JPH1024387A - Filler material foe aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of weld crack, to obtain high strength weld metal excellent in SCC resistance and to prolong the life (SSC life) causing stress corrosion crack of weld zone. SOLUTION: This filler material for aluminum alloy has a composition consisting of, by weight, 4.5-5.5% Mg, 0.3-0.9% Ag, 0.05-0.03% Zr, at least one king element selected among <=0.10 Mn, <=0.10 Cr and the balance Al with inevitable impurities and in which a content of Zr is larger than a content of Mn and a content of Cr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filler metal used for welding a welded structure made of an aluminum alloy, and more particularly to a filler metal for an aluminum alloy capable of improving stress corrosion cracking resistance.

[0002]

2. Description of the Related Art Al-Zn-Mg alloy materials have a relatively high strength and good weldability among various aluminum alloys, and are widely used as high strength aluminum alloy materials for welding structures. I have. On the other hand, Al-Zn-
The Mg-Cu alloy material has the highest strength among aluminum alloy materials, but it has been considered that practical welding is impossible because welding cracks easily occur. In addition, as a high-strength aluminum alloy material for welding structures, 2
Although there is 219 alloy, it is not generally used because of its extremely low corrosion resistance.

[0003] By the way, Al-Zn-Mg based alloys are
It is known that the strength increases as the content of g and Zn increases, while the stress corrosion cracking resistance (SCC resistance) decreases. Therefore, good weldability and SC resistance
Among the practical aluminum alloys satisfying both C properties, the aluminum alloy having the highest strength is JI
There is a S7N01 alloy, which contains Si: 0.30% by weight or less, Fe: 0.35% by weight or less, Cu: 0.20% by weight or less, Mn: 0.20 to 0.7% by weight, Mg:
1.0 to 2.0% by weight, Cr: 0.30% by weight or less, Zn: 4.0 to 5.0% by weight, V: 0.10% by weight or less, Zr: 0.25% by weight or less, Ti: 0.20% by weight or less, with the balance being Al and unavoidable impurities.

[0004] As described above, the 7N01 alloy satisfies both good weldability and SCC resistance. However, even if heat treatment (solution treatment, quenching, and aging treatment) is performed after welding, the 7N01 alloy is not affected. The strength is about 400 N / mm ² , which cannot be said to be high.

Japanese Patent Application Laid-Open No. 3-99793 discloses a filler metal for welding an Al-Zn-Mg alloy which has high strength and improves the SCC resistance of a welded portion. I have. The filler material is Mg: 3.0 to 8.0.
Wt%, Ti: 0.05 to 0.3 wt%, Zn: 0.
5 to 3.0% by weight, B: 0.001 to 0.2% by weight, Ag: 0.02 to 1.0% by weight, and Zr: 0.0
5 to 0.3% by weight, with the balance being Al and unavoidable impurities.

[0006]

However, the use of a filler material disclosed in Japanese Patent Application Laid-Open No.
When the l-Zn-Mg alloy material is welded, there is a problem that welding cracks are easily generated. So, conventionally,
Even when a high-strength aluminum alloy material is used as a material for a welded structure, the A
Al- with lower strength than l-Zn-Mg-Cu alloy material
Al-Mg based JIS 535
6 or a welding material such as JIS 5183.

As described above, even when a high-strength aluminum alloy material is used as the material of the welding base material, when the welding is performed using an Al-Mg-based filler material to suppress the occurrence of welding cracks, Since the strength of the welded joint is governed by the strength of the weld metal, a small amount of a diluting component from the base metal is mixed into the weld metal.
-The properties of an Mg-based alloy. Therefore, not only the condition of the welded joint as it is, but also the heat treatment after the welding (hardening after solution treatment, aging treatment), the aging property is reduced, so the strength of the weld metal is reduced. It is impossible to improve.

On the other hand, the SCC resistance of the weld metal is particularly low because the welded portion is liable to generate residual stress and the base metal and the weld metal have different mechanical and electrochemical properties. It is inferior to the base material. Therefore, stress corrosion cracking of welded structures often occurs at welds.

The present invention has been made in view of the above-mentioned problems, and it is possible to prevent the occurrence of welding cracks and obtain a high-strength weld metal having excellent SCC resistance. Accordingly, it is an object of the present invention to provide a filler metal for an aluminum alloy that can extend the life (SCC life) in which stress corrosion cracking of a weld occurs.

[0010]

According to the present invention, a filler metal for an aluminum alloy according to the present invention comprises: 4.5 to 5.5% by weight of Mg;
g: 0.3 to 0.9% by weight and Zr: 0.05 to 0.30% by weight, and selected from the group consisting of Mn: 0.10% by weight or less and Cr: 0.10% by weight or less. The composition is characterized by containing at least one element described above, the balance being Al and unavoidable impurities, and the content of Zr is larger than the content of Mn and the content of Cr.

It is preferable that the filler further contains 0.05 to 0.20% by weight of Ti.
It is desirable to contain 0.001 to 0.02% by weight.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In order to improve the SCC resistance of a welded part, it is most effective to add Ag to the filler metal. As a result of repeated intensive studies, it was found that the SCC resistance can be most improved in the range of 0.3 to 0.9% by weight.

Further, the present inventors have found that when the Ag content in the filler metal is in the range of 0.3 to 1.2% by weight, Ag has an adverse effect on the occurrence of weld cracks in the weld metal. Further, it has been found that the effect of preventing weld cracking is significantly improved by further adding 0.05 to 0.30% by weight of Zr as compared with the conventional filler metal.

Hereinafter, the chemical components contained in the filler metal for aluminum alloy in the present invention and the reasons for limiting the composition will be described.

Mg: 4.5 to 5.5% by weight Mg is a component that can improve the strength of the weld metal and also increase the effect of preventing weld cracking. When Mg in the filler is less than 4.5% by weight,
The effect of preventing welding cracks decreases. On the other hand, when Mg in the filler material exceeds 5.5% by weight, the SCC resistance of the welded portion decreases. Therefore, Mg in the filler metal is 4.5 to 5.5.
% By weight.

Ag: 0.3 to 0.9% by weight As described above, Ag is an element that can significantly improve the SCC resistance of a weld. Ag in filler metal is 0.3
If the amount is less than% by weight, the effect cannot be sufficiently obtained. On the other hand, if the content of Ag in the filler exceeds 0.9% by weight, the effect is adversely reduced, and the ductility is also reduced, so that the workability is deteriorated. It becomes difficult. Therefore, Ag in the filler metal is 0.3
To 0.9% by weight.

Zr: 0.05 to 0.30 wt% Zr is an element capable of refining the crystal grains of the weld metal. When the crystal grains in the welded portion are refined, the stress applied to the crystal grain boundaries is dispersed, so that the occurrence of welding cracks can be suppressed and the SCC resistance can be improved. If Zr in the filler is less than 0.05% by weight, the effect cannot be sufficiently obtained. On the other hand, if Zr in the filler material exceeds 0.30% by weight, huge crystals are likely to be generated in the weld metal, and the effect of refining the crystal grains is reduced, and the workability is reduced. Therefore, it becomes difficult to manufacture a filler material as a product. Therefore, Zr in the filler material is set to 0.05 to 0.30% by weight.

Mn: 0.10% by weight or less and / or C
r: 0.10% by weight or less Since Mn and Cr coexist with Zr, it is possible to refine the crystal grains of the welded portion, so that the effect of suppressing the occurrence of weld cracking and the effect of improving the SCC resistance are improved. Have. Therefore, in the present invention, one or both of Mn and Cr are contained in the filler material.
If the Mn and / or Cr content in the filler exceeds 0.1% by weight, huge crystals are likely to be generated, and Zr
In the same manner as described above, the effect of refining the crystal grains is reduced, and the workability is reduced, so that it becomes difficult to manufacture a filler metal as a product. Therefore, the filler material should contain 0.10% by weight or less of Mn and / or 0.10% by weight or less of Cr.

As described above, Mn and Cr may be used alone or Mn.
And Cr alone cannot provide the effect of refining the crystal grains, and conversely, welding cracks are likely to occur. Further, in order to prevent weld cracking, the contents of Mn and Cr are made smaller than the content of Zr, that is, the relationship of Zr content> Cr content and Zr content> Mn content is satisfied. It is necessary.

Ti: 0.05 to 0.20% by Weight Ti is also an element capable of suppressing cracking of the weld metal by making the crystal grains of the weld metal fine. For this reason, in the present invention, Ti can be contained in the filler as needed. If the content of Ti in the filler is less than 0.05% by weight, the effect cannot be sufficiently obtained. On the other hand, if the content of Ti in the filler exceeds 0.20% by weight, a compound with aluminum is formed, and the toughness of the weld metal is reduced. Therefore, when Ti is contained in the filler material, the Ti content in the filler material is preferably 0.05 to 0.20% by weight.

B: 0.001 to 0.02% by weight B is an element that can refine the crystal grains of the weld metal and suppress cracks in the weld metal similarly to Ti. Therefore, in the present invention, B can be contained in the filler as needed. If B in the filler is less than 0.001% by weight, the effect cannot be sufficiently obtained. On the other hand, when B in the filler exceeds 0.02% by weight,
Since the toughness of the weld metal is reduced and the viscosity of the molten metal is reduced, weld cracks are likely to occur and welding defects such as blow holes are promoted. Therefore,
When B is contained in the filler material, B in the filler material is 0.1%.
The content is preferably set to 001 to 0.02% by weight.

Since the filler metal for aluminum alloy of the present invention is an Al-Mg alloy, not only Al-Mg but also various other alloys such as Al-Zn-Mg alloy and Al-Mg-Si alloy. Applicable to aluminum alloy. In addition, since the workability is good, it can be processed into a welding wire, and can be used as a filler material in most welding methods such as laser welding, not limited to arc welding such as TIG welding and MIG welding. .

[0023]

EXAMPLES Examples of the filler metal for aluminum alloy according to the present invention will be specifically described below in comparison with comparative examples.

First, an aluminum alloy having the chemical components shown in Table 1 below was cast, and the diameter of the aluminum alloy was determined by an ordinary method.
For example, a 3.2 mm TIG welding rod was manufactured.

Next, using this TIG welding rod,
After welding, the weld crack resistance of the weld metal was evaluated by a Hold Craft crack test, and a tensile test and S
Mechanical properties and SCC resistance were evaluated by measuring the CC life. In the present example, Al-6.0% by weight and Zn-1.5% by weight having a plate thickness of 2 mm as a welding base material.
Mg material was used. Table 2 below shows the welding conditions for each test.

[0026]

[Table 1]

[0027]

[Table 2] The test method of each test is described below.

FIG. 1 is a plan view showing the shape of a welding base metal used in a Hold Craft crack test. As shown in FIG. 1, the welding base material 1 has slits 2 formed at equal intervals from both end surfaces toward the center in a direction orthogonal to the longitudinal direction, and the length of the slit 2 is Is formed so as to be deeper from one end face 1a in the longitudinal direction toward the other end face 1b. In the present embodiment, the length of the welding base material 1 is 76 mm, the width is 44.5 mm, the width of the slit 2 is 1.0 mm, and the distance between the slits 2 is 7.5 mm.
And The distance between the intersection between the line connecting the bottom 2a of the slit 2 and the one end surface 1a of the welding base metal 1 is 38 mm, and 70 mm from the line connecting the bottom 2a of the slit 2 and the one end surface 1a of the welding base material 1. Is 6.4 mm.

After welding the base material 1 thus formed to a plate (not shown), bead-on-plate welding was carried out along the welding destination 3. And the cracking resistance evaluated the ratio of the crack length to the total welding length as a crack rate.

The test piece for the tensile test was subjected to a butt welding by TIG welding, a solution treatment at a temperature of 450 ° C. for 30 minutes, water quenching, and a 24 ° C. at a temperature of 130 ° C.
From the test plate subjected to the time aging treatment (T6 treatment),
An IS No. 5 test piece was prepared by machining. And
The tensile strength of the test piece was measured by performing a tensile test using a universal testing machine.

In the SCC life test, the test pieces
A test plate subjected to a solution treatment at a temperature of 50 ° C. for 30 minutes, then water-quenched and subjected to an aging treatment (T7 treatment) at a temperature of 150 ° C. for 24 hours, and a test plate subjected to the T6 treatment Were prepared, and a test piece from which a margin was removed by machining to make the stress in the welded portion constant was used.

FIG. 2 is a side view showing a test method of the SCC life test. As shown in FIG. 2, both ends 5a of the test jig 5 are bent in a U-shape toward the inside, and a bolt 7 is screwed in the center of the test jig 5 from the outside to the inside. Have been combined. A test piece 6 is arranged inside the test jig 5, and both ends 5a of the test jig 5 are arranged.
Thus, both ends 6a of the test piece 6 are supported from above, and a welded portion 6b formed at the center of the test piece 6 is supported by the bolt 7 from below.

The load stress was adjusted to 20 kg / mm ² by adjusting the bolts of the test piece arranged in this way, and the chromic acid corrosion liquid (3
6 g / liter CrO ₃ -30 g / liter K ₂ Cr ₂ O ₃ -3
g / liter NaCl), and the time until crack generation was measured by visual observation to evaluate the stress corrosion cracking life (SCC life).

FIG. 3 is a graph showing the results of a Hold Craft crack test of Examples and Comparative Examples, taking the crack rate on the vertical axis. As shown in FIG.
1, 2, Comparative Example No. Nos. 4 and 5 use a welding rod made of an Al-Mg-based alloy, and Comparative Example N using a welding rod of a conventional composition made of an Al-Mg-Zn-based alloy
o. As compared with No. 3, the crack rate was a low value. Also, in Example No. 1, 2, Comparative Example No. In Nos. 4 and 5, the Ag content was changed in the range of 0 to 1.27% by weight. Even when the Ag content was changed in this manner, the evaluation results of the weld cracks hardly changed.

FIG. 4 is a graph showing the evaluation results of the tensile tests of the examples and the comparative examples, taking the tensile strength on the vertical axis.
Comparative Example No. Since No. 4 contained no Ag in the welding rod, the tensile strength was the lowest. Also,
Example No. 1, Example No. 2, Comparative Example No. 5 is
The Ag content in the welding rod was gradually increased. As shown in FIG. 4, the tensile strength improved as the Ag content in the welding rod increased.

FIG. 5 is a graph showing the SCC resistance of the example and the comparative example, with the SCC life on the vertical axis. Example No. In Example No. 1, the Ag content was 0.31% by weight. No. 2 has an Ag content of 0.62% by weight. As shown in FIG. No. 2 had the longest SCC life, and in particular, when T7 treatment was performed after welding, no cracking occurred even when immersed in a chromic acid corrosion solution for 960 minutes.

On the other hand, Comparative Example N containing no Ag
o. 4 is Example No. 4. As compared with No. 1, the SCC life was shorter in the case where the T7 treatment was performed. Also, A
g containing 1.27% by weight. 5 is Ag
Comparative Example No. As compared with No. 4, the SCC life was equivalent or shorter.

Next, in order to investigate the relationship between the resistance to weld cracking and the element for refining the crystal grains, an aluminum alloy having the chemical components shown in Table 3 below was cast, and the diameter of the aluminum alloy was determined by a conventional method. For example, a 3.2 mm TIG welding rod was manufactured. Then, the welding base metal is TIG-welded by a method similar to the method shown in FIG.
A crack test was performed to evaluate weld cracking resistance due to the added elements of Zr, Mn, Cr, Ti, and B.

[0039]

[Table 3]

FIG. 6 is a graph showing the results of the Hold Craft crack test of the examples and the comparative examples, taking the crack rate on the vertical axis. FIG. 7 shows the SCC life on the vertical axis. FIG. 8 is a graph showing the SCC resistance of the comparative example, and FIG. 8 is a graph showing the evaluation results of the tensile tests of the example and the comparative example, with the vertical axis representing the tensile strength. Example No. 6
In Nos. To 11, the SCC life and the tensile strength were the same as those of the comparative example, but the cracking ratio was extremely low. In particular, in Example No. 6, 10, and 11 are the same as those in Example Nos. 7 was obtained by adding Ti and / or B within the scope of the present invention. As compared with No. 7, the incidence of cracking was reduced.

On the other hand, in Comparative Example No. Comparative Examples Nos. 12 and 13 were prepared by adding Mn or Cr alone without coexisting with Zr. No. 14 had a Mn content exceeding the upper limit of the range of the present invention, and had Mn and Cr contents larger than the Zr content. In No. 15, the content of Mn and Cr is larger than the content of Zr. Also, in Comparative Example No. Nos. 16 to 19 are those whose Mn, Cr, Ti or B content exceeds the upper limit of the range of the present invention. Therefore, in Comparative Example No. In Nos. 12 to 19, the rate of occurrence of cracks was increased as compared with the examples.

[0042]

As described in detail above, according to the present invention,
Since the component composition in the filler material is appropriately defined, it is possible to prevent the occurrence of welding cracks and obtain a high-strength weld metal having excellent SCC resistance. The life (SCC life) at which stress corrosion cracking occurs can be extended. Further, when the contents of Ti and B to be added to the filler material are appropriately defined, the occurrence of cracks in the weld metal can be suppressed.

[Brief description of the drawings]

FIG. 1 is a plan view showing the shape of a welding base metal used in a Hold Craft crack test.

FIG. 2 is a side view showing a test method of an SCC life test.

FIG. 3 is a graph showing the crack rate on the vertical axis, and shows the H of Examples and Comparative Examples.
It is a graph which shows the test result of an old Craft crack test.

FIG. 4 is a graph showing evaluation results of tensile tests of Examples and Comparative Examples, with the vertical axis representing tensile strength.

FIG. 5 is a graph showing the SCC resistance of Examples and Comparative Examples, with the SCC life on the vertical axis.

FIG. 6 is a graph showing the crack rate on the vertical axis, and shows the H of Examples and Comparative Examples.
It is a graph which shows the test result of an old Craft crack test.

FIG. 7 is a graph showing the SCC resistance of Examples and Comparative Examples, with the SCC life taken on the vertical axis.

FIG. 8 is a graph showing evaluation results of tensile tests of Examples and Comparative Examples, with the vertical axis representing tensile strength.

[Explanation of symbols]

 Reference Signs List 1: welding base material 2: slit 3: welding wire 5: test jig 6; test piece 7: bolt

Claims (3)

[Claims] 1. Mg: 4.5 to 5.5% by weight, Ag:
0.3 to 0.9% by weight and Zr: 0.05 to 0.3
0% by weight, and at least one element selected from the group consisting of Mn: 0.10% by weight or less and Cr: 0.10% by weight or less, with the balance being Al and unavoidable impurities. , Zr content is higher than Mn content and Cr content. 2. The filler metal for an aluminum alloy according to claim 1, further comprising 0.05 to 0.20% by weight of Ti. 3. The filler metal for aluminum alloy according to claim 1, further comprising 0.001 to 0.02% by weight of B.