Brazing of Aluminium Alloys

Brazing of Aluminium Alloys

Brazing of Aluminium Alloys -
Common Base Metals Brazed

Alloy	Melting Range, ° F*	Brazeability
1. 99% min aliminum	1190-1215	A
2. Al-1.2 Mn-1.0 Mg (%)	1165-1205	B
3. Al-0.8 Mg (%)	1170-1205	B
4. Al-2.5 Mg-0.25 Cr (%)	1100-1200	C
5. Al-0.25 Cu-0.6 Si-1.0 Mg-0.2 Cr (%)	1100-1200	A
6. Al-0.45 Mn-1.4 Mg-4.5 Zn-0.13 Cr (%)	1065-1170	B
7. Al-0.6 Cu-5 Si (%)	1065-1170	B
8. Al-0.5 Cu-0.35 Mg-6.5 Zn (%)	1120-1190	A

N.B. :
A : Generally brazeable,
B : Brazeable with special techniques,
C : Limited brazeability.
Filler Metals Used

% Composition				Melting Range ° F	Normal Brazing Range ° F	Form of Filler Alloy	Brazing Process
Si	Cu	Zn	Al
7.5	-	-	92.5	1070-1135	1110-1150	Sheet Cladding	Furnace, Dip
10	4	-	86	970-1085	1060-1120	Rod,sheet	Torch,Furnace,Dip
12	-	-	88	1070-1080	1080-1120	Rod sheet Powder	Torch,Furnace,Dip
10	-	-	90	1070-1095	1090-1120	Sheet,Cladding	Furnace,Dip
10	4	10	76	960-1040	1040-1060	Rod	Torch,Furnace,Dip

Brazing Flux
Fluxes for brazing aluminium alloys usually consist of mixtures of alkali and alkaline earth chlorides and fluorides, sometimes containing cryolite (3NaF.AlF3). A wetting agent may be used to improve the wetting action of the flux.
Flux can be applied dry as supplied by the manufacturer or it can be mixed with water or alcohol and be applied by painting, spraying or dipping. Dry flux can be sprinkled on the joint or the heated filler rod can be dipped into the dry flux. Torch and furnace brazing fluxes are quite active, may severely attack thin aluminium and must be used with care.
Brazed Joints
Commonly used brazed joints are:
(i)Lap
(ii) Flange
(iii) Lock seam
(iv)Tee type

Cleaning of Base Metal Surfaces
Surfaces to be brazed should be pre cleaned using:
(i) Vapour or solvent cleaning (for non-heat-treatable alloys).
(ii) Chemical cleaning (for heat-treatable alloys) in order to produce strong leak-tight joints.

Brazing Methods
Commonly used methods for brazing aluminium alloys are:
Furnace Brazing,
Torch Brazing,
Dip Brazing, and
Flux-lessvacuum Brazing.

Home | Site map | Submit Article | Directory | Search