JP2010221247A - Joint of zinc-based alloy plated steel plate having excellent corrosion resistance of joined portion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joint for obtaining a welding joint of zinc-based alloy plated steel plates having excellent corrosion resistance of a joined portion while securing the joining strength by solving a problem raised during the welding of the zinc-based alloy plated steel plates. <P>SOLUTION: In the joint of the zinc-based alloy plated steel plates, the zinc-based alloy plated steel plates wherein the Al content in the zinc-based alloy plating component is ≥6 mass%, and the plating deposit for single side is ≥50 g/m<SP>2</SP>are joined by using an Al-based joining material containing Si of 5-11 mass%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention mainly relates to a method for joining zinc-based alloy-plated steel sheets used as building materials, and particularly relates to a joint joint of zinc-based alloy-plated steel sheets using an Al-based welding material for obtaining a joint having excellent corrosion resistance. .

  Zinc-based alloy-plated steel sheets are widely used from the viewpoint of improving the corrosion resistance of structural members such as buildings and automobiles. However, when zinc-based alloy-plated steel sheets are used as welded structures, the plating layer applied to the surface of the zinc-based alloy-plated steel sheets disappears in the weld metal and weld heat affected zone (HAZ) that are melted or heated during welding. Or corrosion resistance deteriorates due to damage. For this reason, conventionally, in order to ensure the corrosion resistance of the welded portion, post-coating such as zinc rich paint is generally performed on the welded portion.

  However, this method also requires a painting operation after welding, which is troublesome and has a problem in production efficiency.

  In addition, the anticorrosion by the paint has problems such as peeling off in a relatively short time and difficulty in painting in a narrow area, depending on the use environment. Moreover, it is difficult to say that the corrosion resistance is sufficient.

  On the other hand, as a highly corrosion-resistant zinc-based alloy-plated steel sheet, in recent years, a steel sheet (for example, see Patent Document 1) has been put to practical use with a Zn-Al-Mg-Si-based alloy plating. Has improved. Accordingly, it is necessary to further improve the corrosion resistance of the welded portion, and a new technique for improving the corrosion resistance has been demanded in place of the conventional anticorrosion by painting.

  In order to solve these problems, Patent Document 2 proposes to apply a stainless steel welding material and a copper alloy welding material to the bonding material of the zinc-based alloy-plated steel sheet. However, since both the stainless steel welding material and the copper alloy welding material have a melting point exceeding the boiling point of zinc (about 900 ° C.), the galvanization is evaporated by heating during joining, and defects such as blowholes are generated in the joint. There's a problem. In addition, damage to the galvanized layer due to heat input during bonding is increased.

  In particular, in the joining of thin zinc-based alloy-plated steel sheets with a thickness of about 2 mm or less, the plating component on the back surface of the welded portion evaporates, which has been a cause of corrosion resistance deterioration.

JP 2000-064061 A JP 2006-35294 A

  The present invention is to solve the above-mentioned problems that occur during welding joining of zinc-based alloy plated steel sheets, to secure joint strength, and to obtain a welded joint of zinc-based alloy plated steel sheets with good corrosion resistance at the welded joints. An object of the present invention is to provide a joint joint.

  As described above, both the stainless steel welding material and the copper alloy welding material have a problem that the melting point exceeds the boiling point of zinc. Accordingly, the present inventors have focused on an Al (aluminum) -based bonding material as a bonding material having a melting point lower than the boiling point of zinc, and decided to try to improve the corrosion resistance of the bonded portion by application thereof.

  Usually, when a steel plate and aluminum are joined, it becomes joining between dissimilar metals, and corrosion of a joined part advances by a potential difference between metallic materials. The same phenomenon occurs even when steel materials are joined with an Al-based joining material, and corrosion progresses. For this reason, in joining steel materials, it has been generally considered that the application of an Al-based joining material to a site that requires corrosion resistance is not suitable. In addition, as long as the present inventors can confirm, there is no prior art in which an Al-based bonding material is applied to bonding between zinc-based alloy plated steel sheets.

  As a result of intensive studies to break down such a concept, the inventors of the present invention, in order to ensure the strength of a joint obtained by joining zinc-based alloy plated steel sheets using an Al-based bonding material, It was also found that by strictly controlling the plating composition and the amount of plating deposited in zinc-based alloy plating, the potential difference between different metals can be suppressed and the progress of corrosion can be suppressed. The present invention has been made based on this finding. The gist is as follows.

(1) In a joint joint between zinc-based alloy-plated steel sheets, a zinc-based alloy in which the Al content in the zinc-based alloy plating component is 6% by mass or more and the plating adhesion amount per side is 50 g / m ² or more A bonded joint between zinc-based alloy-plated steel sheets having excellent corrosion resistance at a joint, wherein the plated steel sheet is bonded using an Al-based bonding material containing 5 to 11% by mass of Si.

  (2) The corrosion resistance of the joint according to (1), wherein the zinc-based alloy plating is any one of a Zn-Al-Mg-based alloy plating and a Zn-Al-Mg-Si-based alloy plating. Bonded joints of zinc-based alloy-plated steel sheets with excellent resistance.

  (3) The joint according to (1) or (2), wherein the joint length between the zinc-based alloy plated steel sheets is at least three times the thickness of the zinc-based alloy plated steel sheet. Bonded joint of zinc-based alloy-plated steel sheet with excellent corrosion resistance.

  According to the method for joining zinc-based alloy-plated steel sheets using the Al-based joining material of the present invention, it is possible to dramatically improve the corrosion resistance of the joined portion without performing anticorrosion coating treatment on the joined portion after joining. It becomes. On the other hand, since an Al-based bonding material is used for the bonding metal, the bonding joint strength is lower than the strength of the steel plate base metal, but its necessary functions, such as a container that is required in a severe corrosive environment and the sealing of the bonded portion, If the necessary characteristics are optimized, a remarkable effect can be obtained.

It is a figure which shows the test piece of a lap fillet joint. It is a figure which shows the tensile shear test method. It is a figure which shows the relationship between Al content in the plating component composition of a steel plate, the amount of plating adhesion, and joint strength.

Details of the present invention will be described based on examples.
First, the corrosion resistance when welding with an Al-based bonding material was applied to a zinc-based alloy-plated steel sheet was confirmed by a corrosion resistance experiment by changing the plating type of the plated steel sheet and the type of the Al-based bonding material.

  Table 1 shows the zinc-based alloy plated steel sheets used in the test. Nine types (A to I) of zinc-based alloy-plated steel sheets were prepared based on the plating components, particularly the Al content during plating, the single-sided plating adhesion amount of the steel sheet, and the plate thickness. The zinc-based alloy-plated steel sheet was based on SPCC (JIS G3131 hot rolled mild steel sheet).

  Table 2 shows five types of bonding materials used in the test. There are four types of Al-based bonding materials (pure Al (JIS Z 3232 A1100-WY), 5% Mg-95% Al (JIS Z3232 A5356-WY), 5% Si-95% Al (JIS Z3232 A4040-WY), For comparison with 11% Si-89% Al (without JIS standard)) 309 series stainless steel joining material (309 series flux-cored stainless wire containing Ni: 12%, Cr: 24%) is prepared for comparison did.

  A lap fillet welded joint as shown in FIG. 1 was prepared using these zinc-based alloy-plated steel sheet and bonding material, and this was used as a test piece. Table 3 shows the welding conditions when creating the joint.

  In an actual corrosive environment, joint strength is expected to change with time. Therefore, a combined cycle corrosion test was performed to evaluate the joint strength after the joint was exposed to a corrosive environment. As a combined cycle corrosion test, salt spray (5% NaCl) is 2 hours at 35 ° C., drying (humidity 30%) is 4 hours at 60 ° C., and humidity (humidity 95%) is 50 ° C. for 2 hours as one cycle. The combined cycle corrosion test was repeated 150 cycles.

  After the combined cycle corrosion test, a tensile test was performed as shown in FIG. 2, and the tensile shear strength of the joint was measured. In addition, the strength of the joint portion was represented by breaking strength / base material cross-sectional area (MPa).

  Table 3 shows the joining conditions when producing each joint and the evaluation results of the corrosion resistance and strength of the welds. The corrosion resistance test was the above-mentioned combined cycle corrosion test, and the red rust occurrence state of the joint after the 150 cycle test was evaluated. Those with significant red rust occurred were marked with (X), and those with white rust and plated metallic luster were marked with (O). The tensile shear strength is shown in Table 3 as a reference shear strength of 150 MPa, which is about 1 / √3 of the tensile strength standard of 270 MPa of the base material.

  The steel sheet H employs Zn—Al—Mg based plating with improved corrosion resistance, but the joint strength after the corrosion test was low when no Si was added to the welding material. When the fracture mode was observed, the Al-based bonding metal was peeled off at the bonding interface with the base material. It is considered that since the Fe—Al intermetallic compound was formed at the bonding interface, the bonding interface became a very brittle structure and peeling occurred.

  On the other hand, the one using the Si-based Al bonding material showed good corrosion resistance and good joint strength after the corrosion test. The fracture mode was ductile fracture at the Al-based joint metal part. It is thought that the addition of Si to the Al-based bonding material suppressed the formation of Fe-Al intermetallic compounds at the bonding interface.

  On the other hand, even when a 5% Si-based Al bonding material was used, there was a difference in the tensile shear strength after the combined cycle corrosion test depending on the Al content of the plating component and the plating adhesion amount. That is, the corrosion resistance of the joint can be improved by increasing the amount of Al in the plating component. Although the melting point of the Al-based bonding material is about 660 ° C., the arc plasma that is a heat source reaches several thousand ° C., so that the galvanization directly under the arc plasma evaporates and the galvanization in the heat affected zone is damaged.

  Similarly, Al in the plating component is also evaporated by the heat of the arc plasma, but the boiling point of Al is as high as about 2000 ° C. compared to the boiling point of zinc at about 900 ° C., and evaporation is reduced. As a result, since the heat-affected zone is protected by the Al component by containing 6% or more of Al in the plating component, it is considered that the corrosion resistance was good.

  From this result, if the combination of Si-added Al bonding material and zinc-based alloy-plated steel sheet containing 6% or more Al component during plating, good corrosion resistance is obtained even after welding, and tensile shear strength of 150 MPa is secured. I knew it was possible.

  Next, an experiment was conducted on how the joint strength is affected by the Al content in the plating component composition of the zinc-based alloy-plated steel sheet to be the base material and the plating adhesion amount on one surface of the steel sheet.

The Al content in the plating component composition of the zinc-based alloy-plated steel sheet is 0.1%, 4%, 6%, 11%, 15%, and 18%, and the plating adhesion on one side is 30 g / m ² and 50 g, respectively. Test materials to be / m ² , 100 g / m ² , and 150 g / m ² were prepared. These test materials were welded with a 5% Si-based bonding material to prepare a lap fillet joint test piece similar to the above.

These joint test pieces were subjected to a combined cycle corrosion test similar to the above corrosion resistance test, and then a tensile test was performed to determine the tensile shear strength of the joint.
The result is shown in FIG. When the Al content in the plating component composition is 4% or less, or when the plating adhesion amount is 30 g / m ² or less, the fracture strength at the joint is low (less than 150 MPa), and the fracture position is also unstable at the fracture interface. It became a form. In these corrosion test pieces, corrosion of the joint progressed, red rust was generated from the heat affected zone of the base metal, and thinning due to corrosion occurred in the Al bonded metal part.

  On the other hand, when the Al content is 6% or more and the plating adhesion amount is 50 g / m 2 or more, a relatively good joint strength with a breaking strength of 150 MPa or more is exhibited, and the joint strength before corrosion and after 150 cycles of corrosion test Changed little. Almost no thinning of red rust or Al bonding metal was observed at the joint after the corrosion test, indicating good joint corrosion resistance. Since the Al content in the plating component composition has increased, the evaporation of the Al component during welding is small as described above, and as a result of the formation of an Al protective film on the heat-affected zone on the surface of the base material, good corrosion resistance is achieved. It is thought that it was possible to secure.

  Thus, the Al content in the plating component affects the joint strength after the corrosion test. From the results shown in FIG. 4, the lower limit of the Al content in the plating component was 6%. The upper limit is not particularly specified, but if the Al content in the plating component exceeds 19%, the sacrificial anticorrosive effect of the plated steel sheet itself is insufficient and the corrosion resistance of the bent portion is lowered, so the upper limit may be 19%. desirable.

Moreover, about the plating adhesion amount, in order to ensure the corrosion resistance of a suitable junction part, the lower limit was set to 50 g / m2. Although an upper limit is not specified in particular, the upper limit is preferably set to 150 g / m ² with reference to the amount of coating on a general zinc-based alloy-plated steel sheet for building materials.

Next, the Si addition range of the Si-added Al-based bonding material was examined.
When a 5% Si-based bonding material was used, the test piece subjected to the tensile shear test was broken in the weld metal, and the breaking strength (tensile shear strength) was 150 MPa or more.

  This suppresses the diffusion of the iron component of the base metal into the bonding metal by increasing the Si concentration in the Al-based bonding metal, and consequently suppresses the growth of the Fe—Al alloy layer at the bonding interface. This is considered to be possible. In addition, it is considered that relatively good joint strength was obtained because the strength of the Al-bonded metal increased due to an increase in the amount of Si in the bonded metal.

  From the above examination, it has become clear that addition of Si is effective as an alloy component of the Al-based bonding material. When the addition amount of Si is 5% or less, the effect of suppressing the formation of Fe-Al intermetallic compounds and the effect of improving the strength of the Al bonding metal are not sufficient, and when the addition amount of Si exceeds 11%, Al bonding is performed. Since the metal becomes brittle, the appropriate Si addition amount is set to 5 to 11%.

  In the present invention, it is confirmed that there is no problem even if Mg or Si is contained in addition to Al as the plating component composition. In particular, Zn-Al-Mg alloy-plated steel materials have attracted attention as building materials having excellent corrosion resistance in recent years. By applying the present invention, the scope of application of the structures in the Zn-Al-Mg-based alloy plated steel materials can be increased. It is much more widespread and the effect is great.

  In the Zn—Al—Mg-based alloy plated steel material, Al: 6 to 19%, Mg: 0.5 to 10%, and the remaining Zn is plated. In the Zn—Al—Mg—Si-based alloy plating, Al: 6 A plating composed of ˜19%, Mg: 0.5 to 10%, Si: 0.01 to 2%, and the balance Zn is generally used.

  For example, a “Superdimer (registered trademark)” steel plate manufactured by Nippon Steel Corp. with 11% Al, 3% Mg, 0.2% Si, and the balance mainly Zn or 7% Al and 3% Mg There are “ZAM (registered trademark)” steel plates manufactured by Nisshin Steel Co., Ltd., mainly containing Zn in the balance. However, the present invention is not limited to these steel materials and plating component compositions.

Next, the strength of the joint will be examined.
In this invention, since Si system Al joining material is used for the joining of a steel plate, it is inferior to the base material strength of a steel plate from a viewpoint of welded joint strength. Therefore, even if the corrosion resistance is equivalent to the base zinc-based alloy-plated steel sheet, the joint becomes a neck in the strength as a structure.

  In order to eliminate this neck, it is effective to lengthen the contact portion length (Lu, Ld in FIG. 1) and the surfacing height (Lh) of the joint metal in the joint. For example, in the case of lap fillet welding between steel plates, the contact length is about the plate thickness, but aluminum is about 1/3 the strength of iron, so if the contact length is at least three times the plate thickness Good. Since the contact area increases, the risk of corrosion between dissimilar metals increases, but there is no particular problem if a joining material and a steel plate within the scope of the present invention are selected.

  The present inventors performed a test in which Zn + 11% Al + 3% Mg + 0.2% Si plating was applied, and steel plates having a coating adhesion amount of 90 g / m 2 and a plate thickness of 1.2 mm were bonded together with a 5% Si-added Al bonding material. It was. At this time, each of the test pieces whose joint lengths (Lu, Ld, and Lh in FIG. 1) were 2 mm, 3 mm, 4 mm, and 6 mm, respectively, was subjected to a tensile shear test after the combined cycle corrosion test. As a result, the joint lengths of 2 mm and 3 mm are broken in the joining metal, but the 4 mm test piece is broken at the joining metal portion or the steel plate base material, and the 6 mm test piece is made of the steel plate base material. It was broken.

  Also from this result, if the joint length is 3 times or more the plate thickness, it can have a tensile shear strength equivalent to the base material tensile strength. It is desirable that the joint length is 10 times or more the plate thickness in order to perform stable welding. However, since the method of applying the force of the structure is complicated, when a force other than the tensile shear force is applied, a countermeasure suitable for it is necessary, but the basic idea is the same.

  According to the method for joining zinc-based alloy-plated steel sheets using the Al-based joining material of the present invention, it is possible to dramatically improve the corrosion resistance of the joined portion without performing anticorrosion coating treatment on the joined portion after joining. It becomes. Therefore, it is needless to say that it is a technology that dramatically expands the application range of zinc-based alloy-plated steel sheets with enhanced corrosion resistance function, and it is considered that it will contribute widely to the development of the industrial field.

DESCRIPTION OF SYMBOLS 1 Zinc type alloy plating 2 Base material of zinc type alloy plating steel plate 3 Al type joining metal Lu, Ld Junction length Lh Junction surplus height

Claims (3)

In joints between zinc-based alloy plated steel plates,
A zinc-based alloy-plated steel sheet having an Al content in a zinc-based alloy plating component of 6% by mass or more and a plating adhesion amount per side of 50 g / m ² or more is 5 to 11% by mass of Si. A bonded joint between zinc-based alloy-plated steel sheets excellent in corrosion resistance of the joint, characterized by bonding using a copper-based bonding material.   The said zinc-type alloy plating is either Zn-Al-Mg-type alloy plating and Zn-Al-Mg-Si type alloy plating, It was excellent in the corrosion resistance of the junction part of Claim 1 characterized by the above-mentioned. Joined joint of zinc-based alloy plated steel sheet.   The joint according to claim 1 or 2, wherein, in a joint joint between zinc-based alloy plated steel sheets, the length of the joint and the surplus height are three times or more the plate thickness of the zinc-based alloy plated steel sheet. Bonded joint of zinc-based alloy-plated steel sheet with excellent corrosion resistance.

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