JP3726034B2 - Aluminum alloy welded joints and aluminum alloy sheet base materials for welded joints - Google Patents

Description

【００８３】
【表２】

【００８４】
【表３】

【００８５】
【発明の効果】
本発明によれば、側辺部底面割れを防止した6000系Al合金材継手および溶接継手用Al板母材を提供を提供することが可能となる。したがって、特性の優れた過剰Si型を含めた6000系Al合金板材の自動車用途などへの拡大を図れる点でも、工業的な価値が大きい。
【図面の簡単な説明】
【図１】本発明に係るAl合金板母材の結晶粒の規定の定義を示す説明図である。
【図２】本発明に係る隅肉溶接Al合金継ぎ手を示す説明図である。
【図３】本発明に係る突き合わせAl合金継ぎ手を示す説明図である。
【図４】過剰Si型AA6022Al合金材継手の側辺部溶接部に生じた側辺部底面割れを示す平面図である。
【図５】側辺部底面割れの試験に用いた溶接用試験片（板）を示す平面図である。
【符号の説明】
1;6000系Al合金材、2;Al合金材の側辺部、3;溶接部 (溶接線) 、
4;側辺部底面割れ、5;継手、6;Al合金材、7;溶接トーチ、[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a 6000 series aluminum alloy welded joint (hereinafter, aluminum is simply referred to as Al) and an aluminum alloy welded base material for the welded joint, which prevent weld cracks on the bottom surface of the welded portion on the side of the joint.
[0002]
[Prior art]
For members such as panels, frames, and members of transport equipment such as automobiles, there are joints (welded joint members) in which the molded Al alloy plates are welded together or the molded Al alloy plates and Al alloy profiles are welded together. It has come to be used.
[0003]
As the Al alloy plate base material for these welded joints, 5000 series stipulated in the AA to JIS standards conventionally used as Al alloys for welded structures and 6000 series such as 6063 and 6061 (hereinafter referred to as AA to JIS). 7N01, 7003 and other 7000 series Al alloy rolled plates (thick plates are hot-rolled plates, thin plates are cold-rolled plates) are used.
[0004]
Among these 6000 series (Al-Mg-Si series) Al alloys, Si / Mg is 1 or more, such as 6061, 6N01, 6016, 6111, 6022, etc. according to AA or JIS standards. Excess Si type 6000 series Al alloy base metal contained in is treated with solution treatment and quenching treatment (quality symbol T4) and subsequent aging treatment (quality symbol T6), overaging treatment (quality symbol) T7) Excellent in age-hardening properties in later properties.
[0005]
For this reason, the excess Si type 6000 series Al alloy ensures formability with low proof stress during molding such as press molding and bending, and heats at a relatively low temperature such as 170 ° C in the paint baking process of the molded parts. However, it has the characteristic that the required strength can be satisfied by increasing the yield strength. Further, since the amount of alloying elements is small as compared with the 5000 series and 7000 series Al alloys, it is excellent in recyclability such that scrap can be reused as a melting raw material of the original 6000 series Al alloy.
[0006]
However, 6000 series Al alloy sheet base material, especially excess Si type 6000 series Al alloy sheet base material, is reverse to the Al alloy sheet base material such as 5000 series and 7000 series because of its excellent age hardening. However, there is a problem that the weldability (joint strength) is lowered during welding.
[0007]
The problem of this joining property is that the distance (end length) from the side part (end to edge) of the part to be welded to the weld line is short, and the welded part (side part welded part) ) Becomes noticeable when welding.
[0008]
That is, when welding a joint with fillet welding, butt welding, etc. using at least one Al alloy plate base material as an excess Si type 6000 series Al alloy, ), There is a problem that macro weld cracks that run along the weld line (welding line) are likely to occur. The crack at the bottom of the side welded portion is a remarkable tendency of the 6000 series Al alloy sheet base material, and particularly in the excess Si type 6000 series Al alloy sheet base material. And other Al alloys other than 6000 series such as 5000 series and 7000 series do not cause or hardly cause this weld bottom crack.
[0009]
In addition, this weld bottom crack usually occurs in the entire Al alloy system during welding, and welds such as the weld metal part (welded part) and the vicinity or the surrounding heat-affected part (hereinafter referred to as HAZ). The micro weld crack generated in the joint is a peculiar phenomenon that is completely different from the generation mechanism described later.
[0010]
  FIG. 4 shows weld cracks at the bottom of the weld that occur in the side welds of the 6000 series Al alloy base metal. Fig. 4 shows a 2 mm thick excess Si type AA6022Al alloy base metal (Si; 0.9%, Mg; 0.6%) test piece 1a shown in a plan view in Fig. 5, and a side portion 2 of the test piece 1a to be welded. To the weld line 3 (hereinafter referred to as end length)tThe welding state of the bottom face 1b of the specimen is shown when welding is performed with various changes. The welding method was simply a bead-on welding method, and welding was performed with a constant penetration depth. In FIG. 4, (a) is an end length of 32 mm, (b) is an end length of 24 mm, (c) is an end length of 16 mm, and (d) is an end length of 8 mm.
[0011]
As shown in FIG. 4, in FIGS. 4 (a) and 4 (b), the end length is relatively long, no weld crack is generated at the weld line 3a (bottom of the welded portion). On the other hand, as shown in FIGS. 4 (c) and 4 (d), macro weld cracks 4a and 4b running along the weld line 3a are generated as the end length becomes shorter. That is, as the end length becomes shorter, macro weld cracks are more likely to occur particularly on the side welded portion bottom surface 1b of the excess Si type 6000 series Al alloy plate base material.
[0012]
In addition, the tendency of cracks at the bottom of the welded portion on the side of the side of the 6000 series Al alloy base metal (hereinafter simply referred to as the side of the bottom of the base) is unlikely to occur with a welding method in which individual weld lines are very short. However, the weld line has a relatively long weld line and uses a heat source such as an arc, that is, high-speed arc welding such as TIG (MIG), laser welding, electron beam welding, etc. Prominent when forming. Furthermore, this tendency also occurs in the friction stir welding (FSW) method, which is a joining method in which the weld joint does not reach a relatively high temperature.
[0013]
And when such a side part bottom crack arises, the intensity | strength of Al alloy welded joint will fall remarkably and the serious problem that it cannot apply to the said members, such as a car, will arise.
[0014]
Conventionally, various improvement methods such as welding conditions have been performed from the side of welding methods such as arcing for the softening and cracking of the welded portion of the Al alloy welded joint. For example, (1) as exemplified in Japanese Patent Application Laid-Open No. 11-104860, etc., a method of welding with low heat input as much as possible, or welding joining while cooling, (2) quenching and tempering the joint after welding Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 5-222498, there is a method of recovering softening by heat treatment, such as age hardening treatment after welding materials (T1, T4 materials) before age hardening treatment.
[0015]
[Problems to be solved by the invention]
However, as described above, the side-side bottom crack, which is the subject of the present invention, is unlikely to occur in other 5000 series and 7000 series Al alloys that have been applied to the above-mentioned members such as automobiles. Therefore, the 6000 series Al alloy sheet is a new problem caused by the use of the welding application member such as an automobile, and as described above, it is also a problem specific to the 6000 series Al alloy sheet.
[0016]
Conventionally, in Japanese Patent Application Laid-Open No. 61-23580, etc., the difference in heat conduction due to the difference in the thickness of the welded material between the large-thickness member and the small-thickness member of the Al alloy material (the smaller-thickness member It has been publicly known as a problem that there is a difference in the heating rate between the two due to low heat dissipation (a thick-walled member has a slower temperature rise and a lack of heat).
[0017]
However, the problems of these known techniques are different from the side part bottom cracks which are the problems of the present invention. In addition, since the mechanism is different from the side bottom crack, the solution that installs a medium thickness member in the middle to buffer the heating rate difference is also a solution for the side bottom crack itself. I don't get it. Therefore, the side-side bottom crack, which is the subject of the present invention, has not been elucidated in detail so far, and no direct solution has been proposed.
[0018]
The present invention has been made paying attention to such circumstances, and its purpose is to prevent side-side bottom cracks, in particular, excess Si type 6000 series aluminum alloy joints and aluminum joints for welded joints. The material is to be provided.
[0019]
[Means for Solving the Problems]
  In order to achieve this object, the gist of claim 1 of the present invention 6000 series aluminum alloy joint is a welded joint obtained by welding a 6000 series aluminum alloy sheet base material defined in AA to JIS standards,Before welding to the fitting,The crystal grain of the aluminum alloy plate base materialThe rolling direction of the base material,The crystal grains are elongated in the direction perpendicular to the weld line direction, and the aspect ratio of the crystal grains (average grain size r in the direction perpendicular to the weld line direction)₁And average particle size r in the plate thickness direction_tRatio r₁/ r_t) Is 2 or more, and the average grain size r in the thickness direction_tIs 100 μm or less.
[0020]
  In order to achieve this object, the gist of claim 2 of the 6000 series aluminum alloy joint of the present invention is a welded joint in which the aluminum alloy welded joint has a welded portion on the side of the joint, and at least the welded joint The crystal grains of the base material of the aluminum alloy plate at the bottom of the welded part on the side of the joint, Before welding to the joint, the rolling direction of the base material,The crystal grains are elongated in the direction perpendicular to the weld line direction, and the aspect ratio of the crystal grains (average grain size r in the direction perpendicular to the weld line direction)₁And average particle size r in the plate thickness direction_tRatio r₁/ r_t) Is 2 or more, and the average grain size r in the thickness direction_tIs 100 μm or less.
[0021]
As a result of investigating the relationship between the base material structure of the 6000 series Al alloy sheet and the side part bottom cracks, the present inventors have found that the crystal grain shape of the bottom part of the welded part in the side part of the welded joint is particularly It was found that the side-side bottom cracks are correlated.
[0022]
In other words, when a 6000 series Al alloy hot-rolled sheet (a cold-rolled sheet is also used for a thin sheet of 2 mm or less) is used as a welding base material, a normal 6000 series Al alloy whose hot-rolling finishing temperature is higher than the recrystallization temperature Hot-rolled sheets are equiaxed (spherical) grains with an aspect ratio of about 1 in the thickness section parallel to the rolling direction.
[0023]
On the other hand, when the hot rolling finish temperature is lower than the recrystallization temperature and the hot rolling reduction rate and strain rate are increased, the crystal grains of the 6000 series Al alloy hot rolled sheet extend in the rolling direction (longitudinal direction of the sheet). Further, fine flat crystal grains having an aspect ratio of 1 or more in the plate thickness section parallel to the rolling direction and an average particle size in the rolling direction larger than the average particle size in the plate thickness direction are obtained.
[0024]
The present inventors have found that the side surface bottom crack is less likely to occur in the case of a flat crystal grain than in the case of an equiaxed crystal grain in the 6000 series Al alloy plate base material. I found out. It was also found that this tendency becomes prominent when the crystal grain elongation direction of the 6000 series Al alloy sheet base material at the bottom of the weld joint on the side of the weld joint is correlated with the weld line direction of the joint.
[0025]
That is, as the 6000 series Al alloy plate base material at the bottom of the welded portion on the side of the welded joint is made into flat crystal grains elongated in a direction perpendicular to the weld line direction, the flat crystal grains Aspect ratio (average grain size r perpendicular to the weld line direction)₁And average particle size r in the plate thickness direction_tRatio r₁/ r_t) Is 2 or more, the effect of preventing cracks on the bottom face of the side portion becomes remarkable.
[0026]
Furthermore, even if the crystal grains of the Al alloy plate base material are flat, the present inventors lose the effect of suppressing the side-side bottom cracks due to the flat crystal grains, The upper limit of the grain coarsening is the average grain size r in the plate thickness direction of the crystal grains at the bottom of the weld joint side part._tIt was also found that it is about 100 μm.
[0027]
As described above, in order to prevent cracks on the bottom side of the side portion, correlate the elongation direction of the crystal grains of the base material of the 6000 series Al alloy plate in the bottom portion of the welded joint side portion with the weld line direction of the joint. is necessary. For this reason, the definition of the flat crystal grain shape in the present invention is defined not as a material such as an Al alloy hot-rolled sheet but as a structure of a 6000 series Al alloy plate welded base material.
[0028]
Also, when using 6000 series Al alloy hot-rolled sheet as the base material of Al alloy sheet, before welding to the joint, condition of hot rolling of Al alloy sheet and tempering treatment conditions such as T4, T6, T7 after hot rolling Depending on the heat treatment conditions such as age hardening accompanying the forming process, the flat crystal grain shape and crystal grain size as the Al alloy plate base material may change. Depending on these conditions, there is a possibility that the definition of the flat crystal grain shape and grain size as the Al alloy sheet base material in the present invention is not included. For this reason, the definition of the flat crystal grain shape and grain size in the present invention is not the state of the hot rolled sheet, but the structure of the 6000 series Al alloy weld base material after the hot-rolled sheet is formed or tempered. To do.
[0029]
The reason why the 6000 series Al alloy base metal structure (the crystal grain shape of the bottom portion of the welded portion on the side of the welded joint) correlates with the bottom of the side portion is thought to be as follows.
[0030]
First, as for the situation on the welded part side, in the side part welded part where the end length of the 6000 series Al alloy plate base material is short, the Al alloy plate near the welded part is longer than other welded parts with sufficiently long end lengths. The mass of the base material is extremely small. For this reason, heat input by welding is not easily dissipated by heat transfer through the Al alloy plate base material. As a result, during welding, the bottom of the side welded portion tends to be held on the higher temperature side, which exceeds 550 ° C., than the bottom of the other welded portions.
[0031]
On the other hand, in the case of 6000 series Al alloy plate base material, the base material is related to the Al-Mg-Si (excess Si type) composition and tempering treatment such as T4, T6, T7, etc. From the material stage, many intermetallic compounds are originally present at the grain boundaries. As a result, an unsolidified portion (unsolidified intermetallic compound) inevitably exists in the HAZ grain boundary at the bottom of the side weld. The intermetallic compound at the unsolidified portion or grain boundary is particularly large in the 6000 series Al alloy plate base material such as excess Si type, and is liable to cause a bottom crack at the side portion.
[0032]
This is because when the maximum temperature of the bottom surface of the side welded part is maintained on the high temperature side exceeding 550 ° C., the solidification timing is delayed only in the unsolidified part or the intermetallic compound part of the grain boundary. This is because, when the contraction stress is applied during the contraction, the grain boundary of the unsolidified portion cannot be withstood and becomes a micro crack that makes it easy to open the mouth, resulting in a side face bottom crack.
[0033]
For example, in the case of butt welding of an Al alloy plate base material and an Al alloy plate base material, when the welded portion (melted portion) shrinks as the welded portion solidifies, there is a shrinkage stress that tends to spread the welded portion outward. Acts on the weld. At this time, if the maximum temperature of the bottom of the side welded part is maintained on the high temperature side exceeding 550 ° C, the 6000 series Al alloy plate base material, particularly the HAZ grain boundary on the bottom of the side part, , The timing of solidification is delayed. For this reason, the restraint force of the matrix is relatively weak, the transmission and absorption of the contraction stress is insufficient, and the side face bottom cracks are likely to occur.
[0034]
The tendency is that the excess Si-type 6000 series Al alloy plate base material with more unsolidified parts, the higher the maximum temperature of the bottom of the side part at the time of welding exceeds 550 ° C, and the higher the temperature exceeds 550 ° C. The longer it is held at temperature, the stronger it becomes.
[0035]
Here, when the structure of the 6000 series Al alloy base metal (joint side side weld bottom) is a regular equiaxed crystal grain, the grain boundary area in the plate thickness direction is large and the grain boundary direction is in the plate thickness direction. Is linear with respect to. For this reason, the binding force of the matrix becomes relatively weak. As a result, the micro cracks at the grain boundaries of the unsolidified part that occur when the shrinkage stress acts during the solidification shrinkage of the weld are likely to propagate in the plate thickness direction, and the transmission and absorption of the shrinkage stress becomes insufficient. It tends to lead to the occurrence of cracks on the bottom of the side part.
[0036]
On the other hand, the grain interface area in the plate thickness direction is increased as the weld bottom surface portion on the side portion of the weld joint is made to be fine flat crystal grains elongated in a direction perpendicular to the weld line direction as in the present invention. And the grain boundary direction is non-linear with respect to the plate thickness direction. For this reason, the binding force of the matrix becomes relatively strong. As a result, when the shrinkage stress acts, micro cracks in the grain boundary of the unsolidified portion are difficult to propagate in the thickness direction, and the transmission of the shrinkage stress It is presumed that absorption is sufficiently performed and cracking of the bottom of the side portion does not occur.
[0037]
According to this side side bottom crack mechanism, if the maximum temperature of the side side bottom is set to 550 ℃ or less, side side bottom cracks will not occur, but depending on the joint design and welding conditions, the side There is a possibility that the maximum temperature at the bottom of the weld zone will be maintained on the high temperature side exceeding 550 ° C.
[0038]
It is also effective to reduce the unsolidified portion of the HAZ grain boundary of the 6000 series Al alloy plate base material (specific intermetallic compound at the grain boundary of the base material), which is another cause of the side face bottom crack. is there. However, especially in the case of excess Si type 6000 series Al alloy plate base material, there are cases where intermetallic compounds at the grain boundaries cannot be reduced due to characteristics such as age hardening and restrictions on production.
[0039]
Therefore, even when the maximum temperature of the bottom surface of the side-side welded part is maintained on the high temperature side exceeding 550 ° C, or even when the maximum temperature of the bottom surface of the side-side part can be 550 ° C or lower, Even if it is an excess Si type 6000 series Al alloy sheet base material with many unsolidified parts, or even a 6000 series Al alloy sheet base material with a small number of unsolidified parts, the side part bottom cracks are ensured In order to prevent this, in the present invention, the bottom surface portion of the welded portion on the side of the welded joint has a fine and flat crystal grain structure elongated in a direction perpendicular to the weld line direction.
[0040]
Making the base structure of the 6000 series Al alloy sheet of the present invention a fine and flat crystal grain structure elongated in a direction perpendicular to the welding line direction, as described above, strengthening the binding force of the matrix and welding It leads to sufficient transmission and absorption of shrinkage stress during solidification. And this point suppresses not only the side side bottom cracks of the main object of the present invention but also micro or macro weld cracks that occur in weld joints such as weld metal parts and HAZ during normal welding construction. It also leads to an effect.
[0041]
Therefore, in the present invention, the side face bottom crack does not occur, in other words, even in the case of a welded joint that does not have a welded part (side welded part) with a short end length, during normal welding construction. It can be applied for the purpose of suppressing micro or macro weld cracks that occur in welded joints such as weld metal parts and HAZ. For this reason, claim 1 of the present invention also includes the case of a welded joint that does not have a side-side weld where a side-side bottom crack occurs.
[0042]
Further, since the present invention has an excellent effect of suppressing side side bottom cracks as described above, as described in claim 3, among 6000 series Al alloys, the tendency of side side bottom cracks is particularly large. : 0.4 to 0.8% (mass%, the same applies hereinafter), Mg: It is preferably applied to an excess Si type 6000 series Al alloy material containing 0.4 to 0.8%.
[0043]
DETAILED DESCRIPTION OF THE INVENTION
 (Grain structure)
The definition of the crystal grain structure of the Al alloy sheet base material of the present invention will be described using an example of a butt weld joint shown in FIG. In Fig. 1, 5a is a welded joint, 1 is a 6000 series Al alloy plate base material to be welded, 6 is the same 6000 series or other Al alloy plate base material, 1b is the bottom of the side edge of the Al alloy plate base material 1, 2 is a side portion of the Al alloy base material 1, 3 is a welded portion, and x is an end length from the side portion 2 to the weld line 3a.
[0044]
In FIG. 1, in the present invention, as described above, the crystal grain structure of at least the welded portion bottom surface 1b of the side portion of the welded joint of the 6000 series Al alloy plate base material 1 used for the joint is the direction A of the weld line 3a. Crystal grains 7 elongated in the direction B perpendicular to the direction of the crystal grains 7 and the aspect ratio of the grains 7 (average grain size r perpendicular to the weld line direction r₁And average particle size r in the plate thickness direction_tRatio r₁/ r_t) Is 2 or more and the average grain size r in the thickness direction t_tIs 100 μm or less (L is the plate width direction).
[0045]
Average grain size r in the direction B perpendicular to the direction A of the weld line 3a₁And average grain size r in the thickness direction t_tRatio r₁/ r_tIs less than 2, it is close to the normal equiaxed crystal grains described above, the grain boundary area in the plate thickness direction is large, and the grain boundary direction is linear with respect to the plate thickness direction. For this reason, the restraining force of the matrix becomes relatively weak, and microcracking at the grain boundaries of the unsolidified part that occurs when the shrinkage stress in the direction of the arrow indicated by Z in FIG. Tends to propagate in the plate thickness direction, and the transmission and absorption of the contraction stress becomes insufficient, and the side surface bottom surface cracks are likely to occur.
[0046]
The average particle size r in the thickness direction t_tIf it exceeds 100 μm, not only the specific intermetallic compound at the grain boundary that can be the unsolidified part, but also the grain boundary precipitate itself that has precipitated at the grain boundary, and the precipitate-free zone formed along the grain boundary. (PFZ: Precipitation Free Zone) itself gets bigger. For this reason, when the shrinkage stress acts in the middle of solidification shrinkage of the welded portion, it acts as a starting point of microfracture and a point that promotes propagation of fracture, including microcracking at the grain boundaries of the unsolidified part, Cracks easily develop along the grain boundaries, and side side bottom cracks are likely to occur.
[0047]
The crystal grain structure control of the 6000 series Al alloy sheet base material is mainly performed by a hot rolling process of the 6000 series Al alloy sheet for manufacturing the 6000 series Al alloy sheet base material, as will be described later.
[0048]
However, in the present invention, it is allowed to be a mixed grain structure or a composite structure in which equiaxed recrystallized grain structures having an aspect ratio of about 1 are mixed within a range that does not inhibit the side-side bottom-surface crack suppressing effect. As a matter of fact, it is difficult to make the structure of a 6000 series Al alloy sheet 100% pure fine flat grain structure by controlling the hot rolling process, and such control is not economical. In addition to this meaning, there is also a variation in the fine flat crystal grains themselves. In the present invention, as defined in the claims, the grain diameter r of the crystal grains in the direction perpendicular to the weld line direction is used.₁And grain size r_tEach value (measured value) is averaged.
[0049]
The grain size r of these crystal grains₁And grain size r_tThe measurement of the 6000 series Al alloy plate base material before welding construction, after electrolytic etching the plate thickness direction cross section perpendicular to the weld line direction, the same cross section with an optical microscope of 50 times magnification, Observe 10 fields in the range of plate thickness x 0.1mm and measure (calculate) the average value. At this time, as described above, if equiaxed recrystallized grains exist in the flat crystal grains, the equiaxed recrystallized grains are also measured and averaged.
[0050]
 (Al alloy for base material)
The Al alloy for the base material used in the present invention is applicable to all 6000 series (Al-Mg-Si series) Al alloys defined in AA or JIS standards. However, among these 6000 series Al alloys, the tendency of cracks on the bottom of the side portion is particularly large, Si / Mg is 1 or more, Si is excessively contained with respect to Mg content, 6N01, 6016, 6111, 6022 Excess Si type 6000 series Al alloy is the target and effective.
[0051]
As a preferable component composition of the Al alloy for the base material of the present invention, in order to satisfy the required properties such as the required strength for the welded structure, Mg: 0.2 to 1.0% (mass%, the same shall apply hereinafter), Si: It is preferable that Si is excessively selected from the range of 0.6 to 1.6%.
[0052]
In addition, other alloy elements such as Mn, Cr, Zr, Ti, B, Fe, Zn, Ni, and V are basically impurity elements. However, from the viewpoint of recycling 6000 series alloys, not only high-purity Al bullion but also 6000 series alloys, other Al alloy scrap materials, and low-purity Al bullion are used as melting materials. Including. For this reason, these elements are allowed to be contained within the JIS or AA standards as long as they do not impair the effect of improving various properties intended by the present invention. Therefore, in the present invention, being defined in AA to JIS standards means that these standards are satisfied.
[0053]
 (Manufacture of base materials)
The Al alloy sheet base material itself in the present invention is manufactured as a hot rolled sheet having a sheet thickness of 2 mm or more by conventional processes such as melting, casting, homogenizing heat treatment, hot rolling and the like. If the thickness of the Al alloy sheet base material is 2 mm or less, it is further subjected to intermediate annealing if necessary, and is formed into a cold-rolled sheet by cold rolling.
[0054]
In the manufacturing process, in order to make the microstructure of the 6000 series Al alloy hot-rolled sheet into fine flat crystal grains defined in the present invention, the hot-rolling conditions are controlled. That is, for example, it is preferable to set the finishing temperature in hot rolling to a recrystallization temperature (300 to 400 ° C.) or lower and further increase the rolling reduction rate and strain rate of hot rolling. On the other hand, when the finishing temperature of hot rolling is higher than the recrystallization temperature, an equiaxed recrystallization structure is mainly developed.
[0055]
The flat crystal grains of the 6000 series Al alloy hot-rolled sheet manufactured in this way are the crystal grains in the plate thickness section parallel to the rolling direction of the plate, and the crystal grains perpendicular to the weld line direction referred to in the base material. Average particle size r₁The average grain size in the rolling direction corresponding to_tIt becomes a fine flat crystal grain structure (with an aspect ratio of 2 or more) that is longer than the average grain size in the thickness direction corresponding to.
[0056]
For this reason, in order to use a 6000 series Al alloy hot-rolled sheet as a joint base material, the base material direction in various welded joints is set so that the average grain size in the base material rolling direction is larger than the weld line direction. Average grain size r₁It is necessary to use them in correspondence or correspondence so that When this base material direction is changed and the average particle diameter (extended) in the base material rolling direction is parallel to the weld line direction, etc. The effect of suppressing the side surface bottom surface cracking is reduced in relation to the direction of action of the shrinkage stress.
[0057]
In addition, these Al alloy hot-rolled sheets (including cold-rolled sheets) are subjected to solution treatment and quenching treatment (appropriate symbol T4) after or before appropriate forming processing such as pressing and bending into a joint shape. ) And subsequent aging treatment (quality symbol T6) and overaging treatment (quality symbol T7) and used as a base material for welded joints or welded parts.
[0058]
These tempered Al alloy hot-rolled plates, etc. are not limited to the grain shape structure control of the present invention, and the grain boundary structure control is not limited to the HAZ grain boundary that leads to the side-side bottom cracks. It is preferable to suppress as much as possible the specific intermetallic compounds at the unsolidified portion and the grain boundary of the base material that causes the solidified portion.
[0059]
For this purpose, it is preferable to mainly control the tempering process together with the manufacturing history of the alloy component and hot composition processing or in response to the alloy component and the manufacturing history.
[0060]
More specifically, (1) Solution treatment is performed at a high temperature of 510 ° C. or higher as solution treatment conditions. (2) Increase the cooling rate during quenching after solution treatment to 300 ° C / min or higher. For this purpose, the final solution treatment and quenching treatment should be carried out in a continuous heat treatment furnace capable of heat treatment by continuously passing a coil or the like (3) instead of a batch type. preferable. In the case of the batch type, the cooling rate is slowed down, and the specific intermetallic compound form that is the main cause of side-side bottom cracks is likely to occur particularly in excess excess Si type 6000 series Al alloy sheet base material.
[0061]
Further, in the quenching treatment after the solution treatment, it is not simply cooled to room temperature and left as it is, but as a preliminary aging treatment, (4) once quenched to room temperature and then reheated to a temperature of 50 to 120 ° C. Or 5) Hold the quenching end temperature at a high temperature of 50-120 ° C and hold it for 0.2-24 hours, or reheat and hold it at a temperature of 50-120 ° C for 0.2-24 hours. It is preferable to keep it wound up as it is or after reheating. This preliminary aging treatment makes it difficult to form the specific intermetallic compound form.
[0062]
In addition, when performing aging treatment of a 6000 series Al alloy plate base material before welding, compared with normal aging treatment and overaging treatment conditions, (6) the aging treatment temperature is set to the low temperature side of 80 to 160 ° C, It is preferable to set the aging treatment time to a sub-aging treatment range on the short side of 1 to 10 hours. When performing normal aging treatment or overaging treatment, especially in the excessive Si type 6000 series Al alloy plate base material, the above-mentioned specific intermetallic compound form that is the main cause of side side bottom cracks tends to occur. Because there is, attention is necessary.
[0063]
 (Welding method)
The welding method targeted by the present invention is welding of a 6000 series Al alloy plate base material, and has a welding construction site with a short end length, and a heat source such as an arc is liable to cause a bottom crack at the side portion. This is a fusion welding method with a long welding line.
[0064]
  As described above, the cause or mechanism of the side-side bottom surface cracking of the 6000 series Al alloy material is the maximum temperature of the bottom-side welded portion with a short end length and the unsolidified portion of the HAZ grain boundary during solidification of the welded portion. It is a metallurgical problem called correlation. Therefore, it is a common problem that occurs regardless of the type of welding method in a fusion welding method in which this metallurgical phenomenon occurs in common.
[0065]
Examples of such welding methods include high-speed arc welding such as TIG (TIG) and MIG (MIG), welding methods such as laser welding and electron beam, and friction stir welding (FSW) methods. Therefore, the welding method which does not produce the side part bottom face crack of a 6000 series Al alloy material welded joint is not considered.
[0066]
 (Welded joint)
In addition, the welded joint targeted by the present invention uses a 6000 series Al alloy plate base material as one or both base materials, has a welding construction site with a short end length, and can cause a bottom crack at the side portion. If the joint has high performance, it can be applied to various welded joints such as fillet welding shown in FIG. 2 and butt welding shown in FIG. In FIGS. 2 and 3, 5b and 5c are welded joints, 1 is a 6000 series Al alloy plate base material to be welded, 6 is the same 6000 series or other Al alloy plate base material, and 1b is an Al alloy plate base material. Reference numeral 1 denotes a bottom face of the side part, 2 denotes a side part of the Al alloy base material 1, 3 denotes a welded part, x denotes an end length from the side part 2 to the weld line 3a, and 7 denotes a welding torch.
[0067]
In these welded joints, appropriate shapes such as plates, profiles and pipes are selected as a combination of joints in accordance with the design shape of the automobile member or the like. In addition, welded joints are not necessarily 6000 series Al alloy plate base materials or excess Si type 6000 series Al alloy plate base materials, but are the same as ordinary Al alloy joints or depending on the purpose, 3000 series, 5000 series , 6000 series, 7000 series Al alloy materials with different components and alloys may be used for joining to the 6000 series Al alloy hot-rolled sheet base material.
[0068]
 (Welding conditions)
Each welding condition in the welded joint of the present invention is performed within the range of ordinary methods of each welding method. For example, basic welding conditions such as use of filler metal, groove shape, welding posture, torch advance angle, shielding conditions (Ar gas flow rate), welding current, welding voltage, welding speed, etc. Follow various welding and aluminum handbooks.
[0069]
In the welding process of the welded joint of the present invention, it is preferable to control the temperature of the bottom surface of the side-side welded portion to 550 ° C. or less from the viewpoint of reducing the basic condition for generating the side-side bottom surface cracks. However, in the welded joint of the present invention, as described above, even when the temperature of the bottom surface of the side side welded portion exceeds 550 ° C., the side surface bottom surface crack can be suppressed. Therefore, it is also an advantage of the present invention that no special welding method and conditions are required, including temperature control of the bottom surface of the side welded portion, and that it can be performed within the range of ordinary methods of each welding method.
[0070]
By the way, the method of controlling the maximum temperature of the bottom of the side welds to 550 ° C or less is to reduce the heat input to the side welds and to remove heat from the parts such as the weld bottoms and side surfaces, where heat is easily removed. A known means such as removing heat by contacting a metallurgy such as the above is appropriately selected.
[0071]
 (Fused material)
The filler material (bar) used for welding is based on the correlation with the above-mentioned side side bottom cracks, and the Al alloy filler material itself also has an unsolidified portion of the HAZ grain boundary (specific intermetallic compound at the grain boundary of the base metal). It is preferable that the composition of the component is small.
[0072]
In this regard, even if 5000 series Al alloy filler metal such as 5356 specified in JIS standard is added, the unsolidified portion of the HAZ grain boundary is small, and 4000 series Al alloy filler material has less of the HAZ grain boundary. There are many unsolidified parts. In particular, in fusion welding of an excess Si type 6000 series Al alloy sheet base material, the 4000 series Al alloy filler metal is liable to cause deterioration of the characteristics of the weld joint joint. Therefore, in particular, in the welded joint of the excess Si type 6000 series Al alloy plate base material, it is preferable to select from 5000 series Al alloy filler metal.
[0073]
【Example】
Next, examples of the present invention will be described. First, various 6000 series Al alloy hot-rolled sheets (2.5 mm thick) with 6063, 6061, 6022, and 6111 alloy compositions as shown in Table 1 have a hot rolling ratio of 95% or higher and hot rolling. The finishing temperature was set to be equal to or lower than the recrystallization temperature, and a flat and fine crystal grain-based structure defined in the present invention was prepared as an invention example Al alloy hot-rolled sheet. On the other hand, for example, a 6000 series Al alloy hot-rolled sheet (2 mm thick) with a fine equiaxed recrystallization main structure with a hot rolling finishing temperature equal to or higher than the recrystallization temperature and a total rolling reduction of 90% is also compared. Prepared as an example hot rolled sheet.
[0074]
Then, T4 tempering treatment (solution hardening) was performed on the hot-rolled sheets of the inventive examples and the comparative examples under the same conditions, and the specific unsolidified portion of the HAZ grain boundary and the grain boundary of the base material that caused it There were many specific intermetallic compounds of the above, and it was set as a disadvantageous joint base material condition in which the side face bottom cracks easily occur. The solution treatment for tempering is performed by heating the base material after cutting to a joint specimen size in a glass furnace to 520 to 530 ° C x 60 seconds, followed by air cooling and quenching with a fan (cooling rate is 200 ° C./min).
[0075]
The tempered hot rolled sheets of the inventive examples and comparative examples were each subjected to a 3% stretch by simulating the forming process, and the joint base material was used as a joint base material by the measurement method described above, and perpendicular to the weld line direction. Grain size r₁And grain size r_tWas measured. In the inventive examples, some equiaxed recrystallized grains existed in the flat crystal grains. Therefore, the equiaxed recrystallized grains were also measured and averaged. Table 2 shows the grain size conditions of these crystal structures.
[0076]
Next, a welded joint was manufactured by using the 5356Al alloy filler metal between the tempered plate base materials of the invention example and the comparative base plate materials.
[0077]
  The welded joint is welded with the end length t of one Al alloy plate base material 1 being 10 mm, and this portionFigure ThreeButt welding (welding length 140mm) shown in Fig. 1 is used for MIG welding, TIG welding, CO₂Performed by laser welding. Each welding condition is shown in Table 3. In any welding, the maximum temperature at the bottom surface of the side welded part was set to a temperature exceeding 550 ° C. at which the side part bottom cracks are likely to occur.
[0078]
The welded joint thus obtained was examined for the presence of cracks and the length (mm) on the bottom side. Then, a specimen of the welded joint was taken and the tensile strength (σ_B) Was measured according to JIS Z 2241. The base metal specific efficiency (joint efficiency) of the welded joint was also calculated from the tensile strength of the base metal. These results are shown in Table 2. The proof stress of the hot-rolled sheet subjected to the T4 tempering treatment is 190 MPa at 6063, 255 MPa at 6061, 225 MPa at 6022, and 280 MPa at 6111.
[0079]
As is clear from Table 3, the grain size r of the crystal grains perpendicular to the weld line direction₁And grain size r_tThe welded joints of Invention Examples No. 1 to 5 satisfying the present invention provisions are MIG welding, TIG welding, CO₂Regardless of the welding method such as laser welding, side side bottom cracks do not occur, and the joint strength is 95% or more in terms of the base metal specific efficiency.
[0080]
On the other hand, the aspect ratio of crystal grains (average grain size r in the direction perpendicular to the weld line direction)₁And average particle size r in the plate thickness direction_tRatio r₁/ r_t) Is less than 2 and / or the average grain size r in the thickness direction_tThe welded joints of Comparative Examples Nos. 6 to 14, which are made of a combination of Al alloy plate base materials with a thickness exceeding 100 μm, are MIG welding, TIG welding,₂Regardless of the welding method, such as laser welding, side side bottom cracks occur in common, and the joint strength is remarkably low at less than 90% in base metal efficiency.
[0081]
The results of the above examples support the critical significance of the present invention for preventing side side bottom cracks in 6000 series Al alloy welded joints including excess Si type.
[0082]
[Table 1]

[0083]
[Table 2]

[0084]
[Table 3]

[0085]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide provision of the 6000 series Al alloy material joint which prevented the side part bottom face crack, and the Al plate base material for welded joints. Therefore, the industrial value is also great in that the 6000 series Al alloy sheet material including the excess Si type having excellent characteristics can be expanded to automobile applications.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing the definition of the definition of crystal grains of an Al alloy sheet base material according to the present invention.
FIG. 2 is an explanatory view showing a fillet welded Al alloy joint according to the present invention.
FIG. 3 is an explanatory view showing a butt Al alloy joint according to the present invention.
FIG. 4 is a plan view showing a side-side bottom crack generated in a side-side weld of an excess Si type AA6022Al alloy joint.
FIG. 5 is a plan view showing a welding test piece (plate) used for a test of a side face bottom crack.
[Explanation of symbols]
1; 6000 series Al alloy material, 2; side of Al alloy material, 3; weld (welding line),
4; side side bottom crack, 5; joint, 6; Al alloy material, 7; welding torch,

Claims (4)

A welded joint made by welding a 6000 series aluminum alloy sheet base material stipulated in AA to JIS standards. Before welding the joint to the joint, the crystal grains of the aluminum alloy sheet base material are aligned in the rolling direction of the base material. And crystal grains elongated in a direction perpendicular to the weld line direction, and the aspect ratio of the crystal grains (average grain size r _{1 in the} direction perpendicular to the weld line direction and average grain diameter in the plate thickness direction) aluminum alloy welded joint, characterized in that r _t and the ratio r ₁ / r _t) is 2 or more, and an average particle size r _t in the thickness direction and 100 [mu] m or less. The aluminum alloy welded joint is a welded joint having a welded portion on the side portion of the joint, and at least before the crystal grains of the aluminum alloy plate base material on the bottom portion of the welded portion on the side portion of the welded joint are welded to the joint A crystal grain extending in a direction perpendicular to the weld line direction in the rolling direction of the base metal, and an aspect ratio of the crystal grain (average grain size r ₁ perpendicular to the weld line direction and thickness direction of the average particle ratio r ₁ / r _t) of the diameter r _t is 2 or more, and aluminum alloy welded joint according to claim 1, wherein the average particle diameter r _t in the thickness direction and 100 [mu] m or less.   The 6000 series aluminum alloy sheet base material is an excess Si type 6000 series aluminum alloy hot rolled sheet containing Si: 0.4 to 0.8% (mass%, the same shall apply hereinafter) and Mg: 0.4 to 0.8%. The aluminum alloy welded joint described.   The 6000 series aluminum alloy plate base material used for the aluminum alloy welded joint according to any one of claims 1 to 3.

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