JP5426947B2 - Paste flux for fusion welding of Zn-Al-Mg alloy plated steel sheet - Google Patents

Description

  The present invention relates to a paste-like flux for fusion welding of Zn—Al—Mg alloy plated steel sheets.

  Hot dipping refers to dipping a steel material in a molten metal bath and applying a metal coating on the surface. Zinc has been most commonly used as a coating metal. Such hot dipping is widely applied to steel plates, steel pipes, steel wires, shaped steels, and the like, and is excellent in corrosion resistance, so that it is used for various structural materials.

  Among them, Zn-Al-Mg alloy-plated steel sheet with Zn-Al-Mg alloy plated on the steel sheet surface has much better corrosion resistance than hot-dip galvanized steel sheet, and it is used for automobiles, building materials, and home appliances. It is about to be used for products and the like (see Patent Document 1). Such Zn—Al—Mg alloy-plated steel sheet is almost always formed into a molded product having a required shape by various means, and they are combined in various ways and welded to obtain a final product.

  Various welding methods are known, but for building materials and automobile parts, etc., considering relatively high joint strength, relatively thick plate thickness, electrode life in resistance welding, etc. In many cases, fusion welding is employed. In this fusion welding, since the joint portion including the base material is melted and welded, in the fusion welding of the plated steel sheet, not only the base material but also the plating layer on the surface thereof is melted. Evaporate.

  Here, in the Zn-Al-Mg alloy-plated steel sheet, the melting point of the plating layer is considerably lower than the melting point of the base steel sheet, so in some areas of the welded part and around the welded part, during or after welding. When a plating layer exists on the surface of a steel sheet in a molten state for a certain period of time and a tensile stress of a certain level or more acts on the steel sheet in such a state, a crack called a molten metal embrittlement crack occurs in the base steel sheet. In particular, it has been pointed out that when a plurality of conditions overlap when a Zn-Al-Mg alloy-plated steel sheet is melt welded, this molten metal embrittlement crack is likely to occur near the heat-affected zone of the base metal. (See Patent Document 1).

  In order to solve such problems in fusion welding of Zn-Al-Mg alloy-plated steel sheet, potassium fluoroaluminate is already attached to the fusion-welded part of Zn-Al-Mg alloy-plated steel sheet and fusion welding is performed. By removing magnesium and aluminum components, which are alloy plating components, from the weld zone, increasing the melting point of the hot-dip metal, and allowing the molten metal containing the magnesium component to penetrate into the grain boundaries of the coarse crystal grains in the weld heat affected zone There has been proposed a welding method that suppresses the occurrence of molten metal embrittlement cracks (see Patent Document 1). In this welding method, potassium fluoroaluminate is a powder by itself, so that an aqueous dispersion of potassium fluoroaluminate is sprayed and dried to adhere potassium fluoroaluminate to the weld. .

  However, the method of spraying and drying an aqueous dispersion of potassium fluoroaluminate on the welded part is difficult to adopt because it causes dripping depending on the welded part of the Zn-Al-Mg alloy-plated steel sheet. After evaporating, potassium fluoroaluminate is only adhered to the surface of the welded portion of the steel sheet as a powder, so that there is a problem that it easily peels off from the surface of the steel sheet due to vibration or impact.

  Then, while using alcohol and glycol ether as an organic solvent and using 12-hydroxystearic acid as a gelling agent, it is tried to obtain a paste-like composition containing potassium fluoroaluminate (patent). Reference 2), the resulting composition hardly gels or is very poor. And since the composition obtained does not have thixotropic property, there exists a problem which is inferior to the applicability | paintability at the time of apply | coating to the fusion-welded part of a Zn-Al-Mg alloy plating steel plate, and raise | generates dripping. That is, conventionally, a paste-like flux containing potassium fluoroaluminate has not been obtained.

Japanese Patent Application Laid-Open No. 2005-118797 JP 2007-31535 A

  As a result of intensive studies to solve the above-described problems in fusion welding of Zn—Al—Mg alloy-plated steel sheets, the present inventors have used a benzylidene sorbitol-based gelling agent as a gelling agent. By combining the solvent and resin optimally and making potassium fluoroaluminate into a paste form, it has thixotropy, so it has excellent coating properties and does not cause dripping during coating. Furthermore, the dryness of the coating film is moderate, and the dried coating film formed in this way has excellent adhesion to the surface of the steel sheet, thus greatly facilitating the fusion welding work of the Zn-Al-Mg alloy-plated steel sheet and improving the efficiency. The present invention has been completed by finding that a practical paste-like flux capable of increasing the resistance can be obtained.

  Therefore, as described above, the present invention contains Zn-Al-Mg alloy-plated steel sheet fusion welded paste containing fluoroaluminic acid as an essential component and obtained by using a benzylidene sorbitol-based gelling agent as a gelling agent. It is a flux, has thixotropy, and therefore has excellent coating properties, does not cause dripping upon coating, and has a moderate drying property. Further, the drying formed in this way The purpose of the present invention is to provide a practical paste-like flux that has excellent adhesion to the surface of the steel sheet, thus making the fusion welding work of the Zn-Al-Mg alloy-plated steel sheet significantly easier and increasing the efficiency. To do.

  According to the present invention, it contains at least one benzylidene sorbitol-based gelling agent selected from the group consisting of an organic solvent, a resin, potassium fluoroaluminate and dibenzylidene sorbitol, tribenzylidene sorbitol, and derivatives thereof. A paste-like flux for fusion welding of a Zn—Al—Mg alloy-plated steel sheet is provided.

  The paste-like flux for fusion welding of Zn-Al-Mg alloy-plated steel sheet of the present invention contains fluorinated aluminate as an essential component, and is obtained using a benzylidene sorbitol-based gelling agent as a gelling agent, It has thixotropic properties, and therefore has excellent coating properties, does not cause dripping during coating, and the coating film has an appropriate drying property. Thus, the fusion welding operation of the Zn—Al—Mg alloy-plated steel sheet can be remarkably facilitated, the efficiency can be increased, and the utility is excellent.

  The paste-like flux for fusion welding of Zn—Al—Mg alloy-plated steel sheet according to the present invention is at least one selected from the group consisting of organic solvents, resins, potassium fluoroaluminate and dibenzylidene sorbitol, tribenzylidene sorbitol, and derivatives thereof. The benzylidene sorbitol-based gelling agent is contained.

  In the present invention, the Zn—Al—Mg alloy plating usually comprises 0.05 to 10% by weight of Mg, 4 to 22% by weight of Al, and the balance Zn, but if necessary, Ti is 0.1% by weight or less, B May be 0.045% by weight or less and / or Si may be 2.0% by weight or less.

  In the paste-like flux according to the present invention, the organic solvent is not particularly limited, but at least one selected from the group consisting of alcohols, glycols, glycol ethers and glycol ether esters is preferably used. Specific examples of such a preferable organic solvent include alcohols such as methanol, ethanol, isopropyl alcohol, 3-methyl-3-methoxybutanol, 3-methoxy-1-butanol, and the like. Examples include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and the like, and examples of glycol ethers include methyl ether, ethyl ether, propyl ether, butyl ether, and phenyl ether of the above glycols. Examples of glycol ether esters include acetates of the above glycol ethers.

  In the present invention, such an organic solvent is appropriately determined in relation to other components, but is usually 20 to 78% by weight, preferably 25 to 60% by weight, based on the weight of the paste-like flux. Used in a range. When the amount of the organic solvent used is too large, it may be difficult to gel each component together during the production of the paste-like flux. On the other hand, when the amount of the organic solvent is too small, it is difficult to dissolve or disperse each component in the paste-form flux during production, and there is a possibility that a uniform gel cannot be formed.

  According to the present invention, the organic solvent preferably includes glycol ethers among those described above, and in particular, those including at least one selected from the group consisting of ethylene glycol monobutyl ether and propylene glycol monobutyl ether are preferably used. It is done.

  In particular, according to the present invention, the organic solvent is preferably a mixed solvent of propylene glycol monomethyl ether and ethylene glycol monobutyl ether so that the obtained paste-like flux has an appropriate drying property. Is a mixed solvent of propylene glycol monomethyl ether and ethylene glycol monobutyl ether, and in this mixed solvent, the proportion of propylene glycol monomethyl ether is preferably in the range of 63 to 75% by weight.

  When the organic solvent is composed of propylene glycol monomethyl ether, the resulting paste-like flux has a drying rate that is too high, and when applied to the surface of the steel sheet, a dry coating film is formed quickly. It may be difficult to extend and difficult to apply. On the other hand, when the organic solvent is composed of ethylene glycol monobutyl ether, on the contrary, the drying rate of the obtained paste-like flux is too slow, which may reduce the efficiency of the welding operation. In addition, if welding is performed before the paste-like flux forms a dry coating film, the coating film is not yet sufficiently adhered to the surface of the steel sheet, so the problem is that the coating film peels off from the surface of the steel sheet and volatilizes. Arise.

  Here, according to the present invention, as described above, the organic solvent is a mixed solvent of propylene glycol monomethyl ether and ethylene glycol monobutyl ether, and in this mixed solvent, the proportion of propylene glycol monomethyl ether is 63 to 75% by weight. When it is within the range, the obtained paste-like flux has an appropriate drying rate, is easy to apply, and can improve the efficiency of the welding operation.

  In the present invention, the gelling agent is a component for bringing the components together into a solid and making the resulting gelled product have thixotropic properties. Examples of such a gelling agent include dibenzylidene sorbitol, tribenzylidene. At least one benzylidene sorbitol type selected from the group consisting of sorbitol and derivatives thereof is preferably used.

  Examples of the derivatives of dibenzylidene sorbitol include compounds in which the benzene nucleus in the benzylidene group of dibenzylidene sorbitol is substituted with an alkyl group having 1 to 3 carbon atoms or a halogen atom at an arbitrary position. Examples include [di (p-methylbenzylidene)] sorbitol, [di (m-ethylbenzylidene)] sorbitol, [di (p-chlorobenzylidene)] sorbitol, and the like.

  Examples of the derivative of tribenzylidene sorbitol include compounds in which the benzene nucleus in the benzylidene group of tribenzylidene sorbitol is substituted with an alkyl group having 1 to 3 carbon atoms or a halogen atom at an arbitrary position. Examples include [tri (p-methylbenzylidene)] sorbitol, [tri (m-ethylbenzylidene)] sorbitol, [tri (p-chlorobenzylidene)] sorbitol, and the like. The gelling agents exemplified above may be used alone or in combination of two or more.

  In the paste-like flux according to the present invention, the content of the gelling agent is usually in the range of 1 to 7.5% by weight, preferably 2.5 to 7.5% by weight, based on the weight of the flux. It is a range. When there are too many gelling agents, depending on the amount of organic solvent used, it may be difficult to dissolve in an organic solvent, and the resulting flux has too high gel hardness. Therefore, the coating property on the surface of an iron plate or a steel plate is inferior, and it may be difficult to form a uniform coating film.

  The paste-like flux according to the present invention contains potassium fluoroaluminate as a component for removing magnesium and aluminum components when welding a Zn—Al—Mg alloy plated steel plate.

Examples of potassium fluoroaluminate include monopotassium tetrafluoroaluminate (K [AlF ₄ ]), dipotassium pentafluoroaluminate (K ₂ [AlF ₅ ]), and tripotassium hexafluoroaluminate (K ₃ [AlF ₆ ]). In the present invention, these are used singly or as a mixture of two or more.

In the present invention, the ratio of potassium fluoroaluminate in the paste-like flux is usually in the range of 20 to 65% by weight, preferably in the range of 35 to 60% by weight, based on the weight of the paste-like flux. . When the amount of potassium fluoroaluminate in the paste-like flux is less than 35% by weight, the coating film formed on the surface of the Zn-Al-Mg alloy-plated steel sheet by the paste-like flux becomes a molten metal brittle It does not have the effect of preventing cracking. However, when the amount of potassium fluoroaluminate exceeds 65% by weight, the obtained paste-like flux is too hard and the applicability to the steel sheet surface is poor.

  In the present invention, the resin generally serves to combine the components in the production of the paste-form flux, and as an adhesive for the formed coating film when the obtained paste-form flux is applied to the steel sheet surface. To play a role. In the paste-like flux according to the present invention, as such a resin, in particular, a polyvinyl butyral resin is preferably used in the range of 1 to 7.5% by weight, and preferably in the range of 2.5 to 7.5% by weight.

  When the amount of the polyvinyl butyral resin in the pasty flux exceeds 7.5% by weight, the viscosity of the resulting pasty flux is too high, resulting in poor applicability, while the amount of the resin is less than 1% by weight. Sometimes, in the production of a paste-like flux, not only is it difficult to integrate the components together into a gel, but the resulting paste-like flux does not have sufficient adhesion to the steel sheet surface.

  The paste-like flux by this invention is not limited at all in the manufacturing method. Basically, the above-described components may be mixed uniformly to form a single gel, that is, a paste. An example of a preferable manufacturing method is given. That is, for example, the organic solvent is heated to a temperature of about 70 ° C. and stirred, and the resin is added and dissolved therein. Then, the obtained resin solution is heated at the same temperature as above and stirred. Add and disperse potassium fluoroaluminate. Next, the obtained mixture is heated to the same temperature as described above and stirred, and the above-mentioned benzylidene sorbitol-based gelling agent is added and dissolved therein, thus obtaining a raw material solution. If necessary, the raw material solution is subsequently heated to maintain the dissolution of the gelling agent in the raw material solution, and the raw material solution is poured into a molding container having a desired shape, cooled and gelled. Then, the paste-form flux which has such a shape can be obtained.

  According to the present invention, the viscosity of the paste-like flux can be arbitrarily adjusted according to the organic solvent to be used, the gelling agent, the type and blending amount of the resin, the blending amount of potassium fluoroaluminate, etc. The value measured with a split meter (2 kg load) at 20 ° C. is preferably in the range of 10 to 100 mm.

Hereinafter, the present invention will be described with reference to comparative examples together with examples of the present invention, but the present invention is not limited to these examples. As potassium fluoroaluminate, an equimolar mixture of monopotassium tetrafluoroaluminate (K [AlF ₄ ]) and tripotassium hexafluoroaluminate (K ₃ [AlF ₆ ]) was used.

  An aqueous solution of potassium fluoroaluminate was coated with a Zn-Al-Mg alloy-plated steel sheet (a Zn-Al-Mg alloy obtained by subjecting a low-carbon steel hot-rolled steel sheet with a thickness of 4.0 mm to hot-dip Zn-Al-Mg alloy plating. In the plated steel sheet, the plating layer is made of aluminum 6% by weight, magnesium 3% by weight and the remainder zinc. The same shall apply hereinafter) and sprayed and dried to deposit potassium fluoroaluminate powder. It has already been confirmed that molten metal embrittlement cracks do not occur in the vicinity of the heat affected zone when fusion welding is performed on such a weld (Patent Document 1). Therefore, here, the drying property of the coating film of the paste-like flux, the applicability of the paste-like flux, the adhesion property of the dried coating film to the steel plate surface, and the thixotropic property (dripping property) were examined. The results are shown in Table 1.

Examples 1-4
The components shown in Table 1 were used in the amounts shown in Table 1 to obtain paste fluxes.

Comparative Examples 1-4
The components shown in Table 1 were used in the amounts shown in Table 1 to obtain paste fluxes.

Dryness of the coating film of paste-like flux Take a small amount of flux with a paintbrush having synthetic hair under environmental conditions of temperature 20 ° C. and relative humidity 65%, and apply 80 mg / 20 cm on the surface of the Zn—Al—Mg alloy plated steel sheet. ^A thin film was applied at a ratio of ² to form a coating film, and the surface of the coating film was touched with a finger to examine the time until it was confirmed that the coating film was dry (not wet). Thus, when the drying speed of the coating film is moderate (5 to 15 minutes, which is suitable for actual welding work), when the drying speed is slightly high (1 to less than 5 minutes) or when the drying speed is When slightly slow (over 15 minutes and up to 20 minutes), B, and when the drying speed is too fast (less than 1 minute) or when the drying speed is too slow (when over 20 minutes), C.

Paste flux applicability In the same way as in the drying property of the coating film, a small amount of flux is taken with a paintbrush and applied to the surface of a Zn-Al-Mg alloy-plated steel sheet, the extension of the flux and the uniformity of the coating film Based on the evaluation. The case where both the extension of the flux and the uniformity of the coating film were good was designated as A, the case where at least one was somewhat bad, B, and the case where at least one was bad, C.

Adhesiveness of paste-like flux As with the drying property of the coating film, a small amount of flux is taken with a paintbrush and thinly applied at a rate of 80 mg / 20 cm ^{2 on} the surface of the Zn-Al-Mg alloy-plated steel sheet. After standing for 30 minutes and confirming that the coating film has dried as described above, the surface of the coating film is rubbed with a finger three times so that the load is 1 kg on the platform scale. Then, the degree of peeling of the coating film was examined. The case where the coating film was not peeled at all was designated as A, a part of the coating film was peeled off as B, and the case where the coating film was completely peeled off was designated as C.

Thixotropic property Flux was applied to the surface of a vertically-arranged Zn—Al—Mg alloy-plated steel sheet at a rate of 1 g / 10 cm ² , and after 1 minute, the distance of the flux hanging downward was measured with a ruler. A when the sag of the flux is less than 1 cm and excellent in thixotropy A, B when the sag of the flux is 1 cm or more and less than 5 cm and the thixotropy is not sufficient, B, the distance of sag of the flux Was 5 cm or more, and C was defined as no thixotropic property.

Viscosity Using a spreader, the spread of the dump (diameter of the circle) at a temperature of 20 ° C. and a load of 2 kg was measured with a ruler.

In Table 1, each component means the following.
Organic solvent 1: Propylene glycol monomethyl ether Organic solvent 2: Ethylene glycol monobutyl ether (butyl cellosolve)
Resin: Kuraray Co., Ltd. polyvinyl butyral resin “MOWITAL B-30H”
Gelling agent 1: Dibenzylidene sorbitol gelling agent 2: 12-hydroxystearic acid manufactured by Shin Nippon Rika Co., Ltd.

  As is apparent from the results shown in Table 1, the paste-like flux according to the present invention has excellent applicability, the formed coating film has an appropriate drying rate, and the dried coating film has excellent adhesion to the steel sheet surface. Have Furthermore, since the paste-like flux according to the present invention has thixotropy, it has a relatively low viscosity when applied to a Zn-Al-Mg alloy-plated steel sheet. Therefore, even when the welded portion is an inclined surface or a vertical surface, so-called dripping does not occur.

  On the other hand, since the paste-like fluxes of the comparative examples all use 12-hydroxystearic acid as a gelling agent, they do not have thixotropic properties, and accordingly, Zn-Al-Mg alloy plated steel sheets. When the welded portion is an inclined surface or a surface extending in the vertical direction, the flux applied to such a surface is dripping drastically, making the welding operation very inefficient.

  The paste-like flux according to the present invention has thixotropy, is excellent in applicability to the fusion welded portion of a Zn-Al-Mg alloy-plated steel sheet, and does not cause dripping during application, but also adheres to the steel sheet. Because it is excellent in performance, welding work is greatly facilitated.

Claims (2)

20 to 78% by weight of organic solvent, 1 to 7.5% by weight of resin, 20 to 65% by weight of potassium fluoroaluminate, and at least one benzylidene selected from the group consisting of dibenzylidene sorbitol, tribenzylidene sorbitol and derivatives thereof The organic solvent is a mixed solvent of propylene glycol monomethyl ether and ethylene glycol monobutyl ether, and the proportion of propylene glycol monomethyl ether is 63 to 75% by weight. A paste-like flux for fusion welding of a Zn-Al-Mg alloy-plated steel sheet, characterized by having thixotropic properties in the range.   The paste-like flux for fusion welding of Zn-Al-Mg alloy-plated steel sheet according to claim 1, wherein the resin is a polyvinyl butyral resin.