Metal treatment – Stock – Aluminum base
Reexamination Certificate
2002-02-15
2004-02-24
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Aluminum base
C420S541000, C420S544000, C420S553000
Reexamination Certificate
active
06695935
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an aluminium-magnesium alloy with a magnesium content in the range of 3.5 to 6 wt. % in the form of rolled products and extrusions, which are particularly suitable to be used in the form of sheets, plates or extrusions in the construction of welded or joined structures, such as storage containers and vessels for marine and land transportation. Extrusions of the alloy of the invention can be used as stiffeners in engineering constructions. Further the invention relates to a method of manufacturing the alloy of the invention.
DESCRIPTION OF THE PRIOR ART
For this invention reference is being made to aluminium wrought series alloys having a designation number in accordance with the Aluminium Association as published in February 1997 under “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys”.
In aluminium-magnesium alloys, theoretically, at room temperature up to about 1.8 wt. % Mg can be retained in solid solution. However, under practical conditions, up to about 3.0 wt. % Mg can be retained in solid solution. As a consequence, in aluminium-magnesium alloys containing more than 3.5 wt. % magnesium, the magnesium in solid solution is unstable and this unstable solid solution leads to grain boundary, anodic precipitations of Al
8
Mg
5
intermetallics which in turn renders the material to be susceptible to corrosion attack. Mainly due to this reason, AA5454-series material in the soft temper (O-temper) are used in the construction of vessels which are expected to serve at temperatures above 65° C. In case of service temperatures below 65° C., AA5083-series material in the soft temper are commonly used. Material of the AA5083-series is significantly stronger than AA5454-series. Although stronger, the inferior corrosion resistance of the AA5083-series material limits its use to those applications where long term corrosion resistance at above ambient temperatures is not required. Because of the corrosion related problems, in general AA5xxx-series material having magnesium levels of only up to 3.0 wt. % are currently accepted for use in those applications which require service at temperatures above 80° C. This limitation on the magnesium level in turn limits the strength that can be achieved after welding and consequently on the allowed material thickness that can be used in the construction of structures such as tanker lorries.
Some disclosures of Al—Mg alloys found in the prior art literature will be mentioned below.
U.S. Pat. No. 4,238,233 discloses an aluminium alloy for cladding excellent in sacrificial anode property and erosion-corrosion resistance, which consists essentially of, in weight percentage:
Zn
0.3 to 3.0%
Mg
0.2 to 4.0%
Mn
0.3 to 2.0%
balance aluminium and incidental impurities and further containing at least one element selected from the group consisting of:
In
0.005 to 0.2%
Sn
0.01 to 0.3
Bi
0.01 to 0.3%
provided that the total content of In, Sn and Bi being up to 0.3%.
This disclosure does not relate to the field of welded mechanical construction.
JP-A-05331587 discloses an aluminium alloy having a chemical composition of Mg 2.0 to 5.5% and 1 to 300 ppm, in total, of one or more elements selected from the group consisting of Pb, In, Sn, Ga and Ti, balance aluminium and impurities. Optionally further element like Cu, Zn, Mn, Cr, Zr, Ti may be added as alloying elements. The minor addition of Pb, In, Sn Ga, and Ti is to improve the adhesion of a plating film. Also, this disclosure does not relate to the field of welded mechanical construction.
FR-A-2,329,758 discloses an aluminium-magnesium alloy having Mg in the range of 2 to 8.5% and further having Cr in a range of 0.4 to 1.0% as a mandatory alloying element. This disclosure does not relate to the field of welded mechanical construction.
U.S. Pat. No. 5,624,632 discloses an substantially zinc-free and lithium-free aluminium alloy product for use as a damage tolerant product for aerospace applications.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an aluminium-magnesium alloy in the form of a rolled product or an extruded product or a drawn product, combined with substantially improved long term corrosion resistance after welding as compared to those of the standard AA5454 alloy and having improved strength as compared to those of the standard AA5083 alloy.
A further object of present invention is to provide an aluminium-magnesium alloy in the form of a rolled product or an extruded product or a drawn product, combined with substantially improved exfoliation resistance after welding as compared to those of the standard AA5083 alloy.
Another object of present invention is to provide an aluminium-magnesium alloy in the form of a rolled product or an extruded product or a drawn product, combined with substantially improved exfoliation resistance after welding in a sensitised condition as compared to those of the standard AA5083 alloy.
According to the invention there is provided an aluminium-magnesium alloy product, preferably in the form of a rolled product or an extruded product or a drawn product, for welded mechanical construction, having the following composition, in weight percent:
Mg
3.5-6.0
Mn
0.4-1.2
Zn
0.4-1.5
Zr
0.25 max.
Cr
0.3 max.
Ti
0.2 max.
Fe
0.5 max.
Si
0.5 max.
Cu
0.4 max.
one or more selected from the group:
Bi
0.005-0.1
Pb
0.005-0.1
Sn
0.01-0.1
Ag
0.01-0.5
Sc
0.01-0.5
Li
0.01-0.5
V
0.01-0.3
Ce
0.01-0.3
Y
0.01-0.3
Ni
0.01-0.3
others
(each) 0.05 max.
(total) 0.15 max.
balance aluminium.
By the invention we can provide aluminium-magnesium alloy products in the form of a rolled product or an extrusion, with substantially improved long term corrosion resistance in both soft temper (O-temper) and work- or strain-hardened temper (H-tempers) as compared to those of the standard AA5454 alloy and having improved strength as compared to those of the standard AA5083 alloy in the same temper. Further, alloy products of the present invention have also been found with improved long term exfoliation corrosion resistance at temperatures above 80° C., which is the maximum temperature of use for the AA5083 alloy. Further, the alloy products in accordance with the invention have been found to have an improved exfoliation corrosion resistance, in particular when brought in an sensitised condition.
The invention also consists in a welded structure having at least one welded plate or extrusion of the alloy set out above. Preferably the proof strength of the weld is at least 140 MPa.
The invention also consists in the use of the aluminium alloy of the invention as weld filler wire, and is preferably provided in the form of drawn wire.
It is believed that the surprisingly improved properties available with the invention are achieved by a careful selection of the combination of alloying elements. Particularly higher strength levels in both strain- or work-hardened (H-tempers) and soft tempers (O-tempers) are achieved by increasing the levels of Mg, Mn and adding Zr, and the long term corrosion resistance at higher Mg levels is achieved by precipitating anodic Mg and/or Zn containing intermetallics within the grains. In accordance with the invention it has been found that the grain interior precipitation can be further promoted by deliberate addition of one or more of the following elements selected from the group consisting of: Bi 0.005 to 0.1, Pb 0.005 to 0.1, Sn 0.01 to 0.1, Ag 0.01 to 0.5, Sc 0.01 to 0.5, Li 0.01 to 0.5, V 0.01 to 0.3, Ce 0.01 to 0.3, Y 0.01 to 0.3, and Ni 0.01 to 0.3.
The precipitation of Mg and/or Zn containing intermetallics within grains effectively reduces the volume fraction of grain boundary precipitated and highly anodic, binary AlMg intermetallics and thereby providing significant improvement in the corrosion resistance to the aluminium alloys at higher Mg levels employed. And furthermore, the deliberate additions of the indicated elements in the indicated ranges not only enhances grain body precipitation of anodic intermetalli
Haszler Alfred Johann Peter
Sampath Desikan
Combs Morillo Janelle
Corus Aluminium Walzprodukte GmbH
Stevens Davis Miller & Mosher LLP
Wyszomierski George
LandOfFree
Exfoliation resistant aluminium magnesium alloy does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exfoliation resistant aluminium magnesium alloy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exfoliation resistant aluminium magnesium alloy will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297609