JP5431797B2 - Al alloy welded joint - Google Patents

Description

  The present invention relates to an Al alloy welded joint, and more particularly, to an Al alloy welded joint that realizes joint characteristics with high strength and low crack sensitivity in welding of an Al alloy base material made of an aluminum (Al) alloy having a predetermined alloy composition. Is.

  Conventionally, in order to reduce the weight of structural members, devices, parts, etc. in various fields such as industrial use, construction, transportation, daily necessities, household goods, etc., aluminum ( Al) material has been adopted. In such applications, when high tensile strength of 250 MPa or more is required, conventionally, Al—Zn—Mg-based 7000 prescribed in AA to JIS standards such as 7003 and 7N01. Based Al alloy extrusions have been used. In addition, a member that provides at least a part of the final shape or structure intended in such an application is composed of a plurality of Al materials according to the complexity of the shape, and the plurality of Al materials are TIG. It is melted and welded using a welding technique such as MIG or the like to form an integral structure member. In such melt welding, from an Al—Si based 4000 series Al alloy such as 4043 and 4047, In the case where the conventional filler metal is used, there is a problem that the weld metal breaks at a low-strength weld metal portion in the weld joint because the strength of the weld metal is low. The four-digit numbers (including English letters) such as “7003” and “4043” used here indicate Al alloys defined in AA to JIS standards.

  Therefore, in order to increase the strength of the weld metal part formed in the fusion welding of an Al material made of a 7000 series Al alloy, Al—Mg such as 5554, 5356, 5183, etc. are used as the filler material used in such a fusion welding. A filler metal made of a 5000 series Al alloy is disclosed in “Light Metal Welding”, Vol. 45, no. 10, pp. 461-470 (2007) (Non-Patent Document 1). However, in order to further reduce the weight of the target member, in order to increase its thinness and strength, the Mg amount, Zn amount, or Cu amount of the 7000 series Al alloy that provides the Al material constituting such a member is set. If it is increased, the filler material made of the 5000 series Al alloy as described above is insufficient to reduce the weld crack sensitivity, and the weld metal part has a lower strength than the base metal heat-affected zone (HAZ). There are inherent problems.

  Moreover, since 7000 series Al alloy is sensitive to weld crack sensitivity, in order to reduce such weld crack sensitivity, for example, in Unexamined-Japanese-Patent No. 1-143791 (patent document 1), Mg: 6-10 wt. %, Zr: 0.25 to 1.5 wt% Al alloy filler material has been proposed, and in JP-A-5-169290 (Patent Document 2), Zn: 1 to 6%, Mg: 3 to 6% (Zn ≦ Mg), Mn: 0.2 to 0.9%, Cr: 0.05 to 0.5%, Ti: 0.05 to 0.2%, B: 0.01 Al alloy filler containing -0.2%, Zr: 0.05-2% is disclosed in JP 2000-317676 (Patent Document 3), Zn: 5-8%, Mg: 1 -3%, Cu: 2-4%, Sc: 0.03-3.0%, Cr: 0.05-0 An Al alloy filler containing 2%, V: 0.01 to 0.5%, Ti: 0.005 to 0.2%, and Ag: 0.03 to 2% is further disclosed in JP-T-2001-519239. In the gazette (Patent Document 4), Mg: 5.0 to 6.5%, Mn: 0.4 to 1.2%, Zn: 0.4 to <2.0%, Zr: 0.05 to 0 Al alloy filler containing 3%, Cr: 0.3% or less, Ti: 0.2% or less, Fe: 0.5% or less, Si: 0.5% or less, Cu: 0.25% or less Each material has been proposed. And in those filler materials, the weld crack sensitivity is reduced by adding Zr or adding Sc.

  However, in order to increase the strength of the joint (welded metal part) in the welded joint, it is necessary to control the hardness of the welded metal part and the most softened part in the heat-affected zone (HAZ) of the base metal. In addition, it was necessary to control the Mg content of the filler metal. Therefore, it is considered that the Mg content of the filler material is 5.5% or more. At that time, if the Zr content is increased or Sc is contained, as in the prior art. In the metal structure, a large crystallized product is formed. When producing a filler material having a wire diameter of 1.6 mm or 2.4 mm, the drawing process is adversely affected. In the middle of the drawing process, a problem such as cutting is caused, and the manufacture becomes difficult, or the productivity is deteriorated. Furthermore, in addition to such problems, there is a risk that giant crystals may be formed in the weld metal due to the presence of Mg, Zr, and Sc, and as a result, the joint strength decreases and the characteristics of the welded joint are stable. There is a problem that there is a fear of not doing. Therefore, when the Mg content in the Al alloy giving the filler material is 5.5% or more and the joint portion is strengthened, it is also entangled with the components of the base material, It was necessary to obtain an effective alloy composition.

Japanese Unexamined Patent Publication No. 1-143791 JP-A-5-169290 JP 2000-317676 A Special table 2001-519239 gazette

“Light metal welding”, Vol. 45, no. 10, 461-470 pages (2007)

  Here, the present invention has been made in the background of the circumstances as described above, and the problem to be solved is that in a joined body obtained by fusion welding of a predetermined Al material, the weld crack sensitivity is reduced. An object of the present invention is to provide a technique capable of easily realizing a welded joint with reduced strength and excellent strength characteristics.

In the present invention, in order to solve such problems, Cu: 0.01 to 0.50%, Mg: 1.2 to 2.1%, and Zn: 5 on a mass basis. include .0 8.5%, the Al alloy matrix having an alloy composition and the balance of Al and inevitable impurities, in mass, Mg: 5.5~8.0%, Cr: 0.05 ~ 0.25%, Ti: 0.25% or less, Si: 0.4% or less, Fe: 0.4% or less, Cu: 0.1% or less, Zr: 0.05% or less, and Zn: 0 A weld metal part formed by melt welding, using a Al alloy filler material having an alloy composition including Al and inevitable impurities, the balance of which is 25% or less, and being melt welded The maximum thickness of the base material is t ₁ , the center hardness is Hv _1, and the thickness of the heat affected zone of the base material is t ₂ . And further the hardness of the outermost softening unit when the Hv _2, the following relationship:
t ₁ × Hv ₁ ≧ 1.9 × t ₂ × Hv ₂
Hv ₁ ≧ 70
The gist of the present invention is an Al alloy welded joint characterized by satisfying the above.

In addition, according to one of the desirable embodiments of the Al alloy filler material according to the present invention, the filler material further contains 0.05 to 1.0% by mass of Mn. The toughness of the weld metal part can be further advantageously achieved.

  As described above, in the Al alloy welded joint according to the present invention, a specific amount of Mg, Zr, Si, Fe, Cu is used in fusion welding of an Al alloy base material having an alloy composition containing a predetermined amount of Cu, Mg, Zn. , Cr, Zn, and Ti, with the balance being an alloy composition consisting of Al and unavoidable impurities, and the hardness of the weld metal part as well as the most softened part in the heat-affected zone (HAZ) of the base metal By controlling the hardness, it is possible to effectively enhance the strength, elongation, and other characteristics of the joined part (welded part or welded metal part) of the bonded Al alloy base material, and to advantageously reduce weld cracking susceptibility. Thus, a high strength and sound welded joint can be stably realized.

  And by adopting the configuration according to the present invention, the hardness balance between the heat affected zone of the base metal and the weld metal portion is adjusted, and it becomes possible to preferentially break from the heat affected zone of the base metal. The ductility could be advantageously improved.

In an Al alloy welded joint obtained by melting and welding a plate-like Al alloy base material, an outline of a cross section in a direction across the weld metal part is shown, and the distance from the center of the weld metal part in such a cross section Is an example of the relationship between Vickers hardness and Vickers hardness, wherein (a) is a schematic partial view of a cross section of such a welded joint, and (b) is the distance from the center of the weld metal part and Vickers. It is a graph which shows the relationship with hardness.

  By the way, as an Al alloy base material to be welded in the present invention, an alloy composition containing a specific amount of Cu, Mg and Zn and the balance being Al and unavoidable impurities in obtaining a joint having excellent characteristics. A predetermined Al material made of a 7000 series Al alloy is used.

  In the 7000 series Al alloy that gives such Al material, Cu (copper), which is one of the alloy components, has the effect of improving the strength of Al material and improving stress corrosion cracking resistance, and its content If it is less than 0.01% (mass basis, the same applies hereinafter), these effects are not sufficient, so that it is contained in a proportion of at least 0.01% or more. In addition, when the Cu content increases, the extrudability of the Al material deteriorates and the quenching sensitivity of the Al material increases, and even if quenching is performed immediately after extrusion, the quenching may be delayed. The upper limit of the Cu content needs to be 0.50% because sufficient strength cannot be obtained even if the quality or T6 refining is performed.

Moreover, since Mg (magnesium) is a main element that enhances the strength of the Al alloy, it is necessary to contain it in a proportion of 1.2 % or more in order to fully exert the effect. On the other hand, if the Mg content is too high, the strength increases, but the elongation decreases and the workability deteriorates, and the extrusion pressure increases during the extrusion molding of the Al material, making the extrusion operation difficult. Therefore, the upper limit of the Mg content needs to be 2.1%. Thereby, the elongation of 4.0% or more required for maintaining the workability is advantageously ensured. Note that in the above to advantageously exhibit excellent effect by the inclusion of such Mg, as the Mg content, and the proportion of 1.3 to 2.1% especially are advantageously employed.

Furthermore, Zn (zinc) is an element that coexists with Mg, imparts aging properties to the Al alloy, and exhibits a function of improving hardness by a predetermined aging treatment (artificial aging). In order to exhibit it, it will be used at a content of 5.0 % or more. However, this Zn also increases in hardness as its content increases, but the elongation decreases, causing problems that workability deteriorates and cracking during extrusion tends to occur. The Zn content needs to be stopped to 8.5% or less. Incidentally, the Zn content, good Mashiku is 6.0 to 8.5%, the range in particular 7.5 to 8.5%, and being advantageously employed.

  Various Al materials composed of a 7000 series Al alloy having such an alloy composition are formed from known billing methods such as extrusion molding, forging molding, casting molding, etc. from billets obtained using such an Al alloy. According to the present invention, it is manufactured in various known forms, such as solid structures, hollow structures, shapes, planks, etc., and is a member for the intended use as an Al material (base material) targeted by the present invention. It will be used to form.

  In the present invention, when a plurality of Al materials obtained as described above are used and they are united by butt and fusion welding so as to give a member for the intended use, a specific alloy composition is used. The welding operation using the Al alloy filler metal having the above is adopted, and the resulting Al joint material is integrated in the resulting welded joint, so that the member of the target structure has excellent characteristics. It is formed by holding.

  By the way, the specific filler material used in the present invention is Mg: 5.5-8.0%, Cr: 0.05-0.25%, Ti: 0.25% or less, Si: 0.4 %, Fe: 0.4% or less, Cu: 0.1% or less, Zr: 0.05% or less, and Zn: 0.25% or less, with the balance being Al and inevitable impurities. However, when the content of these elements is out of the specified amount, various problems are caused.

  That is, Mg (magnesium) is an additive element essential for increasing the strength (hardness improvement) of weld metal and contributing to the reduction of weld crack sensitivity, and in obtaining its effective additive effect. Although it is necessary to set it as 5.5% or more content, when the content exceeds 8.0%, when casting the billet for wire manufacture, it is Mg-Si type in the metal structure. An embrittled layer is formed, which makes it difficult to draw the wire and makes it impossible to obtain a filler material having a target wire diameter.

  In addition, Cr (chromium) is effective in reducing weld cracking susceptibility. For this reason, Cr (chromium) is contained in a proportion of 0.05% or more, so that its content exceeds 0.25%. Thus, when a billet for wire production is cast, a drawing process is performed to produce coarse Al-Cr crystals (intermetallic compounds) in the metal structure to obtain a wire as a filler material. Poses a difficult problem.

  Furthermore, Ti (titanium) has an effect of refining the metal structure. Therefore, Ti (titanium) is contained in a proportion not exceeding 0.25%. If the Ti content is too high, when a billet for wire production is cast, an Al-Ti coarse crystallized product (intermetallic compound) is generated in the metal structure, and the drawing process is performed. Causes problems that make operation difficult.

  Furthermore, Si (silicon), Fe (iron), Cu (copper), Zr (zirconium), and Zn (zinc) are all impurity elements, each of which is less than the content specified above. Need to be controlled. Incidentally, when the Si content increases, when casting a billet for manufacturing a wire, an Mg-Si embrittled layer is formed, and it becomes difficult to draw the wire. There is also a problem that when the Fe content is increased, when a billet for producing a wire is cast, a coarse Al-Fe crystallized product (intermetallic compound) is generated, and the drawing process operation becomes difficult. This is because if the Cu content is excessively increased, a problem that the weld cracking sensitivity of the weld metal portion is increased is caused. If the Zr content is excessively increased, coarse crystallized substances are formed in the weld metal portion. (Intermetallic compound) is generated, causing a problem that the drawing operation becomes difficult. In addition, when the Zn content is excessively increased, an Mg—Zn-based embrittled layer is formed in the weld metal part, Low joint properties, especially hardness This is because allowed to problems.

  In the present invention, in addition to the alloy composition of the filler material, 0.05 to 1.0% of Mn (manganese) is further advantageously contained. This additional alloy component, Mn, is a component that contributes to increasing the toughness of the weld metal, and in order to fully exhibit its effect of addition, it is necessary to contain 0.05% or more, If the content is too high, when casting billets for wire production, coarse Al-Mn based crystals (intermetallic compounds) are generated, making it difficult to draw. To come up with.

  And the filler material in this invention is produced in accordance with a conventional method using Al alloy which has an alloy component mentioned above, Comprising: Generally, the diameter prescribed | regulated by JIS-Z-3232, and tolerance | permissibility It will be realized as a welding rod or electrode wire of the difference.

  In addition, in the fusion welding of the Al material using such a filler material, known fusion welding techniques such as arc welding such as MIG welding and TIG welding, laser welding, and electron beam welding are appropriately employed. The plurality of Al materials are integrally joined through the weld joint formed by the above-described filler material to form a joined body that gives a member having a desired shape or structure.

And in this invention, when melt-welding the above-mentioned Al material (base material) using a filler material like this, by optimizing the components of the base material and the filler material, Although the hardness of the heat affected zone of the metal part and the base material can be controlled, the thickness of each part is also related to the best state of breaking preferentially at the heat affected part of the base material. Therefore, it was constructed so as to satisfy the following relational expressions (1) and (2) so that the intended purpose could be advantageously achieved.
t ₁ × Hv ₁ ≧ 1.9 × t ₂ × Hv ₂ (1)
Hv ₁ ≧ 70 (2)
[However, t ₁ : Maximum thickness of the weld metal part Hv ₁ : Central hardness of the weld metal part, in other words, at half the thickness of the heat affected part (base metal) thickness at the central part of the weld metal part. Corresponding part hardness t ₂ : thickness of heat-affected zone of base metal Hv ₂ : hardness of softest part in heat-affected zone of base metal]

Here, in FIG. 1A, in the joined body obtained by fusion welding the plate-shaped Al alloy base materials 2 and 2, the outline of the cross section in the direction crossing the weld metal part 4 is partially shown. In such a cross-sectional view, t ₁ is the central portion of the weld metal portion 4 that corresponds to the maximum thickness of the weld metal portion 4 (corresponding to a substantially butt center portion of the two base materials 2 and 2). the thickness of, and the thickness of the heat-affected zone of the base material 2 (HAZ): t ₂ becomes equal to the thickness of the substantially base material 2. Further, the center hardness of weld metal part 4: Hv ₁ is the center in the width direction (transverse direction) of weld metal part 4 and the thickness center part of the base metal equivalent part in weld metal part 4, in other words. This is a portion corresponding to a half position of the thickness (t ₂ ) of the base material 2, that is, in the cross section of FIG. 1A, the center line Y of the weld metal portion 4 and the thickness direction of the base material 2. This refers to the cross-sectional hardness at the O position that is the intersection with the straight line X passing through the center. Further, the hardness of the softest part of the heat affected zone (HAZ): Hv ₂ is the heat affected zone (HAZ). in the cross section of the part thickness direction center of the (t _2/2 position), as the hardness distribution obtained by hardness measurements at 1mm intervals (left-right direction in the drawing) longitudinal direction shown in FIG. 1 (b), The value with the smallest hardness will be adopted. Such hardness (Hv) is measured at a load of 1 kgf using a Vickers hardness tester in accordance with JIS-Z-2244, in a cross section perpendicular to the joining direction. is there.

In the above relational expression (1), if the value on the right side is larger than the left side, there is a problem that the weld metal part (bond part) 4 in the welded joint breaks, and the relational expression (2) In this case, even when Hv ₁ is less than 70, the hardness of the weld metal part 4 becomes too small regardless of the plate thickness, and similarly, the problem that the weld metal part 4 breaks is caused. Therefore, the thickness (t ₂ ) of the base material 2 is selected so as to satisfy the above relational expressions (1) and (2), and the target maximum thickness of the weld metal part 4 ( t ₁ ) is realized, and predetermined melt welding operations are performed so as to realize the hardness: Hv ₁ , Hv _{2 of} each weld metal part 4 and heat affected zone (HAZ). It will be implemented. The thicknesses t ₁ and t ₂ are appropriately selected according to the type of welding operation, the welding conditions, and the target joined body. For example, t ₂ is an arc welding operation. If t ₁ is generally greater than 0.5 mm, and t ₁ is determined in relation to the thickness of t ₂ , and if t ₁ is thick, the welding operation is repeated and Thickness to be achieved: t ₁ .

  By the way, the joined body obtained by joining a plurality of Al materials (base materials) obtained as described above is a member for a target application in a state where T4 tempering or T6 tempering is applied. Will be used. Here, such T4 tempering and T6 tempering can be carried out by performing solution treatment and natural aging treatment or artificial aging treatment in the same manner as before, and are obtained by welding as described above. However, in general, an Al material (base material) before welding is used so that the joined body has a history of predetermined solution treatment and natural aging treatment or artificial aging treatment. ), A predetermined solution treatment is performed, and then a plurality of such Al materials are integrally joined by a welded joint formed by the above-described fusion welding, and then the obtained joined body is obtained. On the other hand, a natural aging treatment or an artificial aging treatment is performed so that a T4 tempering or a T6 tempering is performed as a whole, thereby obtaining a member for the intended use.

  Furthermore, in such T4 tempering and T6 tempering, as solution treatment conditions, generally, treatment conditions consisting of holding at a temperature of 450 to 520 ° C. for 0.5 to 10 hours are adopted, Even in the artificial aging treatment in the T6 tempering, generally, treatment conditions that are maintained at a temperature of 90 to 210 ° C. for 3 to 24 hours are adopted.

  In the joined body of Al material (base material) thus obtained, a plurality of Al materials constituting the joined body are joined by a welded joint formed using a specific filler material. In addition, since the welded joint portion has excellent strength characteristics, the weld cracking sensitivity is effectively reduced, and particularly high strength. By using an Al material formed of a predetermined 7000 series Al alloy, the base material strength is 250 MPa or more, the joint strength is 200 MPa or more, and the joint elongation is 4% or more. It can be obtained as a joining member having characteristics, and thus can be advantageously used as a member constituting at least a part of structural members, parts, products and the like for various uses.

  Hereinafter, representative examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited by the description of such examples. It goes without saying. In addition to the following examples, the present invention includes various changes and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the specific description described above. It should be understood that improvements can be made.

  First, Al alloys having various alloy compositions shown in Tables 1 to 3 below were melted, and various billets were produced by a normal DC casting method. Next, the obtained billet was homogenized and then directly extruded according to a conventional method to obtain various plate-like Al materials having a plate thickness of 3.0 mm or 4.0 mm. Further, each of these various Al materials was subjected to a solution treatment at 460 ° C. for 1 hour to prepare various test base materials for a welding test described later.

  On the other hand, also for the filler material, after melting Al alloys having various alloy compositions shown in Tables 4 to 6 below, billets were prepared in the same manner as described above, and then homogenized, and further directly The material for drawing was obtained by extrusion. Then, various target filler materials were produced by the drawing process similar to the past as a welding wire whose wire diameter is 1.6 mm.

  Next, using each of the two base materials made of various Al materials shown in Tables 1 to 3 above, the end portions in the respective extrusion directions were butted together, and the filler materials shown in Tables 4 to 6 were used. Various welding tests consisting of MIG welding using the same number were performed as shown in Tables 7 to 9 below. The MIG welding conditions were as follows: current: 210 A, welding speed: 80 cm / min, shield gas: Ar, shield gas flow rate: 10-15 L / min.

  And various things of the target member tempered by T6 were manufactured by performing the artificial aging treatment of 150 degreeC x 8 hours with respect to the joined body obtained in each welding test.

For the various joining members thus obtained, whether or not cracks have occurred in the welded joint portion, while evaluating by observing a cross section perpendicular to the joining direction of the welded joint portion, respectively, For the welded joint part, the maximum thickness (t ₁ ) of the weld metal part and the thickness (t ₂ ) of the heat affected zone (HAZ) are measured, and the center hardness (Hv ₁ ) and heat effect of the weld metal part are measured. The softened part hardness (Hv ₂ ) of the part (HAZ) is measured from its cross section with a load of 1 kgf with a Vickers hardness tester in accordance with JIS-Z-2244, and further subjected to a tensile test. The measurement was performed on the elongation of each joint, and the breaking position was examined.

  In addition, the tensile test of each joint is carried out by using a No. 5 tensile test piece defined in JIS-Z-2201 so that the length direction is the extrusion direction of the base material and the weld metal part at the central part of the test piece. Was cut out from each welded joint so as to be positioned, and a tensile test was carried out in accordance with JIS-Z-2241 while leaving extras.

  In the evaluation of the fracture position, the fracture occurred in the weld metal part, or occurred at the boundary part (bond part) between the weld metal part and the base material part, or the thermal effect of the base material part. It was evaluated whether it occurred in the part (HAZ).

  And the result of said test and evaluation was combined with the following Table 7-Table 9, and was shown.

As is clear from the results of Tables 7 to 9, a base material (No. 1 to 27), which is an Al material made of a 7000 series Al alloy having a specific alloy composition, is used, and this is used as a solution of the alloy composition according to the present invention. In welding tests 1 to 27, which were MIG welded with the additive (No. 1 to 27), a welded joint having excellent physical properties such as hardness and elongation was obtained, and also excellent in crack susceptibility, It is recognized that a welded joint structure having excellent fracture characteristics can be obtained with the fracture position serving as a heat affected zone (HAZ).

  On the other hand, the alloy composition of the Al material to be welded is outside the scope of the present invention (used base material No. 58 to 64), or the alloy composition that gives the filler material is outside the scope of the present invention. (Welding material Nos. 31-57, 65-72), in the welding tests 31-72, the elongation decreases, the hardness of the weld metal part becomes too low, and the fracture position It has become clear that there are not a few problems in the use as the intended joining member, causing problems such as bond portions and weld metal portions and cracking. In welding tests 66 to 69 and 72, the filler material No. Breaking was caused during the drawing processes of 66 to 69 and 72, so that a welding wire having a target wire diameter could not be obtained, and therefore each welding test could not be performed.

2 Al alloy base material 4 Weld metal part

Claims (2)

On the mass basis, Cu: 0.01 to 0.50%, Mg: 1.2 to 2.1%, and Zn: 5.0 to 8.5%, with the balance being Al and inevitable impurities An Al alloy base material having an alloy composition is Mg: 5.5 to 8.0%, Cr: 0.05 to 0.25%, Ti: 0.25% or less, Si: 0.4 on a mass basis. %, Fe: 0.4% or less, Cu: 0.1% or less, Zr: 0.05% or less, and Zn: 0.25% or less, with the balance being Al and inevitable impurities. Using an Al alloy filler material having a welded joint obtained by fusion welding,
The maximum thickness of the weld metal portion formed by the fusion welding is t ₁ , the center hardness is Hv ₁ , the thickness of the heat affected zone of the base material is t _2, and the softest portion the hardness of when the Hv _2, the following relationship:
t ₁ × Hv ₁ ≧ 1.9 × t ₂ × Hv ₂
Hv ₁ ≧ 70
An Al alloy welded joint characterized by satisfying the requirements. The Al alloy welded joint according to claim 1, wherein the filler material further contains 0.05 to 1.0 mass% of Mn.

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