JPH03122247A - 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 7% Zn, 0.3 to 3.0% Mg, 0.03 to 0.4% Ag, 0.01 to 1% Fe, 0.01 to 1% Cu, 0.05 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. Ag improves the stress corrosion cracking resistance and strength, but in the case of more than the upper limit, the weldability is deteriorated. Fe improves the weldability, 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 ore than the upper limit, the weld cracking property is deteriorated. 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 toughness is deteriorated. Mn, Cr, Zr and B stabilized the structure, 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 as rolled materials, extruded materials, and forged materials.

For more details, see Aluminum for welding with excellent stress corrosion cracking resistance.
-Relating to a Zn-Mg-based high-strength aluminum alloy.

(Conventional technology and its issues) In recent years, in architecture, vehicles, ships, aircraft, etc.

As aluminum alloys become thinner and lighter, the demand for weldable high-strength aluminum alloys is increasing. Conventionally, Al-Zn-Mg alloys and Al-Zn-Mg-Cu alloys have been considered as aluminum alloys for these uses. This type of high-strength aluminum alloy becomes stronger as the Zn and Mg contents increase, but there is a tendency for stress corrosion susceptibility and welding agent susceptibility to increase accordingly, and also for rolling.

Hot workability in extrusion, forging, etc. also deteriorates.

A707 is a typical high-strength aluminum alloy used for structural materials, and can be formed by rolling, extrusion, forging, etc.
There are 5 alloys. The strength of this alloy is among the highest among aluminum alloys, but because it contains Cu, weldability is extremely poor, and joints are bolted.

Must be mechanically joined by rivets, etc.

Additionally, the alloy is highly susceptible to stress corrosion cracking.

Conventionally, T6 treatment, which is the heat treatment that originally provides the highest strength, carries the risk of stress corrosion cracking.

It is often used in T7 treatment, which stabilizes the structure by tempering at a higher temperature or for a longer time.

Among the 7000 series aluminum alloys, A7NO1 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. In addition, A7003 with good extrudability also has good weldability.
An aluminum alloy with excellent stress corrosion cracking resistance. However, these alloys have relatively low strength and are therefore unsuitable for applications requiring higher strength. As mentioned above, it is extremely difficult to obtain an aluminum alloy that satisfies all aspects of strength, stress corrosion cracking resistance, and weldability using conventional techniques, and also has excellent formability through extrusion, rolling, forging, etc. Met.

(Problems to be Solved by the Invention) The present invention satisfies all aspects of strength, stress corrosion cracking resistance, and weldability that could not be solved by conventional techniques, and furthermore, extrusion, rolling! The purpose of this invention is to provide a material that has excellent moldability such as two-layer construction.

(Means for Solving the Problems) The present inventors focused on the above-mentioned circumstances, and found that satisfaction was obtained in all of the above five aspects of strength, stress corrosion cracking resistance, and weldability, and moreover, Extrusion, rolling.

In order to develop an aluminum alloy with excellent formability during forging, etc., we changed the type and content of one alloy component.

Various considerations were made. As a result, we found that the above object could be achieved by specifying the types and content of the alloy components as shown below.1 We completed the present invention.

That is, 1. The composition of the high-strength aluminum alloy for welding which is excellent in stress corrosion cracking resistance according to the present invention is as follows: 4-7% Zn, Mg
0.3-3.0% by weight, Ag0.03-0°4% by weight,
Fe0.01-1% by weight, Cu0.01-1% by weight
, Ti0.005-0.2% by weight, V0.01
~0.2% by weight, and Mn0.01~1.5
Weight % Cr 0.01=0.6 weight % Z r 0.
01-0.25 heavy view.

At least one of 80.0001 to 0.08
The gist is that it contains one or more species, and the remainder consists of aluminum and unavoidable impurities.

(Function) The reasons for limiting the types and contents of the components of the aluminum alloy according to the present invention are as follows.

Zn is an essential element for increasing the strength of alloys as a hardening element, and if the content is less than 4% by weight, its effect will be small, and if it exceeds 7% by weight, stress corrosion cracking resistance, weldability, and workability will be reduced. deteriorates. The most preferable content of Zn is 4~
It is 7% by weight.

Mg, like Zn, is an element essential for improving strength; if the content is less than 0.3% by weight, sufficient strength cannot be obtained, and if the content exceeds 3.0% by weight, the stress resistance will be reduced. Corrosion cracking, weldability, and workability deteriorate. Therefore, the most preferable Mg content is 0.3 to 3.0% by weight.

Ag is an element that improves stress corrosion cracking resistance and strength. If the content is less than 0.03% by weight, the effect is small, and if the content exceeds 0.4% by weight, there is a risk of deterioration of weldability. be. Therefore, the most preferable AgO content is 0
．． 03 to 0.4% by weight.

Fe is an element that improves weldability, and the content is 0.
If the content is less than 1.0% by weight, the effect will be small, and if the content exceeds 1.0% by weight, the toughness and workability will deteriorate. Therefore,
The most preferable content of Fe is 0.01 to 1.0% by weight.

Cu is an element that improves stress corrosion cracking resistance.If the content is less than 0.01% by weight, the effect is small, and if it is contained in excess of 1% by weight, the weld cracking property is deteriorated. Therefore, the most preferable content of Cu is 0.01-1% by weight.
It is.

Ti is an element that refines the three structures and improves weldability, but if the content is less than 0.005% by weight, the main effect is small, and if the content exceeds 0.2% by weight, giant compounds will be generated. There is a risk of deterioration of toughness and workability. Therefore, the most preferable content of 5Ti is 0.005 to 0.2% by weight.

(2) is an element that improves stress corrosion cracking resistance, and if the content is less than 0.01% by weight, its main effect will be small;
If the content exceeds 2% by weight, the toughness will deteriorate. Therefore, the most preferable content of (1) is 0.01 to 0.2% by weight.

Mn, Cr, Zr, and B are all elements that are added to stabilize the structure, and one or more types are added, but when the content is less than 0.01% by weight of Mn, Cr
．． Less than 0.01 weight%, Zr less than 0.01% by weight, 80.
If it is less than 0.0001% by weight, the effect of grain refinement will be reduced;
If B exceeds 0.25% by weight and B exceeds 0.08% by weight, a giant compound will be generated and there is a risk of deteriorating toughness and workability.

In the alloy of the present invention, it is necessary to limit Si and Ni as impurities to less than 0.2% by weight of Si and less than 0.03% by weight of Nj. If each content exceeds the limit value, weldability will be deteriorated.

〔Example〕

An embodiment of the present invention will be described below.

Alloys having the compositions of the present alloy, comparative material, and conventional alloy shown in Table 1 were cast into extrusion ingots (9 inch diameter) using a semi-continuous water-cooled casting device. This 9-inch diameter rod-shaped ingot was
After homogenization at 0°C for 12 hours, they were heated to 430'C and made into 5mm thick and 100mm wide pieces using an extruder.
It was extruded into a rectangular piece of mm. During extrusion processing, the extrudability of each alloy was evaluated using the maximum extrusion speed at which the rectangular material 5 could be extruded without surface defects or cracks. The results are shown in Table 2. Each material is heated to 460°C after extrusion.
After solution treatment at 1 hour, quenching was performed, and tempering treatment was performed at 120'C for 24 hours.

Table 2 also shows the results of tensile tests, stress corrosion cracking tests, and weld cracking tests performed on the materials produced in this way. The test method is shown below.

[Test method] (1) Workability (extrudability) (a) Extrusion conditions: Ingot size -------9 inch diameter (219II+a+φ) Extrusion temperature ---1----430" C (b) Extrusion size: 5 nm x 100 mgm (c) Evaluation method: Judgment was made based on whether the extrusion speed was equivalent to A7075.

○・-A 7075 limit extrusion speed or higher×・-・A70
(2) 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: Tensile strength, yield strength, and elongation are measured and judged based on the 9th standard.

0-1 Tensile strength 50 kg4/mm” or more Δ-Tensile strength 40 kgf/- or more and less than 50 kgf/-×-Tensile strength 4
Less than 0 kgf/l1l11'' (3) Stress corrosion cracking test (a) Test piece: JIS H8711 No. 1 test piece (b) Test method: Based on JIS H8711.

Jig for stress loading/No. 1 test piece Load 75% of proof stress using Test solution: immersion/3.5s NaC5 solution.

Alternate immersion (10 minute immersion cycle).

50 minutes drying) 30 days (c) Evaluation : Observation of occurrence of stress corrosion cracking 〇-No cracking X: Cracking occurred.

(4) Weld cracking test (b) Welding conditions: Welding method---TIG filler metal No electrode---Thorium tungsten rod, 3. 2mn+φ Welding current--180A Arc voltage--19■ Welding speed--30cm/ff1in Argon gas flow! ---101A/l1in (c) cracking evaluation:
Measure the crack length and judge based on the 9th standard.

○--Crack length less than 30mm Δ-・-Crack length 30mm or more Less than 50mm ×・・・-Crack length 501 or more From the results in the table, all of the results are according to the invention example.

The extrusion workability 1 strength, stress corrosion cracking resistance, and weldability were all excellent, whereas the comparative alloy and conventional alloy were inferior in any of the properties.

(Effects of the Invention) As can be understood from the above, the present invention provides an aluminum alloy for welded structures that has higher strength than conventional alloys, has excellent stress corrosion cracking resistance, and It is possible to provide an aluminum alloy for welded structures that has hot workability such as extrusion, rolling, and forging.

Compared to conventional alloys, it can better meet the demands for thinner and lighter welded structural materials.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a fishbone crack test piece. 1...Fishbone-shaped crack test piece, 1a...
・Weld bead, 1b...Weld crack, lc...
・Crack length, ld...Welding direction.

Claims (1)

[Claims] Zn4-7% by weight, Mg0.3-3.0% by weight, Ag
0.03-0.4% by weight, Fe0.01-1% by weight, C
u0.01-1% by weight, Ti0.005-0.2% by weight
, V0.01 to 0.2% by weight, and Mn0.
01-1.5% by weight, Cr0.01-0.6% by weight, Z
r0.01-0.25% by weight, B0.0001-0.0
A high-strength aluminum alloy for welding having excellent stress corrosion cracking resistance, characterized in that it contains at least one or two or more of 8% by weight, and the remainder consists of aluminum and unavoidable impurities.