JP4640995B2 - Steel plate for brazing joint with aluminum material, joining method and joint using the steel plate - Google Patents

Description

  The present invention relates to a joining technique between a steel plate and an aluminum-based material required in an assembly process such as an automobile structure, and more specifically, a steel plate suitable for joining with an aluminum-based material by brazing, and the steel plate and The present invention relates to a joining method with an aluminum-based material, and a joined joint joined by the method.

  When joining steel sheets, which are a type of iron-based material, and aluminum-based materials (a collective term for aluminum and aluminum alloys), brittle intermetallic compounds are likely to form at the joints, so that the joints have high reliability and reliability. It was very difficult to get a part.

  As countermeasures against this, a number of conventional techniques have been disclosed as follows.

  For example, a method of providing an iron-chromium layer having a specific composition on the surface of an iron-based material and superimposing it on aluminum and heating it while applying pressure (see Patent Document 1), an iron-based material layer and an aluminum alloy layer prepared in advance A method of laser welding, resistance welding or seam welding with a two-layer clad material made of (see Patent Documents 2 to 4), a method of spraying an aluminum-based sprayed material at a joint of an iron-based material and performing TIG welding (Patent) (Refer to Document 5), a method of plating and brazing aluminum, copper, zinc, or the like on the joint portion of an iron-based material (see Patent Documents 6 and 7), nitride, carbide or potassium silicofluoride having a rock salt structure on the joint surface And a brazing method (see Patent Documents 8 and 9).

  However, the above prior art has the following problems.

  A method in which an iron-chromium layer having a specific composition is provided on the surface of an iron-based material and is heated and bonded while being superposed on aluminum (see Patent Document 1) is a method of bonding members having a relatively simple shape such as a flat plate. However, since it cannot be applied when the shape of a member such as a pressed product is complicated, the applicable range is narrow and the versatility is poor.

  In a method of laser welding, resistance welding or seam welding (see Patent Documents 2 to 4) by interposing a two-layer clad material comprising an iron-based material layer and an aluminum alloy layer prepared in advance (see Patent Documents 2 to 4), an iron-based material and an aluminum-based material Since the clad material is inserted between the two plates, the joining of the two plates becomes the joining of the three plates. For this reason, there is a problem that the stability of quality cannot be ensured because an insertion process and a fixing process of an insert material (clad material) are required at the time of actual construction and the process becomes complicated.

  A method in which an aluminum-based thermal spray material is sprayed on a joint portion of an iron-based material and TIG welding is performed (see Patent Document 5), and a method in which plating of aluminum, copper, zinc, or the like is performed on the joint portion of an iron-based material and brazed (Patent Document 6) And 7), a method of forming a brazing layer of a rock salt structure nitride, carbide or potassium silicofluoride and brazing (see Patent Documents 8 and 9) requires spraying, plating, and coating processes. As described above, since the process becomes complicated, there is a problem that quality stability cannot be secured.

  In any of the above methods, in addition to the above problem, there is a problem that the equipment cost becomes high because a new equipment must be incorporated into the current welding line. Furthermore, in the method using a clad material, the clad material itself must be manufactured by joining an iron-based material and an aluminum-based material. Therefore, the production conditions are severely restricted, and an inexpensive and stable performance clad material is required. It was difficult to obtain.

  As one of the backgrounds in which various methods as described above have been proposed for joining an iron-based material and an aluminum-based material, an intermetallic compound that is brittle at the joint when the iron-based material and the aluminum-based material are directly melt-bonded. May be generated and cracking is likely to occur. For this reason, when directly joining an iron-based material and an aluminum-based material, including the case of joining using a brazing material, how to form a fragile intermetallic compound layer near the interface between the iron-based material and the aluminum-based material. It is extremely important not to generate them.

  From such a viewpoint, there has been proposed a method (see Patent Documents 10 and 11) in which components of the brazing material (or brazing wire) are adjusted to suppress the formation of intermetallic compounds in the joint.

However, according to the study by the present inventors, even if the components of the brazing material (or brazing wire) are appropriately selected, the joint joint obtained by brazing the steel plate and the aluminum-based material is shear tensile. Aside from the strength, it has been found that the peel strength may be significantly reduced.
JP 63-235083 A JP-A-4-81288 Japanese Unexamined Patent Publication No. 7-47477 Japanese Patent Laid-Open No. 11-197846 Japanese Patent Laid-Open No. 11-291043 JP-A-62-238066 JP-A-5-185217 JP-A-8-257743 Japanese Patent Laid-Open No. 9-225631 JP-A-3-285761 JP 2003-33865 A

Therefore, the present invention has an object to provide a steel plate that can provide a joint joint excellent not only in shear tensile strength but also in peel strength by brazing and joining with an aluminum-based material. An object of the present invention is to provide a bonding method and a bonded joint.

  The invention according to claim 1 is any one steel plate selected from the group consisting of an alloyed hot dip galvanized steel plate, hot dip galvanized steel plate, electrogalvanized steel plate, cold rolled steel plate and hot rolled steel plate, % By mass (hereinafter the same), C: 0.05 to 0.25%, Si: 1.5% or less, Mn: 0.1 to 3.5%, P: 0.05% or less, S: An aluminum-based material characterized by containing 0.03% or less, Al: 0.1% or less, the balance being Fe and inevitable impurities, and satisfying C + (Si + Mn) /40≧0.15 This is a steel plate for brazing.

  Invention of Claim 2 is a steel plate for brazing joining with the aluminum-type material of Claim 1 which further contains 1.0% or less of 1 type or 2 types in total among Cr and Mo. .

  The invention according to claim 3 further includes one or more of Ti, Nb, V, and Zr in a total of 0.1% or less, and the aluminum-based material according to claim 1 or 2 A steel plate for brazing.

  Invention of Claim 4 is a steel plate for brazing joining with the aluminum-type material of any one of Claims 1-3 which contains B: 0.003% or less further.

  The invention according to claim 5 further includes the aluminum-based material according to any one of claims 1 to 4, further containing one or two of Cu and Ni in a total of 0.6% or less. A steel plate for brazing.

  Invention of Claim 6 is a steel plate for brazing joining with the aluminum-type material of any one of Claims 1-5 which contains 0.005% or less of Ca further.

  Invention of Claim 7 joins the steel plate of any one of Claims 1-6, and an aluminum-type material by brazing, The joining method of the steel plate and aluminum-type material characterized by the above-mentioned. It is.

  The invention according to claim 8 is the method for joining the steel sheet and the aluminum-based material according to claim 7, wherein the brazing is MIG brazing or TIG brazing.

  Invention of Claim 9 is joined by the method of Claim 7 or 8, and the thickness of the intermetallic compound layer in the central part of the joint interface is 2 μm or less, and a steel plate, It is a joint joint with an aluminum-based material.

  By using the steel sheet according to the present invention, the brittle iron-aluminum metal generated at the interface with the aluminum-based material by concentrating C, Si, and Mn on the surface of the joint of the steel sheet by heating when brazing with the aluminum-based material Formation and growth of intermetallic compounds are suppressed, and the layer thickness is limited to a certain value or less. As a result, a bonded joint excellent not only in shear tensile strength but also in peel strength can be obtained.

Embodiment
(1) Configuration of Steel Sheet According to the Present Invention First, the reasons for limiting chemical components of the steel sheet according to the present invention will be described.

  C is an essential element for generating a low-temperature transformation structure such as martensite and increasing the strength of the steel sheet. If this C amount is low, a predetermined low-temperature transformation structure amount cannot be obtained, resulting in insufficient strength. The lower limit is 0.05%. However, if it is contained excessively, formability and weldability are hindered, so the upper limit of the content is made 0.25%. A more preferable range of the C content is 0.05 to 0.20%.

Si is a solid solution strengthening element effective for increasing the strength while suppressing a decrease in the elongation of the steel sheet. However, if the content is too large, the chemical conversion property and the plating adhesion such as galvanization are deteriorated, so the upper limit is made 1.5%. A more preferable upper limit of the Si content is 1.0%.

Mn, like C, is an essential element for increasing the strength of the steel sheet. However, if the content is large, ductility deteriorates, so the upper limit is made 3.5%. On the other hand, if the content is less than 0.1%, the effect is too small, so the lower limit is made 0.1%. A more preferable range of the Mn content is 0.5 to 0.03%.

P is an element effective for strengthening the steel sheet and increasing the ductility, but on the other hand, it easily segregates at the grain boundary, lowers the grain boundary strength and lowers the toughness, so the upper limit is made 0.05%. A more preferable range of the P content is 0.01 to 0.03%.

S is an impurity. If the content is large, inclusions in the steel increase and the workability deteriorates, so the upper limit is made 0.03%. A more preferable upper limit of the S content is 0.015%.

Al is an element useful as a deoxidizer for molten steel. However, if the content exceeds 0.1%, the cleanliness of the steel sheet is impaired and surface flaws are liable to occur, so the upper limit is made 0.10%. A more preferable range of Al content is 0.03 to 0.06%.

Next, the reason for the provision of C + (Si + Mn) /40≧0.15 will be described. According to the study by the inventors, a phenomenon in which C, Si, and Mn are concentrated on the surface of the joint portion of the steel sheet by heating when brazing with the aluminum-based material was recognized. Although the detailed mechanism is not clear at this stage, when the degree of concentration of C, Si, and Mn exceeds a certain level, the formation and growth of brittle iron-aluminum intermetallic compounds formed at the interface with the aluminum-based material may occur. It was remarkably suppressed and the thickness of the intermetallic compound was found to be limited to a certain value or less.

Here, it is considered that the thickness of the intermetallic compound layer has a great influence on the joint strength, that is, the shear tensile strength and the peel strength. That is, when the thickness exceeds a certain value, the strain generated inside the intermetallic compound layer increases, and the fracture occurs from the inside of the intermetallic compound layer, which is brittle with respect to external loads. That is, the joint strength decreases rapidly. On the other hand, when the thickness of the intermetallic compound layer is limited to a certain value or less, the breakdown is mainly caused by an external force, the intermetallic compound layer and the aluminum-based material, or the intermetallic compound layer. Since it occurs from the interface of the steel plates, the fracture strength, that is, the joint strength is maintained high.

As described above, it was found that, as a result of concentrating C, Si and Mn, the thickness of the intermetallic compound layer is limited to a certain value or less, and as a result, a joint joint having excellent peel strength as well as shear tensile strength can be obtained.

The thickness of the intermetallic compound layer has a strong correlation with C + (Si + Mn) / 40, and when C + (Si + Mn) / 40 is 0.15 or more, the thickness of the intermetallic compound layer is 2 μm or less, which is the above constant value. It has been found that when the thickness of the intermetallic compound layer becomes 2 μm or less, which is the above-mentioned constant value, the required strength can be obtained for both the shear tensile strength and the peel strength (see Examples below). From the above, it was defined as C + (Si + Mn) /40≧0.15.

In addition to the above, the steel sheet according to the present invention may contain the following chemical components.

Cr and Mo are effective elements for improving the hardenability of the steel sheet. However, when these elements are contained excessively, the ductility is lowered and the cost is high because the metal is expensive. Therefore, the upper limit of the content is 1.0% in terms of the total amount of Cr and Mo. In addition, Cr and Mo may contain only one sort, and may contain both.

  Ti, Nb, V, and Zr are contained for the purpose of refining the structure and strengthening the precipitation. However, if these elements are contained excessively, precipitates increase and ductility is remarkably deteriorated, so the upper limit of the content is 0.1% in terms of the total amount of Ti, Nb, V and Zr. In addition, these elements may contain only any 1 type, and may contain any 2 or more types.

  B is a useful element that greatly improves the hardenability of the steel sheet and is effective in improving the toughness of the quenched structure. However, if contained excessively, the effect is saturated and ductility is lowered, so 0.003% is made the upper limit of the content.

  Cu and Ni are extremely useful elements for densifying the generated rust, remarkably reducing the corrosion rate of the steel sheet in the atmospheric environment, and improving delayed fracture resistance. Further, since these elements are electrochemically noble elements than iron, they synergistically improve the corrosion resistance of the steel sheet. However, the excessive content of these elements may cause embrittlement during hot rolling, and the production cost increases because it is an expensive metal. Therefore, the upper limit of the content is 0.6% in terms of the total amount of Cu and Ni. Cu and Ni may contain only one of them or both of them.

  Ca is an element useful for reducing the sulfide inclusions themselves and for controlling the form of the resulting sulfide inclusions. However, if the content is excessive, the effect is saturated and the cleanliness of the steel is deteriorated. Therefore, the upper limit is made 0.005%.

  The steel sheet according to the present invention may be any one of an alloyed hot-dip galvanized steel sheet, hot-dip galvanized steel sheet, electrogalvanized steel sheet, cold-rolled steel sheet, and hot-rolled steel sheet. Here, when an alloyed hot-dip galvanized steel sheet, hot-dip galvanized steel sheet or electrogalvanized steel sheet (these are collectively referred to as “galvanized steel sheet”), when brazing with an aluminum-based material, the interface between the galvanizing and the brazing material , A layer composed of an intermetallic compound and an oxide is formed. Then, zinc, which is a plating component in this layer, diffuses into the brazing material while depriving oxygen from the oxides on the surface of the base steel plate and the aluminum-based material (generally referred to as dissimilar metal member). As a result, the surface of the dissimilar metal member is activated to cause the wetting of the brazing material, and a compound layer composed of the brazing material component and the dissimilar metal member component is formed on the dissimilar metal member surface, and the compound The brazing material adheres firmly through the layer, and a plating layer made of the brazing material is formed (see paragraph [0006] of Patent Document 7). Therefore, when a galvanized steel sheet is used, it is presumed that a joint having a higher bonding strength can be obtained than when a cold-rolled steel sheet or a hot-rolled steel sheet, which is a bare steel sheet not subjected to galvanization, is used. However, even if it is a cold-rolled steel plate or a hot-rolled steel plate, which is a bare steel plate, the activation of the surface of the dissimilar metal member by zinc is not expected as long as it has the composition defined by the present invention. The effect of suppressing the formation and growth of intermetallic compounds by the concentration effect of C, Si and Mn, which is the effect of the present invention, is still obtained, and naturally belongs to the technical scope of the present invention.

(2) Joining method using steel sheet according to the present invention By brazing a steel sheet made of the above chemical component with an aluminum-based material, the intermetallic compound layer thickness at the center of the joint interface becomes 2 μm or less, together with shear tensile strength. A joint joint with excellent peel strength can be obtained.

  Here, the brazing material is not particularly limited as long as it is a brazing material generally used for joining aluminum-based materials. For example, a copper alloy, a Ni alloy, an aluminum alloy, or the like can be used.

  Further, as a brazing method, in addition to a normal manual brazing method, a MIG brazing method (refer to Patent Document 11) or a TIG brazing method in which a general-purpose welding apparatus is used to braze by an arc. It can also be used. In addition, as a welding form used for the MIG brazing method, there are a direct current MIG and an alternating current MIG due to a short-circuit arc, a pulse arc, a spray arc, etc. in relation to the droplet transfer phenomenon. The effect of the present invention can be obtained and is not limited. As welding conditions, current: 40 to 90 A, voltage: 8 to 12 V, and welding speed: 40 to 200 cm / min are recommended.

  Hereinafter, the present invention will be described in more detail based on examples.

  Using an aluminum alloy-based MIG brazing wire, a lap fillet welding test was performed on a steel sheet A having various chemical components shown in Table 1 and an aluminum-based material B. The welding conditions are: current: 85 A, voltage: 10 V, speed: 180 cm / min. Moreover, Ar (flow rate is 25 L / min) was used as the shielding gas, and the target position of the arc was the lower plate side corner portion 11b.

  Specifically, an A6022 aluminum alloy plate B (lower plate 12) as an aluminum-based material having a thickness of 1.0 mm and a steel plate A (upper plate 11) having a thickness of 1.0 to 1.4 mm are overlapped. A lap fillet joint was formed, and welding (joining) between the steel plate A and the aluminum alloy plate B was performed using the aluminum alloy MIG brazing wire 13 (see FIG. 1). In addition, as the steel plate A, the galvannealed steel plate (GA) was used. As the aluminum alloy MIG brazing wire 13, an aluminum alloy MIG brazing wire containing 1.5 to 7.5% of Si was used.

  The plane size of the test piece was 150 mm × 400 mm for both the steel plate A and the aluminum alloy plate B, and a welding wire (MIG brazing wire) 13 having a diameter of 1.2 mm was used.

  After welding (joining), a test piece for joint strength evaluation having a plate width of 25 mm was taken, sandwiched between shear tensile test pieces shown in FIG. 2 or a jig, and bent at a position of 10 mm from the joint (end face of the upper plate 11). The peel test piece shown in FIG. Then, a shear tensile test and a peeling test were performed at a speed of 10 mm / min using each test piece, and the joint strength was calculated according to the following formula (1).

  Formula (1) (joint strength) = (maximum load point load) / (joint length)

Further, the shear tensile test piece (before the test) was cut perpendicularly to the weld bead to produce a sample for cross-sectional observation, and the central portion E of the bonding interface D shown in the macro photograph of FIG. Was photographed at a magnification of 400, and as shown in the micrograph of FIG. 4 (b), a region with a length of 15 μm was taken in the direction along the bonding interface D, and three regions at the center and both ends of this region were taken. The thicknesses d _{1 to} d ₃ of the intermetallic compound layer F in the above are measured, and the values obtained by arithmetically averaging these three thicknesses d _{1 to} d ₃ are defined in the present invention as “metal at the center of the bonding interface” The thickness of the intermetallic compound layer (hereinafter also simply referred to as “the thickness of the intermetallic compound layer”) ”.

Table 1 shows the plating type, steel composition, mechanical properties (measured with JIS No. 5 test piece), plating adhesion amount and plate thickness of each steel plate used in the main welding test. Table 2 shows the thickness, shear tensile strength, and peel strength of the intermetallic compound at the central portion of the joint interface of the joint obtained in this welding test.

  FIG. 5 shows the relationship between C + (Si + Mn) / 40 of the steel sheet and the thickness of the intermetallic compound layer, FIG. 6 shows the relationship between the thickness of the intermetallic compound layer and the shear tensile strength of the joint, and FIG. The relationship between the thickness of a compound layer and the peeling strength of a joint is shown. From FIG. 5, when C + (Si + Mn) / 40 <0.15, the thickness of the intermetallic compound layer exceeds 2 μm, and from FIGS. 6 and 7, when the thickness of the intermetallic compound layer exceeds 2 μm, the shear tensile strength and peeling It can be seen that the strength also decreases rapidly. Furthermore, the steel types No. 1 in Table 1 and Table 2 were used. As is clear from the data of 10 to 14, 18 to 20, 22 (comparative examples) and FIG. 8, it is not sufficient that the contents of individual elements including C, Si and Mn simply satisfy the component range of the present invention. It can be seen that unless the value of C + (Si + Mn) / 40 satisfies the range defined by the present invention (0.15 or more), neither the shear tensile strength nor the peel strength can be obtained sufficiently.

  Further, as a result of EPMA line analysis in the direction perpendicular to the bonding interface D of FIG. 5 (b), the steel plate of the invention example (steel type No. 6), as shown in FIG. It was recognized that C, Si, and Mn were concentrated at a high concentration on the joint surface.

  Therefore, by using a steel sheet that simultaneously satisfies the component range of each element defined by the present invention and C + (Si + Mn) /40≧0.15, even if brazed to an aluminum-based material, not only the shear tensile strength but also the tensile strength is reduced. It was confirmed that a joint joint having a high peel strength and a stable high value was obtained.

It is sectional drawing which shows the overlap fillet welding method typically. It is sectional drawing which shows the structure of a shear tension test piece typically. It is sectional drawing which shows typically the structure of a peeling test piece. It is a cross-sectional photograph for demonstrating the position which measures the thickness of an intermetallic compound layer, (a) is a macro photograph, (b) is a microscope picture. It is a graph which shows the relationship between C + (Si + Mn) / 40 and the thickness of an intermetallic compound layer. It is a graph which shows the relationship between the thickness of an intermetallic compound layer, and shear tensile strength. It is a graph which shows the relationship between the thickness of an intermetallic compound layer, and peeling strength. It is a graph which shows the relationship between C and (Si + Mn) of a steel plate, and the range of invention. It is a figure which shows the EPMA line analysis result of the joining interface vicinity.

Explanation of symbols

11 ... Upper plate 11b ... Lower plate side corner 12 ... Lower plate 13 ... MIG brazing wire (welding wire)
14 ... Arc torch (welding torch)
A ... Steel plate B ... Aluminum-based material (aluminum alloy plate)
C ... brazing material (welded metal)
D ... Bonding interface E ... Central part F ... Intermetallic compound layer

Claims (9)

  An alloyed hot-dip galvanized steel sheet, hot-dip galvanized steel sheet, electrogalvanized steel sheet, cold-rolled steel sheet, and hot-rolled steel sheet, and any one type of steel sheet in mass% (the same applies hereinafter). C: 0.05 to 0.25%, Si: 1.5% or less, Mn: 0.1 to 3.5%, P: 0.05% or less, S: 0.03% or less, Al: 0 A steel plate for brazing and joining with an aluminum-based material, characterized by containing 1% or less, the balance being Fe and unavoidable impurities, and satisfying C + (Si + Mn) /40≧0.15.   Furthermore, the steel plate for brazing joining with the aluminum-type material of Claim 1 which contains 1 type or 2 types in total among Cr and Mo 1.0% or less.   Furthermore, the steel plate for brazing joining with the aluminum-type material of Claim 1 or 2 which contains 0.1% or less of 1 type or 2 types or more in total among Ti, Nb, V, and Zr.   Furthermore, the steel plate for brazing joining with the aluminum-type material of any one of Claims 1-3 which contains B: 0.003% or less.   Furthermore, the steel plate for brazing joining with the aluminum-type material of any one of Claims 1-4 which contains 0.6% or less of 1 type or 2 types in total among Cu and Ni.   Furthermore, the steel plate for brazing joining with the aluminum-type material of any one of Claims 1-5 which contains Ca: 0.005% or less.   A method for joining a steel plate and an aluminum-based material, comprising joining the steel plate according to any one of claims 1 to 6 and an aluminum-based material by brazing.   The joining method of the steel plate and aluminum-type material of Claim 7 whose said brazing is MIG brazing or TIG brazing.   A joined joint between a steel plate and an aluminum-based material, wherein the joint is joined by the method according to claim 7 or 8, and the thickness of the intermetallic compound layer at the center of the joining interface is 2 μm or less.

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