Aluminium extrusion alloy

Details Aluminium extrusion alloy Aluminium extrusion alloy

2000-06-07

2002-05-21

Wyszomierski, George (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Heating or cooling of solid metal

C148S697000, C228S207000, C228S214000, C228S223000

Reexamination Certificate

active

06391129

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an aluminium extrusion alloy and extruded sections thereof, containing Mn, Mg, Cu and Si, which aluminium extrusion alloy is particular suitable for application in brazed assemblies, and further to a method of its manufacture.
DESCRIPTION OF THE RELATED ART
In the prior art, aluminium alloys are the alloys of choice for heat exchanger applications. These alloys are selected for their desirable combination of strength, low weight, good thermal and electrical conductivity, brazeability, corrosion resistance and formability.
Typical applications include automotive heater cores, radiators, evaporators, condensers, charge air coolers, and transmission/engine oil coolers.
At present brazed beat-exchanger devices, such as for example automotive radiators, are often provided with mechanical fasteners made of extruded Aluminium Association (AA)6063-series alloy, preferably in a T8-temper. A T8-temper involves solution heat treatment of the extruded product, cold working and then artificially ageing. This application requires excellent mechanical properties and a good machinability of the extruded product for putting in a mechanical thread. Additionally at least a reasonable corrosion resistance is required. The chemical composition of standard AA6063 alloy is, in weight percent:
Si
 0.2-0.6
Mg
0.45-0.9
Fe
0.35 max.
Cu
 0.1 max.
Mn
 0.1 max.
Cr
 0.1 max.
Zn
 0.1 max.
Ti
 0.1 max.
Further the AA6063 alloy is extensively used in the T6 (artificially aged) temper. When AA6063 alloy is being applied in combination with a Controlled Atmosphere Brazing (CAB) process, a brazing flux is applied to enhance the brazeabilty of the brazing alloy. A well known CAB brazing process is the Nokolok (trade name) brazing process and involves the use of a non-corrosive flux made up of a mixture of potassium and fluoroaluminates. The flux functions at brazing temperatures by melting, spreading and dissolving the oxide film. However, due to the presence of the magnesium in the AA6063 alloy the flux material tends to get poisoned by the formation of MgO, which results in a bond of poor quality. This disadvantage can only be partly be overcome by applying higher loads of brazing flux material. Another solution would be the application of mechanical fasteners made of AA3003 material since it comprises magnesium in a range of up to 0.05%. But this material is too weak to put in a thread, leading to pull out on testing. The chemical composition of standard AA3003 alloy is, in weight percent:
Si
<0.6
Fe
<0.7
Cu
0.05-0.20
Mn
1.0-1.5
Zn
0.10
balance aluminium and inevitable impurities.
Some other disclosures of aluminium extrusion alloys found in the prior art literature will be mentioned below.
U.S. Pat. No. 5,342,459 (Alcoa) discloses an aluminium extrusion alloy and a method of its manufacture, the alloy consisting of, in weight percent:
Mg
0.5-1.3
Si
0.4-1.2
Cu
0.65-1.2 
Mn
0.1-1.0
balance aluminium and inevitable impurities.
U.S. Pat. No. 4,589,932 (Alcoa) discloses an aluminium extrusion alloy and a method of its manufacture, the alloy consisting of, in weight percent:
Mg
0.5-1.3, preferably 0.7-1.2
Si
0.4-1.2, preferably 0.6-0.9
Cu
0.6-1.1, preferably 0.6-0.95
Mn
0.1-1.0, preferably 0.2-0.6
Fe
<0.6
and with the proviso that %Mg>%Si+(0.1 to 0.4)
balance aluminium and inevitable impurities.
In order to improve the machining characteristics of the alloy each of lead and bismuth in a range of 0.3 to 0.7% may be added to the alloy.
EP-A-0676480 (Northwest Aluminum) discloses two very wide groups of high strength Al-Mg-Si extrusion alloys.
The first group of aluminium alloys consists of in weight percent:
Si
0.2-2.0
Mg
0.3-1.7
Cu
0.32-1.2 
Mn
  0-1.1
Cr
0.01-0.4 
at least one element selected from the group consisting of:
V
0.01-0.3
Be
0.001-0.1 
Sr
0.01-0.1
balance aluminium and inevitable impurities.
The second group of aluminium alloys consists of, in weight percent:
Si
0.6-1.2
Mg
1.0-1.6
Cu
0.4-1.0
Mn
<0.05
Cr
0.05-0.3 
at least one element selected from the group consisting of:
V
0.01-0.3
Be
0.001-0.05
Sr
0.01-0.1
balance aluminium and inevitable impurities.
Both aluminium extrusion alloys are preferably provided in a T6-temper condition.
WO-A-99/07906 (Hoogovens) discloses an aluminium alloy for welded structures and brazing application, having the following composition in weight percent:
Mg
0.5-1.5
Zn
0.1-3.8
Si
0.05-1.5 
Mn
0.2-0.8
Zr
0.05-0.25
Cr
<0.3
Cu
<0.3
Fe
<0.5
Ag
<0.4
Ti
<0.2
balance aluminium and inevitable impurities.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an aluminium extrusion alloy capable of obtaining post-brazing mechanical properties and corrosion resistance at least comparable to standard AA6063, and being capable of being processed in at least a Controlled Atmosphere Brazing (CAB) process.
A further object of the present invention is to provide an aluminium extrusion alloy having machinability characteristics at least equal to standard AA6063 extruded products, typically in a T8-temper.
Another object of the present invention is to provide a method of manufacturing extruded sections of the new aluminium alloy.
And another object of the present inventions is to provide a method of manufacturing an assembly of brazing components, wherein one of the components is made from the aluminium extrusion alloy of the invention.
According to the invention in one aspect there is provided an aluminium extrusion alloy having the following composition in weight percent:
Mn
1.0-1.4
Cu
0.2-2.0
Mg
0.1-0.6
Si
0.15-1.0 
Fe
 0.8 max.
Zn
0.25 max.
Ti
0.15 max.
Cr
0.35 max.
Zr and/or V in total 0.35 max.
others up to 0.05 each, total 0.15
balance Al, and with the proviso that (Cu+Mg)>0.7.
In this way it is achieved that the aluminium extrusion alloy of the invention has similar post-braze mechanical strength as compared to AA6063 in the same temper and better than AA3003 material, a corrosion resistance as tested in a SWAAT test environment equivalent to AA6063 material in the same temper, and further the machinability characteristics of the present extrusion alloy are equal to or better than AA6063 material in the same temper and better than AA3003 material. Further the aluminium extrusion alloy of the invention can be used to manufacture devices via a brazing process, and in particular in a Controlled Atmosphere Brazing process.
It should be mentioned here that the aluminium alloy composition range is known from BP-A-0718072, in which document it is mentioned that the alloy is used as a rolled product only as core alloy for brazing sheet having on at least one side thereof a brazing layer of an aluminium alloy containing silicon as main alloying element.
The reasons for the limitations of the alloying elements of the aluminium extension alloy according to the invention are described below. All compositions are by weight.
Mn is an important alloying element in the alloy according to the invention. And should be in the range of 1.0 to 1.4%. Below 1.0% there is not a sufficient effect, and above 1.4% it may result in the formation of detrimental large intermetallic particles. In this range the Mn present allows for a solid solution hardening effect because sufficient Mn is retained in solid solution for the desired increase in strength.
Cu is one of the main alloying elements in order to obtain the desired strength level, in particular by means of solution hardening. At least 0.2% is required for obtaining the desired strength and corrosion resistance, while a Cu content of over 2.0% does not produce any significant improvements in respect of strength, and may further result in the formation of detrimental low-melting eutectics. A more preferred lower limit for the Cu level is 0.5%. A more preferred Cu content is in a range of 0.65 to 1.5% in order to achieve an optimisation in the desired properties. A very suitable range for the Cu-content is 0.65 to 0.9% as a compromise in mechanical strength after extrusi

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