JP2006283110A - Steel sheet to be jointed with aluminum-based material by brazing, jointing method using the steel sheet, and coupling joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such a steel sheet as to form a coupling joint superior not only in shear tensile strength but also in peeling strength when jointed with an aluminum-based material by brazing. <P>SOLUTION: The steel sheet is any one of steel sheets selected from the group consisting of a galvannealed steel sheet, a hot-rolled steel sheet and a cold-rolled steel sheet; and comprises, by mass%, 0.05-0.25% C, 1.5% Si or less, 0.1-3.5% Mn, 0.05% P or less, 0.03% S or less, 0.1% Al or less while satisfying C+Mn/40≥0.12, and the balance Fe with unavoidable impurities. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 a joint portion of an iron-based material and brazed 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 problems, there is a problem that equipment costs increase because 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 component of the brazing material (or brazing wire) is 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 type of steel plate selected from the group consisting of alloyed hot-dip galvanized steel plate, hot-rolled steel plate and cold-rolled steel plate, in 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: 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 + Mn / 40 ≧ 0.12.

  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 brazing with the aluminum-based material according to any one of claims 1 to 4, further containing 0.6% or less of one or two of Cu and Ni in total. It is a steel plate for adhesive joining.

  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.

  The invention according to claim 9 is a joined joint of a steel plate and an aluminum-based material, which is joined by the method according to claim 7 or 8.

  By using the steel sheet according to the present invention, C and Mn are concentrated on the surface of the joint portion of the steel sheet by heating when brazing with the aluminum material, and the brittle iron-aluminum intermetallic compound formed at the interface with the aluminum-based material. Generation | occurrence | production is suppressed and the joint joint excellent not only in shear tensile strength but in peeling strength is obtained.

Embodiment
(1) Configuration of Steel Sheet According to the Present Invention First, the reasons for limiting the 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 + Mn / 40 ≧ 0.12 will be described. According to the study by the inventors, a phenomenon in which C and Mn are concentrated on the surface of the joint portion of the steel sheet due to heating when brazing with the aluminum material was observed. At this stage, the detailed mechanism is not clear, but if the degree of concentration of C and Mn exceeds a certain level, the formation of brittle iron-aluminum intermetallic compounds formed at the interface with the aluminum-based material is remarkably suppressed. As a result, it was found that a joint joint having excellent peel strength as well as shear tensile strength can be obtained. Furthermore, both the shear tensile strength and the peel strength of this joint have a strong correlation with C + Mn / 40. When C + Mn / 40 is 0.12 or more, the required strength is obtained for both the shear tensile strength and the peel strength. (See the examples below). From the above, it was defined as C + Mn / 40 ≧ 0.12.

  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, when these elements are contained excessively, precipitates increase and the ductility is remarkably deteriorated. Therefore, 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 excessively contained, 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, excessive inclusion of these elements may cause embrittlement during hot rolling, and the production cost is high 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, an excessive content makes the effect saturated and worsens the cleanliness of the steel. 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, a hot-rolled steel sheet, and a cold-rolled steel sheet. Here, when an alloyed hot-dip galvanized steel sheet is used, a layer made of an intermetallic compound and an oxide is formed at the interface between the galvanizing and the brazing material when brazing with the aluminum-based material. 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, it is presumed that when an alloyed hot-dip galvanized steel sheet is used, a joint having a better joint strength can be obtained than when a bare steel sheet not subjected to galvanization is used.

(2) Joining method using the steel plate according to the present invention By joining the steel plate made of the above-described chemical component with an aluminum-based material, a joint joint having excellent peel strength as well as shear tensile 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.

  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. Also, as the aluminum alloy MIG brazing wire 13, an aluminum alloy MIG brazing wire containing 2.5% Si, an aluminum alloy MIG brazing wire (A4043) containing 5% Si, or An aluminum alloy-based MIG brazing wire (A5554) containing 2.5% Mg 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 90 degrees at a position 10 mm from the joint (end face of the upper plate 11). The peel test piece shown in FIG. Then, each test piece was subjected to a shear tensile test and a peel test at a speed of 10 mm / min, and the joint strength was calculated according to the following formula (1) and the strength ratio was calculated according to the formula (2). The joint strength between the A6022 aluminum alloy plates was measured by the same experiment as described above, and the shear tensile strength was 158 N / mm and the peel strength was 30.3 N / mm.

Formula (1) (joint strength) = (maximum load point load) / (joint length)
Formula (2) (strength ratio) = (joint strength) / (joint strength between 6022 aluminum alloy plates)

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 shear tensile strength, peel strength, and strength ratio of the joints obtained in this welding test.

  FIG. 5 shows the relationship between the C + Mn / 40 of the steel plate and the strength ratio of the shear tensile strength of the joint, and FIG. 6 shows the relationship between the C + Mn / 40 of the steel plate and the strength ratio of the peel strength of the joint. From FIG. 5 and FIG. 6, when C + Mn / 40 <0.12, the strength ratio of the shear tensile strength may be less than 80%, and the strength ratio of the peel strength is all less than 50% (steel type No. 2 in Table 2). 15-18), by setting 2C + Mn / 40 ≧ 0.12, the strength ratio of shear tensile strength is always 80% or more, and the strength ratio of peel strength is always 50% or more (Table 2). It can be seen that the steel types No. 1 to 14). Furthermore, the steel types No. 1 in Table 1 and Table 2 were used. As apparent from the data of 17, it is not sufficient that the content of individual elements including C and Mn merely satisfy the component range of the present invention, and the value of C + Mn / 40 is within the range defined by the present invention ( It can be seen that the peel strength cannot be sufficiently obtained unless 0.12 or more is satisfied.

  Further, according to the EPMA analysis in the vicinity of the joint, when the steel plate of the inventive example is used, C and Mn are concentrated at a higher concentration on the surface of the joint portion of the steel plate after brazing than when the steel plate of the comparative example is used. It was recognized that

  Therefore, by using a steel sheet that simultaneously satisfies the component range of each element specified by the present invention and C + Mn / 40 ≧ 0.12, not only the shear tensile strength but also the peel strength can be obtained even when brazed to an aluminum-based material. It was confirmed that a joint having a high value stably 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 graph which shows the relationship between C + Mn / 40 and the strength ratio of shear tensile strength. It is a graph which shows the relationship between C + Mn / 40 and the strength ratio of peeling strength.

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)

Claims (9)

  Any one type of steel plate selected from the group consisting of galvannealed steel plate, hot-rolled steel plate, and cold-rolled steel plate, in 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: 0.03% or less, Al: 0.1% or less, and the balance Fe And a steel plate for brazing joining with an aluminum-based material, characterized by comprising inevitable impurities and satisfying C + Mn / 40 ≧ 0.12.   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 claim | item 1 -4 containing 1 type or 2 types in total of Cu or Ni 0.6% or less.   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 bonded joint between a steel plate and an aluminum-based material, which is bonded by the method according to claim 7 or 8.

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