JPH06346177A - Aluminum alloy for weld structure excellent in stress corrosion cracking resistance and proof stress value after welding - Google Patents

Abstract

PURPOSE:To improve strength, weld crack resistance, and hot workability by specifying Mg, Mn, Cr, Cu, Fe+Si, Zr, Ni, etc. CONSTITUTION:The Al alloy has a composition containing, by weight, 4-8% Mg, 0.32-1.5% Mn, 0.03-0.5% Cr, 0.03-1% Cu, 0.1-1.5% (Fe+Si) so that Fe/Si>2 is satisfied, 0.01-0.25% Zr, and 0.01-0.25% Ni as essential components. Moreover, one or more kinds selected from 0.005-0.2% Ti, 0.0001-0.08% B, 0.03-0.5% Mo, 0.01-0.2% V, and 0.03-5% rare earth element or misch metal are further incorporated. This Al alloy has superior strength including proof stress value after welding, stress corrosion cracking resistance, weld crack resistance, and further hot workability, such as in extrusion, rolling, and forging.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy used as a welded structural material as a rolled material, an extruded material, or a forged material, and more specifically, a welded structure excellent in stress corrosion cracking resistance and a yield strength value after welding. Al-Mg-Mn-based aluminum alloy for use.

[0002]

[Prior art and its problems] Conventional construction, automobiles, vehicles,
In vessels, etc., A5052 and Al, which are Al-Mg alloys with moderate strength, good workability, good corrosion resistance, and good weldability.
A5083, 5456 and the like, which are --Mg--Mn based alloys, were often used. The strength of these aluminum alloys containing Mg as the main additive element increases as the amount of Mg increases, but if the amount of Mg exceeds 3.5%, stress corrosion and peeling corrosion occur in a corrosive environment of 66 ° C or higher. In addition, the hot workability of rolling, extrusion, forging, etc. will deteriorate. Although alloys such as A5052, which is a low Mg content alloy, do not have the risk of stress corrosion cracking, it is necessary to use a thicker material than the high Mg content alloy because of its low strength.
A5083 and 5456 alloys containing Mg in excess of 5% may cause stress corrosion cracking. Further, the conventional A5083 and 5456 alloys containing more than 3.5% Mg have a high yield strength value before welding (in other words, the yield strength value of the base metal), but there is a resentment that the yield strength value decreases after welding. . In recent years, structures such as buildings, automobiles, vehicles, and ships have been made thinner and lighter, and along with that, the strength is high, and welding is possible without the risk of stress corrosion cracking. The demand for aluminum alloys with high yield strength is increasing. However, as described above, the conventional technology is an aluminum alloy that is satisfactory in terms of strength capable of coping with thinning, stress corrosion cracking resistance, and weldability, and is also excellent in formability such as extrusion, rolling, and forging. It was very difficult to get.

[0003]

DISCLOSURE OF THE INVENTION The present invention is not able to be solved by the conventional techniques, but in all aspects of strength including stress resistance after welding, stress corrosion cracking resistance, and weldability (welding crack resistance). It is an object of the present invention to provide a material which is satisfactory and is excellent in hot workability such as extrusion, rolling and forging.

[0004]

[Means for Solving the Problems] The inventors have paid attention to the above-mentioned circumstances, and have evaluated the strength including the proof stress value after welding, stress corrosion cracking resistance, and weldability (welding crack resistance) as described above. With the aim of developing an aluminum alloy that is satisfactory in all aspects and is also excellent in hot workability such as extrusion, rolling, and forging, various types of alloy components and contents were investigated. As a result, they have found that the above object can be achieved by specifying the type and content of alloy components as described below, and have completed the present invention.

That is, the structure of the aluminum alloy for welded structure excellent in the stress corrosion cracking resistance and the yield strength value after welding according to the present invention is as follows. The first invention is Mg4.0 to 8.0% by weight, Mn0.
32-1.5% by weight, Cr0.03-0.5% by weight, Cu0.03-
1.0% by weight, Fe + Si 0.1 to 1.5% by weight and Fe /
Si> 2, Zr 0.01 to 0.25 wt%, Ni 0.01 to 0.25
% Of Ti is an essential component, and 0.005 to 0.2% by weight of Ti, 0.0001 to 0.08% by weight of B, 0.03 to 0.5% by weight of Mo, 0.01 to 0.2% by weight of V, 0.03 to 5.0% by weight of rare earth element or misch metal. The second invention is characterized in that it contains one or more of them, and the balance is Al and inevitable impurities. The second invention is Mg4.0 to 8.0% by weight, Mn0.32 to
1.5% by weight, Cr 0.03 to 0.5% by weight, Cu 0.03 to 1.0% by weight, Ag 0.03 to 1.0% by weight, Fe + Si 0.1 to
Fe / Si> 2, Zr 0.01 to 0.25% by weight, Ni 0.01 to 0.25% by weight, and Ti 0.005 to 0.2% by weight, B 0.0001 to 0.08% by weight, Mo 0.03 to 0.5% by weight. % By weight, V 0.01 to 0.2% by weight,
It is characterized in that it contains one or more of 0.03 to 5.0% by weight of a rare earth element or misch metal, and the remaining Al and unavoidable impurities.

[0006]

The reason for limiting the types and contents of the components of the aluminum alloy according to the present invention will be described as follows.

Mg is an element essential for improving strength,
If the content is less than 4.0% by weight, sufficient strength cannot be obtained.
If it is contained in excess of 0% by weight, stress corrosion cracking resistance and workability are extremely deteriorated and it is difficult to improve it by adding a trace amount of elements.
Therefore, the most preferable content of Mg is 3.0 to 8.0% by weight.
Is.

[0008] Mn is an element that is indispensable for improving strength like Mg, and is an element that improves stress corrosion cracking resistance. If the content is less than 0.32% by weight, its effect is small. If it is contained in excess, the workability and weldability deteriorate. Therefore, the most preferable content of Mn is 0.32 to 1.
5% by weight.

[0009] Cr is an element for improving the strength and stress corrosion cracking resistance. If the content is less than 0.03% by weight, its effect is small, and if it exceeds 0.5% by weight, the workability and toughness are deteriorated. .

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

Fe and Si are elements that improve the weldability, but if the content of Fe + Si is less than 0.1% by weight, the effect is small, and if it exceeds 1.5% by weight, the toughness and workability deteriorate. To do. Further, if the Fe / Si ratio is less than 2, the effect of improving the weldability is small. Therefore, the most preferable contents of Fe and Si are Fe + Si 0.1 to 1.5% by weight and Fe / Si> 2.

Zr is an element that stabilizes the structure, prevents weld cracking, and improves the yield strength after welding. If the content is less than 0.01% by weight, the effect of crystal grain refinement is small and it is effective in preventing cracking. In addition, the yield strength cannot be improved. If Zr is contained in an amount exceeding 0.25% by weight, a huge compound is generated and there is a risk of degrading toughness and workability.
Therefore, the preferable content of Zr is 0.01 to 0.25% by weight.

Ni is an element that improves the yield strength after welding, and if the content is less than 0.01% by weight, the effect is small and 1.5
If it is contained in excess of weight%, the workability deteriorates. Therefore, the preferable Ni content is 0.15 to 1.5% by weight.

Ti and B are elements for refining the structure and improving weldability, and although addition of each alone is effective, addition of both at the same time is more effective. But,
If the content is less than 0.005% by weight of Ti and less than 0.0001% by weight of B, the effect is small. If the content exceeds 0.2% by weight of Ti and 0.08% by weight of B, a huge compound is generated and toughness and workability deteriorate. There is a risk of Therefore, the most preferable content of Ti is 0.005 to 0.2% by weight, and the most preferable content of B is 0.0001 to 0.08% by weight.

V is an element that improves the resistance to stress corrosion cracking and the resistance to welding cracking. If the content is less than 0.01% by weight, its effect is small, and if it exceeds 0.2% by weight, the toughness deteriorates. Therefore, the most preferable content of V is 0.01 to 0.2
% By weight.

The rare earth element or misch metal improves stress corrosion cracking resistance and weld cracking resistance.
If the content is less than 0.03% by weight, its effect is small, and if it exceeds 5.0% by weight, coarse crystallized substances are formed in the alloy and the strength is deteriorated. Therefore, the most preferable content of rare earth element or misch metal is 0.03 to 5.0% by weight. The rare earth elements are La, Ce, Pr, Nd, Sm, etc., and the misch metal is an alloy mainly composed of Ce, La, usually Ce45-50.
% By weight, La20-40% by weight, balance other rare earth elements (Nd,
Sm, Pr, etc.), both rare earth elements and misch metal have the same effect, but rare earth element alone is expensive and it is economically advantageous to add it as misch metal.

Mo is an element to be contained in order to stabilize the structure and prevent welding cracks. If the content is less than 0.03% by weight, the effect of grain refining is small and the effect of crack prevention is small. If it is contained in excess of 0.5% by weight, a huge compound will be generated, which may deteriorate the toughness and workability.

Further, Ag added to the second invention is an element for improving the stress corrosion cracking resistance and the proof stress value after welding. If the content is less than 0.03% by weight, its effect is small and 1.0% by weight. If it is contained in excess of%, the weldability deteriorates. Therefore, the most preferable content of Ag is 0.03 to 1.0% by weight.

[0019]

EXAMPLES An example of the present invention will be described below.
The alloys of the present invention, the comparative alloys, and the conventional alloys having the alloy compositions shown in Tables 1, 2, 3, and 4 were cast into ingots for extrusion (9 inch diameter) using a semi-continuous water-cooling casting device. After homogenizing this 9-inch diameter rod-shaped ingot for 12 hours at 530 ° C, 450 ° C
Heated to 5 mm and width of 1 by extruder.
It was extruded into a 00 mm flat bar. When extruding
The quality of the extrudability of each alloy was evaluated based on the maximum extrusion speed at which the flat rectangular material could be extruded without the occurrence of surface defects or cracks.
The results are shown in Tables 5, 6, 7, and 8. After extrusion, each material was subjected to 2% tensile reconditioning and H111 tempering. The results of the tensile test after welding, the stress corrosion cracking test, and the welding cracking test of the material thus manufactured are shown in Tables 5, 6, 7, and 8 together.

These test methods are shown below. (1) Workability (extrudability) (a) Extrusion conditions: Ingot size: 9 inch diameter (21
9 mmφ) Extrusion temperature: 450 ° C. (b) Extrusion size: 5 mm × 100 mm (c) Evaluation method: Judgment was made based on whether or not the extrusion speed was equal to 5456. ○ ─ equivalent to or higher than the 5456 limit extrusion rate × ─ ─ less than the 5456 limit extrusion rate (2) (a) Welding material: H111 temper (after extrusion, perform 2% tensioning) (b) Welding Method: MIG fully automatic welding (c) Welding conditions: Groove shape I-shape butt welding Welding wire A5356WY 1.2mmφ Welding current 200A Arc voltage 24V Welding speed 50cm / min Shield gas (argon gas) flow rate 25l / min (3) Tension Test (a) Test piece: JIS Z 2201 No. 5 test piece (b) Test method: Amsler universal testing machine, JIS Z 22
Test according to 41. (C) Measured value: Tensile strength, proof stress, and elongation are measured,
Judgment is based on the following criteria. ○ ─ Proof strength value 177 N / mm ² or more × ── Proof strength value less than 177 N / mm ² (4) Stress corrosion cracking test (a) Test piece: JIS H 8711 No. 1 test piece (b) Test method: JIS H 8711 based on. Sensitization treatment-180 ° C x 1000 hours heating Stress load-Using the jig for No. 1 test piece, 75% of the proof stress is a test solution, dipping-3.5% NaCl solution alternating dipping (cycle 10 minutes dipping, 50 minutes drying ) 30 days (c) Evaluation: Observation of occurrence of stress corrosion cracking × ── Crack occurrence ○ ── No crack occurrence (5) Weld crack test (a) Test piece: Fishbone type crack test piece shown in FIG. (B) Welding conditions: Welding method ── TIG filler metal ── Without using electrode ──── Thorium-containing tungsten rod, 3.2 mmφ welding current ─180A arc voltage ─19V welding speed ──30 cm / min Argon gas flow rate--10 l / min (c) Crack evaluation: Measure the crack length and judge according to the following criteria. ○ --Crack length less than 30 mm × --Crack length 30 mm or more

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

[Table 5]

[0026]

[Table 6]

[0027]

[Table 7]

[0028]

[Table 8] As is clear from Tables 5, 6, 7, and 8, the present invention alloy N
o. All of 1 to 7 and 31 to 37 were excellent in extrusion processability, strength, stress corrosion cracking resistance, and weldability, whereas the comparative alloy and conventional alloy were inferior in any of the properties.

[0029]

As described above, in the alloy of the present invention, as an aluminum alloy for welded structure, it has strength and weld cracking resistance superior to those of conventional alloys, and is excellent in stress corrosion cracking resistance. Good hot workability such as extrusion, rolling, forging, etc., compared to conventional alloys
Further, it can suitably meet the demand for thinning and lightening as a welded structural material.

[Brief description of drawings]

FIG. 1 is a plan view showing a fishbone-shaped crack test piece.

[Explanation of symbols]

 1a Weld bead 1b Weld crack 1c Crack length 1d Welding direction

Claims (2)

[Claims] 1. Mg4.0-8.0% by weight, Mn0.32-1.5
% By weight, Cr 0.03 to 0.5% by weight, Cu 0.03 to 1.0% by weight, Fe + Si 0.1 to 1.5% by weight and Fe / Si>
2, Zr 0.01 to 0.25% by weight, Ni 0.01 to 0.25% by weight as an essential component, and Ti 0.005 to 0.2% by weight, B
0.0001 to 0.08% by weight, Mo 0.03 to 0.5% by weight, V 0.
01 to 0.2% by weight, rare earth element or misch metal 0.03 to
Contains one or more of 5.0% by weight, balance A
Aluminum alloy for welded structure, which is excellent in stress corrosion cracking resistance and proof stress value after welding, characterized by comprising 1 and unavoidable impurities. 2. Mg4.0-8.0% by weight, Mn0.32-1.5
% By weight, Cr 0.03 to 0.5% by weight, Cu 0.03 to 1.0% by weight, Ag 0.03 to 1.0% by weight, Fe + Si 0.1 to 1.5% by weight and Fe / Si> 2, Zr 0.01 to 0.25% by weight, N
i 0.01 to 0.25% by weight as an essential component, and Ti0.
005 to 0.2% by weight, B 0.0001 to 0.08% by weight, Mo 0.0
3 to 0.5% by weight, V 0.01 to 0.2% by weight, rare earth element or misch metal 0.03 to 5.0% by weight, containing one or more of them, and the balance consisting of Al and unavoidable impurities An aluminum alloy for welded structures with excellent corrosion cracking resistance and proof stress after welding.