JPH0413833A - High strength aluminum alloy for welding excellent in stress corrosion cracking resistance - Google Patents

Abstract

PURPOSE:To improve the stress corrosion cracking resistance, strength, and weldability of an aluminum alloy by adding trace amounts of Ag, V and rare earth elements or misch metal to an Al-Zn-Mg-Cu series alloy. CONSTITUTION:The compsn. of a high strength Al alloy for welding is formed of, by weight, 5 to 8% Zn, 1.2 to 4.0% Mg, 1.5 to 4.0% Cu, 0.03 to 1.0% Ag, 0.03 to 5.0% rare earth elements or misch metal, 0.01 to 1.0% Fe, 0.005 to 0.2% Ti, 0.01 to 0.2% V, and the balance Al with inevitable impurities. Furthermore, at least one kind among 0.01 to 1.5% Mn, 0.01 to 0.6% Cr, 0.01 to 0.25% Zr, 0.0001 to 0.008% B, and 0.03 to 0.5% Mo is incorporated therein. Ag improves its stress corrosion cracking resistance and strength. V improves it stress corrosion cracking resistance. This alloy has high strength as the material for welded structures and excellent in formability in extruding, rolling, forging or the like.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to high-strength aluminum alloys used as rolled materials, extruded materials, and forged materials for welded structural materials. AI-Zn-Mg for welding
Regarding high-strength aluminum alloys.

(Prior art and its problems) In recent years, construction, 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 Al-Zn-Mg alloys and A
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 susceptibility and weld cracking 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, 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, 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.

(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 strength, stress corrosion cracking resistance, and weldability, and moreover, Extrusion, rolling.

With the aim of developing an aluminum alloy with excellent formability during forging, etc., we changed the types and content of the five alloy components.

Various considerations were made. 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.

Namely, the composition of the high-strength aluminum alloy for welding having excellent stress corrosion cracking resistance according to the present invention is as follows: Zn: 5-8% by weight, weight: GL: 2-4.0% by weight, Cu: 1.5-4.0% by weight.
, Ag0.03-1.0% by weight, Rare earth element or Mitsushi metal 0.03-5.0% by weight Weight e0.01-1.0
Weight %, T io, 005-0.2 weight %, V0.0
1 to 0.2% by weight, and M n O,01
~1.5% by weight, CrO, 01~0.6% by weight,
, Z ro, 01-0.25% by weight, 80.0001
~0.08% by weight, M o 0.03-0.5% by weight
Contains at least one or two or more of the following.

The gist is that the remainder consists of aluminum and unavoidable impurities.

That is, the present invention is /M! This is a Zn-Mg-Cu alloy with improved stress corrosion cracking resistance, strength, and weld cracking resistance by adding Ag, V, and rare earth elements or Mitsushi metal.

(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; if the content is less than 5% by weight, its effect will be small, and if it exceeds 8% by weight, it will reduce stress corrosion cracking resistance, weldability, and workability. deteriorates. The most preferable content of Zn is 5~
It is 8% by weight.

Mg, like Zn, is an element essential for improving strength; if the content is less than 1.2% by weight, sufficient strength cannot be obtained, and if the content exceeds 4.0% by weight, the stress resistance will be reduced. Corrosion cracking, weldability, and workability deteriorate. Therefore, the most preferable Mg content is 1.2 to 4.0% by weight.

Cu, like Zn, is an element essential for improving 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, the stress resistance will be reduced. Corrosion cracking, weldability, and workability deteriorate. Therefore, the most preferable content of Cu is 1.5 to 4.0% 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 Ag content is 0.03 to 1.
It is 0% by weight.

Rare earth elements or Mitsushi metals improve stress corrosion cracking resistance and weld cracking resistance.

If the content is less than 0.03% by weight, the effect will be small.

If it exceeds 5.0% by weight, coarse crystallized substances will form in the alloy.
Decreases strength. Therefore, the most preferable content of rare earth elements or metal is 0.03 to 5.0% by weight. Note that the rare earth element is La.

Ce, Pr, Nd, Sm, etc. Also, Mitsushi metal is an alloy whose main components are Ce and La. 3 Usually Ce45~5
0% by weight, 20-40% by weight of La, and the balance other rare earth elements (Nd, Sm, Pr, etc.).Although both rare earth elements and Mitsushmemo have similar effects, rare earth elements alone are expensive. It is economically advantageous to add it as mitshu metal.

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, toughness and workability will deteriorate. Therefore,
The most preferable content of Fe is 0.01 to 1.0% by weight.

Ti is an element that refines the 9 structure and improves weldability, but if the content is less than 0.005% by weight, the effect is small, and if the content exceeds 0.2% by weight, giant compounds will be generated and the toughness will deteriorate. , there is a risk of deterioration of workability. Therefore,
The most preferable content of Ti is 0.005 to 0.2% by weight
It is.

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

Mn, Cr, Zr, B, and Mo are elements contained to stabilize the structure, and one or more types are added, but the content is less than 0.01% by weight of Mn,
Less than 0.01% by weight of Cr, less than 0.01% by weight of Zr,
If BO, 0OO is less than 1% by weight and Mo is less than 0.03% by weight, the effect of grain refinement will be reduced, and Mn3.0
Weight%, Cr0.6% by weight, Zr0.25% by weight, 8
If Mo is contained in an amount exceeding 0.08% by weight or more than 0.5% 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, Si and Ni are contained as impurities.
It is necessary to limit the content to less than 0.2% by weight of Si 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, they were heated to 430°C and made into pieces with an extruder, each with a thickness of 5 mm and a width of 100 m.
It was extruded into a rectangular piece of m. 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 way. The test method is shown below.

〔Test method〕

(1) Workability (extrudability) (a) Extrusion conditions: Ingot size---9 inch diameter (2
19mmφ) Extrusion temperature 430°C (b) Extrusion size: 5mm×100mm (c) Evaluation method: Judgment was made based on whether the extrusion speed was equivalent to A7075.

0---A More than the limit extrusion speed of 7075

Test based on JIS Z 2241.

(C) Measured values: Tensile strength, yield strength, and elongation are measured and judged based on primary standards.

O-Tensile strength 55 kgf/mm" or more Δ--Tensile strength 50 kgf/12 or more and less than 55 kgf/mm" x-Tensile strength less than 50 kgf/mm2 (3) Stress corrosion cracking test (a) Test piece : JIS H8711 No. 1 test piece (b) Test method: Based on JIS H8711.

Stress loading - Using a jig for No. 1 test piece, load 75% of the yield strength with test solution, immersion - Alternate immersion in 3,5zNaCI solution (50 minutes of immersion and drying) for 30 days (C) Evaluation: Stress corrosion cracking Observation of occurrence ×=-
Cracking ○ - No cracking (4) Weld cracking test (a) Test piece: Fishbone type test piece shown in Figure 1 (b) Welding conditions: Welding method - T I G filler Material---------Not used Electrode------) Tungsten rod with lithium, 3.2mmφ Welding current---180A Arc voltage・-19■ Welding speed--- ---30cm/ll1in argon gas flow rate -404! /min (c) Crack evaluation: Measure the crack length and judge based on secondary criteria.

〇-Crack length less than 30mm 8-Crack length 30 or more 50 less than mm ×-Crack length 50mm or more Table 2 From the results in the table, all of the results are according to the invention example.

While extrusion processability 2 strength, stress corrosion cracking resistance, and weldability were all excellent, comparative alloys, especially those containing Ag, V, rare earth elements, or minsch metals outside the scope of the present invention, and conventional alloys were all excellent. It was inferior in that characteristic.

(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, this material can better meet the demands for thinner and lighter welded structural materials.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a fishpone crack test piece. 1- Fishbone type crack test piece weld bead weld crack crack length welding direction

Claims (1)

[Claims] Zn5-8% by weight, Mg1.2-4.0% by weight, Cu1
．． 5 to 4.0% by weight, Ag 0.03 to 1.0% by weight, rare earth element or misch metal 0.03 to 5.0% by weight,
Fe0.01-1.0% by weight, Ti0.005-0.2
% by weight, V0.01-0.2% by weight, and M
n0.01~1.5% by weight, Cr0.01~0.6% by weight, Zr0.01~0.25% by weight, B0.0001~
A welding material with excellent stress corrosion cracking resistance characterized by containing at least one or two or more of 0.08% by weight and 0.03 to 0.5% by weight of Mo, with the remainder consisting of aluminum and unavoidable impurities. High strength aluminum alloy.