JPH03122245A - High strength aluminum alloy for welding excellent in stress corrosion cracking resistance - Google Patents

Abstract

PURPOSE:To offer the plate material excellent in formability as well as strength, stress corrosion cracking resistance and weldability by specifying the kinds and contents of the alloy components in an Al-Zn-Mg series alloy plate material. CONSTITUTION:The Al alloy contains, by weight, 4 to 8% Zn, 0.3 to 3.0% Mg, 0.01 to 1% Fe, 0.01 to 1% Cu, 0.005 to 0.2% Ti and 0.01 to 0.2% V, furthermore contains one or more kinds among 0.01 to 1.5% Mn, 0.01 to 0.6% Cr, 0.01 to 0.25% Zr and 0.0001 to 0.08% B and the balance Al. Fe improves the weldability and stress corrosion cracking resistance, but in the case of more than the upper limit, the toughness and workability are deteriorated. Cu improves the stress corrosion cracking resistance, but in the case of more than the upper limit, the weld cracking is easy to produce. Ti improves the strength and weldability, but in the case of more than the upper limit, the toughness and workability are deteriorated. V improves the stress corrosion cracking resistance, but in the case of more than the upper limit, the workability and toughness are deteriorated. Mn, Cr, Zr and B improve the strength and stress corrosion cracking resistance, but in the case of more than the upper limit, the toughness and workability are deteriorated.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a high-strength aluminum alloy used for welded structural materials, and more specifically, to an Al-Zn-Mg-based high-strength aluminum alloy for welding that has excellent stress corrosion cracking resistance. Regarding aluminum alloys.

[Prior Art] In recent years, buildings, vehicles, ships, aircraft, etc. have become increasingly thin and lightweight, and the demand for weldable high-strength aluminum alloys has increased. Conventionally, aluminum alloys for these uses include A1-Zn-Mg alloys and A1-Zn-Mg alloys.
l-Zn Mg-Cu alloys have been considered. This type of high-strength aluminum alloy becomes stronger as the Zn and Mg contents increase, but there is a tendency for stress corrosion cracking susceptibility and welding cracking susceptibility to increase accordingly, and also for hot processing such as rolling. Sexuality also deteriorates.

A7075 alloy is a typical high-strength aluminum alloy that can be formed by rolling and is used for structural materials. The strength of this alloy is among the highest among aluminum alloys, but because it contains Cu, its weldability is extremely poor, and it must be joined by mechanical joining such as bolting or rivets. In addition, since this alloy is highly susceptible to stress corrosion cracking, conventional T6 treatment, which is the heat treatment that originally provides the highest strength, has the risk of causing stress corrosion cracking, so tempering at a higher temperature or for a longer time is required. It is often used with T7 treatment to stabilize the tissue.

However, the strength of the T7 treated material is lower than that of the T6 treated material.

Among the 7000 series aluminum alloys, A7NO1 and A7003 are known as aluminum alloys that can be formed by rolling and have excellent weldability and stress corrosion cracking resistance. However, these alloys have relatively low strength and are therefore unsuitable for applications requiring higher strength. As mentioned above, with conventional techniques, it has been extremely difficult to obtain an aluminum alloy that is satisfactory in all aspects of strength, stress corrosion cracking resistance, and weldability, and also has excellent formability such as rolling.

[Problem to be solved by the invention]

The purpose of the present invention is to provide a plate material that satisfies all aspects of strength, stress corrosion cracking resistance, and weldability, which have not been possible with conventional techniques, and also has excellent formability such as rolling. That is.

[Means to solve the problem]

The present inventors focused on the above-mentioned circumstances, and found that the above-mentioned material was satisfied in all aspects of strength, stress corrosion cracking resistance, and weldability, and was also excellent in formability such as rolling. In hopes of developing an aluminum alloy, various studies were conducted by changing the types and content of alloy components.

As a result, it was discovered that the above object could be achieved by specifying the type and content of the alloy components as described below, and the present invention was completed.

That is, in the present invention, Zn is 4 to 8 wt%, Mg is 0.3 to 3.
0 wt%, Fe 0.01-1 wt%, Cu 0.
01-1 wt%, T i 0.005-0.2 wL%
, V0.1 to 0.2 wt%, and further contains M n0.
01-1.5wt%, Cr0.01-0.6-t%, Z
r 0.01~0.25wt%, B 0.0001~
This is a high-strength aluminum alloy for welding that has excellent stress corrosion cracking resistance and is characterized by containing one or more of 0.08 wt% and the remainder consisting of aluminum and unavoidable impurities.

[Effect]

The reasons for adding the components of the aluminum alloy according to the present invention and the reasons for their limitations will be described below.

Zn forms fine Zn-Mg precipitates together with Mg and contributes to the strength of the material. If the content is less than 4.0 wt%, the effect will not be sufficient, and if it exceeds 8 ht%, stress corrosion cracking resistance, weldability, and workability will deteriorate.

Like Zn, Mg is an essential element for improving strength, and if the content is less than 0.3 wt%, sufficient strength cannot be obtained.
3. If the content exceeds OwL%, stress corrosion cracking resistance,
Weldability and workability deteriorate.

Fe has the effect of improving weldability and refining the structure of the material to improve stress corrosion cracking resistance. If the content is less than 0.01 wt%, sufficient effects cannot be obtained; If the content exceeds Owt%, toughness and workability will deteriorate.

Cu is an element that improves stress corrosion cracking resistance, and if the content is less than 0.01 wt%, a sufficient effect cannot be obtained;
If the content exceeds 11 t%, weld cracking is likely to occur.

Ti is an element that refines the structure and improves weldability, but if the content is less than 0.005 wt%, a sufficient effect cannot be obtained, and if the content exceeds 0.2 wt%, it will be a huge product. There is a high risk that this will result in deterioration of toughness and workability.

■ is an element that improves stress corrosion cracking resistance, and if the content is less than 0.01 wt%, a sufficient effect cannot be obtained;
．． If the content exceeds 1 wt%, workability and toughness will decrease.

Mn, Cr5Zr, and B all have the effect of refining the structure and improving strength and stress corrosion cracking resistance. If the content is below each lower limit, these effects will not be sufficient,
If the content exceeds the upper limit, giant products will occur and the toughness,
There is a risk of deteriorating workability.

The impurities contained in the alloy of the present invention are Si<0.2
wt%, N i <Q, Q3t%, A g <0.
If the amount of other elements alone is less than 0.03 wt%, the properties of the alloy of the present invention will not deteriorate.

〔Example〕

An embodiment of the present invention will be described below. Alloys having the compositions of the present alloy, comparative alloy, and conventional alloy shown in Table 1 were cast into ingots having a thickness of 300++ uu and a width of 800 mm by DC casting. After homogenizing this ingot at 490°C for 12 hours, it was hot rolled (450'C) and cold rolled into a plate material with a thickness of 5 am. After rolling each material, 480
Quenched after solution treatment for 1 hour at 120 °C and 24 hours at 120 °C.
Tempering treatment was performed for an hour.

Table 2 shows the results of tensile tests, stress corrosion cracking tests, and weld cracking tests performed on the materials thus manufactured.

Test method (1) Tensile test (a) Test piece: JIS Z 2201 No. 5 test piece (b) Test method: Amsler universal testing machine, JIS
Test based on Z2241.

(C) Measured values: Measure tensile strength, yield strength, and elongation, and judge based on the following criteria.

O...Tensile strength 50 kgf/- or more Δ...Tensile strength 40 kgf/- or more and less than 50 kgf/-x...Tensile strength less than 40 kgf/- (2) Stress corrosion cracking test (a) Test piece: JIS H8711 No. 1 test piece (c) Test method: Based on JIS H8711.

Stress load: Using a No. 4 test piece jig, load 75% of the proof stress with test solution, immersion: 3.5% NaCl solution, alternating immersion (10 minute immersion cycle, 50 minute drying) 30 days: Stress corrosion Observation of the presence or absence of cracking O...Cracking occurred, ×...No cracking (3) Weld cracking test (C) Evaluation [Yes]) Welding conditions: Welding method...TiG filler metal...
・Not used Electrode: Tungsten rod containing thorium, 3.2 mm Welding current: 180 A Arc voltage: 19 V Welding speed: 30 CIn/min Argon gas flow rate: 1Oj! /cAin(C) Crack evaluation: Measure the crack length and judge based on the following criteria.

O...Crack length less than 30ffllB△...Crack length 30ffi11 or more and less than 50trm×
...Crack length of 50 mm or more As is clear from Table 2, the present invention alloys Nα1 to 4 were all excellent in strength, stress corrosion cracking resistance, and weldability, whereas the comparative alloys Nα5 to 7. Conventional alloy 8
~IO was inferior in some properties.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an aluminum alloy for welded structures that has higher strength than conventional alloys and has excellent stress corrosion cracking resistance. Compared to the case of conventional alloys, this material can better meet the demand for thinner and lighter welded structural materials, and has a significant industrial effect.

[Brief explanation of drawings]

FIG. 1 shows a plan view of a Finschborn crack test piece. 1...Fishbone-shaped crack test piece, 1a...
・Weld bead, 1b...Weld crack, lc...
・Crack length, 1d...Welding direction

Claims (1)

[Claims] Zn4-8wt%, Mg0.3-3.0wt%, Fe
0.01-1wt%, Cu0.01-1wt%, Ti0
．． 005-0.2wt%, V0.1-0.2wt%, and further contains Mn0.01-1.5wt%, Cr0.0
1-0.6wt%, Zr0.01-0.25wt%, B
A high-strength aluminum alloy for welding having excellent stress corrosion cracking resistance, characterized in that it contains one or more of 0.0001 to 0.08 wt%, and the remainder consists of aluminum and unavoidable impurities.