claim 8 , wherein the Al—Si brazing clad layer has a Si content of 10% to 13%.
10 . The multi-layered brazing sheet product according to claim 8 , wherein the Al—Si brazing clad layer has a Mg content of 0.02% to 0.5%.
11 . The multi-layered brazing sheet product according to claim 8 , wherein the Al—Si brazing clad layer has a Bi content of 0.06% to 0.30%.
12 . The multi-layered brazing sheet product according to claim 1 , wherein a surface of the multi-layered brazing sheet is surface treated with an alkaline or acidic etchant.
13 . The multi-layered brazing sheet product according to claim 1 , wherein the covering clad layer has a thickness X 1 and the Al—Si brazing clad layer has a thickness X 2 and wherein X 2 ≥2.5X 1 .
14 . The multi-layered brazing sheet product according to claim 13 , wherein X 2 >3X 1 .
15 . The multi-layered brazing sheet product according to claim 1 , wherein the Al—Si brazing clad layer comprises at least 0.05 wt. % Ti.
16 . The multi-layered brazing sheet product according to claim 1 , wherein the 3xxx alloy core layer has a Cu content in the range of 0.25 wt. % to 1.1% wt. %.
17 . A process for the production of a braze heat exchanger, comprising the steps of:
providing at least one aluminium alloy multi-layered brazing sheet product according to claim 1 ; and
brazing in a flux-free controlled atmosphere brazing (CAB).
18 . The process of claim 17 , wherein the multi-layered brazing sheet is surface treated with an alkaline or acidic etchant before a brazing step.