JP2006130541A - Different metal joined member joined by welding ferrous alloy member and aluminum alloy member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a different metal joined member which can show the merits such as the excellent joining strength, the high productivity, etc. substantially equal to those of the same metal welded member, by completely eliminating the demerits and the problems in the prior arts in joining a ferrous alloy member and an aluminum alloy member, for example, traditional steel and so-called 5000 series aluminum alloy. <P>SOLUTION: The different metal joined member joined by welding the ferrous alloy member and the aluminum alloy member by the heat input from the ferrous alloy member side has a welding solidified portion in which a melted and solidified portion B of the ferrous alloy in the ferrous alloy member and a penetrated and solidified portion C of the ferrous alloy in the aluminum alloy member have been composed so as to be continuously integrated. Further, the cross-sectional area S2 of the melted and solidified portion is 4.0 to 14 times as large as that of the cross-sectional area S1 of the penetrated and solidified portion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a joined body obtained by joining an iron-based alloy member and an aluminum-based alloy member by welding, and more particularly to a dissimilar metal welded joint having excellent joint strength at the welded portion.

  In recent years, there has been a strong demand for improved fuel efficiency and recyclability by reducing the weight of cars with cost performance in order to improve the global environment.

  Aluminum (hereinafter sometimes abbreviated as “aluminum”) is lighter at 2.7 than the specific gravity of steel, 2.7, excellent in corrosion resistance and recyclability, and has a specific strength about twice that of steel, and is complicated by the extrusion method. It is a desirable metal for reducing the weight of a vehicle. Aluminum, on the other hand, has a longitudinal elastic modulus of about one-third and strength less than one-half that of steel, good thermal conductivity, and high solidification shrinkage, making welding more difficult than steel and lower material costs than steel. It is also difficult to use as a car material such as high.

  Therefore, if it is possible to make a hybrid using the advantages of steel and aluminum, it will be possible to meet the needs of the car.

  In order to enable this hybridization, a bonding technique with excellent bonding characteristics is essential.

  However, when an iron-based alloy and an aluminum-based alloy are melted and directly bonded, a brittle intermetallic compound is generated, and therefore, sufficient bonding strength cannot be obtained, making practical application extremely difficult. For this reason, it is difficult to use a 5000 series aluminum alloy containing magne, the brazing method, the friction welding method, or the members are mechanically joined to each other, which restricts the shape of the joining material, the productivity, and the incidental equipment. The mechanical joining method and the insert material joining method with great restrictions on the members to be used have been put into practical use.

However, each of these joining methods has the following disadvantages and problems, and there are many limitations, so that it has been difficult to make a hybrid using the characteristics of steel and aluminum.
(Mechanical joining method)
This is a method of mechanically joining members together such as bolt joining, rivet joining, screw joining, mechanical clinch, hemming, and mechanical molding joining. However, this method is generally inferior to welding of homogeneous materials (such as steels) in terms of shape constraints, joining accuracy, productivity, and versatility of joined parts.
(Brazing method)
In this method, the brazing material that serves as a medium between the members is melted and joined. Although this method has also been proposed as a method for joining steel and aluminum (Patent Document 1, etc.), the active surface of both metals is removed without removing the oxide film of steel and aluminum by flux and dissolving the base metal. It is necessary to produce an appropriate compound with the raw material. In order to obtain this appropriate compound, restrictions are imposed on the reliability of the material of the brazing material, the material and shape of the joined product, the joining strength, and the joining quality. Therefore, the workability, productivity and versatility of joining are generally accompanied by disadvantages compared to welding of homogeneous materials (such as steel).
(Friction welding method)
This is a solid phase bonding that uses frictional heat generated by sliding the members while rotating the members while applying pressure. However, since this method requires pressure rotation, there are restrictions on the shape of the joined parts, it is necessary to treat burrs generated during joining, the longitudinal welding such as beat welding is difficult, and Mg-containing aluminum alloys ( 5000 type) is generally inferior to welding of homogeneous materials (such as steel) in terms of workability, versatility, and productivity, such as difficulty in welding due to generation of oxide (MgO).
(Insert material joining method)
In this method, a clad material is inserted between members and joined by spot welding or the like. However, this method has restrictions on the part shape associated with the insert of the clad material, inferior workability and cost problems, and is generally more common than welding of homogeneous materials (such as steel). It is inferior.
JP-A-5-111757

  In view of the background of the joining technology of the above-described conventional steel and 5000 series aluminum alloy such as an iron-based alloy member and an aluminum-based alloy member, the present invention completely eliminates these disadvantages and problems and welds homogeneous members together. The development and practical application of an epoch-making dissimilar metal joined body that can enjoy advantages such as excellent joining strength and high productivity, which are substantially the same as those, and its joining technology have been made as its subject.

The present invention has been completed to solve such a problem, and the gist of the present invention is as follows.
(1) A dissimilar metal welded joint in which an iron-based alloy member and an aluminum-based alloy member are welded by heat input from the iron-based alloy member, and the solidification of the iron-based alloy melted and solidified in the iron-based alloy member And a solidified solid portion of the iron alloy solidified by melting into the aluminum alloy member continuously and integrally formed, and a cross-sectional area of the solidified solid portion of the molten solidified portion is A welded joint of dissimilar metals having a cross-sectional area of 4.0 to 14 times.
(2) The dissimilar metal welded joint according to claim 1, wherein the surface width of the melted and solidified portion is 1.9 to 2.8 mm, and the depth of the melted and solidified portion is 0.2 or more.

  ADVANTAGE OF THE INVENTION According to this invention, the dissimilar metal joining body of the iron-type alloy member and the aluminum-type alloy member provided with the outstanding joining strength can be provided. This welding method can realize high productivity because an iron-based alloy and an aluminum-based alloy can be directly joined, and can also join a 5000-series aluminum alloy for a strength member. It leads to improvement of strength. Thus, the present invention provides a remarkable effect in terms of practicality in this kind of technical field.

  The present inventor has reviewed the welding method, which has been considered difficult in the past, for the joining of iron-based alloy members made of steel or the like and aluminum-based alloy members made of a 5000-series aluminum alloy, and is there a possibility of realization? I decided to try again. Therefore, as a result of various welding experiments and examinations, heat was input from the iron-based alloy member side using a welding method with a high heat input density and aspect ratio such as laser welding, and rapidly from the aluminum-based alloy member side. It is confirmed that the joint strength can be increased as a supersaturated solid solution structure in which aluminum is supersaturated with iron in the joint part of both members by rapidly solidifying the joint part by heat absorption and cooling. A patent application (Japanese Patent Application No. 2004-213426) was filed.

  Further, further experiments were conducted and these results were comprehensively analyzed. As a result, the iron-based alloy melted by heat input from the iron-based alloy member side and solidified by heat removal from the aluminum-based alloy member side and rapid cooling. A welded joint composed of a melted and solidified portion of the iron alloy in the region of the member and a melted and solidified portion of the iron alloy that is similarly melted in the region of the iron-based alloy member and then solidified in the region of the aluminum-based alloy member It has been found that the solidification profile of the body has an important influence on the joint strength and quality, and the present invention has been completed.

  FIG. 1 shows a schematic cross-sectional view of the welded joint of the present invention. Here, 1 is an iron-based alloy member, 2 is an aluminum-based alloy member, and 3 is a joint surface of both members. A portion having a wine cup shape between the iron-based alloy member 1 and the aluminum-based alloy member 2 is a welded solidified portion formed by melting and re-solidifying by welding of this joined body (sometimes abbreviated as a solidified portion). Is shown.

  The welded solidified portion is composed of a melted and solidified portion B corresponding to a cup portion in which the iron alloy is melted and solidified as it is in the region of the iron-based alloy member 1 and an iron-based alloy melted in the region of the iron-based alloy member 1 thereafter. A shell-like melted and solidified portion A corresponding to a gripped portion that has melted and solidified in the region of the alloy member 2 is integrally formed so as to penetrate and be continuous with the joint surface 3.

  The melted and solidified portion B is substantially a solid solution phase of an iron-based alloy, while the melted and solidified portion A is a supersaturated solid solution phase in which aluminum of an aluminum-based alloy is solid-dissolved to 5-40% supersaturated in an iron-based alloy. . Here, the solid solution amount of aluminum is higher as it is closer to the interface with the aluminum alloy member. Both are confirmed by the results of EPMA surface analysis, AES analysis, and the like. Moreover, this melted and solidified portion A becomes an actual welded joint between the iron-based alloy member 1 and the aluminum-based alloy member 2, and plays an important role in maintaining its high joint strength. There are no brittle intermetallic compounds that cause a significant reduction in bonding strength in this bonded portion. This fact is also confirmed by AES analysis.

  In addition, this welded joint that bites into the aluminum-based alloy member 2 in a bullet shape is the primary anchor effect of the entire bullet-shaped portion, and further, the fine irregularities formed on the outer surface of this bullet-shaped portion are aluminum alloy members. The joint strength is further enhanced by both the actions of the secondary anchor effect generated by biting into the inner surface of 2.

  The weld solidified portion composed of the melt solidified portion A and the melt solidified portion B exhibits a wine cup shape as a whole, and more specifically has the following numerical profile to maximize joining. Strength and quality can be ensured.

  First, as shown in FIG. 1, in this welded body profile, the cross-sectional area S2 of the melted and solidified part B is 4.0 to 14 times the cross-sectional area S1 of the melted and solidified part A in the profile of the welded solidified part. It is essential to satisfy the relationship of S2 / S1 = 4.0-14.

  When S2 / S1 is less than 4.0, the heat input is basically insufficient, and the required amount of iron-based alloy dissolved in the iron-based alloy member 1 and the aluminum-based alloy member 2 and the aluminum-based material The amount of penetration into the alloy cannot be secured, and it becomes difficult to form a shell-like penetration solidification part A composed of a rapidly solidified solidified structure of a supersaturated solid solution phase in which an aluminum alloy aluminum is solid-dissolved in an iron alloy in an amount of 5 to 40% supersaturated. . As a result, the joining of the iron-based alloy member 1 and the aluminum-based alloy member 2 becomes impossible (unjoined), a joining failure occurs, and sufficient joining strength cannot be obtained. The iron-based alloy member 1 is contracted, and large bubbles are generated in the melted and solidified portion A and the melted and solidified portion B, resulting in frequent quality defects.

  On the other hand, under the condition where S2 / S1 exceeds 14, the heat input is excessive, and the melting width (surface width) and the melting amount of the iron-based alloy (steel) in the aluminum-based alloy member 2 become too large. Due to the generation of excessive metal vapor, a bumping phenomenon occurs, so that the amount of penetration into the aluminum-based alloy becomes unstable, and it is impossible to sufficiently form the bullet-like melt-solidified portion A. Therefore, the joining of the iron-based alloy member 1 and the aluminum-based alloy member 2 becomes almost impossible, and the intended sufficient joining strength cannot be expected. In addition, generation of embrittlement compounds, cavities, and shrinkage occur at the bonding interface, and blow-holes are generated in the melt-solidified portion A and the melt-solidified portion B, which causes a serious problem in terms of quality.

  In addition to the above conditions, as shown in the figure, it is preferable that the surface width (dissolution width) D of the melted and solidified portion B is 1.9 to 2.8 mm.

  There are two cases where this D is less than 1.9 mm. One of them is a case where the heat input is insufficient, and a sufficient amount of molten iron alloy that forms the solidified solidified portion A to penetrate into the aluminum-based alloy member 2 side to obtain the bonding strength cannot be secured. In this case, since the amount of molten iron alloy is small, the length of the joining interface between the iron alloy and aluminum is short, the joining interface is easily peeled off due to solidification shrinkage of the steel, and the anchor effect due to the biting of the iron alloy is difficult to obtain. Strength is lowered. The other case is when the heat input per unit area is excessive. In this case, the generation of excessive metal vapor makes it difficult to keep the keyhole open, and abnormal bumping and bubble entrainment occur frequently. Further, since the melting width (surface width) of the iron-based alloy (steel) on the heat input surface is narrow, a dent abnormality occurs due to the volume reduction of the melted and solidified portion A that has digged into the aluminum-based alloy member 2 side. In either case, good bonding strength and bonding quality cannot be obtained stably.

  On the other hand, in the case where D exceeds 2.8 mm, the heat input is excessive, the amount of molten iron alloy that bites into the aluminum alloy member 2 side is excessive, the cooling rate becomes slow, and the iron alloy is stably added to the iron alloy. It is difficult to obtain a rapidly solidified structure mainly composed of a supersaturated solid solution phase in which aluminum is dissolved in supersaturation at 5 to 40%. Due to the primary and secondary anchoring effects of the bullet-shaped melted and solidified part A, bonding strength can be obtained, but the bonding quality is not good, such as bumping abnormality due to excessive heat input, bubble entrapment failure, dent abnormality after solidification, and the quality is stable. Will not.

  Further, as shown in the figure, it is preferable that the depth E of the melted and solidified portion A is 0.2 or more in the profile of the solidified portion.

  If the penetration depth of the iron-based alloy is reduced, the length of the joint interface between the iron-based alloy and the aluminum-based alloy is shortened, and the strength deterioration of the joint structure and the steel solidification shrinkage stress due to the reduction of the heat removal effect by the aluminum-based alloy. Separation of the bonding interface due to. In particular, the difference in melting point between an iron-based alloy such as steel and an aluminum-based alloy is as great as about 1000 ° C. Therefore, if it takes a long time from the solidification of the steel to the solidification of the aluminum, a brittle layer is formed at the joint interface. , Bonding peeling frequently occurs. Therefore, if the penetration depth of steel is less than 0.2, peeling of the joint portion occurs, and it becomes difficult to obtain normal joining quality.

  Next, preferable welding conditions and the like for manufacturing the joined body of the present invention will be described.

First, it is advantageous to employ a laser welding method such as carbon dioxide spray welding as the welding method. Unlike the arc welding method, this laser welding method is characterized in that a weld bead having a very high heat input density (10 ⁶ W / cm ² or more) and an extremely high aspect ratio (penetration depth / penetration width) can be obtained. . Therefore, heat input sufficient for melting and joining can be instantaneously performed in a state where the penetration width of the joining portion of the iron-based alloy and the aluminum-based alloy is reduced, so that cooling after the heat input is rapid (cooling rate: 100 K / s Thus, the joint can be rapidly solidified, whereby the joint can be made into a fine rapidly solidified structure of several μ to 10 μm or less, and at the same time a supersaturated solid solution phase can be obtained.

  In addition, when the iron-based alloy member 1 and the aluminum-based alloy member 2 are welded by this laser welding, the heat input is less heat-reflected, the specific gravity is larger than that of aluminum, and the own weight is used well to penetrate the molten metal. It is good to carry out from the iron-based alloy side which can form the said melt solidification part easily.

  Laser welding conditions that provide sufficient bonding strength are basically high energy density, stable heat input from the iron side, and a sufficient amount of iron melted in a short time while securing a relatively wide melting width. 1 is made to bite in an appropriate amount in a bullet shape, thereby enabling the formation of the melt-solidified portion A of FIG. 1 that exhibits both the primary and secondary anchor effects described above. In order to satisfy this condition, as shown in FIG. 2, first, the laser beam (R) is irradiated from the iron-based alloy member (1) side to perform heat input, and is generated inside the molten iron (M). It is necessary to prevent the metal vapor (V) from being contained in the keyhole (K) and to prevent bumping by the vapor (V). Moreover, it is necessary to adjust heat input so that molten iron (M) does not scatter. When the molten iron (M) is inserted into the aluminum alloy member (2), dents due to shrinkage tend to occur on the iron side surface after solidification. In order to prevent the occurrence of excessive dents on the solidified surface, the heat input needs to be performed not only in the welding depth direction but also in the width direction in order to supplement the amount of molten iron (M) from around the heat input during solidification. The heat input in the width direction causes the metal vapor (V) obtained with the generation of the keyhole (K) to emit plasma on the iron surface, that is, near the upper side of the keyhole (K), and a plasma cloud (P ) It is important to maintain it continuously.

  As specific welding conditions for producing the joined body of the present invention using carbon dioxide laser welding, it is recommended that the heat input is 700 to 775 W and the welding speed is 375 to 400 mm / min.

  Hereinafter, the present invention capable of obtaining good melting and joining quality of steel and aluminum will be described in detail based on experimental examples.

(Example)
Laser welder (YB-L150A8 made by Matsushita Welding Systems Co., Ltd., nozzle diameter 4, 5φ, welding speed: 400mm / min, output form) Laser was irradiated from the stainless steel pipe side using CW) and welded. Tables 1 and 2 show the results of investigating the bonding strength, bonding quality, and weld solidified profile of these stainless steel-aluminum bonded bodies. In addition, the evaluation criteria of joining strength and joining quality are as follows.

[Joint strength]
A: Breakage of base material, B: Joint efficiency of 75% or more, B: Joint efficiency of 20% or more and less than 75%, X: Unjoined or joint efficiency of less than 20%.

[Joint quality]
◎: The joint interface consists of a continuous unique structure and has no bubble defects, dent abnormalities, or shrinkage abnormalities. ○: The joint interface consists of a continuous specific structure, but has minute bubbles, dents, or shrinkage defects. △: Partially bonded interface is made of a specific structure, X: Unbonded or bonded interface is made of a brittle compound.

  When investigating and measuring the profile of the welded solidified part, if a brittle metal compound was formed around the solidified part, it was determined from the dimensions excluding this part.

  From the experimental results in Tables 1 and 2, in the profile of the welded solidified portion, the cross-sectional area ratio (S2 / S1) of the molten solidified portion and the penetration solidified portion of the iron alloy (stainless steel) is within the range of the present invention (4.0 to 14). ) (Examples No. 1 to 4, 11, 12, 15, 16) satisfying) have good bonding interfaces, all have been subjected to base material fracture in the tensile test, and have excellent bonding strength and quality. I understand.

  On the other hand, in the comparative examples (Nos. 6 to 9, 13, 14, and 17) in which S2 / S1 exceeded the upper limit of the present invention, most of the results showed poor results in both bonding strength and quality. In the comparative example of No. 10, the heat input was remarkably insufficient, and the formation of the melted and solidified portion became impossible.

  Moreover, although the comparative example (No5) in which S2 / S1 is less than the lower limit of the present invention satisfies the bonding strength, the bonding quality is insufficient, and it cannot be satisfied as a bonded body by a normal welding method. However, even when S2 / S1 is less than 4 at 2.9 as in this comparative example (No. 5), the molten steel bites into the aluminum side in a cannonball shape, and further locally at the interface with the aluminum. Spot welding where S2 / S1 is 2.5 or more, considering that it can be easily welded even if it is difficult to obtain a joint strength enough to break the base metal because it exerts a double anchor effect that bites into aluminum. It is suitable for. However, when S2 / S1 is less than 2.5, the shrinkage increases and the cooling rate of the molten steel that has penetrated into the aluminum becomes slow, brittle intermetallic compounds are generated, and the anchor effect cannot be exhibited. Not applicable.

  Further, the joined bodies of the examples having joint strength and quality superior to those in Tables 1 and 2 are within the scope of the present invention in terms of the surface width (D) of the melted and solidified part of the iron alloy in the profile of the welded solidified part. It is found that the following 1.9 to 2.8 mm is satisfied. On the other hand, when this D is less than 1.9 or exceeds 2.8, the bonding strength or quality is not sufficient as shown in the comparative example, which is inappropriate as a bonded body.

  Further, with regard to the depth (E) of the penetration solidified portion in the profile of the weld solidified portion, the example in which the range satisfies 0.2 mm or more is excellent in the bonding strength and the bonding quality as compared with the comparative example not satisfying this. You can also see from these tables.

Schematic sectional view of a welded joint according to the present invention The schematic diagram which shows the state at the time of joining of the iron-type alloy member and aluminum-type alloy member by the laser welding in this invention.

Explanation of symbols

1: Iron-based alloy member 2: Aluminum (nium) -based alloy member 3: Bonding surface A: Dissolved solidified portion B: Dissolved solidified portion C: Dissolved solidified width D: Surface width of dissolved solidified portion E: Depth of dissolvable solidified portion F: Thickness of the iron-based alloy member S: Cross-sectional area of the melt-solidified portion S2: Cross-sectional area of the melt-solidified portion R: Laser light M: Molten iron K: Keyhole V: Metal vapor P: Plasma cloud

Claims (2)

  A dissimilar metal welded joint in which an iron-based alloy member and an aluminum-based alloy member are welded by heat input from the iron-based alloy member side, wherein the melt-solidified portion of the iron-based alloy melted and solidified in the iron-based alloy member The welded solidified portion of the iron-based alloy melted and solidified in the aluminum alloy member has a continuous welded solidified portion, and the cross-sectional area of the melted solidified portion is equal to the cross-sectional area of the melted solidified portion. A welded joint of dissimilar metals, characterized by 4.0 to 14 times. The dissimilar metal welded joint according to claim 1, wherein a surface width of the melted and solidified portion is 1.9 to 2.8 mm, and a depth of the melted and solidified portion is 0.2 or more.

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