JP2002115019A - Aluminum alloy having excellent weld crack resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy having excellent weld crack resistance in an arc welding method. SOLUTION: The aluminum alloy material in which no generation peak at <=550 deg.C can be practically seen in the cooling curve from melt obtained by measuring thermal change in the solidification process of the aluminum alloy material to be welded by means of differential thermal analysis can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy material (hereinafter, aluminum is simply referred to as Al) having excellent resistance to weld cracking when being subjected to fusion welding of an arc or the like.

[0002]

2. Description of the Related Art 5052, 508 are used as Al alloys for welding structures.
5000 specified in AA to JIS standards such as 3, 5154, 5182
System (hereinafter abbreviated as AA to JIS), 70N such as 7N01, 7003
Al alloy wrought materials of the 00 series and the like (collectively referred to as rolled sheet materials, extruded materials, forged materials, etc .; hereinafter, also referred to as Al alloy materials) are widely used.

Also, recently, excellence in workability and formability such as extrusion, rolling, forging and the like, and corrosion resistance, and excellent recyclability due to the small number of alloying elements, 6063, 6N
Also, 6000 series Al alloy materials specified in AA to JIS standards such as 01 and 6061 have been attracting attention as structural materials for transportation equipment such as automobiles.

[0004] These Al alloy materials are used as a base material to be welded.
It is mainly welded and joined as a welding structural member such as a joint by an arc welding method such as TIG or MIG. In addition, at the time of arc welding of these Al alloy materials, as specified in JIS Z 3604, typically, 4043, 4047, BA4145B, 535
A filler material such as 6, 5183 is used as appropriate.

[0005] However, when an Al alloy material for a structural material such as the 6000 series is used as a base material and joined by an arc welding method or the like, a problem may occur in that joint strength is reduced. This is considered to be caused by welding cracks when these Al alloy materials were welded.

[0006] Generally, weld cracks include cracks in weld metal (Depo) such as bead cracks, crater cracks, micro cracks (microfischer), and heat affected zones near joint welds.
(Hereinafter referred to as HAZ) cracks,
A problem in the case of Al alloys, such as those based on welding, is weld cracking that occurs in HAZ.

Conventionally, welding cracks generated in HAZ (hereinafter referred to as
Welding cracks), welding conditions such as selection of filler metal, restraint conditions, gaps and groove conditions, selection of welding speed and welding current, etc. are mainly used for welding such as TIG (TIG) and MIG (MIG). From the side, the welding conditions have been improved.
For example, the `` Manual for Preventing Weld Cracking in Aluminum Alloy MIG Welds '' (edited by The Japan Institute of Light Metal Welding Structure, published in 1983) discloses that welding conditions that result in underheat input or excessive heat input should be avoided. I have.

[0008] Various improvements from the base material side have also been proposed. For example, for 6000 series Al alloy, JP-A-9-41063
And control of the components and the crystal grain size, such as suppression of the excess Si amount and addition of expensive elements such as Sc, as disclosed in JP-A-9-279280 and the like.

Further, JP-A-9-168888, JP-A-10-29648
Control of the components of the filler metal, as disclosed in, for example, Japanese Patent Publication No. 3 (2003), has also been proposed.

[0010]

However, the improvement from the welding operation side so far has been to actually prevent or suppress welding cracks by trial and error after actually welding. In addition, it is a fact that the effect is remarkably small as compared with the improvement from the base material side.

Further, the improvement from the base material side is not practical because it sacrifice other basic characteristics such as strength and cost, even if it prevents welding cracks. In addition, the improvement of the filler metal is significantly less effective than the improvement from the base metal side,
After all it is not practical.

According to these conventional techniques, when the condition on the base material side such as the material of the Al alloy is largely changed, or when the condition on the welded structural member side such as the joint structure is largely changed, the welding crack is reduced. It is difficult to control with good reproducibility. In addition, the problem of reduced welding efficiency due to the try and error cannot be ignored.

On the other hand, if the weld cracking resistance of the Al alloy base material can be easily evaluated and predicted, the Al
Effective improvement of welding crack resistance on the alloy base material side, appropriate selection and improvement of Al alloy filler material, and effective and efficient improvement of the welding conditions can be performed. Also, Al
It is also possible to perform quality control on the resistance to welding cracking of the alloy material as an Al alloy base material product.

The present invention has been made in view of such circumstances, and an object thereof is to provide an Al alloy material having excellent resistance to weld cracking in fusion welding such as arc welding.

[0015]

In order to achieve this object, the gist of the aluminum alloy material excellent in resistance to welding cracking according to the present invention is that the thermal change during the solidification process of the aluminum alloy material to be welded. In the cooling curve from the melt obtained by the differential thermal analysis, the exothermic peak at 550 ° C. or lower is substantially not observed.

The present inventors have determined the presence or absence of an exothermic peak at 550 ° C. or lower in a cooling curve (a so-called DTA curve) from a melt obtained by measuring the thermal change in the solidification process of an Al alloy material by differential thermal analysis. The appearance of exothermic peaks, such as peak size and peak size, correlates with welding cracking resistance (HAZ cracking resistance) in melt welding, and similarly, thermal changes in the melting process of Al alloy materials The inventors of the present invention found that the manner in which the endothermic peak at 600 ° C or lower in the heating curve (so-called DTA curve) from the solid phase obtained by analysis was correlated with the resistance to weld cracking in fusion welding. It was made.

Here, the differential thermal analysis method is a known analysis method also abbreviated as DTA method. The outline is that a reference substance that does not thermally change in the measurement temperature range and a measurement target substance are placed in the same container (the reference substance itself may be used as the container), and both are set under equivalent conditions. Originally
While heating or cooling at a constant rate (ambient temperature), the temperature difference (differential temperature) between them is continuously measured. Then, qualitative and quantitative analysis is performed based on the state of the temperature change.

In the present invention, by using the principle of the differential thermal analysis, welding crack resistance is evaluated based on the state of thermal change in the solidification process (cooling process) and melting process (heating process) of an Al alloy material. . That is, as described above, the exothermic peak at 550 ° C. or lower of the cooling curve from the melt obtained by measuring the thermal change during the solidification process of the Al alloy material by differential thermal analysis,
The thermal change during the melting process of the Al alloy material was measured by differential thermal analysis, and the heating curve from the solid phase was found to have substantially no endothermic peak at 600 ° C or lower. Evaluate as Al alloy material.

However, as will be described later, the correlation between the Al alloy material and the weld cracking resistance is determined by the presence or absence of an exothermic peak at 550 ° C. or less in the cooling curve.
It is stronger than the presence or absence of the endothermic peak in the following.

Therefore, in the present invention, the cooling curve
The presence or absence of an exothermic peak at 550 ° C or lower is an essential requirement for the Al alloy material to have excellent weld cracking resistance. Then, the presence or absence of an endothermic peak at 600 ° C. or lower in the heating curve is determined by
As described in claim 2, more preferable requirements are set.

As described above, the present invention can provide an Al alloy material having excellent resistance to weld cracking and evaluate the weld crack resistance of an Al alloy base material for which data on the resistance to weld cracking is still insufficient. It can also be used as a method. And, without actually welding, the effective improvement of the weld cracking resistance of the Al alloy base material side, the appropriate selection and improvement of the Al alloy filler metal, and the effective and efficient Improvements can be made.

Further, the Al alloy material of the present invention is further applied as an Al alloy material having excellent resistance to weld cracking.
Quality control of weld cracking resistance as an Al alloy base material product can also be performed.

Since the Al alloy material of the present invention has such an excellent effect, it is applied to a 6000 series Al alloy specified in AA or JIS standards, in which the problem of weld cracking resistance is severe, as set forth in claim 3. preferable.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION (Differential Thermal Analysis) The differential temperature measured by differential thermal analysis indicates a thermal change in the solidification process of the Al alloy material in the process of cooling the Al alloy material after welding. In addition, in the process of raising the temperature of the Al alloy material during welding, it shows a thermal change in the melting process of the Al alloy material. In addition, the start temperature of the exothermic reaction in the temperature decreasing process of the Al alloy material represents the liquidus line, and the end temperature represents the solidus line, respectively. The start temperature of the endothermic reaction in the temperature rising process of the Al alloy material is the solidus line, and the end temperature is the solidus line. The liquidus lines are indicated respectively.

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 differential thermal analysis are generally obtained by differential thermal analysis, DTA curve (the cooling curve and the heating curve are hereinafter referred to as a DTA curve). As the same type of thermal analysis method, there is a differential scanning calorimetry method (DSC method) and the like, but in consideration of reproducibility of measurement, the present invention formulates only the differential thermal analysis method.

In the case of differential thermal analysis of an Al alloy material, a metal having a sufficiently higher melting point than the Al alloy material to be measured is selected as the reference substance. Although the measurement differential temperature does not greatly change depending on the type of the reference substance, platinum is selected as the reference substance in the present invention in consideration of reproducibility of measurement.

The differential thermal analyzer used for the differential thermal analysis in the present invention is a commercially available differential thermal analyzer capable of accurately and reproducibly measuring the differential temperature in the measurement temperature range required for the evaluation of the resistance to welding cracking. It can be selected as appropriate.

FIGS. 1 and 2 show, as an example, the measured DT of a 6000 series Al alloy extruded material of No. 8 comparative example in the examples described later.
Each A curve is shown. FIG. 1 is a DTA curve of the Al alloy material during the cooling process from the melt. The maximum exothermic peak around 630 ° C. indicates the main solidification reaction of the Al alloy material. Figure 2 shows Al
It is a DTA curve in the process of raising the temperature of the alloy material. The maximum endothermic peak near 660 ° C. indicates a main melting reaction of the Al alloy material.

First, as is clear from FIG.
In addition to the main solidification reaction zone (maximum exothermic peak), the DTA curve of the system-based Al alloy material can be recognized even though the exothermic peak (final exothermic peak) around 530 ° C. below 550 ° C. referred to in the present invention is small. .

Also, in FIG. 2, the DTA curve of the 6000 series Al alloy material of No. 8 shows that, besides the main melting reaction zone (maximum endothermic peak) of 660 ° C., An endothermic peak around 570-580 ° C (first endothermic peak) is observed.

Assuming that the No. 8 6000 series Al alloy material is actually welded, the results of FIG. 1 show that when the HAZ of the Al alloy material is once melted and then re-solidified, the HAZ is only around 630 ° C. The solidification state is not completed, the molten state (unsolidified part) remains partially, and the unsolidified part (alloy component compound) is solidified again at around 530 ° C in the region below 550 ° C. .

As a result, in the No. 8 6000 series Al alloy material, even if the solidification of the weld metal part (Depo) is completed, the solidification delay in which the solidification of the HAZ part is not completed occurs, and the welding crack is generated in the HAZ part. Can easily be said to occur.

Further, from the results shown in FIG.
In addition to the main melting range of 660 ° C., the welded portion of the Al alloy material has an endothermic peak at about 570 to 580 ° C. at 600 ° C. or lower, which is referred to in the present invention. It is considered that the main melting occurs again at around 660 ° C. after a part of the low alloy component compound is once melted.

Therefore, from this result, as in FIG. 1, even in the case of No. 8 6000 series Al alloy material, the solidification of the weld metal (Depo) is completed even with the HAZ in the same manner as in FIG. Is not completed, solidification delay occurs, and it can be said that welding cracks are likely to occur in the HAZ.

On the other hand, when substantially no exothermic peak at 550 ° C. or an endothermic peak at 600 ° C. or less is observed in the DTA curves of FIGS. It can be said that there is no alloy component compound that causes a delay), and that no weld cracks occur in the HAZ portion.

In the present invention, in the DTA curves of FIGS. 1 and 2, the curves at 550 ° C. or lower and 600 ° C. or lower gradually change, and the exothermic peak at 550 ° C. or lower and the endothermic peak at 600 ° C. or lower do not change. If it is clear and the presence of peaks (inflection points) cannot be specified, these peaks shall not be recognized substantially.

As will be described later, the No. 8 6000 series
Compared to the results of MIG welding test of Al alloy material and confirmation of weld cracking, the DTA curve
The relationship between the peak below ℃ and the HAZ weld crack becomes clear.
That is, in the DTA curve, peaks at 550 ° C. or lower and 600 ° C. or lower were observed, and this No. 8 6000 series Al alloy material had weld cracks. On the other hand, in the invention examples in which the peak was not substantially observed, no weld crack was generated.

Therefore, these results support that the presence or absence of peaks at 550 ° C. or lower and 600 ° C. or lower in the DTA curve correlates with the above-mentioned weld cracking resistance. Further, an Al alloy material in which these peaks are not substantially observed can be evaluated as a material excellent in welding crack resistance.

The Al alloy material of the present invention is particularly applicable to various welding methods, such as TIG, MIG, and arc spot, which are commonly used for ordinary joint welding, and laser, electron beam, and plasma welding methods. . Further, the joint to be welded may be the same Al alloy material, or may be an Al alloy material having a different component, which will be described later, according to the purpose, similarly to a normal Al alloy joint.

(Improvement of Al alloy base material) In order to improve the weld cracking resistance of the Al alloy base material, the amount of alloying elements in the Al alloy base material should be reduced in order to reduce the solidification delay of the Al alloy base material HAZ. It is preferable to control.

As one of the most effective examples, a transition element such as Fe, Mn, or Cr is contained. These elements form dispersed particles during homogenizing heat treatment and subsequent hot working, such as extrusion or rolling. Since these dispersed particles have an effect of hindering the movement of the grain boundary after recrystallization, fine crystal grains can be obtained. The amounts of these elements when added are F
e: Adjust within the range of 0.2 to 1.0%, Mn: 0.2 to 1.0%, Cr: 0.01 to 1.0%.

The main elements of each Al alloy material, for example, 60
In the case of the base Al alloy base material, the main element S is selected within a range that does not impair the required properties of the welded structural material such as strength.
Adjust i and Mg content. In particular, excess Si type 6000 series Al
In the case of an alloy base material, the susceptibility to weld cracking increases,
Adjustments such as lowering the content within the specified range and increasing the Mg content are made.

However, even when the amount of alloying elements in the Al alloy material is controlled, in other words, even when the amount of alloying elements in the Al alloy material is the same, the structure of the Al alloy material is changed due to the difference in the manufacturing conditions of the Al alloy material. 550 ° C in the DTA curve if
The exothermic peak below or the endothermic peak below 600 ° C. may differ significantly. Therefore, the quality of the weld crack resistance of the product Al alloy material needs to be controlled by the exothermic peak at 550 ° C. or lower and the endothermic peak at 600 ° C. or lower in the DTA curve specified in the present invention.

Further, in the present invention, since the welding crack resistance of the Al alloy base material is improved, there is no need to improve the welding conditions, and the welding efficiency such as the welding speed can be further increased. is there. However, if necessary, the welding operation conditions such as the control of the amount of heat input and the amount of heat removal may be improved. Furthermore, in the joint specifications, the groove shape for butt joints and T joints can be changed from I, V, X, U, H, J, K, fillet, etc. An optimum shape including a groove angle and the like can be appropriately selected.

(Applicable Al Alloy Material) The Al alloy material used in the present invention must satisfy various required characteristics such as the strength as a welded joint, high joint strength (joint efficiency), and corrosion resistance.
In this regard, 5000 series and 6000 series specified in AA to JIS standards,
Known Al alloy materials for welding structures, such as 7000 series, can be suitably used.

However, from the viewpoint of recyclability, such as a small amount of alloy, the component standard of 6000 series Al alloy for welded structures (60
82, 6061, 6N01, 6151, 6063 etc.), the basic composition is Mg: 0.2-1.0% (mass%, the same applies hereinafter)
, Si: 0.3 to 1.6%, and it is preferable to apply a 6000 series Al alloy material. Hereinafter, the content of typical elements will be described.

Mg: 0.2-1.0%. Mg forms a compound phase (Mg ₂ Si, etc.) with Si during artificial aging, and further forms a compound phase with Cu and Al in a Cu-containing composition to provide high strength (proof stress) during use It is an indispensable element for. If the content of Mg is less than 0.2%, high strength (proof stress) cannot be obtained. On the other hand, if the content exceeds 1.0%,
At the time of casting and quenching of the Al alloy base material, coarse particles are crystallized or precipitated to impair workability and the like. Therefore,
The content of Mg is in the range of 0.2 to 1.0%.

Si: 0.3 to 1.6%. Si is also compounded with Mg by compound aging (Mg ₂ S
i) are essential elements for imparting high strength (proof stress) during use. If the content of Si is less than 0.3%, sufficient strength cannot be obtained. On the other hand, when the content exceeds 1.6%, the workability is inhibited as in the case of Mg. Therefore, the content of Si is set in the range of 0.3 to 1.6%.

Next, Fe, Mn, Cr, Ti, B, etc. are selectively contained depending on the purpose, and may be used.

For example, Fe: 0.2-1.0%, Mn: 0.2-1.0%, C
For r: 0.01 to 1.0%, these transition elements form dispersed particles during the homogenizing heat treatment of the Al alloy base material and during subsequent hot working such as extrusion or rolling. Since these dispersed particles have an effect of hindering the movement of the grain boundary after recrystallization, fine crystal grains can be obtained. If the content is less than each of the lower limits, this effect cannot be obtained. On the other hand, if the content is excessive (exceeding the upper limit), a coarse intermetallic compound is easily formed at the time of melting and casting, and becomes a starting point of breakage during processing. Therefore, the content of these elements when contained, respectively: Fe: 0.2-1.0%, Mn: 0.2
To 1.0%, Cr: 0.01 to 1.0%.

Ti: 0.0001 to 0.1%. Ti is an element that refines the crystal grains of the ingot. However, if the content of Ti is less than 0.001%, this effect cannot be obtained. On the other hand, if the content of Ti exceeds 0.1%, coarse crystals are formed and the workability is reduced.
Therefore, it is preferable that the amount of Ti when it is contained is in the range of 0.0001 to 0.1%.

B: 1 to 300 ppm. B, like Ti, is an element added for refining the crystal grains of the ingot. But,
If the content of B is less than 1 ppm, this effect cannot be obtained.
When the content exceeds 300 ppm, a coarse crystallized product is also formed and the processability is reduced. Therefore, when B is contained, the amount of B is preferably in the range of 1 to 300 ppm.

Further, the Al alloy material (base material) used in the present invention
Is manufactured as a plate material or a shape material (a shape material whose cross-sectional shape such as a hollow cross-section is essentially the same at any position in the length direction) by a rolling process or an extrusion process by a conventional method. That is, the molten Al alloy melt-adjusted within the component specification range is subjected to, for example, a continuous casting rolling method, a semi-continuous casting method (D
C), and a normal melting casting method such as C is appropriately selected for casting. Next, this Al alloy ingot is subjected to a homogenizing heat treatment, hot rolling-tempering treatment (solution treatment and quenching treatment and age hardening treatment), extrusion processing-tempering treatment, hot forging-tempering treatment,
Alternatively, an Al alloy material having a desired cross-sectional shape such as a plate material, a shape material, a forged material, or the like is obtained by a combination thereof.

[0054]

(Embodiment 1) Next, an embodiment of the present invention will be described. The ingots of Al alloy compositions No. 1 to 10 shown in Table 1 were
After being melted by a casting method, a homogenizing heat treatment was performed, and a flat extruded material having a thickness of 1.8 to 3.5 mm was formed by extrusion.

Each of these Al alloy materials was subjected to differential thermal analysis under the above conditions to determine a DTA curve, and an exothermic peak at 550 ° C. or less, an endothermic peak at 600 ° C. or less, and a peak generation temperature were determined. Table 3 shows the results.

On the other hand, the same Al alloy materials were butt-welded under the conditions shown in Table 2 by the MIG automatic welding method, which is an arc welding method using a filler metal, to produce joints. Then, the cross section of the HAZ portion of these joints was observed with a 100-fold optical microscope, and the presence and size of weld cracks were investigated.

The mechanical properties (strength) of the Al alloy material and the joint were measured in accordance with the JIS method to calculate the joint efficiency. Table 4 shows the results.

As is apparent from Table 3, the DTA curve of 550
In the inventive examples Nos. 1 to 5, in which no exothermic peak at a temperature of not more than 600 ° C and an endothermic peak at a temperature of not more than 600 ° C are not observed, the HAZ has no weld crack. Further, as is clear from Table 4, Invention Example N
o.1 to 5 are excellent with high joint strength and high joint efficiency of 70% or more.

On the other hand, in Comparative Examples Nos. 8, 9, and 10, in which the exothermic peak at 550 ° C. or less and the endothermic peak at 600 ° C. or less were observed in the DTA curves, the comparative examples No. 8, 9, and 10 And HAZ have weld cracks.
Among them, Comparative Example No.
9 and 10 have particularly low joint efficiencies of 35 to 41%. Also,
Comparative Examples Nos. 7 and 8 having a joint efficiency of 67 to 69% also have a remarkably lacking reliability as a joint because even small weld cracks occur.

As is clear from Table 3, Invention Example No. 6
In the DTA curve, an exothermic peak at 550 ° C or lower is not observed, but an endothermic peak at 600 ° C or lower is observed. As a result, although there was no weld cracking of the HAZ, the joint efficiency was particularly low at 60%, as compared with the other invention examples. Then, Comparative Example No. 8 was DTA
Although no endothermic peak is observed below 600 ° C. in the curve, an exothermic peak is observed below 550 ° C.
As a result, in Comparative Example No. 8, micro cracks were generated in the HAZ, and the reliability as a joint was significantly lacking.

From these results, the correlation with the welding crack resistance of the Al alloy material is stronger in the presence or absence of an exothermic peak at 550 ° C. or lower in the DTA curve than in the endothermic peak in 600 ° C. or lower in the DTA curve. This is supported. Also, to evaluate and predict the weld crack resistance of Al alloy materials, and
The critical significance of the requirements of the present invention as an Al alloy material having excellent weld cracking resistance is supported.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

According to the present invention, excellent weld cracking resistance is obtained.
Al alloy material can be provided. In addition, it is also possible to evaluate the weld crack resistance of each Al alloy material as an Al alloy base material. That is, it is possible to effectively improve the welding crack resistance on the Al alloy base material side without actually performing welding. Therefore, the industrial value is large in that the expansion of the application of the wrought aluminum alloy to the structural material can be promoted.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an exothermic peak at 550 ° C. or lower of a DTA curve by differential thermal analysis of the present invention.

FIG. 2 is an explanatory diagram showing an endothermic peak at 600 ° C. or lower of a DTA curve by differential thermal analysis of the present invention.

Claims (3)

[Claims] 1. In a cooling curve from a melt obtained by measuring a thermal change in a solidification process of an aluminum alloy material to be welded by differential thermal analysis, an exothermic peak at 550 ° C. or less is substantially not observed. Aluminum alloy material with excellent weld cracking resistance. 2. In a heating curve from a solid phase obtained by measuring a thermal change in a melting process of the aluminum alloy material to be welded by differential thermal analysis, an endothermic peak at 600 ° C. or less is substantially recognized. The aluminum alloy material having excellent weld cracking resistance according to claim 1. 3. The method according to claim 1, wherein the aluminum alloy material is AA to JIS.
The aluminum alloy material excellent in weld crack resistance according to claim 1 or 2, which is a 6000 series aluminum alloy specified in a standard.