7005 aluminium alloy

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7005 aluminium alloy:

A heat treatable high strength alloy with high corrosion resistance and high weldability
Good for structural applications particularly in marine and transport.

1 Applications of aluminium alloy 7005

1.1 Forms of products

Figure 1 give, for each major field of aluminium wrought products application, the availability of alloy 7005. They are drawn products and extruded products.
The last column indicates whether the alloy is in conformity [Y or N (Yes or No)] with the requirements for the chemical composition of wrought aluminium and wrought aluminium alloys used for the production of materials and articles intended to be in contact with foodstuff.

The keys for Table A.7 are:

Y: Yes
N: No
X: Applicable item

Figure 1 – The fragment of Table A.7 of EN 573-3 for aluminium alloy 7005 [2]

1.2 Typical uses [1]

Extruded structural members such as bicycle frames, cross members, comer posts, side posts, and stiffeners for trucks, trailers, cargo containers, and rapid transit cars.
Welded or brazed assemblies requiring moderately high strength and high fracture toughness, such as large heat exchangers, especially where solution heat treatment after joining is impractical.
Sports equipment such as tennis racquets and softball bats.

2 Chemical composition of aluminium alloy 7005

2.1 Nominal chemical composition [1]

4,6Zn-1,4Mg-0,5Mn-0,1Cr-0,1Zr-0,03Ti

2.2 Chemical composition

Figure 2 – The fragment of Table 7 of EN 573-3 for aluminium alloy 7005

2.3 Chemical composition according to ASTM B 221 [3]

Figure 3 – The fragment of Table 1 of ASTM B221 for aluminium alloy 7005

3 Mechanical properties of aluminium alloy 7005

3.1 Typical mechanical properties [1]

Tensile strength:

O temper: 193 MPa
T53 temper: 393 MPa
T6, T63, T6351 tempers: 372 MPa

Yield strength:

O temper: 83 MPa;
T53 temper: 345 MPa
T6, T63, T6351 tempers: 317 MPa

Elongation

(in 50 mm (2 in.) or 4d where d is diameter of tensile test specimen):

O temper: 20%
T53 temper: 15%
T6, T63, T6351 tempers: 12%.

3.2 Mechanical properties according to EN 755-2 [4]

Figure 4 – Table 54 of EN 755-2 for aluminium alloy 7005

3.3 Mechanical properties according to ASTM B 221 [3]

Figure 5 – The fragment of Table 2 of ASTM B221 for aluminium alloy 7005

4 Density

2,78 g/cm³

5 Thermal Properties [1]

Liquidus temperature: 643 ºC
Solidus temperature: 604 ºC
Coefficient of thermal expansion, linear (20 to 100 ºC): 23,1 ∙ 10^-6 m/(m ∙ K)
Annealing temperature: 345 ºC
Solution temperature: 400 ºC

6 Heat treatment of aluminium alloy 7005

6.1 Temper T53

[1]:

press quench from hot working temperature,
naturally age 72 h at room temperature,
then two-stage artificially age 8 h at 100 to 110 ºC
plus 16 h at 145 to 155 ºC

Figure 6 – The fragment of Table 2 of ASTM B 918 for aluminium alloy 7005 [6]

6.2 Extrusion Press Solution Heat Treatment

Figure 7 – The fragment of Table 1 of ASTM B 807 with additions [5]

Figure 8 – The fragment of Table 3 of ASTM B 807 with additions [5]

7 Welding of aluminium alloy 7005

7.1 General notes

Source [7]:

Al-Zn-Mg alloys such as 7005 will resist hot cracking better and exhibit superior joint performance than the Al-Zn-Mg-Cu alloys such as 7075.
The Mg content in this group (Al-Zn-Mg) of alloys would normally increase the cracking sensitivity.
Adding Zr to refine grain size effectively reduces the cracking tendency.
This alloy group welds easily with the high magnesium filler alloys such as 5356, which ensures the weld contains sufficient magnesium to prevent cracking.
The recommendation of silicon-based filler alloys, such as 4043, for these alloys is not desirable because the excess Si introduced by the filler alloy can result in the formation of excessive amounts of brittle Mg2Si particles in the weld.

Source [8]:

Aluminium alloy 7005 as a lower-strength non-copper-containing alloy of 7XXX series alloys is fairly well weldable.
Some of the loss of strength in the heat affected zone can be recovered by suitable heat treatment.
The alloy will be age naturally but it make up to 30 days for ageing to proceed to completion.
The strength loss is less than that in the 6XXX series (for example, alloy 6061).
This, coupled with the natural ageing characteristic, makes this alloy a popular choice for structural applications where on-site repair and maintenance work may be required.

7.2 Heat-Affected Zone in welded aluminium alloy 7005

The loss in strength and hardness in the weld region is typical for aluminium and its alloy, including alloy 7005 (Figure 9).
The elongation values increase at first but then fall slightly at the weld middle, this fall being caused by precipitations.

Figure 9 – Characteristic Mechanical and Technological Values
of the HAZ of AlMg4,5 Mn (7005) [9]

7.3 Strength of welded joints of aluminium alloy 7005 [9]

The weldable, self-hardening Al-Zn-Mg alloys, incuding 7005, have to be handled differently than the other heat-treatable alloys.
The reason for this is the relatively large solution treatment range (350 – 500 °C) and the slow ageing effect at room temperature (natural ageing).
The solution treatment and quenching occur at much lower levels than for the other heat-treatable alloys.
The full strength is regained after a room temperature ageing time of 90 days (Figure 10).
This effect cannot be attained without additional heat input and quenching for Al-Mg-Si types of alloys, such as alloy 6061. A slight increase of strength can be attained by artificial ageing (Figure 11).

Figure 10 – Heat-Affected Zone in Welded Aluminium Joints [9]

Figure 11 – Strength of Welded Joints after Aging [9]

7.4 Natural and artifical ageing of weld joint

Alloy 7005 have ability to age-harden in the heat-affected zone up to about 80 % of the parent metal by natural aging and can be recover 100 % of strength if artifically aged after welding [10]

8 Precautions in use of aluminium alloy 7005 [1]

To avoid stress-corrosion cracking, stresses in the transverse direction should be avoided at exposed machined or sawed surfaces.
Parts should be cold formed in O temper, then heat treated; alternatively, parts may be cold formed in W temper, followed by artificial aging.
In parts intended for service in aggressive electrolytes such as seawater, selective at-tack along the heat-affected zone in a weld-ment or torch-brazed assembly can be avoided by postweld aging.
When the service environment is conducive to galvanic corrosion, 7005 should be coupled or joined only to aluminum alloy components having similar electrolytic solution potentials; alternatively, joint surfaces should be protected or insulated.

Sources:

Aluminum and Aluminum Alloys, ed. J. R. Davis – 1996
EN 573-3
ASTM B 221
EN 755-2
ASTM B 807
ASTM B 918
Welding Aluminum—Questions and Answers – A Practical Guide for Troubleshooting Aluminum Welding-Related Problems / T. Anderson – 2010
The Welding of Aluminium and Its Alloys / G. Mathers – 2002
TALAT 4204
J.T. Staley // Aluminum alloys – Contemporary Research and Applications – Volume 31 – Academic Press, Inc. – 1989

Aluminium Guide