JP2915490B2 - High strength aluminum alloy for welded structural materials with excellent resistance to stress corrosion cracking - Google Patents

Description

The present invention relates to a high-strength aluminum alloy used as a rolled material, an extruded material, and a forged material for a welded structural material, and more particularly, to a material excellent in stress corrosion cracking resistance. The present invention relates to an Al-Zn-Mg high strength aluminum alloy for welding structural materials.

(Prior art and its problems) In recent years, in buildings, vehicles, ships, aircrafts, and the like, thinning and weight reduction have been progressing, and the demand for weldable high-strength aluminum alloys has been increasing. Conventionally, aluminum alloys for these applications include Al-Zn-Mg alloys and Al-Zn-Mg-
Cu alloys have been considered. This type of high-strength aluminum alloy has higher strength as the amount of Zn and Mg increases, but it tends to increase the susceptibility to stress corrosion cracking and welding cracking. Hot workability also deteriorates.

A7075 can be formed by rolling, extrusion, forging, etc., and is a typical high-strength aluminum alloy used for structural materials.
There are alloys. Although the strength of the alloy belongs to the highest among aluminum alloys, the weldability is remarkably poor due to the inclusion of Cu, and the joining must be performed by mechanical joining such as bolting and rivets. In addition, since the alloy has high sensitivity to stress corrosion cracking, there is a risk that stress corrosion cracking may occur in the T6 treatment, which is the heat treatment that originally provides the highest strength, so tempering at a higher temperature or for a longer time is required. Often used in T7 treatment to stabilize the performed tissue.

Among the 7000 series aluminum alloys, A7N01 is well known as an aluminum alloy that can be formed by rolling, extrusion, forging, etc., and has excellent weldability and stress corrosion cracking resistance. A7003, which has good extrudability, is also an aluminum alloy with excellent weldability and stress corrosion cracking resistance. However, these alloys have relatively low strength and are not suitable for applications requiring more strength. As described above, it is extremely difficult to obtain an aluminum alloy that is satisfactory in all aspects of strength, stress corrosion cracking resistance, and weldability, and that has excellent formability such as extrusion, rolling, and forging. there were.

(Problems to be Solved by the Invention) The present invention has a strength,
Satisfaction was obtained in all aspects of stress corrosion cracking resistance and weldability.
Moreover, it is an object of the present invention to provide a material excellent in forming such as extrusion, rolling, and forging.

(Means for Solving the Problems) The present inventors have paid attention to the above-mentioned circumstances, and as described above, have been satisfied in all aspects of strength, stress corrosion cracking resistance, and weldability, and With the aim of developing an aluminum alloy with excellent formability such as extrusion, rolling, and forging, various studies were conducted by changing the type and content of alloy components. As a result, the inventors have found that the above objects can be achieved by specifying the types and contents of alloy components as described below, and have completed the present invention.

That is, the composition of the high-strength aluminum alloy for welding according to the present invention, which is excellent in stress corrosion cracking resistance, is defined as Zn 5 to 8 wt%, Mg 1.2
~ 4.0% by weight, Cu 1.5% by weight to 4.0% by weight or less, Ag 0.0
3 to 1.0% by weight, rare earth element or misch metal 0.03 to 5.
0% by weight, Fe 0.01 to 1.0% by weight, Ti 0.005 to 0.2% by weight, and Mn 0.01 to 1.5% by weight, Cr 0.01 to 0.6% by weight,
Zr0.01 ~ 0.25% by weight, B0.0001 ~ 0.08% by weight, Mo0.03 ~
The gist is that at least one or more of 0.5% by weight is contained, and the balance consists of aluminum and unavoidable impurities.

That is, the present invention improves stress corrosion cracking resistance and strength and weld cracking resistance by adding Ag and a rare earth element or a misch metal to an Al-Zn-Mg-Cu alloy.

(Operation) The reasons for limiting the types and contents of the components of the aluminum alloy according to the present invention will be described below.

Zn is an indispensable element for increasing the strength of the alloy as a hardening element. If its content is less than 5 wt%, its effect is small, and if it exceeds 8 wt%, stress corrosion cracking resistance, weldability,
Workability deteriorates. The most preferred content of Zn is 5 to 8% by weight.

Mg, like Zn, is also an indispensable element for improving the strength. If the content is less than 1.2% by weight, sufficient strength cannot be obtained.
If the content exceeds 4.0% by weight, the stress corrosion cracking resistance, weldability and workability deteriorate. Therefore, the most preferred content of Mg is 1.2-4.0% by weight.

Cu, like Zn, is also an indispensable element for improving the strength. If the content is less than 1.5% by weight, sufficient strength cannot be obtained, and if the content exceeds 4.0% by weight, stress corrosion cracking resistance , Weldability and workability deteriorate. Therefore, the most preferable content of Cu is more than 1.5% by weight and 4.0% by weight or less.

Ag is an element that improves the stress corrosion cracking resistance and strength. If its content is less than 0.03% by weight, its effect is small.
If the content exceeds 1.0% by weight, the weldability deteriorates. Therefore, the most preferable content of Ag is 0.03 to 1.0% by weight.

Rare earth elements or misch metals improve stress corrosion cracking resistance and weld cracking resistance.
If the content is less than 03% by weight, the effect is small, and if the content exceeds 5.0% by weight, coarse crystals are formed in the alloy and the strength is deteriorated.
Therefore, the most preferable content of the rare earth element or the misch metal is 0.03 to 5.0% by weight. La, Ce, Pr, Nd, Sm, etc. are rare earth elements, and Ce,
An alloy containing La as the main component, usually Ce45-50% by weight, La20-4
0% by weight, balance consisting of other rare earth elements (Nd, Sm, Pr, etc.). Both rare earth elements and misch metals have the same effect, but rare earth elements alone are expensive and must be added as misch metal. Is more economically advantageous.

Fe is an element that improves weldability, and its content is 0.01%.
If the content is less than 1.0% by weight, the effect is small, and if the content exceeds 1.0% by weight, toughness and workability deteriorate. Therefore, the most preferable content of Fe is 0.01 to 1.0% by weight.

Ti is an element that refines the structure and improves the weldability, but its effect is small when its content is less than 0.005% by weight.
If the content exceeds 0.2% by weight, a giant compound is generated, and there is a risk that toughness and workability are deteriorated. Therefore, the most preferable content of Ti is 0.005 to 0.2% by weight.

Mn, Cr, Zr, B, and Mo are elements to be contained for stabilizing the structure, and one or more of them are added. Less than wt%, Zr
If the content is less than 0.01% by weight, B is less than 0.0001% by weight, and Mo is less than 0.03% by weight, the effect of grain refinement is reduced, and Mn 3.0% by weight, Cr 0.6% by weight, Zr 0.25% by weight, B0 If the content is more than .08% by weight and 0.5% by weight of Mo, a giant compound is generated, and there is a risk of deteriorating toughness and workability.

In the alloy of the present invention, Si and Ni were
It is necessary to limit to less than 0.03% by weight and less than 0.03% by weight of Ni. If the content exceeds the respective limit values, the weldability is reduced.

Example An example of the present invention will be described below.

The alloys of the present invention, the comparative material, and the conventional alloys shown in Table 1 were extruded into an ingot (9
Inch diameter). This 9-inch diameter bar-shaped ingot is 47
After homogenizing at 0 ° C for 12 hours, the mixture was heated to 430 ° C and extruded by an extruder into a rectangular piece having a thickness of 5 mm and a width of 100 mm. At the time of extrusion, the extrudability of each alloy was evaluated at the maximum extrusion speed at which the rectangular material could be extruded without surface defects or cracks. Table 2 shows the results.
Each material was extruded, quenched after solution treatment at 460 ° C. for 1 hour, and tempered at 120 ° C. for 24 hours.

Tensile test, stress corrosion cracking test on the material manufactured in this way. And the results of welding crack test
Also shown in the table. The test method is shown below.

〔Test method〕

(1) Workability (extrusion) (a) Extrusion conditions: ingot size ... 9 inch diameter (219 mm
φ) Extrusion temperature 430 ° C. (b) Extrusion size: 5 mm × 100 mm (c) Evaluation method: Judgment was made based on whether or not the extrusion speed was equivalent to A7075.

以上: Exceeds the limit extrusion rate of A7075 x …… Exceeds the limit extrusion rate of A7075 (2) Tensile test (a) Test piece: No. 5 test piece of JIS Z 2201 (b) Test method: Amsler universal testing machine, JIS Z Test based on 2241.

(C) Measured value: Measure the tensile strength, proof stress, and elongation, and judge according to the following criteria.

〇 ...... tensile strength of 55 kgf / mm ² or more delta ...... tensile strength 50 kgf / mm ² or more and less than ^{55kgf / mm 2 x ...... 50kgf /} mm less than ² (3) Stress corrosion cracking test (a) test piece: JIS H No. 1 test piece of 8711 (b) Test method: Based on JIS H 8711.

Stress loading: 75% of the proof stress was applied using a No. 1 test piece jig, and immersion: 3.5% NaCl solution, alternate immersion (period immersion for 10 minutes, drying for 50 minutes) for 30 days (c) Evaluation: stress corrosion resistance (4) Weld cracking test (a) Test piece: Fishbone type test piece shown in Fig. 1 (b) Welding condition: Welding method: TIG solution Additive: Not used Electrode: Thorium-containing tungsten rod 3.2 mmφ Welding current: 180 A Arc voltage: 19 V Welding speed: 30 cm / min Argon gas flow rate: 10 l / min (c) Crack evaluation: crack length Measure and judge according to the following criteria.

〇: Crack length less than 30mm Δ …… Crack length 30mm or more and less than 50mm x …… Crack length 50mm or more From the results shown in the table, all of the examples according to the present invention were excellent in extrudability, strength, stress corrosion cracking resistance, and weldability, while the comparative alloys, especially Ag and rare earth elements or misch metal were excellent. Those outside the scope of the present invention and conventional alloys were inferior in any of the properties.

(Effects of the Invention) In the present invention, as can be understood from the above, as an aluminum alloy for a welded structure, it has higher strength than conventional alloys, and is excellent in stress corrosion cracking resistance. It can provide an aluminum alloy for welded structures that possesses hot workability such as extrusion, rolling, and forging, and is more suitable for requests for thinner and lighter welded structural materials than conventional alloys. It can correspond to.

[Brief description of the drawings]

FIG. 1 is a plan view showing a fishbone type cracked test piece. 1 ... Fishbone type crack test piece 1a ... Weld bead 1b ... Weld crack 1c ... Crack length 1d ... Welding direction

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-59-118865 (JP, A) JP-A-60-5862 (JP, A) JP-A-62-250149 (JP, A) JP-A 61-118 238937 (JP, A) JP-A-63-96241 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 21/00-21/18

Claims (1)

(57) [Claims] 1-5% by weight of Zn, 1.2-4.0% by weight of Mg, Cu1.5
More than 4.0% by weight, more than 4.0% by weight, 0.03 to 1.0% by weight of Ag, 0.03 to 5.0% by weight of rare earth element or misch metal, 0.01 to Fe%
1.0% by weight, 0.005 to 0.2% by weight of Ti
1 to 1.5% by weight, Cr 0.01 to 0.6% by weight, Zr 0.01 to 0.25% by weight, B0.0001 to 0.08% by weight, Mo at least one or more of 0.03 to 0.5% by weight, A high-strength aluminum alloy for welded structural materials having excellent resistance to stress corrosion cracking, comprising the remaining aluminum and unavoidable impurities.