JP2002348628A - Aluminum alloy weld joint and base metal sheet of aluminum alloy for weld joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 6000 series aluminum alloy joint, especially of excess Si type or the like, for preventing bottom of a lateral part from cracking, and to provide a base metal sheet of aluminum alloy for weld joint. SOLUTION: The weld joint is manufactured by means of welding a base metal sheet of a 6000 series aluminum alloy. The base metal sheet of the aluminum alloy is characterized by crystal grains which have a shape extended to a transversal direction against a weld line, the aspect ratio (rl /rt , where rl is a mean particle diameter in the transverse direction against the weld line, and rt is a mean particle diameter in a sheet thickness direction) of 2 or more, and a mean particle diameter rt of 100 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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 weld for the welded joint, which prevents weld cracks at the bottom of the welded portion at the side of the joint. It is about the base material.

[0002]

2. Description of the Related Art Panels, frames, members, and the like of transport machines such as automobiles are formed by joining joints of formed Al alloy sheets or welded joints of the formed Al alloy sheets and Al alloy profiles. (A welding joint member) is used.

[0003] As these Al alloy sheet base materials for welded joints, AA to AA, which are conventionally widely used as Al alloys for welded structures, are used.
5000 series specified by JIS standard and 6000 such as 6063 and 6061
System (hereinafter AA to JIS are omitted), 7N01, 7003, etc.
Aluminum alloy rolled plate (thick plate is hot rolled plate, thin plate is cold rolled plate)
Is used.

[0004] Among the 6000 series (Al-Mg-Si series) Al alloys, the content of Si / Mg is 1 or more, such as 6061, 6N01, 6016, 6111, 6022, etc. in the AA or JIS standards. Excess Si type 6000 series Al alloy base material containing excessive Si is subjected to solution treatment and quenching treatment (quality symbol T4) and subsequent aging treatment (quality symbol T6), overaging treatment ( T7) Excellent in age hardenability especially in later properties.

[0005] For this reason, the excess Si type 6000 series Al alloy has a low yield strength at the time of forming such as press forming and bending, and maintains the formability. It has the property of increasing the proof stress even at low temperature heating and satisfying the required strength. In addition, the 50
Since the amount of alloying elements is smaller than that of the Al alloys such as the 00 series and the 7000 series, it is excellent in recyclability such that scrap can be reused as a raw material for dissolving the original 6000 series Al alloy.

However, the base material of 6000 series Al alloy sheet,
Si type 6000 series Al alloy plate base material is, due to its excellent age hardening property, compared to the 5000 type or 7000 type Al alloy plate base material,
Conversely, at the time of welding, there is a problem that the joinability (joint strength) is reduced.

[0007] The problem of this joining property is particularly that the distance (edge length) from the side (end to edge) of the portion to be welded of the member to the welding line is short. This is remarkable when welding is performed on the (welded part).

That is, in fillet welding or butt welding,
Excess Si-based 6000 series Al
When welding a joint as an alloy, there is a problem that a macro weld crack which runs along a welding line (welding line) on a bottom surface (back surface) of the welded portion in a side welded portion is likely to occur. Cracking at the bottom of this side weld is a remarkable tendency of the 6000 series Al alloy sheet base metal,
This tendency is particularly strong in the base material of the alloy sheet. And, with other Al alloys other than the 6000 series, such as the 5000 series and the 7000 series, the weld bottom cracks do not occur or hardly occur.

[0009] The cracks at the bottom of the welded portion are generally liable to occur in the Al alloy system in general during welding, and the welded metal portion (welded portion) and a heat affected zone (hereinafter, referred to as HA) near or around the welded metal portion.
Micro weld cracks that occur in welded joints such as Z) are completely different peculiar phenomena including the mechanism of occurrence described below.

FIG. 4 shows weld cracks at the bottom of the weld at the side welds of the 6000 series Al alloy base metal.
Figure 4 shows a 2mm thick excess Si type AA6022 shown in plan view in Figure 5.
The base material of the Al alloy plate (Si; 0.9%, Mg; 0.6%) is a test piece 1a, and the distance from the side 2 of the test piece 1a to be welded to the welding line 3 (hereinafter,
This shows the welding state of the bottom surface 1b of the test piece when welding is performed while variously changing x). The welding method was a simple bead-on welding method with a constant penetration depth. In FIG. 4, (a) has an end length of 32 mm, and (b)
Is 24 mm, (c) is 16 mm, and (d) is 24 mm.
8 mm.

As shown in FIG. 4, in FIGS. 4 (a) and 4 (b) having relatively long end lengths, no weld cracks occur at the weld line 3a (the bottom surface of the welded portion). On the other hand, as shown in FIGS. 4 (c) and 4 (d), as the end length becomes shorter, macro weld cracks 4a and 4b running 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 side welded bottom surface 1b of the 6000 series Al alloy plate base material such as excess Si type.

The tendency of cracks at the bottom of the weld at the side of the base material of the 6000 series Al alloy plate (hereinafter simply referred to as “bottom at the bottom of the side”) occurs in a welding joining method in which the individual welding lines are very short. Hateful. However, the fusion welding method using a heat source such as an arc having a relatively long welding line, i.e., TIG, MIG (M
This is remarkable when forming joints by welding with high-speed arc welding such as IG), laser welding, or electron beam welding.
Furthermore, this tendency also occurs in a friction stir welding (FSW) method, which is a welding method in which a welded joint does not become relatively hot.

[0013] When such side surface bottom cracks occur, the strength of the Al alloy welded joint is remarkably reduced, causing a serious problem that it cannot be applied to the above-mentioned members such as automobiles.

[0014] Conventionally, various measures for improving the welding conditions such as arc have been carried out from the side of the welding method such as arc for the softening and cracking of the welded portion of the Al alloy welded joint. For example, as exemplified in Japanese Patent Application Laid-Open No. 11-104860, welding with the lowest possible heat input, or welding and joining while cooling, quenching and tempering the joint after welding, or As disclosed in Japanese Patent No. 222498, there is a method of recovering softening by heat treatment, such as performing age hardening treatment after welding materials (T1 and T4 materials) before age hardening treatment.

[0015]

However, the side surface bottom cracks to be solved in the present invention are the same as those of the above-mentioned members such as automobiles. As described above, it hardly occurs. Therefore, 6000
System Al alloy sheet material is a new problem that is used in the welding application member such as an automobile, and, as described above,
This is also a problem peculiar to 6000 series Al alloy sheets.

Conventionally, Japanese Patent Application Laid-Open No. 61-23580 discloses
The difference in heating rate between the large and small thick aluminum alloy members due to the difference in heat conduction caused by the difference in the thickness of the welded material (smaller thick members have less heat dissipation). It has been known as a problem that a large-thick member causes a temperature rise more slowly and a calorific value becomes insufficient.

However, these problems of the prior art are different from the problem of the present invention, which is the problem of the bottom cracks on the sides. Further, since the cause and the mechanism are different from the side bottom crack, the solution of installing the middle thick member in the middle to buffer the heating speed difference is also a solution of the side bottom crack itself. I can't get it. Therefore, the side surface 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.

The present invention has been made in view of such circumstances, and an object of the present invention is to prevent aluminum from cracking at the bottom of the side, and particularly to use aluminum alloy for 6000 series aluminum alloy joints such as excess Si type and welded joints. It is intended to provide an alloy sheet base material.

[0019]

In order to achieve this object, the gist of claim 1 of the 6000 series aluminum alloy joint according to the present invention is that a 6000 series aluminum alloy sheet base material specified in AA to JIS standards is welded. A welded joint formed by forming crystal grains of a base material of an aluminum alloy plate in a direction perpendicular to a welding line direction, and an aspect ratio of the crystal grains (at right angles to the welding line direction). Average particle size in direction
r ₁ and the plate thickness direction of the average particle the diameter r _t of the ratio r ₁ / r _t) was 2 or more, and is to the average particle diameter r _t in the thickness direction and 100 [mu] m or less.

The gist of claim 2 of the present invention, which is also a 6000 series aluminum alloy joint for achieving the above object, is that the aluminum alloy welded joint has a welded portion on the side of the joint, At least the crystal grains of the base material of the aluminum alloy plate at the bottom portion of the welded portion on the side of the weld joint are crystal grains elongated in the direction perpendicular to the weld line direction, and the aspect ratio of the crystal grains (weld line direction average particle sizes of r ₁ and the plate thickness direction of the direction perpendicular to
the ratio r ₁ / r _t) between r _t and 2 or more and an average particle size r _t in the thickness direction is to the 100 [mu] m or less.

The present inventors have investigated the relationship between the base metal structure of the 6000 series Al alloy plate and the cracks at the bottom of the side portion. It was found that the grain shape was correlated with the bottom cracks on the sides.

That is, when a 6000 series Al alloy hot rolled sheet (a cold rolled sheet is used in the case of a thin plate having a thickness of 2 mm or less) is used as a welding base material, the hot rolled finishing temperature is equal to or higher than the recrystallization temperature. System Al
In the hot rolled alloy sheet, equiaxed (spherical) crystal grains having an aspect ratio of about 1 in a sheet thickness section parallel to the rolling direction are formed.

On the other hand, when the hot-rolling finishing temperature is lower than the recrystallization temperature and the rolling reduction and strain rate of the hot-rolling are further increased, the crystal grains of the 6000 series Al alloy hot-rolled sheet are oriented in the rolling direction (longitudinal direction of the sheet). ), Resulting in fine flat crystal grains having an aspect ratio of 1 or more in a sheet thickness section parallel to the rolling direction and an average grain size in the rolling direction larger than the average grain size in the sheet thickness direction.

The present inventors have considered that the shape of this crystal grain is
It has been found that when the base material of the 6000 series Al alloy sheet is flat crystal grains, side cracks are less likely to occur in the case of flat crystal grains than in the case of equiaxial crystal grains. It has also been found that this tendency becomes remarkable when the elongation direction of the crystal grains of the 6000 series Al alloy sheet base material on the bottom surface of the weld at the side of the weld joint is correlated with the weld line direction of the joint.

That is, the bottom of the welded portion on the side of the welded joint
As the base material of the 6000 series Al alloy plate becomes flat crystal grains elongated in the direction perpendicular to the weld line direction, the aspect ratio of the flat crystal grains (average in the direction perpendicular to the weld line direction) the ratio r ₁ / r _t) of the average particle diameter r _t of the particle size r ₁ and the plate thickness direction
By setting it to 2 or more, the effect of preventing the side surface bottom cracks becomes remarkable.

Furthermore, the present inventors have found that even if the crystal grains of the base material of the Al alloy sheet are flat, if the crystal grains are coarsened, the flat crystal grains can suppress the effect of suppressing the side surface bottom cracks. Lost,
The upper limit of the crystal grain coarsening, the average particle diameter of the crystal grains in the thickness direction of the welded portion bottom surface portion of the welded joint side portion r _t with 100 mu
m.

As described above, in order to prevent cracks on the bottom surface of the side portion, the direction of crystal grain extension of the base material of the 6000 series Al alloy plate at the bottom portion of the welded portion on the side portion of the welded joint is set to the direction of the weld line of the joint. It is necessary to correlate. For this reason, the definition of the flat crystal grain shape in the present invention is defined not as a material such as an aluminum alloy hot-rolled sheet but as a structure of a 6000 series Al alloy sheet welding base material.

When a 6000 series aluminum alloy hot-rolled sheet is used as a base material of an aluminum alloy sheet, before welding to a joint, the conditions of hot-rolling of the aluminum alloy sheet and T4, T6, T7, etc. after hot rolling are adjusted. There is a possibility that the flat crystal grain shape and crystal grain size of the Al alloy sheet base material may change depending on the quality treatment conditions and heat treatment conditions such as age hardening accompanying the forming process. Then, depending on these conditions, there is a possibility that the definition of the flat crystal grain shape and the grain size as the base material of the Al alloy sheet in the present invention is out of the range. For this reason, the definition of the flat crystal grain shape and particle size in the present invention is not defined as the state of the hot-rolled sheet, but as the structure of the 6000 series Al alloy welding base material after the hot-rolled sheet has been formed or tempered. I do.

The reason why the base metal structure of the 6000 series Al alloy sheet (the shape of the crystal grains at the bottom surface of the welded joint at the side of the weld joint) is correlated with the bottom crack at the side is considered as follows.

First, as a situation on the welded portion side, in the side edge welded portion of the base material of the 6000 series Al alloy plate where the end length is short, the welded portion is closer to the welded portion than the other welded portion having a sufficiently long end length. The mass of the base material of the Al alloy plate is extremely small. Therefore, the heat input by welding
It is difficult to dissipate heat due to heat transfer through the base material of the Al alloy plate. As a result, during welding, the bottom surface of the side welded portion tends to be more easily maintained at a higher temperature exceeding 550 ° C. than the other welded bottom surfaces.

On the other hand, in the base material of the 6000 series Al alloy sheet, an Al-Mg-Si series (excess Si type) for exhibiting its age hardening characteristics is used.
Due to the relationship between the composition and the refining treatment such as T4, T6, and T7, a large amount of intermetallic compounds originally exist at the grain boundaries from the base metal stage. As a result, an unsolidified portion (unsolidified intermetallic compound) is inevitably present at the HAZ grain boundary on the bottom surface of the side welded portion. And this unsolidified part or intermetallic compound of the grain boundary is particularly large in the 6000 series Al alloy sheet base material such as excess Si type,
It is easy to cause cracks on the side bottom.

When the maximum temperature of the bottom surface of the side weld portion is maintained at a high temperature exceeding 550 ° C., the timing of solidification of only the unsolidified portion and the intermetallic compound portion of the grain boundary is delayed. This is because, when the shrinkage stress is applied during the solidification and shrinkage of the portion, the grain boundary of the unsolidified portion cannot withstand and becomes a micro-crack, so that the mouth is easily opened and the side portion bottom cracks.

For example, in the case of butt welding of an Al alloy plate base material and an Al alloy plate base material, the
When shrinkage of the (fused portion) occurs, shrinkage stress acting to expand the welded portion acts on the welded portion. At this time, if the maximum temperature of the bottom surface of the side welded portion is maintained on the high temperature side exceeding the above 550 ° C., the HA of the base material of the 6000 series Al alloy plate, especially the
Solidification timing is delayed in the unsolidified part at the grain boundary of Z.
For this reason, the binding force of the matrix is relatively weak, and the transmission and absorption of the shrinkage stress become insufficient, which easily leads to the occurrence of cracks at the side bottoms.

This tendency is more pronounced as the excess Si-type 6000 series Al alloy base material having a larger unsolidified portion, as the maximum temperature of the bottom surface of the side portion during welding becomes higher than 550 ° C., and The longer the temperature is kept above ℃,
Become stronger.

Here, when the structure of the base material of the 6000 series Al alloy sheet (joint side portion weld bottom surface) is a normal equiaxed crystal grain, the grain boundary area in the sheet thickness direction is large, and the direction of the grain boundary is large. It becomes linear in the thickness direction. Therefore, the binding force of the matrix becomes relatively weak. As a result, micro-cracks at the grain boundaries of the unsolidified portion, which are generated when the shrinkage stress acts during solidification shrinkage of the welded portion, easily propagate in the sheet thickness direction, and transmission and absorption of the shrinkage stress become insufficient. It is easy to cause cracks on the bottom of the side.

On the other hand, the finer flat crystal grains extending in the direction perpendicular to the direction of the weld line as in the present invention, the more the flat bottom surface portion of the welded portion on the side of the weld joint becomes, The grain boundary area is small, and the direction of the grain boundary is non-linear with respect to the sheet thickness direction. For this reason, the binding force of the matrix becomes relatively strong, and as a result, when the contraction stress acts, micro-cracks at the grain boundaries of the unsolidified portion are less likely to propagate in the sheet thickness direction, and the transmission of the contraction stress is prevented. It is presumed that absorption and absorption were sufficiently performed and cracks did not occur in the side bottom.

According to the mechanism of the side bottom crack, if the maximum temperature of the side bottom is set to 550 ° C. or less, the side bottom crack does not occur. However, depending on the joint design conditions and welding conditions, There is a possibility that the maximum temperature of the bottom surface of the side welded part may be maintained at a high temperature side exceeding 550 ° C.

An unsolidified portion of the HAZ grain boundary of the 6000 series Al alloy sheet base material, which is another cause of the side surface bottom cracks.
It is also effective to reduce (specific intermetallic compound at the grain boundary of the base material). However, especially in the case of an excess Si-type 6000 series Al alloy sheet base material, there may be cases where the intermetallic compound at the grain boundary cannot be reduced due to its properties such as age hardening and manufacturing restrictions.

Therefore, even when the maximum temperature of the bottom surface of the side welded portion is maintained on the high temperature side exceeding 550 ° C., or when the maximum temperature of the bottom surface of the side portion can be reduced to 550 ° C. or less, Furthermore, the excess Si type in which the unsolidified portion increases
Even in the 6000 series Al alloy plate base material, or even in the case of the 6000 series Al alloy plate base material in which the unsolidified portion is reduced, in order to reliably prevent the side surface bottom cracks, in the present invention, The bottom surface of the weld at the side of the weld joint has a fine, flat crystal grain structure extending in a direction perpendicular to the direction of the weld line.

As described above, the formation of the base material structure of the 6000 series Al alloy sheet of the present invention as a fine and flat crystal grain structure elongated in the direction perpendicular to the weld line direction can enhance the binding force of the matrix as described above. In addition, it leads to sufficient transmission and absorption of contraction stress during welding solidification. And this point suppresses not only the side surface bottom cracks of the main object of the present invention, but also micro to macro weld cracks that occur in the weld metal parts or weld joints such as HAZ during normal welding work. It also leads to effects.

Therefore, according to the present invention, even in the case of a welded joint having no side bottom cracks, in other words, no welded portion having a short end length (side-side welded portion), ordinary welding work can be performed. It can be applied for the purpose of suppressing micro- or macro-weld cracks that occur in the weld metal part or the weld joint part such as HAZ at the time. For this reason, claim 1 of the present invention also encompasses a case of a welded joint having no side welded portion where a side bottom crack occurs.

Further, since the present invention has an excellent effect of suppressing the side surface bottom cracks as described above, particularly in the 6000 series Al alloy, the tendency of the side surface bottom cracks among 6000 series Al alloys is reduced. Large, Si: 0.4-0.8% (mass%, the same applies hereinafter), Mg: 0.4
It is preferably applied to an excess Si type 6000 series Al alloy material containing about 0.8%.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION (Crystal Grain Structure) The definition of the crystal grain structure of the base material of the Al alloy sheet of the present invention will be described using an example of a butt welded joint shown in FIG. In FIG. 1, 5a is a welded joint,
1 is a 6000 series Al alloy base metal to be welded, 6 is the same 6000 series or another Al alloy base metal, 1b is a side bottom of the Al alloy base metal 1,
2 is the side of the Al alloy base material 1, 3 is the weld, x is the side 2
Is the end length from to the welding line 3a.

In FIG. 1, in the present invention, it is used for a joint.
6000 series Al alloy sheet base material 1, at least the grain structure of the welded bottom surface 1b portion of the welded joint side, as described above,
With the grain 7 is extended in the perpendicular direction B to the direction A of the weld line 3a, the aspect ratio of the crystal grains 7 (a direction perpendicular to the welding line direction average particle diameter r ₁ and the plate thickness direction of the the ratio r ₁ / r _t) and the average particle diameter r _t is 2 or more, and the thickness direction
The average particle size rt of _t is 100 μm or less (L is the width direction of the sheet)
.

Flatness in a direction B perpendicular to the direction A of the welding line 3a
Uniform particle size r₁And the average grain size r in the thickness direction t _tThe ratio r₁/ r_tBut
If it is less than 2, it is close to the normal equiaxed crystal grains described above.
The grain boundary area in the sheet thickness direction is large, and the direction of the grain boundary is
Direction. For this reason, the matrix
The bundle force becomes relatively weak, and during solidification shrinkage of the weld, Fig. 1
When the contraction stress in the direction of the arrow indicated by Z acts on
The micro-cracks at the grain boundaries of the unsolidified part
It is easy to propagate, and the transmission and absorption of the contraction stress are insufficient.
It is easy to cause cracks on the bottom of the side.

The average grain size rt in the thickness direction _t is 10
If the thickness exceeds 0 μm, not only the specific intermetallic compound at the grain boundary that can be the unsolidified portion, but also the grain boundary precipitate itself precipitated at the crystal grain boundary, or the non-precipitated zone formed along the crystal grain boundary
(PFZ: Precipitation Free Zone) itself becomes large. For this reason, when the shrinkage stress is applied during the solidification shrinkage of the welded portion, it acts as a starting point of minute fracture and a point promoting the propagation of fracture, including micro cracks at grain boundaries of the unsolidified portion, Cracks are easily developed along grain boundaries, and side bottom cracks are easily generated.

The control of the grain structure 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 described later.

However, in the present invention, a mixed grain structure or a composite structure in which the equiaxed recrystallized grain structures having an aspect ratio of about 1 are mixed within a range not to impair the effect of suppressing the side surface bottom cracks. Allow. As a practical problem, it is difficult to make the structure of the 6000 series Al alloy sheet a 100% pure fine flat grain structure by controlling the hot rolling process, and such control is not economical. Including this meaning, there are also variations in the fine flat crystal grains themselves, and in the present invention, as defined in the claims as the average grain size, the grain size r ₁ of the crystal grains in the direction perpendicular to the welding line direction and the sheet thickness direction They are each averaged value of particle size r _t (measured value).

[0049] The measurement of these crystal grains having a grain size r ₁ and the plate thickness direction of the particle size r _t is the 6000 series Al alloy plate base material before being welded construction, perpendicular with respect to the weld line direction After electrolytically etching the cross section in the thickness direction, the same cross section is observed with an optical microscope having a magnification of 50 times in 10 visual fields in a range of thickness × 0.1 mm, and the average value is measured (calculated). At this time, as described above, if there are equiaxed recrystallized grains in the flat crystal grains, the average is measured and averaged including the equiaxed recrystallized grains.

(Al alloy for base material) The Al alloy for base material used in the present invention is 6000 series (Al-Mg-Si
System) The entire Al alloy is applicable and applicable. However,
Among the 6000 series Al alloys, particularly, the tendency of side surface bottom cracks is large, Si / Mg is 1 or more, Si is excessively contained relative to the Mg content, such as 6N01, 6016, 6111, 6022, etc. 6000 series Al alloy of excess Si type is a target and is effective.

As a preferable component composition of the Al alloy for the base material of the present invention, in order to satisfy the required characteristics such as the required strength for the welded structure, Mg: 0.2 to 1.0% (mass%, the same applies hereinafter). , Si: It is preferable to select from the range of 0.6 to 1.6% so that Si becomes excessive.

In addition, Mn, Cr, Zr, Ti, B, Fe, Zn, N
Other alloying elements such as i and V are basically impurity elements. However, from the viewpoint of recycling of 6000 series alloys, when using not only high-purity Al metal but also 6000 series alloys, other Al alloy scrap materials, low-purity Al metal, etc. Including. For this reason, these elements are allowed to be contained within the JIS to AA standards as long as the effects of improving various properties aimed at by the present invention are not impaired. Therefore, being defined in the AA to JIS standards in the present invention means satisfying these standards.

(Manufacture of Base Material) The base material of the Al alloy sheet in the present invention is manufactured as a hot-rolled sheet having a thickness of 2 mm or more by a conventional method such as melting, casting, homogenizing heat treatment, and hot rolling. You. If the thickness of the base material of the Al alloy sheet is 2 mm or less, the sheet is further subjected to intermediate annealing if necessary, and then cold-rolled into a cold-rolled sheet.

In the above manufacturing process, the hot rolling conditions are controlled to make the structure of the 6000 series Al alloy hot rolled sheet into fine flat crystal grains specified in the present invention. 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 to further increase the rolling reduction and strain rate of hot rolling. On the other hand, when the finishing temperature of hot rolling is equal to or higher than the recrystallization temperature, an equiaxed recrystallization structure mainly appears.

The flat crystal grains of the 6000 series Al alloy hot-rolled sheet produced in this manner are characterized by the fact that the crystal grains in the sheet thickness section parallel to the rolling direction of the sheet are perpendicular to the welding line direction of the base material. the average grain size in the rolling direction corresponding to the average particle diameter r ₁ of the crystal grains, elongated than the average particle size in the thickness direction corresponding to the average particle diameter r _t the plate thickness direction referred to the base material (aspect ratio (2 or more).

Therefore, 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 must be
The preform rolling direction (elongated) average particle size, it is necessary to use in matching to to correspond to an average particle diameter r ₁ of the perpendicular direction of crystal grains with respect to the weld line direction. When the base material direction is changed and the average particle size in the base material rolling direction (elongated) is used in such a manner as to be in a direction parallel to the weld line direction, the solidified shrinkage of the welded portion is prevented. Depending on the direction of action of the contraction stress, the effect of suppressing side surface bottom cracks decreases.

Further, these Al alloy hot-rolled sheets and the like (including cold-rolled sheets) are subjected to a solution treatment and a quenching treatment (quality) after appropriate forming such as pressing and bending into a joint shape or before forming. T4) and subsequent aging treatment (T6)
After being overaged (quality symbol T7), it is used as a base material of a welded joint or a welded member.

In addition to the control of the crystal grain shape according to the present invention, these heat-treated Al alloy hot-rolled sheets are used to control the grain boundary structure, leading to the side surface bottom cracks.
It is preferable to suppress the specific unsolidified portion of the HAZ grain boundary and the specific intermetallic compound in the grain boundary of the base material that causes the unsolidified portion as much as possible.

For this purpose, it is preferable to mainly control the temper treatment together with the manufacturing history of the alloy component and the hot composition processing or in accordance with the alloy component and the manufacturing history.

More specifically, the solution treatment conditions include:
Solution treatment is performed at a high temperature of 510 ° C or higher. Increase the cooling rate during quenching after solution treatment to 300 ° C / min or more. For this reason, in the case of a plate material, it is particularly preferable that the final solution treatment and quenching treatment be performed not in a batch system but in a continuous heat treatment furnace capable of performing heat treatment by continuously passing a coil or the like. In the case of the batch type, the cooling rate is slowed down, and in particular, in the excess-excess Si-type 6000 series Al alloy sheet base material, the specific intermetallic compound morphology which is the main cause of the side surface bottom cracks easily occurs.

Further, in the quenching treatment after the solution treatment, instead of simply cooling to normal temperature and leaving it to stand, as a preliminary aging treatment, after quenching once to normal temperature, 50 to 12
Reheat and maintain to a temperature of 0 ° C or set the quenching end temperature
Maintain at a high temperature of 50 to 120 ° C for 0.2 to 24 hours, or reheat and maintain at a temperature of 50 to 120 ° C for 0.2 to 24 hours. Is preferred. This preliminary aging treatment makes it difficult to generate the specific intermetallic compound form.

When the aging treatment of the 6000 series Al alloy sheet base material is performed before welding, the aging treatment temperature is set to a low temperature side of 80 to 160 ° C. as compared with ordinary aging treatment and overaging treatment conditions. It is preferable that the aging treatment time is in the sub-aging treatment range on the short side of 1 to 10 hours. When normal aging treatment or overaging treatment is performed, especially in the excess Si type 6000 series Al alloy sheet base material,
It should be noted that the specific intermetallic compound morphology, which is the main cause of the side surface bottom cracks, tends to occur.

(Welding method) The welding method to which the present invention is applied is a welding of a 6000 series Al alloy plate base material, which has a welded portion where the end length is short, and cracks at the side portions occur. This is a fusion welding method that uses a heat source such as an arc and has a long welding line.

As described above, the cause and the mechanism of the side bottom crack of the 6000 series Al alloy material are, as described above, the maximum temperature of the bottom of the side welded portion having a short end length and the grain boundary of the HAZ at the time of solidification of the weld. This is a metallurgical problem of correlation with the unsolidified portion. Therefore, this is a common problem that occurs in a fusion welding method in which this metallurgical phenomenon commonly occurs regardless of the type of welding method.

Examples of such a welding method include, for example, a high-speed arc welding such as TIG and MIG, a welding method such as laser welding and an electron beam, and a friction stir welding (FSW) method. . Therefore, a welding method that does not cause the side surface bottom crack of the 6000 series Al alloy material welded joint is not targeted.

(Welded joint) The welded joint to which the present invention is directed uses a 6000 series Al alloy plate base material as one or both base materials, has a welded portion where the end length is short, and has If the joint has a high possibility of causing a bottom crack on the side, it can be applied to various welded joints such as fillet welding shown in FIG. 2 and butt welding shown in FIG. Note that in FIGS. 2 and 3,
5b and 5c are welded joints, 1 is a 6000 series Al alloy base material to be welded, 6 is the same 6000 series or another Al alloy base material, 1b is the bottom surface of the side of the Al alloy plate base 1, 2 is A side portion of the Al alloy base 1, 3 is a welded portion, x is an end length from the side portion 2 to the welding line 3a, and 7 is a welding torch.

In these welded joints, appropriate shapes such as plates, sections, pipes, etc.
Selected as a combination of joints. Also, the welded joint is not necessarily a 6000 series Al alloy plate base material or an excess Si type 6000 series Al alloy plate base material, as in a normal Al alloy joint,
Or 3000 series, 5000 series, 6000 series, 7000 series
An Al alloy material having a different composition such as a system or an alloy system may be used and joined to a 6000 series Al alloy hot rolled sheet base material.

(Welding conditions) The welding conditions in the welded joint of the present invention are performed within the range of a usual method of each welding method. For example,
Basic welding conditions such as filler metal use, groove shape, welding posture, torch advance angle, shielding conditions (Ar gas flow rate), welding current, welding voltage, welding speed, etc. are based on JIS standards and various welding conditions. Follow the Aluminum Handbook.

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 welded portion to 550.degree. However, in the welded joint according to the present invention, as described above, even if the temperature of the bottom surface of the side welded portion exceeds 550 ° C., it is possible to suppress the side bottom cracking. Therefore, it is an advantage of the present invention that any special welding method or condition including the temperature control of the bottom surface of the side welded portion is not required, and the welding can be performed within a range of a usual method of each welding method.

Incidentally, the maximum temperature of the bottom surface of the side welded portion was 55
Methods of controlling the temperature to 0 ° C or lower include reducing the heat input to the side welded parts, and removing heat by bringing a metal plate such as copper into contact with an easily heat-dissipating part such as the bottom surface of the welded part or the side surface. Is appropriately selected.

(Filler) The filler (rod) used in the welding is based on the correlation with the above-described side surface bottom crack, and the unsolidified portion (base metal) of the HAZ grain boundary is also present in the Al alloy filler itself. It is preferable to use a component composition which is less likely to be a specific intermetallic compound at the grain boundary.

In this regard, 5356 and the like specified in the JIS standard
Even if the 5000 series Al alloy filler material is added, the unsolidified portion of the HAZ grain boundary is small, and the 4000 series Al alloy filler material tends to increase the unsolidified portion of the HAZ grain boundary. Also, in particular, excess Si
In the welding of base metal of 6000 series Al alloy sheet, 4000 series
The alloy filler metal is liable to cause deterioration in the properties of the welded joint. Therefore, in particular, in the case of a welded joint of an excess Si type 6000 series Al alloy sheet base material, it is preferable to select from among 5000 series Al alloy filler metals.

[0073]

Next, an embodiment of the present invention will be described. First, the table
As shown in Fig. 1, various 6000 series Al alloy hot-rolled sheets (2.5 mm thickness) with 6063, 6061, 6022, and 6111 alloy compositions were prepared by increasing the rolling reduction in hot-rolling to 95% or more and finishing temperature of hot-rolling. At a temperature not higher than the recrystallization temperature to obtain a flat and fine structure mainly composed of crystal grains as defined in the present invention, and to prepare a hot rolled sheet of the invention example Al alloy.
On the other hand, for example, a 6000 series Al alloy hot-rolled sheet (2 mm thick) having a micro-equilibrium recrystallization-based structure with a finishing temperature of hot rolling equal to or higher than the recrystallization temperature and a total reduction rate of 90% was compared. The hot rolled sheet was prepared as an example.

Then, the hot-rolled sheets of these invention examples and comparative examples were subjected to T4 tempering treatment (solution quenching) under the same conditions, so that the specific unsolidified portion of the HAZ grain boundary and the base metal causing the The joint base material conditions are disadvantageous in that a large number of specific intermetallic compounds at the grain boundaries are present and the side surface bottom cracks are likely to occur. In addition,
The solution heat treatment of the temper is performed by heating the base material cut to the size of the joint test piece in a nitrite furnace, performing solution heat treatment at 520 to 530 ° C for 60 seconds, and then air-quenching and quenching with a fan (cooling rate is 200 ° C). / Min)
I went.

The hot rolled sheet of each of the tempered invention examples and comparative examples was stretched by 3% to simulate the forming process, and the plate material was used as a joint base material in the welding line direction by the above-described measurement method. It was measured perpendicular direction of the crystal grains having a grain size r ₁ and the plate thickness direction of the particle size r _t for. In addition, also in the invention example, since some equiaxed recrystallized grains were present in the flat crystal grains, the average was measured by including the equiaxed recrystallized grains.
Table 2 shows the grain size conditions of these crystal structures.

Next, the welded joints of the tempered plate base materials of the invention example and the plate base materials of the comparative example were manufactured using a 5356 Al alloy filler metal.

The welding of the welded joint is performed by using
The end length t is set to 10 mm, and the protrusion shown in FIG.
MIG welding, TIG welding
Contact, CO _TwoThis was performed by laser welding. Each welding condition is
See Table 3. In each case, the welding at the side
The maximum temperature at the bottom of the contact is a disadvantageous condition
As shown in the figure above, the
I made it.

The welded joints thus obtained were examined for the presence or absence of side surface bottom cracks and their length (mm). Then, a test piece of the welded joint is sampled, and the tensile strength (σ _B ) of the welded joint is determined according to JIS Z
It was measured according to 2241. The base metal specific efficiency (joint efficiency) of the welded joint was also calculated from the tensile strength of the base material. Table 2 shows the results. The proof stress of the hot-rolled sheet subjected to T4 tempering treatment was 190 MPa at 6063, 255 MPa at 6061, 225 MPa at 6022, 6111
280MPa.

[0079] Table 3 As is apparent from the invention examples No.1~5 satisfying the present invention defined in the perpendicular direction of crystal grains having a grain size r ₁ and the plate thickness direction of the particle size r _t with respect to the weld line direction Welded joints are MIG
Irrespective of welding methods such as welding, TIG welding, and CO ₂ laser welding, cracks on the bottom of the side are not generated, and the joint strength is 95% or more in the base metal specific efficiency.

On the other hand, the aspect ratio of crystal grains
Is less than 2 and / or thickness direction of the average particle diameter r _t (the ratio r ₁ / r _t and the average particle diameter r _t of the average particle diameter r ₁ and the plate thickness direction of the direction perpendicular to the welding line direction) The welded joints of Comparative Examples Nos. 6 to 14 consisting of a combination of Al alloy sheet base materials exceeding 100 μm
Regardless of the welding method such as MIG welding, TIG welding, or CO ₂ laser welding, cracks on the sides of the sides commonly occur, and the joint strength is significantly lower than the base metal specific efficiency of less than 90%.

The results of the above examples support the critical significance of the present invention for preventing the side surface bottom cracks in 6000 series Al alloy welded joints, including excess Si type.

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

[Table 3]

[0085]

According to the present invention, it is possible to provide a 6000 series Al alloy material joint and an Al plate base material for a welded joint, in which a side surface bottom crack is prevented. Therefore, the industrial value is also large in that the 6000 series Al alloy sheet material including the excess Si type having excellent properties can be expanded to automobile use and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a 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 bottom crack generated in a side weld of an excess Si type AA6022Al alloy material joint.

FIG. 5 is a plan view showing a test piece (plate) for welding used in a test for cracks on the side bottom surface.

[Explanation of symbols]

1; 6000 series Al alloy material, 2; side portion of Al alloy material, 3; welded portion (weld line), 4; bottom crack in side portion, 5; joint, 6; Al alloy material, 7; welding torch,

Claims (4)

[Claims] 1. A welded joint formed by welding a 6000 series aluminum alloy plate base material specified in AA to JIS standards, wherein the crystal grains of the aluminum alloy plate base material are perpendicular to the welding line direction. with the extended was grain, the aspect ratio of the grains (the ratio r ₁ / r _t and the average particle diameter r _t of the average particle diameter r ₁ and the plate thickness direction of the direction perpendicular to the welding line direction)
Was 2 or more, and 100 [mu] m average particle size r _t in the thickness direction
An aluminum alloy welded joint characterized by the following. 2. The aluminum alloy welded joint is a welded joint having a weld at a joint side, and a crystal grain of an aluminum alloy plate base material at least at a bottom portion of the weld at the weld joint side is welded to a weld line. Crystal grains elongated in the direction perpendicular to the direction, and the aspect ratio of the crystal grains
(Ratio r ₁ / r _t and the average particle diameter r _t of the average particle diameter r ₁ and the plate thickness direction of the direction perpendicular to the weld line direction) and 2 or more and an average particle size r _t in the thickness direction The aluminum alloy welded joint according to claim 1, which has a thickness of 100 µm or less. 3. The base material of the 6000 series aluminum alloy plate,
The aluminum alloy welded joint according to claim 1 or 2, which is a hot rolled 6000 series aluminum alloy hot rolled sheet containing Si: 0.4 to 0.8% (mass%, the same applies hereinafter) and Mg: 0.4 to 0.8%. 4. A 6000 series aluminum alloy sheet base material used for the aluminum alloy welded joint according to claim 1. Description: