Aluminum alloy elongated material for laser welding, laser welding joint body, and method for welding aluminum alloy material

Abstract

The present invention provides a 6000-series aluminum alloy ductile material in which a welding crack is suppressed even when high-speed welding is performed using laser welding or the like, a welding method including the aluminum alloy ductile material for welding, a welded joint, and an aluminum alloy material. The present invention relates to an aluminum alloy ductile material for welding, characterized by having a content of Si of 0.3 mass% or more and less than 2.0 mass%, a content of Mg of 0.3 mass% or more and less than 2.0 mass%, containing an interfacial active element that reduces the surface tension of molten aluminum, the interfacial active element being at least any one of Sr, Ca, Sb, Li, and Ba, and a content of the interfacial active element being 0.04 mass% or more and 0.50 mass% or less.

Description

Technical Field

[0001] This invention relates to an aluminum alloy elongated material with excellent weldability, a welded joint comprising the aluminum alloy elongated material, and a welding method for the aluminum alloy elongated material. Background Technology

[0002] Aluminum is lightweight and rust-resistant, and by adding appropriate elements, it can be made to achieve high strength, thus it is widely used in railway vehicles, ships, bridges, and various frame structures. While aluminum has excellent machinability, welding is essential in structural integration.

[0003] However, aluminum is known to have poor weldability compared to iron and other metals, and is prone to cracking due to solidification or liquefaction. Previously, welding speeds were reduced for welding, but with annual demands for increased productivity, there is an urgent need to increase the welding speed of aluminum.

[0004] In contrast, for example, in Patent Document 1 (Japanese Patent Application Publication No. 2016-121385), an aluminum alloy sheet for a housing with excellent laser weldability is disclosed with the aim of providing an aluminum alloy sheet for a housing that can suppress cracks caused by laser welding and a housing formed therefrom. The sheet is characterized in that it contains Si: 2.0% or more and 11.0% or less (mass%, the same below), Fe: more than 0% and 2.0% or less, and the remainder has a chemical composition containing Al and unavoidable impurities. The elongation is 8% or more, and a second phase particle containing Si or Fe is present in the Al matrix. The approximate diameter of the second phase particle is 17 μm or less.

[0005] In the aluminum alloy sheet for the housing described in Patent Document 1, the aluminum alloy sheet for the housing contains an Al-Si alloy with a lower melting point compared to previous 3000 series aluminum alloys, thus allowing the use of a laser with a lower output for welding, easily reducing the amount of aluminum alloy component melted during laser irradiation. Furthermore, because the aluminum alloy sheet for the housing contains an Al-Si alloy, it has a smaller shrinkage rate during solidification compared to 3000 series aluminum alloys. These results in a lower crack sensitivity for the housing aluminum alloy compared to 3000 series aluminum alloys, suppressing cracks after laser welding.

[0006] [Existing technical documents] [Patent Literature] Patent Document 1: Japanese Patent Application Publication No. 2016-121385 Summary of the Invention

[0007] [The problem the invention aims to solve] However, the aluminum alloy sheet for the casing in Patent Document 1 is mainly made of 3000 series aluminum alloy, but 3000 series aluminum alloy also has many shortcomings such as insufficient strength. There is an urgent need to realize an aluminum alloy material that has both excellent weldability and high mechanical properties. More specifically, it is desirable to endow 6000 series aluminum alloy with excellent weldability.

[0008] Furthermore, the welding speed shown in Patent Document 1 is 2 m / min. For example, faster welding speeds are often used in laser welding, so it is difficult to say that it is sufficient from the point of view of high-speed welding.

[0009] In view of the problems in the prior art as described above, the object of the present invention is to provide a 6000 series aluminum alloy extension material that suppresses weld cracks even when high-speed welding is performed using laser welding or the like, a welded joint comprising the aluminum alloy extension material, and a welding method for the efficient use of the aluminum alloy extension material.

[0010] [Technical means to solve the problem] In order to achieve the aforementioned objective, the inventors have repeatedly and diligently studied the composition of aluminum alloys and the relationship between the composition and weld cracks, etc., and found that it is extremely effective to contain an appropriate amount of interfacial active elements (at least one of Sr, Ca, Sb, Li and Ba) in the aluminum alloy and reduce the surface tension of the molten aluminum alloy, thereby achieving the present invention.

[0011] That is, the present invention provides an aluminum alloy extension material for welding, characterized in that, The Si content is 0.3% by mass or more and less than 2.0% by mass. The Mg content is ≥0.3% by mass and <2.0% by mass. It contains interfacial active elements that reduce the surface tension of molten aluminum. The interfacial active element is at least one of Sr, Ca, Sb, Li, and Ba. The content of the surface-active element is above 0.04% by mass and below 0.50% by mass.

[0012] By including an interfacial active element (at least one of Sr, Ca, Sb, Li, and Ba), the surface tension of molten aluminum can be reduced, the fluidity of aluminum in the molten region can be improved, and weld cracks can be suppressed even during high-speed bonding. Here, Sr is preferably selected as the interfacial active element. By adding Sr as the interfacial active element, the surface tension of molten aluminum can be reduced simply and efficiently compared to adding other elements.

[0013] Furthermore, when welding aluminum alloys that do not contain an appropriate amount of interfacial active elements, the metal structure of the weld bead becomes a coarse columnar grain structure, which easily leads to weld cracks. In contrast, if 0.04% by mass or more of an interfacial active element is added, the columnar structure of the weld bead is refined, which can suppress weld cracks. Even if 0.5% by mass or more of an interfacial active element is added, the effect is not improved. Since the addition of interfacial active elements increases the cost of raw materials, the amount added is set to 0.5% by mass or less. Here, a more preferred range for the amount of interfacial active element added is 0.10% by mass or more and 0.20% by mass or less.

[0014] Furthermore, in the aluminum alloy extension material for welding according to the present invention, the content of Si is 0.3% by mass or more and less than 2.0% by mass, and the content of Mg is 0.3% by mass or more and less than 2.0% by mass. By containing 0.3% by mass or more and less than 2.0% by mass of Si and 0.3% by mass or more and less than 2.0% by mass of Mg, high strength of the aluminum alloy extension material for welding can be achieved by utilizing fine precipitates such as Mg2Si.

[0015] Furthermore, in the aluminum alloy extension material for welding according to the present invention, the composition other than the interfacial active element is preferably within the range of 6000 series aluminum alloys (Al-Mg-Si series aluminum alloys) as specified in the Japanese Industrial Standard (JIS). Generally speaking, the elements other than the interfacial active element in the aluminum alloy extension material for welding according to the present invention are only required to be elements added to 6000 series aluminum alloys or their compositional range, and impurities are also permitted as long as they are within the range specified in the JIS standard for 6000 series aluminum alloys.

[0016] Furthermore, the present invention also provides a welded joint, which is formed by fusing two or more components, characterized in that at least one of the components being welded is an aluminum alloy extension material for welding according to the present invention. By having at least one of the components being welded in the welded joint be an aluminum alloy extension material for welding according to the present invention, the welded joint can be manufactured efficiently using high-speed welding. In addition, the generation of defects such as cracks in the welded portion formed by high-speed welding is suppressed, and the welded joint has high strength and reliability.

[0017] Furthermore, the present invention also provides a method for welding aluminum alloy materials, characterized in that welding is performed on the aluminum alloy extension material for welding according to the present invention at a welding speed of 3 mm / min or more. In the method for welding aluminum alloy materials of the present invention, since the aluminum alloy extension material for welding according to the present invention is used in the materials to be welded, the formation of defects such as cracks in the welded portion is suppressed even when the welding speed is set to 3 mm / min or more. From the viewpoint of productivity and suppression of defect formation in the welded portion, the welding speed is preferably set to 4 mm / min or more, and more preferably to 5 mm / min or more.

[0018] Furthermore, in the welding method for aluminum alloy materials of the present invention, laser welding is preferably used. By using laser welding, the welding speed can be easily increased. In addition, for high-speed welding of 5 mm / min or higher, hybrid laser welding can be used, for example. Hybrid laser welding is a joining technique that guides the arc by a cathode point generated by a prior laser, and can achieve improved welding stability, suppression of defect formation, increased joining speed, and increased weld penetration depth.

[0019] [The effects of the invention] According to the present invention, a 6000 series aluminum alloy extension material that suppresses weld cracks even when high-speed welding is performed using laser welding or the like, a welded joint comprising the aluminum alloy extension material, and a welding method for efficiently welding the aluminum alloy extension material can be provided. Attached Figure Description

[0020] Figure 1 This is a schematic cross-sectional view of the vicinity of the welded portion in one embodiment of the aluminum alloy welded joint of the present invention.

[0021] Figure 2 This is a schematic diagram of the fine structure of the welded section 4.

[0022] Figure 3 This is a photograph of the fixture used in the varestraint test.

[0023] Figure 4 This is a schematic diagram of an adjustable restraint crack test.

[0024] Figure 5 This is a photograph of the tissue in the longitudinal section of the weld obtained in Example 3.

[0025] Figure 6 This is a macroscopic photograph of the cross-section of the welded portion obtained in Example 3.

[0026] Figure 7 This is a photograph of the tissue in a longitudinal section of the weld obtained in Comparative Example 1.

[0027] Figure 8 This is a macroscopic photograph of the cross-section of the weld obtained in Comparative Example 1.

[0028] Figure 9 It is a graph showing the relationship between the crack rate and the Sr content of the base material. Detailed Implementation

[0029] The following detailed description, with reference to the drawings, describes representative embodiments of the aluminum alloy extension material for welding, the aluminum alloy welded joint, and the welding method thereof according to the present invention, but the present invention is not limited to these. Furthermore, in the following description, the same or equivalent parts are sometimes labeled with the same symbols, and repeated descriptions are omitted. Additionally, the drawings are for conceptual illustration of the present invention, and therefore the dimensions or proportions of the structural elements shown may sometimes differ from the actual dimensions.

[0030] 1. Aluminum alloy extension material for welding The aluminum alloy extension material for welding of the present invention is characterized by containing 0.3% by mass or more and less than 2.0% by mass of Si, 0.3% by mass or more and less than 2.0% by mass of Mg, and 0.04% by mass or more and less than 0.50% by mass of interfacial active elements. The components are described in detail below.

[0031] (1) Required added elements Si: ≥0.3% by mass and <2.0% by mass Si, together with Mg, forms Mg-Si precipitates, which improve mechanical strength and fatigue strength. When the Si content is less than 0.3% by mass, solid solution strengthening or age hardening is insufficient, failing to achieve the required mechanical and fatigue strength for aluminum alloys. On the other hand, if the Si content is 2.0% by mass or higher, corrosion resistance decreases. Furthermore, the formation of coarse crystals or precipitates can sometimes reduce ductility and machinability.

[0032] Mg: ≥0.3% by mass and <2.0% by mass Mg, together with Si, forms Mg-Si precipitates, which improve mechanical strength and fatigue strength. This effect becomes significant at concentrations of 0.3% by mass or higher, but even with the addition of 2.0% by mass or higher Mg, a contribution to strength is hardly expected. Furthermore, it may form coarse intermetallic compounds that become the starting point for failure, thus reducing mechanical strength and other properties.

[0033] Interfacial active element (at least one of Sr, Ca, Sb, Li and Ba): ≥0.04% by mass and ≤0.50% by mass By including 0.04% to 0.50% by mass of an interfacial active element, the surface tension of molten aluminum can be reduced, improving its fluidity. Even at high-speed welding speeds exceeding 3 m / min, weld cracks can be suppressed. Sr is preferably used as the interfacial active element.

[0034] Furthermore, when welding aluminum alloys without interfacial active elements, the weld bead's microstructure becomes a coarse columnar grain structure, making it prone to weld cracking. In contrast, adding 0.04% by mass or more of an interfacial active element refines the columnar structure of the weld bead, suppressing weld cracking. Even adding 0.5% by mass or more of an interfacial active element does not improve this effect, as the addition of interfacial active elements increases raw material costs, and large amounts may form coarse compounds. Additionally, large amounts of interfacial active elements can easily entrap air during high-speed welding, leading to porosity. From these perspectives, the amount of interfacial active element added is set to 0.5% by mass or less. More preferably, the amount of interfacial active element added is between 0.10% by mass and 0.20% by mass.

[0035] (2) Adding elements arbitrarily Regarding additive elements other than Si and Mg for improving the mechanical properties of aluminum alloys and interfacial active elements for improving weldability, there are no particular limitations as long as they do not impair the effects of this invention, and they can be set within the range of 6000 series aluminum alloys (Al-Mg-Si series aluminum alloys) specified in JIS standards. That is, any additive element is generally acceptable as long as it is an element added to 6000 series aluminum alloys or its composition range, and impurities are also allowed within the range of 6000 series aluminum alloys specified in JIS standards.

[0036] 2. Aluminum alloy welded joint The aluminum alloy welded joint of the present invention is a welded joint formed by fusing two or more components, characterized in that at least one of the components being welded is an aluminum alloy extension material for welding according to the present invention. Hereinafter, the addition of Sr as an interfacial active element will be described. A schematic cross-sectional view near the weld portion in one embodiment of the aluminum alloy welded joint of the present invention is shown in [illustration missing]. Figure 1 middle.

[0037] Figure 1 The cross-section shown is perpendicular to the weld line, indicating that the aluminum alloy welded joint 1 is a structure formed by joining aluminum alloy materials 2 together through a weld portion 4. Here, at least one of the aluminum alloy materials 2 is the aluminum alloy extension material for welding according to the present invention.

[0038] The shape and size of the welded portion 4 are not particularly limited as long as they do not impair the effect of the present invention. They can be appropriately adjusted according to the shape and size of the aluminum alloy material 2 or the desired joint characteristics. The welded portion 4 is preferably formed over the entire area of ​​the joint interface, but it can also be formed locally when the mechanical properties of the joint are not critical.

[0039] Will Figure 1 The microstructure of the welded portion 4 in the diagram is schematically shown. Figure 2 In the solidification direction, a microstructure containing columnar grains is formed from the boundary with the unmelted aluminum alloy 2. As solidification proceeds, a microstructure containing equiaxed grains is formed. Here, by adding Sr, the microstructure of the welded portion 4 is refined, and both the columnar and equiaxed grains are refined compared to the case without Sr.

[0040] 3. Welding methods for aluminum alloy materials (manufacturing methods for aluminum alloy welded joints) The welding method for aluminum alloy materials of the present invention will be described using the manufacture of an aluminum alloy welded joint 1 as an example. By using at least one of the components to be welded (aluminum alloy material 2) as the welding aluminum alloy extension material of the present invention, the aluminum alloy welded joint 1 can be easily manufactured at a welding speed of 3 mm / min or higher.

[0041] Here, the effect of suppressing the formation of defects such as cracks in the weld is extremely significant, and the effect can be fully obtained even by increasing the welding speed. From the viewpoint of productivity and suppressing the formation of defects in the weld, the welding speed is preferably set to 4 mm / min or more, and more preferably to 5 mm / min or more.

[0042] There are no particular limitations on the welding method as long as it does not impair the effect of the present invention. Existing known welding methods can be used. For example, high-speed welding can be easily implemented by using laser welding, and high-speed welding can be implemented more efficiently by using hybrid laser welding.

[0043] In addition, as long as the effect of the present invention is not compromised, appropriate filler materials may be used as needed, and welding conditions other than welding speed may be adjusted appropriately according to the thickness or shape of the materials to be joined.

[0044] The above describes representative embodiments of the present invention, but the present invention is not limited to these and various design changes can be made, all of which are included within the technical scope of the present invention.

[0045] [Example] Example Sr was added to JIS-6063 aluminum alloy, which has poor weldability in 6000 series aluminum alloys, to obtain welding aluminum alloy extension materials (Examples 1 to 3) with the composition (mass%) shown in Table 1. The dimensions and shape of the welding aluminum alloy extension material were set as a plate with a length of 200 mm × width of 190 mm × thickness of 3 mm.

[0046] [Table 1] Secondly, in order to evaluate the characteristics of aluminum alloy extension materials for welding relative to weld cracks, the following methods were used: Figure 3 The test fixture shown is used for welding based on an adjustable restraint crack test. A schematic diagram of the adjustable restraint crack test is shown below. Figure 4 In this experiment, welding is performed under external stress on the materials being joined, and tensile stress applied to the weld joint promotes weld cracking. The bending radius in the adjustable restraint crack test is set to 300 mm.

[0047] Laser welding was performed using an IPG multimode CW fiber laser, with the following settings: laser output: 2600 W, advance angle: 10°, target angle: 90°, welding speed: 5 m / min. Laser welding was carried out by connecting the weld beads. Furthermore, three adjustable restraint crack tests were conducted on each aluminum alloy extension material used for welding.

[0048] As a representative example of the obtained aluminum alloy extension material for welding, a photograph of the microstructure in the longitudinal section of the welded portion of the aluminum alloy extension material for welding obtained in Example 3 is shown below. Figure 5 As can be seen from the longitudinal section photograph, the upper half is the weld zone (weld bead), where both columnar and equiaxed crystals form weld zones containing fine microstructures, and the development of columnar crystal structure is suppressed.

[0049] A macroscopic photograph of a representative cross-section of the welded portion of the aluminum alloy extension material obtained as Example 3 is shown below. Figure 6 However, no weld cracks were observed.

[0050] In addition, tensile tests were conducted on the weldable aluminum alloy elongated material of Example 3, which underwent solution treatment (held in an electric furnace at 540°C for 2 hours followed by water cooling) and artificial aging (175°C for 8 hours). The results showed a tensile strength of 222 MPa, a 0.2% endurance of 178 MPa, and an elongation of 17.5%. Furthermore, the tensile test piece used was test piece No. 14A as described in JIS Z 2241, and the tensile speed was set to 2 mm / min up to 0.2% endurance and 5 mm / min thereafter, in accordance with JIS Z 2241.

[0051] Comparative Examples Except for the composition (mass %) shown in Table 1 as the comparative examples (Comparative Examples 1 and 2), welding based on the adjustable restraint crack test was performed in the same manner as in the examples. A photograph of the microstructure in the longitudinal section of the weld obtained as Comparative Example 1 is shown below. Figure 7 The upper half of the longitudinal cross-sectional photograph shows the weld zone (weld bead), where both columnar and equiaxed grains are coarser than in the example. Furthermore, it is evident that the microstructure containing columnar grains has grown significantly, becoming a detrimental structure for suppressing weld cracks.

[0052] A macroscopic photograph of a representative cross-section of the welded portion of the aluminum alloy extension material obtained as Comparative Example 1 is shown below. Figure 8 In. Figure 8 Large weld cracks were found in the samples.

[0053] In addition, similar to the examples, tensile tests were conducted on the aluminum alloy elongated material for welding of Comparative Example 1, which underwent solution treatment (held in an electric furnace at 540°C for 2 hours followed by water cooling) and artificial aging (175°C for 8 hours). The results showed a tensile strength of 237 MPa, a 0.2% endurance of 189 MPa, and an elongation of 18.8%. No significant differences were found in the tensile test results compared to the aluminum alloy elongated material for welding of Example 3, confirming that the addition of Sr does not adversely affect the mechanical properties of the aluminum alloy elongated material for welding.

[0054] For fusion cracks generated on the surface of the weld bead through the adjustable restraint crack test in the examples and comparative examples, the length of the fusion crack was determined using colorimetric inspection. The measured fusion crack lengths are shown in Table 2 as a ratio (crack rate) of crack length to weld length per 100 mm. Furthermore, the relationship between the crack rate and the Sr content of the base material is shown in… Figure 9 middle.

[0055] [Table 2] In Comparative Example 1, where no Sr was added, the average crack rate was a high value of 45.3%. Furthermore, in Comparative Example 2, where the amount of Sr added was insufficient, the crack rate increased due to the addition of Sr. It is evident that, compared to these cases, the crack rate was significantly reduced by adding an appropriate amount of Sr. In particular, by adding 0.10% by mass or more of Sr, the crack rate was significantly reduced, and in Example 3, where 0.17% Sr was added, crack formation was completely suppressed.

[0056] [Explanation of Symbols] 1: Aluminum alloy welded joint 2: Aluminum alloy material 4: Welded section

Claims

1. An aluminum alloy extension material for laser welding, characterized in that, The Si content is 0.3% by mass or more and less than 2.0% by mass. The Mg content is ≥0.3% by mass and <2.0% by mass. It contains interfacial active elements that reduce the surface tension of molten aluminum. The interfacial active element is at least one of Sr, Ca, Sb, Li, and Ba. The content of the surfactant element is above 0.04% by mass and below 0.50% by mass. The composition other than the interfacial active elements is within the range of 6000 series aluminum alloys specified in the Japanese Industrial Standards.

2. The aluminum alloy extension material for laser welding according to claim 1, characterized in that, The interfacial active element is Sr.

3. The aluminum alloy extension material for laser welding according to claim 1 or 2, characterized in that, The content of the surface-active element is above 0.10% by mass and below 0.20% by mass.

4. A laser-welded joint, comprising two or more components, characterized in that, At least one of the components being welded is an aluminum alloy extension material for laser welding according to any one of claims 1 to 3.

5. A method for welding aluminum alloy materials, characterized in that, The aluminum alloy extension material for laser welding according to any one of claims 1 to 3 is subjected to welding at a welding speed of 3 mm / min or higher.

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