Method for welding titanium foil and method for manufacturing welded components

Abstract

To provide a method for welding a titanium foil by which the titanium foil obtained by rolling and annealing an electrodeposited titanium foil can be applied to welding and defective welding of a welded portion obtained by the welding can be suppressed.SOLUTION: Provided is a method for welding a titanium foil, in which the titanium foil is a foil produced by subjecting an electrodeposited titanium foil obtained by electrodeposition in molten salt electrolysis to cold rolling and annealing, in which surface roughness Ra of both surfaces of the titanium foil is 0.5 μm or less, and the method includes a welding step of welding the titanium foil and another member by fiber laser welding.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for welding titanium foil and a method for manufacturing a welded member.

Background Art

[0002] Welding is a processing method for melting and joining metals, and is widely used in the manufacture of various members, such as machine parts, automobiles, and structures. Among metals, titanium is known as one of the metals having relatively high corrosion resistance. Therefore, for welded members welded using titanium foil, added value based on high functionality can be expected.

[0003] Regarding a method for manufacturing titanium foil, a method is known in which sponge titanium as a melting raw material is melted to cast an ingot, and the ingot is rolled and then the obtained foil-shaped rolled product is annealed (hereinafter, also referred to as "casting and rolling method"). The casting and rolling method can realize sufficient strain introduction into the rolled material by rolling with a large reduction ratio and refinement of the crystal grain size of the titanium foil by subsequent annealing. Regarding welding using the titanium foil manufactured in this way, for example, Patent Document 1 describes that welding was performed using a fiber laser welding machine with a weldment made of pure titanium having a thickness of 0.5 mm.

[0004] By the way, in the casting and rolling method, in order to prepare the sponge titanium used in this method, starting from titanium ore, processes such as chlorination to produce titanium tetrachloride and reduction with metallic magnesium are performed, and processes such as crushing of sponge titanium lumps and electrolysis of magnesium chloride by-produced by reduction are also performed, and a large number of processes are required. The casting and rolling method that requires a large number of processes tends to have a relatively high production cost.

[0005] In consideration of such circumstances, in order to manufacture titanium foil with a relatively small number of processes and at a low cost, an electrodeposition method has been proposed in which titanium is deposited on the cathode in a molten salt bath by molten salt electrolysis to obtain an electrodeposited titanium foil (see Patent Documents 2 to 5).

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-183427 [Patent Document 2] International Publication No. 2020 / 044841 [Patent Document 3] Japanese Patent Publication No. 2021-031723 [Patent Document 4] Japanese Patent Publication No. 2021-134398 [Patent Document 5] International Publication No. 2018 / 159774 [Overview of the project] [Problems that the invention aims to solve]

[0007] When the electrodeposition method is used, the electrodeposited titanium foil on the cathode is often formed relatively thinly by molten salt electrolysis. Since this electrodeposited titanium foil is already thin, there is little room for introducing strain when considering grain refinement by annealing after rolling. Titanium foil produced by rolling and annealing electrodeposited titanium foil tends to have inferior plastic workability compared to titanium foil produced by the casting and rolling method. However, electrodeposited titanium foil has an advantage in terms of manufacturing cost compared to titanium foil produced by the casting and rolling method. In addition, electrodeposited titanium foil is soft and has excellent elastic deformability. If desired three-dimensional shapes can be achieved by plastic processing using electrodeposited titanium foil, which has inferior plastic workability as described above, an expansion of applications can be expected. Therefore, the inventors decided to investigate whether it is possible to achieve various shapes by welding rather than improving the plastic workability of electrodeposited titanium foil to the same level as titanium foil produced by the casting and rolling method. From the above perspective, the inventors attempted to manufacture welded components by laser welding using electrodeposited titanium foil, which can be manufactured at a reduced cost. However, in this case, welding defects were found inside the welded area. These welding defects sometimes involve the formation of multiple cavities of a predetermined size within the welded area. The presence of such cavities can lead to problems such as a decrease in the strength of the welded area.

[0008] Therefore, in one embodiment of the present invention, the objective is to provide a titanium foil welding method that makes titanium foil obtained by rolling and annealing electrodeposited titanium foil applicable to welding, and that can suppress welding defects in the welded part obtained by said welding. [Means for solving the problem]

[0009] The present inventors conducted diligent studies to solve the above problems and found that a titanium foil manufactured by cold rolling and annealing electrodeposited titanium foil obtained by electrodeposition by molten salt electrolysis, wherein the surface roughness Ra of both surfaces of the titanium foil is 0.5 μm or less, and by including a welding step in which the titanium foil and other members are welded by fiber laser welding, it is possible to apply the titanium foil obtained by rolling and annealing electrodeposited titanium foil to welding, and welding defects in the welded part obtained by said welding can be suppressed, and thus the invention exemplified below was created.

[0010] [1] A method for welding titanium foil, The titanium foil is manufactured by cold rolling and annealing an electrodeposited titanium foil obtained by electrodeposition using molten salt electrolysis, and the surface roughness Ra of both surfaces of the titanium foil is 0.5 μm or less. A method for welding titanium foil, comprising a welding step of welding the titanium foil to another component by fiber laser welding. [2] The method for welding titanium foil according to [1], wherein the elongation at break of the titanium foil is 10% or less. [3] The welding method of the titanium foil according to [1] or [2], wherein the micro-Vickers hardness of the titanium foil is 90 Hv or less. [4] The welding method of the titanium foil according to any one of [1] to [3], wherein the thickness of the titanium foil is 0.04 mm or more and 0.15 mm or less. [5] The manufacturing method of a welded member using the welding method of the titanium foil according to any one of [1] to [4]. [6] Before the welding step, an electrodeposition step of obtaining an electrodeposited titanium foil by electrodepositing metallic titanium on an electrode by molten salt electrolysis, a cold rolling step of obtaining a rolled titanium foil by rolling the electrodeposited titanium foil, and an annealing step of obtaining the titanium foil by annealing the rolled titanium foil. The manufacturing method of the welded member according to [https: / / www.patentscope.wipo.int / search / en / detail.jsf?docId=WO2019171444A1&recNum=10&docAn=US&queryString=*%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%3A%DBID=5]].

Advantages of the Invention

[0011] According to an embodiment of the present invention, a titanium foil obtained by rolling and annealing an electrodeposited titanium foil can be applied to welding, and welding defects of a welded portion obtained by the welding can be suppressed. ​​​​​​​​​​​​​​​​​​​​​​​​​​The present invention is not limited to the embodiments described below, and its components can be modified and implemented without departing from its essence. Furthermore, various inventions can be formed by appropriate combinations of the multiple components disclosed in each embodiment. For example, an invention may be formed by deleting some components from all the components shown in an embodiment. Note that some components shown in the drawings are schematic to aid in understanding the embodiments included in the invention, and the sizes and positional relationships shown may not necessarily be accurate.

[0014] [1. Welding method for titanium foil] The titanium foil welding method according to the present invention includes a welding step of welding one component, a titanium foil, to another component by fiber laser welding. The titanium foil used in the welding step is manufactured by cold rolling and annealing electrodeposited titanium foil obtained by electrodeposition by molten salt electrolysis (i.e., obtained by the electrodeposition method). The surface roughness Ra of both surfaces of this titanium foil is 0.5 μm or less.

[0015] As mentioned above, when electrodeposited titanium foil is used directly in the manufacture of welded components by fiber laser welding, welding defects tend to occur easily in the welded parts of the welded components. In order to investigate the cause of this, the inventors examined the surface roughness of both surfaces of the electrodeposited titanium foil and concluded that there is a difference in surface roughness Ra (arithmetic mean roughness) between the surface of the electrodeposited titanium foil that was in contact with the cathode and the surface that was in contact with the molten salt bath, a difference that cannot be ignored in fiber laser welding.

[0016] In fiber laser welding, if the surface roughness Ra of the material being irradiated with laser light is high, the laser light is reflected, and the absorption rate into the material decreases, which is thought to cause variations in the amount of penetration during welding and lead to welding defects. While excessively increasing the laser irradiation output to eliminate variations in the amount of penetration may eliminate welding defects in the welded area, there is a risk that the thin titanium foil may melt through or deform. In other words, having smooth surfaces on both sides of the titanium foil that serves as the base material for welding also means that the thickness of the thin titanium foil is stable, and this is thought to suppress the occurrence of welding defects in fiber laser welding.

[0017] As a result of diligent research, the inventors have found that by cold-rolling and annealing electrodeposited titanium foil to produce titanium foil with a surface roughness Ra of 0.5 μm or less on both surfaces, and using this foil in the welding process, welding defects in the welded parts of welded components can be suppressed. This makes it possible to use electrodeposited titanium foil for welding. Furthermore, this welding method allows for the creation of welded components in a variety of shapes. The following describes preferred embodiments.

[0018] <Molten salt electrolysis> In molten salt electrolysis, electrodeposited titanium foil is obtained by electrodepositing titanium onto electrodes. For molten salt electrolysis, known methods can be used; for example, the methods described in Patent Documents 2 to 5 above can be employed. Furthermore, the contents described in these published documents (manufacturing conditions for electrodeposited titanium foil) can be appropriately modified and adopted. In molten salt electrolysis, the current may be applied at a constant current, or a pulsed current with a pause period may be used during the current application. If a pause period is included during the current application, the current pattern should be selected as appropriate. The method for separating titanium from the electrodes after molten salt electrolysis to obtain electrodeposited titanium foil is not particularly limited. For example, titanium can be peeled off the electrodes using tools such as pliers.

[0019] Furthermore, electrodeposited titanium foil obtained by molten salt electrolysis is known to have a low impurity content because the impurity content is reduced and the titanium is purified during the molten salt electrolysis process. However, when electrodeposited titanium foil is peeled off from the electrode, one surface (the surface that was in contact with the molten salt bath) tends to have a relatively large surface roughness Ra, unlike the other surface (the surface that was in contact with the cathode). As mentioned above, in order to suppress the reflection of laser light during welding, it is necessary to smooth both surfaces of the electrodeposited titanium foil (the surface that was in contact with the molten salt bath and the surface that was in contact with the cathode). Also, having both surfaces of the titanium foil that serves as the base material for welding means that the thickness of the thin titanium foil is stable. For this reason, electrodeposited titanium foil is subjected to cold rolling or other processes to produce titanium foil with smoothed surfaces on both sides, and this titanium foil is used in the welding process.

[0020] The thickness of the electrodeposited titanium foil is, for example, 0.1 mm or more and 0.3 mm or less. If the thickness is less than 0.1 mm, the strength will decrease, and problems such as pinhole formation or fracture of the electrodeposited titanium foil may occur when peeling it off the electrode. On the other hand, manufacturing electrodeposited titanium foil with a thickness exceeding 0.3 mm may be disadvantageous from the standpoint of electricity costs. An example of a method for measuring the thickness of electrodeposited titanium foil is described below. First, using a digital thickness gauge (thickness measuring instrument), select three arbitrary points with a length of 10 mm in the rolling direction (in the case of electrodeposited titanium foil immediately before cold rolling, the direction corresponding to the rolling direction). From these three points, take 10 arbitrary points within the 10 mm length, for a total of 30 measurements. Then, calculate the average value of these measurements. This average value will be taken as the thickness of the electrodeposited titanium foil.

[0021] <Cold rolling> To primarily smooth the surface of the electrodeposited titanium foil (the surface in contact with the molten salt bath), the electrodeposited titanium foil is cold-rolled, for example, using a roll rolling mill. This yields rolled titanium foil. Cold rolling can also be performed under an inert atmosphere or a vacuum atmosphere. However, unlike hot rolling, cold rolling does not raise the temperature of the electrodeposited titanium foil, so there is no need to consider the extreme growth of scale (oxide film) on its surface. For this reason, cold rolling may be performed under an atmospheric atmosphere. Cold rolling under an atmospheric atmosphere is advantageous from the standpoint of cost and equipment operation. In this specification, "cold rolling" means rolling the electrodeposited titanium foil, which is the material to be rolled, at a temperature of 200°C or lower. The temperature of the electrodeposited titanium foil during cold rolling may be 150°C or lower, or even 100°C or lower. Furthermore, the surface roughness Ra of both surfaces of the rolled titanium foil can be adjusted as appropriate by the surface roughness Ra of the rolling rolls of the rolling mill, the roll diameter, etc.

[0022] (Distance between work roles) In one embodiment, from the viewpoint of making one surface of the electrodeposited titanium foil (the surface that was in contact with the molten salt bath) sufficiently smooth, cold rolling may be started with the pair of work rolls in contact with each other, or cold rolling may be started with the pair of work rolls separated, for example, slightly. In other words, the distance between the work rolls can be adjusted as appropriate.

[0023] Furthermore, there are no particular limitations regarding the orientation of the surface of the electrodeposited titanium foil during cold rolling. For example, the electrodeposited titanium foil may be cold-rolled so that one surface of the electrodeposited titanium foil (the surface that was in contact with the molten salt bath) faces upward, or so that one surface faces downward, and the orientation of one surface of the electrodeposited titanium foil (the surface that was in contact with the molten salt bath) may be appropriately changed in consideration of the number of times the foil is passed between the pair of work rolls.

[0024] (Number of times passed) In one embodiment, it is preferable to roll the electrodeposited titanium foil multiple times in order to more reliably smooth one surface of the electrodeposited titanium foil (the surface that comes into contact with the molten salt bath). Furthermore, when using a roll rolling mill with a pair of work rolls, it is preferable to pass the foil between the work rolls multiple times. The number of times the foil passes between the pair of work rolls can be adjusted as appropriate, taking into account the thickness of the electrodeposited titanium foil and the target thickness of the titanium foil to be manufactured, but for example, it may be 3 to 30 times, or 5 to 20 times.

[0025] (Total reduction ratio) In one embodiment, in order to obtain rolled titanium foil of a suitable thickness while obtaining a suitable surface roughness, it is preferable that the total reduction ratio by cold rolling is 10% or more and less than 100%. The total reduction ratio may be, for example, 20% or more and 70% or less, or for example, 30% or more and 60% or less. The total reduction ratio can be calculated by the following formula (1), and may be determined after all passes have been completed. R total ={(t0-t f ) / t0}×100(%)...Equation (1) R total Total reduction rate t0: Thickness immediately before cold rolling t f : Thickness immediately after cold rolling Regarding the method for measuring the thickness, the aforementioned method for measuring the thickness of electrodeposited titanium foil can be used.

[0026] (Washing) Furthermore, after cold rolling and before annealing (described later), cleaning may be performed to remove oil (rolling oil) adhering to the surface of the cold-rolled titanium foil. For cleaning, the rolled titanium foil can be immersed in a cleaning solution, and the cleaning solution can be one or more selected from, for example, deionized water, distilled water, organic solvents, acids, and alkalis.

[0027] <Annealing> One example of annealing conditions is to anneal under vacuum conditions, with an annealing temperature of 600°C or higher and 800°C or lower, and an annealing time of 10 minutes or higher and 60 minutes or lower. By performing annealing, the strain introduced by rolling is appropriately removed, and recrystallization may also occur, often resulting in titanium foil with excellent formability. However, since the strain introduced into the rolled material by cold rolling performed after the electrodeposition process tends to be less than that of the casting rolling method, it is preferable to use welding to form the desired shape.

[0028] <Welding Process> In the welding process, the titanium foil and other components are welded together by fiber laser welding. One example of welding is to bring the ends of the titanium foil and the other components close together and butt them, then irradiate the ends with laser light to join them together (e.g., butt welding). This results in a welded component having the titanium foil and other components joined together at their ends. A welded joint is formed at the boundary between the titanium foil and the other component of the welded component. The grain size of the welded joint may be finer than that of the titanium foil. A welded joint with a fine grain size may have, for example, higher tensile strength than the titanium foil.

[0029] (Fiber laser welding) Fiber laser welding allows for precise adjustment of the laser diameter, making it easier to control the heat input area and form a weld while maintaining the shape of the titanium foil and other components. In fiber laser welding, it is preferable to supply a shielding gas such as argon to the weld area until the titanium foil and other components are welded together, from the viewpoint of suppressing the formation of oxide films and the inclusion of atmospheric components. It is also applicable to welding dissimilar metals with different melting points.

[0030] (Titanium foil) The surface roughness Ra (arithmetic mean roughness) of both surfaces of the titanium foil is 0.5 μm or less, preferably 0.4 μm or less, and more preferably 0.3 μm or less. Since it is preferable that both surfaces of the titanium foil be smooth, the lower limit of the surface roughness Ra is not particularly limited. The surface roughness Ra can be measured in accordance with JIS B0601-2001. In this case, the surface roughness Ra is measured at a total of 10 points at equal intervals in the longitudinal direction in the central part of the titanium foil in the width direction (direction perpendicular to the longitudinal direction (rolling direction) on the surface), and the average value is calculated.

[0031] The elongation at break of titanium foil is, for example, 10% or less. This titanium foil is manufactured using electrodeposited titanium foil obtained by the electrodeposition method, and tends to have a lower elongation at break compared to titanium foil obtained by the casting and rolling method. The method for measuring elongation at break is described below. A sample with a dumbbell shape when viewed from above is taken so that the longitudinal direction is the rolling direction of the titanium foil (or the rolling direction of the final pass if multiple rolling passes are performed). The sample is set in a tensile testing machine and the tensile test is performed at a speed of 0.5 mm / min in accordance with JIS Z2241-2011, except for the conditions specified below (sample shape), to measure the elongation at break at room temperature (25°C). In this case, the sample dimensions are as follows: parallel section width 10 mm, parallel section length 17 mm, gripping section width 20 mm, and radius of curvature of R section 13.5 mm.

[0032] Furthermore, titanium foil manufactured using the electrodeposition method is soft, and its micro-Vickers hardness is 90 Hv or less. The lower limit of the micro-Vickers hardness of the above titanium foil is not particularly limited. This titanium foil is manufactured using electrodeposited titanium foil obtained by the electrodeposition method, and tends to have a lower micro-Vickers hardness compared to titanium foil obtained by the casting and rolling method. The method for measuring micro-Vickers hardness is described below. The hardness will be measured using a Vickers hardness tester in accordance with JIS Z2244-2009. The Vickers hardness test will be performed using a diamond indenter (square pyramidal type) at a temperature of 25°C, with a load of 0.1 kgf and a loading time of 15 seconds.

[0033] Furthermore, the thickness of the titanium foil is, for example, 0.04 mm or more and 0.20 mm or less, or 0.04 mm or more and 0.15 mm or less. Regarding the method for measuring the thickness of the titanium foil, the aforementioned method for measuring the thickness of electrodeposited titanium foil can be used.

[0034] (Other components) The materials of the other components are not particularly limited, but examples include titanium or titanium alloy. The shapes of the other components are also not limited, but examples include foil and components of various shapes. Furthermore, it is preferable that the surface roughness Ra (arithmetic mean roughness) of other components is equivalent to that of the titanium foil mentioned above. That is, the surface roughness Ra is, for example, 0.5 μm or less. The surface roughness Ra can be measured in accordance with JIS B0601-2001.

[0035] [2. Method for manufacturing welded members] The method for manufacturing a welded member according to the present invention uses the titanium foil welding method described above. That is, the manufacturing method includes the welding step of the titanium foil welding method described above.

[0036] In one embodiment, the method for manufacturing a welded member further includes, before the welding process, an electrodeposition step to obtain electrodeposited titanium foil by electrodepositing metallic titanium onto an electrode by molten salt electrolysis, a cold rolling step to obtain rolled titanium foil by rolling the electrodeposited titanium foil, and an annealing step to obtain titanium foil by annealing the rolled titanium foil. Note that the electrodeposition step, cold rolling step, and annealing step correspond to the molten salt electrolysis, cold rolling, and annealing steps described above, respectively, and their contents overlap, so their explanations are omitted. [Examples]

[0037] The present invention will be specifically described based on examples and comparative examples. The following descriptions of examples and comparative examples are merely experimental examples intended to facilitate understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these examples.

[0038] [Preparation of each component to be welded] For the welded members used in Examples 1-2 and Comparative Examples 1-2, the "electrodeposited titanium foil" shown in Table 1 and the "titanium foil produced by cold rolling and annealing the electrodeposited titanium foil" were prepared by the following methods. For the "titanium foil produced by the casting and rolling method" shown in Table 1, commercially available pure titanium foil (standard: JIS H 4600 Class 1) was prepared.

[0039] <Electrodeposited Titanium Foil> To manufacture electrodeposited titanium foil, an electrolytic apparatus 100, as shown in Figure 1, was installed. The dimensions and shape of the bath portion of the electrolytic cell 110 of the electrolytic apparatus 100 were 470 mm in diameter × 500 mm in depth. Note that Figure 1 is a schematic representation of the apparatus configuration, and its scale is not necessarily accurate. Also, to show that each electrode is cylindrical, the upper surface of each electrode is shown in a perspective view.

[0040] Next, molten salt (MgCl2:NaCl:KCl = 2:1:1 (by mass ratio)) was added to the electrolytic cell 110 of the electrolytic device 100, and the temperature of the molten salt was raised to 700°C. Then, approximately 7 mol% of lower titanium chloride (TiCl2 and TiCl3) was supplied to the bath to obtain molten salt bath Bf. After obtaining this molten salt bath Bf, the temperature of molten salt bath Bf was controlled to 500°C.

[0041] Next, as electrodes 120 to be used for molten salt electrolysis, an anode 121 made of metallic titanium and a cathode 122 made of metallic molybdenum were prepared. A cylindrical anode 121 was made using a titanium plate with an inner diameter (diameter) of approximately 160 mm. On the other hand, a cylindrical cathode 122 was made using a molybdenum plate with an outer diameter (diameter) of 100 mm and a height of 250 mm. In the electrolytic cell 110 of the electrolytic device 100, the cylindrical cathode 122 was positioned inside the cylindrical anode 121, and the anode 121 and cathode 122 were arranged so that their height directions were approximately parallel to the depth direction of the molten salt bath Bf. It was confirmed that the surface of the cathode 122 on the anode 121 side was smooth. The distance between the electrodes was kept constant around the entire circumference of the anode 121 and cathode 122. That is, the central axis of the anode 121 and the central axis of the cathode 122 were in the same position.

[0042] A pulsed current was supplied to the anode 121 and cathode 122 via the power supply 130, and molten salt electrolysis was performed in the molten salt bath Bf. Based on the following conditions, metallic titanium was deposited over the entire surface of the cathode 122 on the anode 121 side. <Conditions for molten salt electrolysis> Temperature of molten salt bath: 500℃ Current density when energized: 0.1A / cm 2 Power-on period: 1.5 seconds Power-off period: 7.5 seconds Electrolysis time: 330 minutes

[0043] After the energization was terminated, the cathode 122, on which metallic titanium had been deposited, was removed from the molten salt bath Bf, pickled, and then rinsed with water to remove the molten salt. Furthermore, the cathode 122 on which metallic titanium had been deposited was dried. Finally, the worker used pliers to peel off the metallic titanium from the cathode 122, thereby obtaining electrodeposited titanium foil.

[0044] Next, by cutting the outer periphery of the electrodeposited titanium foil, an electrodeposited titanium foil measuring 220 mm in width and 310 mm in length was obtained. Then, by further cutting this electrodeposited titanium foil, two pieces of electrodeposited titanium foil for rolling, measuring 100 mm in width and 300 mm in length, were obtained. In addition, by following the same method as above, several more electrodeposited titanium foils and electrodeposited titanium foils for rolling were obtained for evaluation and for use in welded components. Using the method described above, the thickness of the electrodeposited titanium foil was measured at 30 points using a digital thickness gauge (thickness measuring instrument), and the average value was calculated. As a result, the calculated thickness of the titanium foil was 0.15 mm.

[0045] <Titanium foil based on electrodeposition method> Next, the electrodeposited titanium foil for rolling was cold-rolled. A two-stage rolling mill with a pair of work rolls was used for cold rolling. Under an atmospheric environment and at room temperature, the electrodeposited titanium foil was passed between the pair of work rolls of the two-stage rolling mill. In the cold rolling process, the rolling direction was kept the same, and the electrodeposited titanium foil passed between the pair of work rolls 20 times. Using the method described above, the thickness of the rolled titanium foil after all passes in cold rolling was measured at 30 points using a digital thickness gauge (thickness measuring instrument), and the average value was calculated. As a result, the calculated thickness of the rolled titanium foil was 0.10 mm. Therefore, based on the above formula (1), the total reduction ratio was calculated to be 33%.

[0046] The rolled titanium foil, after cold rolling, was washed with deionized water to remove any oil adhering to its surface. Then, it was annealed under vacuum conditions at 700°C for 20 minutes to obtain the titanium foil. Furthermore, no defects or cracks originating from the rolling process were observed on the surface of the titanium foil through visual inspection.

[0047] <Evaluation of each welded component> (thickness) Using the method described above, the thickness of each welded component shown in Table 1 was measured at a total of 30 points using a digital thickness gauge (thickness measuring instrument), and the average value was calculated. The results are shown in Table 1.

[0048] (Surface roughness) The surface roughness Ra of each welded component shown in Table 1 was measured in accordance with JIS B0601-2001. The surface of each welded component was measured using a contact-type surface roughness meter (SJ-210, manufactured by Mitutoyo Corporation) according to the method described above, and the average value was calculated. The results are shown in Table 1. In electrodeposited titanium foil, the "bottom surface" refers to the surface that was in contact with the electrolytic surface of the cathode, and the "top surface" refers to the surface that was in contact with the molten salt bath. In Table 1, the surface roughness Ra of the bottom surface of "electrodeposited titanium foil," the top and bottom surfaces of "titanium foil manufactured by cold rolling and annealing electrodeposited titanium foil," and the top and bottom surfaces of "titanium foil manufactured by the casting and rolling method" were all 0.2 μm or less, so the average value is shown as "≦0.2" μm.

[0049] (Elongation at break) For each welded member shown in Table 1, samples were taken using the method described above, and the elongation at break was measured at room temperature (25°C) in accordance with JIS Z2241-2011, except for the conditions specified below (sample shape). When rolling was performed, the sample was taken in a dumbbell shape viewed from above, so that the rolling direction was the tensile direction. The sample size was 10 mm in width of the parallel section, 17 mm in length of the parallel section, 20 mm in width of the gripping section, and 13.5 mm in radius of curvature of the R section. Next, the samples were set in a tensile testing machine and a tensile test was performed at a speed of 0.5 mm / min. The results are shown in Table 1.

[0050] (Micro-Vickers hardness) For each welded component shown in Table 1, the micro-Vickers hardness was measured in accordance with JIS Z2244-2009 using the method described above. The results are shown in Table 1.

[0051] [Table 1]

[0052] [Manufacturing of welded components] (Examples 1-2 and Comparative Examples 1-2) In the welding process, each of the components to be welded shown in Table 2 was prepared, and the longitudinal ends of the components were butted together and welded by fiber laser welding. Furthermore, for titanium foil produced by cold rolling and annealing electrodeposited titanium foil, and titanium foil produced by the casting and rolling method, the longitudinal direction was aligned with the rolling direction. This resulted in welded components having welded joints.

[0053] <Evaluation of welded joints> The welded members obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated as follows.

[0054] (Checking the welded joint) To check for welding defects, ultrasonic testing was used to check for voids inside the welded area. As a result, comparative examples 1 and 2 were determined to have welding defects, and the affected areas were cut in the thickness direction and the cross-sections were observed with an electron microscope. On the other hand, examples 1 and 2 were determined to have no welding defects, and appropriate sections were cut in the thickness direction and the cross-sections were observed with an electron microscope. In the resulting photographs (Figures 2 to 5), welding defects were confirmed as voids (black areas) in the welded area.

[0055] (crystal grain size) In Example 1, the cross-section of the welded portion of the welded member and the cross-section of the titanium foil as a single component were examined, and the grain size of the welded portion of the welded member was found to be finer than the grain size of the titanium foil. The results are shown in Table 2.

[0056] (Confirmation of fractured members using a tensile testing machine) In Example 1, the sample was taken in a dumbbell shape so that the longitudinal direction of the welded member was the longitudinal direction of the sample. The welded part was positioned in the center of the sample. The size of the sample was as follows: parallel section width 10 mm, parallel section length 17 mm, gripping section width 20 mm, and radius of curvature of the R section 13.5 mm. Next, the sample was set in a tensile testing machine, and a tensile test was performed at a speed of 0.5 mm / min in accordance with JIS Z2241-2011, except for the specified conditions (sample shape), to confirm the fracture of the member at room temperature (25°C). Table 2 shows the evaluation results of the members that fractured in the tensile test.

[0057] [Table 2]

[0058] (Discussion based on examples) In Examples 1 and 2, the surface roughness Ra of both surfaces of the titanium foil produced by rolling and annealing electrodeposited titanium foil obtained by electrodeposition was 0.5 μm or less. As a result, no welding defects were observed in the welded portion of the welded member obtained by welding the titanium foil to the other member by fiber laser welding. Furthermore, in Example 1, it was confirmed that the grain size of the welded area was finer than that of the titanium foil, which was one of the components. In addition, a tensile test confirmed that the titanium foil, one of the components, fractured. This is presumed to be because the strength of the welded area was improved due to the refinement of the grain size of the welded area. Furthermore, as shown in Table 1, it was confirmed that titanium foil produced by rolling and annealing electrodeposited titanium foil obtained by electrodeposition had lower elongation at break and micro-Vickers hardness compared to titanium foil produced by casting and rolling. However, in Example 1, no welding defects were observed in the welded parts of the welded members obtained using the above titanium foil, so it is presumed that it can be used as a welded member. In addition, since the above titanium foil has different mechanical properties from titanium foil produced by casting and rolling, it is possible to manufacture welded members that could not be obtained conventionally using the above titanium foil. Furthermore, although the above titanium foil is thought to have lower elongation at break and inferior plastic workability compared to titanium foil produced by casting and rolling, it is possible to manufacture welded members of various shapes including the above titanium foil by applying fiber laser welding. In addition, since the above titanium foil can be manufactured with fewer manufacturing steps and at a lower cost than titanium foil produced by casting and rolling, it is considered to be suitably applicable to the application fields of titanium foil produced by casting and rolling from a cost perspective. Furthermore, in Example 2, a welded member was obtained by welding a titanium foil manufactured by cold rolling and annealing electrodeposited titanium foil obtained by electrodeposition to a titanium foil manufactured by casting and rolling using fiber laser welding, and no welding defects were observed in the welded portion of this welded member. From this, it can be inferred that welding of the above-mentioned titanium foil with titanium foil manufactured under completely different conditions is also possible.

[0059] On the other hand, in Comparative Examples 1 and 2, the surface roughness Ra of the electrodeposited titanium foil obtained by the electrodeposition method (the surface that was in contact with the molten salt bath during molten salt electrolysis) exceeded 0.5 μm, and welding defects were observed in the welded portion of the welded member obtained by fiber laser welding the electrodeposited titanium foil to other members. [Explanation of Symbols]

[0060] 100 Electrolyzer 110 Electrolytic cell 120 electrodes 121 Anode 122 Cathode 130 Power supply Bf molten salt bath

Claims

1. A method for welding titanium foil, The titanium foil is manufactured by cold rolling and annealing an electrodeposited titanium foil obtained by electrodeposition using molten salt electrolysis, and the surface roughness Ra of both surfaces of the titanium foil is 0.5 μm or less. A method for welding titanium foil, comprising a welding step of welding the titanium foil to another component by fiber laser welding.

2. The method for welding titanium foil according to claim 1, wherein the elongation at break of the titanium foil is 10% or less.

3. The method for welding titanium foil according to claim 1, wherein the micro-Vickers hardness of the titanium foil is 90 Hv or less.

4. The method for welding titanium foil according to claim 1, wherein the thickness of the titanium foil is 0.04 mm or more and 0.15 mm or less.

5. A method for manufacturing a welded member, using the titanium foil welding method described in any one of claims 1 to 4.

6. The method for manufacturing a welded member according to claim 5, further comprising: an electrodeposition step to obtain electrodeposited titanium foil by electrodepositing metallic titanium onto an electrode by molten salt electrolysis before the welding step; a cold rolling step to obtain rolled titanium foil by rolling the electrodeposited titanium foil; and an annealing step to obtain the titanium foil by annealing the rolled titanium foil.

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