JPH03122246A - 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 1.0% Ag, 0.01 to 1% Fe, 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. 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 the more than the upper limit, the toughness and workability are 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 stabilize the structure, but in the case of more than the upper limit, the toughness and workability are deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a high-strength aluminum alloy used for welded structural materials as rolled materials, extruded materials, and 12-molded 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 weld cracking susceptibility to increase accordingly, and also for rolling.

Hot workability, such as extrusion, 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, the T6 treatment, which is the heat treatment that originally provides the highest strength, has the risk of stress corrosion cracking, so it cannot be used with the T7 treatment, which stabilizes the structure by tempering at a higher temperature or for a longer time. many.

Among the 7000 series aluminum alloys, A7NOl 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.

(Problem to be solved by the invention) The present invention cannot be solved using conventional techniques.

The purpose is to provide a material that is satisfactory in all aspects of strength, stress corrosion cracking resistance, and weldability, and that is also excellent in formability by extrusion, rolling, forging, etc.

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

With the aim of developing an aluminum alloy with excellent formability in forging and other processes, various studies were conducted by changing the type and content of one alloy component.

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

That is, 1. The composition of the high-strength aluminum alloy for welding having excellent stress corrosion cracking resistance according to the present invention is as follows: 4 to 7% by weight of Zn, Mg
0.3-3.0% by weight, Ag0.03-1.0% by weight,
F e0.01-1wt% Weight T i 0.005
~0.2% by weight, V0.01~0.2% by weight, and.

Mn 0.01-1.5% by weight, Cr 0.01
~0.6% by weight.

Z r 0.01-0.25 weight, B0.0O
At least one or two of O1 to 0.08 double fire
The gist is that it contains more than 100% of aluminum and the remaining 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 57% by weight, stress corrosion cracking resistance, weldability, and workability will deteriorate. to degrade. 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 decrease. 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 will be small, and if the content is more than 1.0% by weight, weldability will deteriorate. Therefore, the most preferable content of Ag is 0.03 to 1
．． It is 0% by weight.

Fe is an element that improves weldability, and the content is 0.
If it is less than 0.01% by weight, the effect will be small.

If the content exceeds 1.0% by weight, toughness and workability will deteriorate. Therefore, the most preferable content of Fe is 0.01-
It is 1.0% by weight.

Ti is an element that refines the m weave and improves weldability, but when the content is 0. If the content is less than 0.00% by weight, the effect will be small, and if the content exceeds -0.2% by weight, there is a risk that giant compounds will be generated and the toughness and workability will deteriorate. Therefore, the most preferable Ti content is 0. oos~0.2
Weight%.

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

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
．． 01% by weight, less than 0.01% by weight of Zr, B0.
If 0OO is less than 1% by weight, the effect of grain refinement will be reduced, and if Mn is 3.0% by weight, Cr is 0.6% by weight,
If the content exceeds 0.25 ml 1 Jt% of Zr and 0.01 ml 1 weight % of B, a giant compound will be generated and there is a risk of deteriorating toughness and workability.

In the alloy of the present invention, Si, Cu, and Ni are.

It is necessary to limit the impurities to less than 0.2% by weight of Si, less than 0.03% by weight of Cu, and less than 0.03% by weight of Ni. 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 homogenizing at 0°C for 12 hours, the mixture was heated to 430°C and extruded using an extruder into rectangular pieces each having a thickness of 5 mm and a width of 100 mm. During extrusion processing, the extrudability of each alloy was evaluated using the maximum extrusion speed at which the rectangular material could be extruded without surface defects or cracks. The results are shown in Table 2. After extrusion, each material was solution-treated at 460'C for 1 hour, quenched, and tempered 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 manner. The test method is shown below.

〔Test method〕

[1) Workability (extrudability) (a) Extrusion conditions: Ingot size: -9 inch diameter (219ms+φ) Extrusion temperature: -430°C (b ) Extrusion size: 5alIIlxlOOI (c) Evaluation method:
Judgment was made based on whether the extrusion speed was equivalent to A7075.

O...More than the limit extrusion speed of A7075 ×...Less than the limit extrusion speed of A7075 (2) Tensile test (a) Test piece: JIS Z 2201 No. 5 test piece (b) Test method: Amsler universal test Machine.

Test based on JIS Z 2241.

(c)ijl! I constant value: Measure tensile strength, yield strength, and elongation and judge based on primary standards.

0-1 Tensile strength 50 kgf/am" or more Δ...-
Tensile strength 40kgf/1Ila+" or more 50kgf/l
ll11! Less than x-...-Tensile strength less than 40 kgf/m+m" (3)
Stress corrosion cracking test (a) Test piece: No. 1 test piece of JIS 118711 (b) Test method: Based on LrS H8711.

Stress load / No. 1 test piece load 75% of proof strength using Test solution, immersion/3.5x NaCl solution.

Alternate immersion (10 minute immersion cycle).

50 minutes drying) 30 days (C) Evaluation: Observation of occurrence of stress corrosion cracking ×-・
-Cracking ○...No cracking (4) Weld cracking test (b) Welding conditions: Welding method---TIG filler metal---1---Not used Electrode-------Thorium-filled tungsten rod, 3.2mmφ Welding current---1BOA Arc voltage---19■ Welding speed---30cm/win Argon gas flow Ji ---1042/ll1n(c)
Crack evaluation: Measure the crack length and judge based on the 9th standard.

0-...Crack length less than 30mm Δ--Crack length 301℃ 1m or more and less than 50mm ×-
...Crack length: 50 mm or more According to the results in the table, none of the products according to the present invention were tested.

It was excellent in all of extrusion workability, strength, stress corrosion cracking resistance, and weldability, 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 the conventional alloy 5, and has excellent stress corrosion cracking resistance. We provide aluminum alloys for welded structures that have hot workability such as extrusion, rolling, and forging.

Compared to conventional alloys, this material 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. ■...Fishbone-shaped crack test piece, 1a...
・Weld bead, 1b...Weld crack, 1c...
・Crack length, 1d...Welding direction.

Claims (1)

[Claims] Zn4-7% by weight, Mg0.3-3.0% by weight, Ag
0.03-1.0% by weight, Fe0.01-1% by weight, T
Contains i0.005-0.2% by weight, V0.01-0.2% by weight, and Mn0.01-1.5% by weight, Cr
Contains at least one or two or more of 0.01 to 0.6% by weight, 0.01 to 0.25% by weight of Zr, and 0.0001 to 0.08% by weight of B, with the remainder consisting of aluminum and inevitable impurities. A high-strength aluminum alloy for welding with excellent stress corrosion cracking resistance.