JP3726033B2 - Aluminum alloy welded joints and wrought aluminum alloys for welded joints - Google Patents

Description

【００８３】
【表２】

【００８４】
【表３】

【００８５】
【表４】

【００８６】
【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合金展伸材の自動車用途などへの拡大を図れる点で、工業的な価値が大きい。
【図面の簡単な説明】
【図１】 6000系Al合金母材の示差熱分析によるDTA 曲線(530℃近傍における発熱ピーク無し) を示す説明図である。
【図２】 6000系Al合金母材の示差熱分析によるDTA 曲線(530℃近傍における発熱ピーク無し) を示す説明図である。
【図３】 6000系Al合金母材の示差熱分析によるDTA 曲線(530℃近傍における発熱ピーク有り) を示す説明図である。
【図４】 5356Al合金溶加材の示差熱分析によるDTA 曲線(550℃以下における発熱ピーク無し) を示す説明図である。
【図５】 4043Al合金溶加材の示差熱分析によるDTA 曲線(550℃以下における発熱ピーク有り) を示す説明図である。
【図６】継手側辺部溶接部の凝固過程を4 段階に分けて示す模式図である。
【図７】板材や形材同士の隅肉溶接を示す説明図である。
【図８】板材や形材同士の突き合わせ溶接を示す説明図である。
【図９】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。
【図１０】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。
【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;HAZ 、6;粒界、7;Al合金材、8;溶接トーチ、
t;端長さ、X;発熱ピーク、A 、B;DTA 曲線[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 wrought 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]
Joints (welded joint members) in which Al alloy base materials such as molded plates and profiles are welded together are used for members such as panels, frames, and members of transport equipment such as automobiles. Yes.
[0003]
As these Al alloys for welded joints, 5000 series prescribed in AA to JIS standards, which are conventionally widely used as Al alloys for welded structures, and 6000 series such as 6063, 6061 (hereinafter, AA to JIS are omitted), 7N01 7000 series and other Al alloy wrought materials (generic name for rolled plate material, extruded profile, forged material, etc., hereinafter also referred to simply as Al alloy material).
[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. The excess Si type 6000 series Al alloy contained is subjected to solution treatment and quenching treatment (quality symbol T4), subsequent aging treatment (quality symbol T6), after overaging treatment (quality symbol T7). In particular, it has excellent age-hardening properties.
[0005]
For this reason, the excess Si type 6000 series Al alloy secures formability with low proof stress during molding on the above-mentioned transport aircraft member, and even when heated at a relatively low temperature such as 170 ° C. in the paint baking process of the molded member. It has the characteristics that it can meet the required strength 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 materials, especially excess Si type 6000 series Al alloy materials, have superior age-hardening properties. There is a problem that (bonding strength) is lowered. The problem of this joining property is that, particularly, the welded part (side part welded part) has a short distance (end length) from the side part (end part to edge part) of the part to be welded to the weld line. ) Becomes noticeable when welding.
[0007]
That is, when welding joints with fillet welding or butt welding, etc., using at least one of the Al alloy materials as an excess Si type 6000 series Al alloy, the bottom side (rear surface) of the welded portion There is a problem that macro weld cracks tend to occur along the weld line (welding line). The crack at the bottom of the side welded portion is a remarkable tendency of the 6000 series Al alloy material, and the tendency is particularly strong in the excess Si type 6000 series Al alloy 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.
[0008]
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.
[0009]
FIG. 10 shows a weld crack at the bottom of the weld that occurs in the side weld of the 6000 series Al alloy material. FIG. 10 shows a 2 mm thick excess Si-type AA6022Al alloy plate (Si; 0.9%, Mg; 0.6%) test piece 1a shown in a plan view in FIG. 9, welded from the side part 2 of the test piece 1a to be welded. The welded state of the bottom surface 1b of the test piece when the distance to the line 3 (hereinafter referred to as the end length) t is varied and welded is shown. The welding method was simply a bead-on welding method, and welding was performed with a constant penetration depth. In FIG. 10, (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.
[0010]
As shown in FIG. 10, in FIGS. 10 (a) and 10 (b), which have a relatively long end length, no weld crack occurs in the portion of the weld line 3a (the bottom of the weld). On the other hand, as shown in FIGS. 10 (c) and 10 (d), as the end length becomes shorter, macro weld cracks 4a and 4b that run along the weld line 3a are generated. That is, as the end length becomes shorter, macro weld cracks are more likely to occur, particularly at the bottom of the side welded part of the 6000 series Al alloy material such as excess Si type.
[0011]
In addition, the tendency of cracks on the bottom surface of the welded part on the side part of the 6000 series Al alloy material (hereinafter simply referred to as side part bottom cracking) does not occur in welding joining methods such as spot welding where the 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.
[0012]
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.
[0013]
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.
[0014]
[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 material is a new problem caused by being used for the welding application member such as an automobile, and as described above, it is also a problem specific to the 6000 series Al alloy material.
[0015]
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).
[0016]
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.
[0017]
The present invention has been made paying attention to such circumstances, and an object of the present invention is to provide a 6000 series aluminum alloy joint such as an excess Si type in which cracking on the side face bottom surface is prevented. .
[0018]
[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 that a 6000 series aluminum alloy base material specified in AA to JIS standards is welded using an aluminum alloy filler metal. The welding construction is a welded joint including a welded portion on the side part of the joint, and the aluminum alloy base material and the aluminum alloy filler metal, Before welding In the cooling curve from the melt obtained by measuring the thermal change in the solidification process of each material by differential thermal analysis, the aluminum alloy base material has an exothermic peak near 530 ° C, and the aluminum alloy filler material has 550 Each exothermic peak at a temperature below 0 ° C. is not substantially recognized, and there is no weld crack on the bottom surface of the welded portion of the side portion.
[0019]
As a result of investigating the cause of cracks on the bottom side of the side portion of the 6000 series Al alloy base material, the present inventors have found the existence (behavior) of the specific unsolidified portion of the grain boundary of HAZ during solidification of the weld and the end length. It has been found that this is caused by a correlation with the maximum temperature of the bottom surface of the short side weld.
[0020]
First, in the case of 6000 series Al alloy 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 this stage, many intermetallic compounds originally exist 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 in the unsolidified part or grain boundary is particularly large in the 6000 series Al alloy base material such as the excess Si type, which is a main cause of the side face bottom crack.
[0021]
If the main cause of the side-side bottom crack is the intermetallic compound at the grain boundary in the 6000 series Al alloy base material, it may be reduced. However, reducing the intermetallic compound itself at the grain boundary in the 6000 series Al alloy base metal is difficult in terms of metallurgy and leads to a reduction including the useful intermetallic compound in the grain. It degrades basic properties such as excellent age-hardening properties.
[0022]
In this regard, the present inventors have further studied, the main cause of the side-side bottom cracks is a specific intermetallic compound among the intermetallic compounds of the grain boundary, in the 6000 series Al alloy base material It has also been found that it is not necessary to reduce the intermetallic compound itself or the entire grain boundary. In addition, this means that the interfacial intermetallic compound at the grain boundary is not degraded by the tempering treatment such as T4, T6, T7, etc., without degrading the basic properties such as age hardening, so that a specific intermetallic compound does not occur. It also means that the form can be controlled.
[0023]
However, it is difficult to identify (specify) the name of the specific intermetallic compound at the grain boundary, which is the main cause of the side bottom cracks. For this reason, in this invention, the intermetallic compound of the grain boundary which becomes the main cause of a side part bottom face crack is specified from the surface of the property correlated with the side part bottom face crack.
[0024]
That is, in the cooling curve from the melt obtained by measuring the thermal change in the solidification process of both materials by differential thermal analysis, the exothermic peak near 530 ° C (exothermic peak by differential thermal analysis) This is the reason why it is not substantially recognized, and only the specific intermetallic compound that is the main cause of the side face bottom crack is removed from the Al alloy base material by the form control or the like. Trying to reduce.
[0025]
The specific exothermic peak by the differential thermal analysis is the behavior at the time of welding of the specific intermetallic compound at the grain boundary correlated with the side-side bottom crack of the Al alloy base material, that is, the above-described HAZ of the side-side weld bottom. It correlates well with the behavior of the unsolidified part of the grain boundary. This will be described below in relation to the generation mechanism of the side face bottom crack.
[0026]
In the side part welded portion having a short end length of the 6000 series Al alloy base material, the mass of the Al alloy material in the vicinity of the welded portion is significantly smaller than other welded portions having a sufficiently long end length. For this reason, the heat by welding is hardly dissipated by heat transfer through the Al alloy 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.
[0027]
The correlation between the maximum temperature at the bottom of the side weld and the unsolidified portion of the HAZ grain boundary (specific intermetallic compound at the grain boundary) will be described with reference to FIG. FIG. 6 is a schematic diagram showing the solidification process of the side welded part from the top to the bottom phases 1 to 3. As shown in the uppermost figure and the second figure in FIG. 6, for example, in the case of butt welding of Al alloy materials 1, the welded part 3 (molten part) contracts as the welded part 3 solidifies. At this time, shrinkage stress in the direction of the arrow acts on the weld 3. At this time, in the 6000 series Al alloy base material, unsolidified portions 6 exist particularly at the grain boundaries of HAZ 5 on the bottom face 1b of the side portion.
[0028]
Here, 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 6, so that the shrinkage during the solidification shrinkage of the welded part 3 occurs. When stress is applied, as shown in the diagram on the right side of the phase 2 in FIG. 6, the grain boundary 6 in the unsolidified portion cannot withstand and becomes a micro crack 6a to open the mouth. For this reason, the restraining force of the matrix is weakened at the bottom surface of the side portion, and the transmission and absorption of the contraction stress is insufficient, and as shown in the right side diagram of phase 3 in FIG. It leads to outbreak.
[0029]
The tendency is that the excess Si type 6000 series Al alloy base material with more unsolidified parts, the higher the maximum temperature of the bottom of the side part during welding exceeds 550 ° C, and the temperature exceeding 550 ° C. The longer it is held, the stronger it will be.
[0030]
On the other hand, when the maximum temperature at the bottom of the side portion is 550 ° C. or less, the solidification timing delay of the unsolidified portion 6 in the solidification process does not occur so significantly that the micro crack 6a is caused by the shrinkage stress. As a result, when the shrinkage stress acts during the solidification shrinkage of the welded portion 3, as shown in the diagram on the left side of the phase 2 in FIG. 6, the restraining force of the matrix at the bottom of the side portion is not weakened. The contraction stress is transmitted and absorbed smoothly, and the grain boundary solidification and melted portion contraction proceed and finish smoothly. This process or result is the same as the solidification of other Al alloy materials, and as shown in the diagram on the left side of Phase 3 in FIG.
[0031]
Therefore, if the maximum temperature at the bottom of the side edge is set to 550 ° C or lower, cracks at the bottom of the side edge will not occur, but the maximum temperature at the bottom of the side welded portion may be 550 ° C depending on the joint design conditions and welding conditions. There is a possibility of being held on the high temperature side exceeding.
[0032]
Even when the maximum temperature of the bottom surface of the side edge welded part is maintained on the high temperature side exceeding 550 ° C, or when the maximum temperature of the bottom surface of the side edge portion can be reduced to 550 ° C or less, the side surface bottom surface cracks In order to reliably prevent the present invention, in the present invention, unsolidified portion 6 present at the grain boundary of HAZ 5 on the bottom surface of the 6000 series Al alloy base material, which is the other cause of the crack on the bottom surface of the side portion. This also reduces the unsolidified portion of HAZ grain boundaries (specific intermetallic compounds at the grain boundaries of the base metal) that become unsolidified when the temperature reached at the bottom of the side welds is near 550 ° C, causing solidification timing delays. To do.
[0033]
The above-mentioned unsolidified portion of the HAZ grain boundary that becomes unsolidified when the temperature reached the bottom of the side welded portion is near 550 ° C. and causes a delay in the solidification timing corresponds to a specific exothermic peak by the differential thermal analysis. Yes. That is, the specific exothermic peak near 530 ° C in the cooling curve from the melt obtained by measuring the thermal change in the solidification process of the Al alloy base material by differential thermal analysis is the same as the unsolidified part of the HAZ grain boundary. In addition, it is a component that causes a timing delay of solidification in the solidification process. From the metallurgical point of view of the Al alloy structure, the specific exothermic peak by the differential thermal analysis and the unsolidified portion of the HAZ grain boundary (specific intermetallic compound at the grain boundary of the base material) It turns out that even if it is not the same substance, it corresponds at least.
[0034]
The correlation between the cause of the side crack at the bottom of the side and the specific exothermic peak by differential thermal analysis is different from that of the 6000 series Al alloy base material, and the 5000 series and 4000 series, etc., which are standardized by JIS The same is true for the Al alloy filler metal. However, in the case of Al alloy filler metal, the component composition of the unsolidified portion of the HAZ grain boundary (specific intermetallic compound at the grain boundary), which causes the cracks on the bottom of the side part, is different due to the difference in the component composition. Therefore, in the case of Al alloy filler metal, unlike the 6000 series Al alloy base material, the unsolidified portion of the HAZ grain boundary is measured by differential thermal analysis for the thermal change in the solidification process of these Al alloy filler materials. In the cooling curve from the melt obtained in this way, it correlates with a specific exothermic peak below 550 ° C.
[0035]
Therefore, the specific exothermic peak by the differential thermal analysis correlates well with the behavior at the time of welding of the specific intermetallic compound at the grain boundary correlating with the side part bottom crack of the Al alloy base material and the Al alloy filler metal, In this invention, a side part bottom face crack is evaluated by whether the specific exothermic peak by the said differential thermal analysis exists.
Further, by making the Al alloy base material and the Al alloy filler material substantially free from specific heat generation peaks by the differential thermal analysis, the welding operation includes a welded portion on the side portion of the joint. Prevents cracks at the bottom of the side of the aluminum alloy welded joint.
[0036]
Since the present invention has the excellent effects as described above, as described in claim 2, among the 6000 series Al alloys, the present invention is particularly applied to excess Si type 6000 series Al alloy materials that have a large tendency to crack at the sides. It is preferable.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
(Differential thermal analysis)
The applicant must first submit Japanese Patent Application 2000- 307855 No. (Filing date: October 6, 2000) was filed for an invention of an Al alloy material (base material) for joints based on a specific exothermic peak by differential thermal analysis as in the present invention. Specifically, in order to prevent micro weld cracks that occur at welded joints such as the welds and HAZ of Al alloy joints, a specific exothermic peak by differential thermal analysis is defined as an exothermic peak at 550 ° C or lower. Al alloy material that is not accepted.
[0038]
The present inventors have made this patent application 2000- 307855 As described above, it has been found again that the specific exothermic peak by this differential thermal analysis can be applied to the evaluation criteria for the side face bottom cracking property with completely different generation mechanisms as compared with the usual weld cracking that is the subject of the issue. The present invention has been made.
[0039]
The differential temperature measured by differential thermal analysis indicates the thermal change in the solidification process of the Al alloy material during the temperature drop process of the Al alloy material after welding. Moreover, in the temperature rising process of the Al alloy material during welding, a thermal change in the melting process of the Al alloy material is shown.
Also, the start temperature of the exothermic reaction during the temperature drop process of the Al alloy material represents the liquidus and the end temperature represents the solidus line, respectively, and the start temperature of the endothermic reaction during the temperature rise process of the Al alloy material represents the solidus line and the end temperature. Each liquidus is represented.
[0040]
The cooling curve from the melt and the heating curve from the solid phase obtained by measuring the thermal change in the solidification process of this Al alloy material by the differential thermal analysis are generally the curves by the differential thermal analysis, that is, the DTA curves. (The cooling curve and the heating curve are hereinafter referred to as a DTA curve). In addition, as a thermal analysis method of the same kind, there is a differential scanning calorimetry method (DSC method), but in consideration of the reproducibility of measurement, in the present invention, it is formulated only for the differential thermal analysis method.
[0041]
In the case of differential thermal analysis of an Al alloy material, a metal having a sufficiently higher melting point than the measurement target Al alloy material is selected as the reference material. Although the measurement differential temperature does not change greatly depending on the type of the reference material, in consideration of the reproducibility of the measurement, platinum is selected as the reference material in the present invention.
[0042]
The differential thermal analyzer used for the differential thermal analysis in the present invention is a commercially available differential thermal analyzer, as long as the differential temperature in the measurement temperature range necessary for the evaluation of the side face bottom face crackability can be measured accurately and with good reproducibility. It can be selected appropriately.
[0043]
1 to 5 show, as an example, DTA curves of an Al alloy base material and an Al alloy filler material of Examples described later. 1 to 5, A1 to A5 are DTA curves in the process of cooling from the melt of the Al alloy base material, and the maximum exothermic peak near 630 ° C. indicates the main solidification reaction of the Al alloy material. B1 to B5 are DTA curves in the temperature rising process of the Al alloy material, and the maximum endothermic peak around 660 ° C. indicates the main melting reaction of the Al alloy material.
1 and 2 are DTA curves of 6000 series Al alloy base material of Example B and D of Table 2 to be described later, FIG. 3 is a DTA curve of 6000 series Al alloy material of Comparative Example C, and FIG. 4 is an example of invention. The DTA curve of the 5356Al alloy filler used is shown in FIG. 5. FIG. 5 is the DTA curve of the 4043Al alloy filler used in the comparative example.
[0044]
First, the DTA curve of the 6000 series Al alloy material in FIG. 3 (Comparative Example C) shows the exothermic peak X1 near 530 ° C. (532 ° C.) as referred to in the present invention, in addition to the main solidification reaction region (maximum exothermic peak).
Although the (final exothermic peak) is small, it is recognized.
[0045]
On the other hand, in the DTA curves of the 6000 series Al alloy materials of FIGS. 1 and 2 (Invention Examples B and D), no exothermic peak (final exothermic peak) near 530 ° C. is observed.
[0046]
In addition, in the DTA curve of the 4043Al alloy filler metal in FIG. 5, in addition to the main solidification reaction zone (maximum exothermic peak), a large exothermic peak X2 (final exothermic peak) at 550 ° C. or lower (542 ° C.) referred to in the present invention. ) Is allowed.
[0047]
On the other hand, in the DTA curve of the 5356Al alloy filler metal in FIG. 4, no exothermic peak (final exothermic peak) at 550 ° C. or lower is observed.
[0048]
In the present invention, as in the DTA curves of FIGS. 1, 2, and 4, the curve gradually changes except in the main coagulation reaction zone (maximum exothermic peak), and the exothermic peak (final end) at around 530 ° C. Exothermic peaks) are not recognized at all or are unclear, and when the existence of peaks (inflection points) cannot be specified, these exothermic peaks are not substantially recognized.
[0049]
From these results, when producing a welded joint using the 6000 series Al alloy material of FIG. 3 (Comparative Example c) as a base material and the 4043Al alloy filler material of FIG. Assuming the case where the short side welded part is held at a higher temperature than 550 ° C, the 6000 series Al alloy material in Figs. 1 and 2 was used as the base material, and the 5356 Al alloy filler material in Fig. 4 was used. As compared with the case, it is predicted that the side-side bottom crack mechanism due to the solidification timing delay of the unsolidified portion in the solidification process is likely to occur.
[0050]
And, compared with the welded joint test results in Example Table 3 described later, the above-mentioned specific exothermic peak is not recognized, using the 6000 series Al alloy material of FIGS. When the 5356Al alloy filler material of FIG. 4 is used, as shown in Invention Examples 2 and 4, the side portion bottom cracks do not occur. On the other hand, in the welded joint using the 6000 series Al alloy material of FIG. 3 in which the specific exothermic peak was recognized as a base material, regardless of 5356 of FIG. 4 or 4043 Al alloy filler material of FIG. 5, Comparative Example 8, 13 street side face bottom cracks have occurred.
[0051]
Therefore, these results confirm that the presence or absence of the specific exothermic peak in the DTA curve correlates with the side face bottom crack. In addition, it is possible to evaluate that the Al alloy base material and Al alloy filler metal in which these exothermic peaks are substantially not observed, or a joint welded using these, does not cause side-side bottom cracks. .
[0052]
(Target Al alloy base material)
The base material Al alloy used in the present invention covers all 6000 series (Al-Mg-Si series) Al alloys specified in AA to JIS standards, and among them, a specific exothermic peak by the differential thermal analysis is substantially present. Those not allowed are applicable. Among 6000 series Al alloys, especially the tendency of side-side bottom cracks is large, Si / Mg is 1 or more, Si is excessively contained with respect to Mg content, 6N01, 6016, 6111, 6022, etc. Excess Si type 6000 series Al alloy is targeted and effective.
[0053]
However, as a preferred component composition of the base material Al alloy 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 applies hereinafter), Si: 0.6 It is preferable that Si is excessively selected from a range of ˜1.6%.
[0054]
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 satisfying these standards.
[0055]
The Al alloy base material itself in the present invention is melted, cast, homogenized heat treatment, hot working (rolling, extrusion, forging), if necessary, intermediate annealing, cold working (rolling, forging) by conventional methods such as rolling, Plates and profiles (such as hollow sections whose cross-sectional shape is essentially the same at any position in the length direction) are manufactured as forgings.
[0056]
These Al alloys are subjected to solution treatment and quenching treatment (quality symbol T4), subsequent aging treatment (quality symbol T6), and overaging treatment (quality symbol T7). Used as
[0057]
However, these manufactured and tempered Al alloys suppress the specific unsolidified portion of the HAZ grain boundary that leads to the bottom cracks on the side edges and the specific intermetallic compound at the grain boundary of the base material that causes it. Furthermore, it is necessary that the specific exothermic peak by the differential thermal analysis is not substantially recognized. For this purpose, the tempering process is mainly controlled together with the manufacturing history of the alloy component and hot composition processing, or in response to the alloy component and the manufacturing history.
[0058]
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 slow, and particularly in the excessive excess Si type 6000 series Al alloy base material, the specific intermetallic compound form that is the main cause of side side bottom cracks is likely to occur, and differential thermal analysis. An exothermic peak near 530 ° C. is likely to occur.
[0059]
Further, in the quenching treatment after the solution treatment, as a preliminary aging treatment, instead of simply cooling to room temperature, and (4) once re-heated to a temperature of 50 to 120 ° C. after quenching to room temperature. 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. By this preliminary aging treatment, the specific intermetallic compound form is less likely to be generated, and an exothermic peak in the vicinity of 530 ° C. by differential thermal analysis is less likely to occur.
[0060]
In addition, when aging treatment is performed, compared to normal aging treatment and overaging treatment conditions, (6) the aging treatment temperature is a low temperature of 80 to 160 ° C and the aging treatment time is a short time of 1 to 10 hours. It is preferable to make it the sub-aging treatment range of the side. When performing normal aging treatment or overaging treatment, especially in excessive excess Si type 6000 series Al alloy base material, the specific intermetallic compound form that is the main cause of side side bottom cracks is likely to occur, differential heat Care must be taken because an exothermic peak near 530 ° C. tends to occur by analysis.
[0061]
(Welding method)
The welding method targeted by the present invention is welding of a 6000 series Al alloy material, which has a welding construction site with a short end length, and easily uses a heat source such as an arc, which easily causes cracks on the bottom of the side portion. This is a fusion welding method with long wires.
[0062]
As described above, the cause or mechanism of the side-side bottom cracks of the 6000 series Al alloy material are the maximum temperature of the bottom-side welded part with a short end length and the unsolidified part of the HAZ grain boundary during solidification of the welded part. 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.
[0063]
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, a welding method in which individual weld lines such as spot welding are short and the side face bottom crack of the 6000 series Al alloy material welded joint does not occur is not targeted.
[0064]
(Welded joint)
In addition, a welded joint targeted by the present invention has a welding construction site with a short end length, and is a joint that has a high possibility of causing side-side bottom cracks. It can be applied to various welded joints such as fillet welds and butt welds of plates and profiles shown in FIG. 7 and 8, 1 is a 6000 series Al alloy material to be welded, 7 is the same 6000 series or other Al alloy material, 1b is a bottom surface of the side of the Al alloy material 1, and 2 is an Al alloy material 1. , 3 is a welded portion, t is an end length from the side portion 2 to the weld line 3a, and 8 is a welding torch.
[0065]
In these welded joints, appropriate shapes such as plates, profiles and pipes are selected as a combination of joints according to the design shape of the automobile member and the like. In addition, welded joints are not necessarily 6000 series Al alloy materials or excess Si type 6000 series Al alloy materials, but in the same manner as ordinary Al alloy joints or depending on the purpose, 3000 series, 5000 series, 6000 series, Al alloy materials with different components and alloys such as 7000 series may be joined together.
[0066]
(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.
[0067]
However, in the welded joint of the present invention, as described above, even if the temperature of the bottom surface of the side portion welded portion is increased, the side surface bottom surface cracking can be suppressed. It is preferable to control the temperature of the bottom of the side welded portion to 550 ° C. or lower. Therefore, it is also an advantage of the present invention that no special welding method or conditions are required, including the temperature of the bottom surface of the side welded portion, and the welding can be performed within the ordinary range of each welding method.
[0068]
The method of controlling the maximum temperature at the bottom of the side welded part to 550 ° C or less is to reduce the heat input to the side welded part. A well-known means such as removing heat by bringing the metal plate into contact is appropriately selected. In other words, the method for controlling the maximum temperature of the bottom of the side welded portion to 550 ° C. or lower can be carried out without using any special means and using known means without significantly changing the welding conditions.
[0069]
In addition, the welded portion other than the side welded portion bottom surface having a short end length that causes cracks on the side portion bottom surface is sufficiently long, so that the welding heat is easily radiated through the Al alloy material. For this reason, means for setting the maximum temperature of the bottom of the side-side welded portion to 550 ° C. or lower is basically unnecessary.
[0070]
(Fused material)
In the cooling curve from the melt obtained by measuring the thermal change in the solidification process of the Al alloy filler metal by differential thermal analysis based on the correlation with the side face bottom crack described above. No specific exothermic peak at 550 ° C or lower is observed.
[0071]
In this regard, the 5000 series Al alloy filler metal such as 5356 defined in JIS standards hardly recognizes this specific exothermic peak, and the 4000 series Al alloy filler metal tends to recognize this specific exothermic peak. In particular, in melt welding of an excess Si type 6000 series Al alloy base material, the 4000 series Al alloy filler metal tends to cause deterioration of the characteristics of the welded joint joint. Therefore, in particular, in the welded joint of the excess Si type 6000 series Al alloy base material, it is preferable to select one having no specific exothermic peak from among the 5000 series Al alloy filler metals.
[0072]
【Example】
Next, examples of the present invention will be described. First, various 6000 series Al alloy plates (2 mm thickness) and profiles (2 mm thickness flat plate) having 6063, 6061, 6022, and 6111 alloy compositions as shown in Table 1 were manufactured by a conventional method. These were tempered (heat-treated) as shown in Table 2, and there were no exothermic peaks near 530 ° C by differential thermal analysis. A, B, C, D, E 6000 series Al alloy matrix group A, b, c, d, e 6000 series Al alloy base material group having the specific exothermic peak was made separately.
[0073]
Of the tempering in Table 2, the solution treatment conditions were as follows.
In the case of continuous processing and entry, the base material after cutting into a test piece size is simulated in a glass stone furnace, simulating continuous processing in base material mass production, and solution treatment of 520 to 530 ° C x 60 seconds and Water quenching was performed (cooling rate was 300 ° C./min or more), and after the quenching, the sample was reheated and maintained at a high temperature of 80 to 100 ° C. for 2.0 hours. In the case of batch processing and entry, the batch processing in mass production of base material is simulated, and the base material after cutting into a test piece size is heated in a glass furnace at a relatively low speed to form a solution at 510 ° C for 10 hours. It was air-cooled and quenched with a treatment and a fan (cooling rate was less than 300 ° C./min), reheated after quenching, and maintained at a high temperature of 80 to 100 ° C. for 2.0 hours.
[0074]
In addition, the selective aging treatment was performed under the following conditions.
In the case of sub-aging treatment and entry, the sub-aging treatment was performed under the conditions of 130 ° C. × 6 hours (heating and cooling rate 40 ° C./hr). In the case of aging treatment and entry, aging treatment was performed under the condition of 155 ° C. × 6 hours. In the case of overaging treatment and entry, the aging treatment was performed under the condition of 180 ° C. × 6 hours.
[0075]
A specific exothermic peak was investigated by differential thermal analysis of these tempered materials (base materials), and the presence or absence of an exothermic peak near 530 ° C was evaluated. The results are shown in Table 2 together with the position of the exothermic peak (temperature, ° C.) and the end temperature of exotherm (° C.).
[0076]
Next, there is no specific exothermic peak by differential thermal analysis, A, B, C, D, E 6000 series Al alloy base material, and the specific exothermic peak of a, b, c, d, e Use a 6000 series Al alloy base material, the same base material, 5356Al alloy filler metal without specific exothermic peak in Fig. 4 and 4043Al alloy filler metal with specific exothermic peak in Fig. 5 to make a welded joint. Produced.
[0077]
The welded joint is welded with the end length t of one Al alloy base material 1 being 10 mm, and butt welding (welding length 140 mm) shown in FIG. 8 is used for MIG welding, TIG welding, CO ₂ Performed by laser welding. Each welding condition is shown in Table 4. In any welding, the maximum temperature at the bottom face of the side-side welded part was deliberately set at a temperature exceeding 550 ° C. at which the side-side part bottom face crack was 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 3.
[0079]
As is apparent from Table 3, the A, B, C, D, E 6000 series Al alloy base material without the specific exothermic peak by the differential thermal analysis, and the 5356 Al alloy filler metal without the specific exothermic peak of FIG. Welded joints of Invention Examples Nos. 1 to 5 consisting of a combination of MIG welding, TIG welding, CO ₂ Regardless of the welding method such as laser welding, the side face bottom crack does not occur, and the joint strength is 78% or more and 100% in terms of the base metal specific efficiency.
[0080]
On the other hand, it consists of a combination of an Al alloy base material and a 4043 Al alloy filler material, a 6000 series Al alloy base material having the specific exothermic peak in either one or both, and an Al alloy filler material. The welded joints of Comparative Examples No. 6 to 16 are MIG welding, TIG welding, CO ₂ Regardless of the welding method such as laser welding, cracks on the sides of the side part of 50mm or more are common and the welded part cannot be guaranteed. Also, the joint strength is low.
[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 material welded joints, including excess Si type.
[0082]
[Table 1]

[0083]
[Table 2]

[0084]
[Table 3]

[0085]
[Table 4]

[0086]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the 6000 series Al alloy material coupling which prevented the side part bottom face crack. Therefore, the industrial value is great in that the 6000 series Al alloy wrought material including the excess Si type with excellent characteristics can be expanded to automotive applications.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a DTA curve (no exothermic peak near 530 ° C.) by differential thermal analysis of a 6000 series Al alloy base material.
FIG. 2 is an explanatory diagram showing a DTA curve (no exothermic peak near 530 ° C.) by differential thermal analysis of a 6000 series Al alloy base material.
FIG. 3 is an explanatory diagram showing a DTA curve (with an exothermic peak near 530 ° C.) by differential thermal analysis of a 6000 series Al alloy base material.
FIG. 4 is an explanatory diagram showing a DTA curve (no exothermic peak at 550 ° C. or lower) by differential thermal analysis of a 5356Al alloy filler metal.
FIG. 5 is an explanatory diagram showing a DTA curve (with an exothermic peak at 550 ° C. or lower) by differential thermal analysis of 4043Al alloy filler metal.
FIG. 6 is a schematic diagram showing the solidification process of the joint side welds in four stages.
FIG. 7 is an explanatory view showing fillet welding between plate members and shapes.
FIG. 8 is an explanatory view showing butt welding between plate members and shapes.
FIG. 9 is a plan view showing a welding test piece (plate) used for a test of a side face bottom crack.
FIG. 10 is a plan view showing a side face bottom crack generated in a side edge weld of an excess Si type AA6022Al alloy joint.
[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; HAZ, 6; grain boundary, 7; Al alloy material, 8; welding torch,
t; end length, X; exothermic peak, A, B; DTA curve

Claims (3)

AA to JIS standard 6000 series aluminum alloy base material is welded using an aluminum alloy filler metal, and the welding is a welded joint including a welded portion on the side of the joint, In the cooling curve from the melt obtained by measuring the thermal change in the solidification process of each aluminum alloy base material and aluminum alloy filler metal by differential thermal analysis before welding , the aluminum alloy base material No exothermic peak in the vicinity of 530 ° C, and no exothermic peak in the aluminum alloy filler metal at 550 ° C or less, and there is no weld crack on the bottom of the weld on the side. A featured aluminum alloy welded joint. The aluminum alloy welded joint according to claim 1, wherein the 6000 series aluminum alloy base material is an excess Si type, and the exothermic peak of the base material is around 532 ° C.   A 6000 series aluminum alloy wrought material defined in AA or JIS standard used for the aluminum alloy welded joint according to claim 1 or 2.

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