Aluminium-magnesium weld filler alloy

Details Aluminium-magnesium weld filler alloy Aluminium-magnesium weld filler alloy

2000-06-23

2002-07-09

Wyszomierski, George (Department: 1742)

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

C228S262500, C228S262510, C420S541000, C420S543000, C420S545000

Reexamination Certificate

active

06416884

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an aluminium-magnesium-base weld filler alloy, which is particularly suitable to be used in the construction of large welded structures such as storage containers and vessels for marine and land transportation. For example, the weld filler alloy of this invention can be used in the welded construction of marine transportation vessels such as catamarans of monohull type, fast ferries, high speed light craft. The weld filler alloy of the present invention can also be used in construction of numerous other structures such as LNG tanks, silos, tanker lorries, pressure vessels, bridges, and railway wagons. Further, the invention relates to a method of manufacturing an aluminium-base weld wire, and to a method of constructing welded constructions.
DESCRIPTION OF THE RELATED ART
Al—Mg-base weld filler alloys are extensively used in large welded constructions such as storage containers and vessels for land and marine transportation. One of the standard alloys is the AA5183 alloy having the nominal composition, in wt. %:
Mg
4.3-5.2
Mn
0.5-1.0
Zn
0.25 max.
Cr
0.05-0.25
Ti
0.15 max.
Fe
0.40 max.
Si
0.40 max.
Cu
0.10 max.
others
(each)
0.05 max.
(total)
0.15 max.
balance aluminium.
In particular, AA 5183 weld wire is widely used in the welded construction of marine vessels such as ships, catamarans and high speed craft. The main reason for the versatility of the AA5183 alloy is that it provides good combinations of high strength, corrosion resistance, bendability and weldability. The strength of the weld joint of AA 5183 alloy can be increased without significant loss in ductility by increasing the Mg percentage in the alloy. However, increasing the % of Mg in Al—Mg-base weld filler alloys is accompanied by a drastic reduction in corrosion resistance.
Some other disclosures of Al—Mg alloys found in the prior art literature will be mentioned below.
The Japanese patent application no. JP-A-05169290 proposes a filler alloy containing, in wt. %:
Zn
  1-6
Mg
  3-6 (here, Zn ≦ Mg)
Mn
 0.2-0.9
Cr
0.05-0.5
Ti
0.05-0.2
B
0.01-0.2
Zr
0.05-0.2
balance aluminium.
The proposed filler alloy is applied in welding techniques having a solidifying speed of higher than 1-3×10
2
° C./sec, and whereby Zr may be incorporated more than the quantity of the solid solution.
The British patent application GB-A-2000806 proposes a filler alloy, the composition of the filler alloy is, in wt. %:
up to 5.5% Mg
0.2-0.5% Cu
balance essentially aluminium.
In the examples and in the sub-claims the composition is more restricted to:
Zn
 1.0-4.0, preferably 2.7-3.3
Mg
 2.0-5.0, preferably 3.7-4.3
Cu
 0.2-0.5, preferably 0.25-0.35
Mn
 0.3-2.5, preferably 0.35-0.45
Ti
0.05-0.2
Cr
0.05-0.3
Zr
0.05-0.2
Si
less than 0.2
Fe
less than 0.4
balance aluminium.
In the examples the Cu addition is mentioned as compulsory. The filler alloy disclosed has been found suitable for welding constructional parts of AlZnMg alloys to themselves or to other aluminium alloys.
The European patent application EP-A-0799900 relates to an aluminium alloy in the form of plate or extrusion for large welded structures, with improved properties over those of standard AA5083 series. The composition of the proposed material is, in wt. %:
Mg
4.5-7.0
Mn
0.4-1.2
Zn
0.5-5.0
Zr
0.3 max.
Cr
0.3 max.
Ti
0.2 max.
Fe
0.5 max.
Si
0.5 max.
Cu
0.4 max.
balance aluminium and inevitable impurities.
The patent application cited does not give any indication about the use as weld filler alloy and to the improvements over standard AA5183 filler alloy.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an Al—Mg-base weld filler alloy with improved strength of welded aluminium alloy joints as compared to those of the standard filler alloys such as AA5183 alloy. It is also an object to provide Al—Mg base weld filler alloy which can offer ductility, bendability and corrosion resistance at least equivalent to those standard Al—Mg base weld wires, such as AA5356 and in particular AA5183.
According to the invention there is provided an aluminium-magnesium-base weld filler alloy, having the following composition in weight percent:
Mg
 5.0-6.5
Mn
 0.4-1.2
Zn
 0.4-<2.0
Zr
0.05-0.3
Cr
 0.3 max.
Ti
 0.2 max.
Fe
 0.5 max.
Si
 0.5 max.
Cu
0.25 max.
balance Al and inevitable impurities.
By the invention we can provide welded aluminium joints having higher strength than the standard AA5183 welds. Weld filler alloys in accordance with the invention have been found very successful for the welding constructional parts of AlMg alloys to themselves or to other aluminium alloys. More particularly, very good results are obtained in the case where the weld filler alloy in accordance with the invention is applied for the welding of constructional parts of AlMg alloys, which AlMg alloys are within the same chemical compositional range as the inventive weld filler alloy.
Further it has been found that the higher Mg content in combination with the higher Zn content in comparison with standard AA5183 filler wire, has an increased freezing range, in the range of 568-639° C. for the weld filler alloy of this invention against 574-638° C. for standard AA5183 alloy. The advantages of this increased freezing range in particular emerge when the weld filler alloy of this invention is used when constructing welded constructions, e.g. a smooth transition from the weld bead to the base material, which reduces the notch effect and by this improving fatigue performance of joints. Further during fusion welding, at those places where the weld bead overlaps with the base material, surface oxides e.g. aluminium-oxides are present. The increased fluidity of the weld filler alloy of this invention leads to more adherence and hence reduces deleterious “overlap” effects. And additionally a relatively more flat bead and finer or smoother ripples on the surface of the weld seam is obtained.
It is believed that the improved properties available with the invention, particularly higher strength levels in the weld seam, results from increasing the levels of Mg and Mn, and adding Zr. The good corrosion resistance at higher Mg levels results from uniformly precipitating relatively less anodic Mg and Zn containing intermetallics in the microstructure of the weld seam.
The reasons for the limitations of the alloying elements of the aluminium base weld filler alloy according to the present invention are described below. All composition percentages are by weight.
Mg: Mg is the primary strengthening element in the weld filler alloy. Mg levels below 5.0% do not provide the required strength to the weld seam and when the addition exceeds 6.5%, manufacturing weld wires from the weld filler alloy becomes immensely difficult. The manufacturing difficulty arises due to severe cracking during continuous or semi-continuous casting and subsequent processing. The preferred level of Mg is 5.0-6.0% as a compromise between ease of fabrication and strength.
Mn: Mn is an essential additive element. In combination with Mg, Mn provides the strength to the welded joints. Mn levels below 0.6% cannot provide sufficient strength to the welded joints. Above 1.2% the manufacturing of feed stocks for subsequent wire drawing becomes extremely difficult. The preferred minimum for Mn is 0.7% for strength.
Zn: Zn is an importance additive for corrosion resistance of the weld seams. Zn also contributes to some extent to the strength of the weld seams. Below 0.4%, the Zn addition does not provide sufficient corrosion resistance equivalent to that of AA 5183 alloy welded joints. Due to weldability reasons, the Zn level is restricted to <2.0%. More preferably the Zn level is restricted to a maximum of 0.9%. In a further preferred embodiment the Mg/Zn-ratio is larger than 5 in order to achieve a favourable combination of strength and corrosion resistance properties.
Zr: Zr is important to achieving strength improvements in the weld seams. Zr is also important for resistance against cracking dur

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