JP3476246B2 - Resistance spot welding method for Al and Al alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance spot welding method used in fields related to transportation equipment such as automobiles, and more specifically to Al and Al alloys excellent in normalization of nugget formation and long life of electrodes. Of the resistance spot welding method.

[0002]

2. Description of the Related Art In recent years, Al and Al alloys have excellent corrosion resistance and aesthetics (design), and because of their light weight, they have been used in a wide range of fields such as outer panels of household electric appliances and building materials. ing. Further, recently, it has come to be used also in the field of automobiles and the like by taking advantage of the above characteristics of Al alloys, and there are increasing opportunities to use resistance spot welding for use.

However, Al and Al alloys have about three times as high thermal conductivity and electric conductivity as iron, and resistance spot welding utilizing local heat generation requires high current and short time welding. The welding range is very limited and requires careful attention. Fig. 1 shows a schematic diagram of the resistance spot welding method. As shown in Fig. 1, oxide films t ₁ and t ₂ having extremely high resistance are likely to grow on the surface of Al and Al alloys by heat treatment or the like. This causes resistance heat generation immediately below the electrodes and wear of the electrodes resulting in shortening of the electrode life and deterioration of strength. In addition, such resistance heating causes the electrode material to drop into the Al and Al alloy plates and penetrate into the grain boundaries, resulting in deterioration of corrosion resistance.

Further, when the plate thicknesses are different, melting of the joint portion occurs in the initial state at the contact interface of the plates as in the case of the same plate thickness, but thereafter, sufficient penetration is obtained on the thin plate side. There is a problem such as not. As a result, it is difficult to obtain a welded portion that exhibits sufficient strength on the thin plate side, which causes deterioration of welding quality such as strength deterioration and dispersion. Also, the phenomenon that the nugget is caused by one side has been confirmed in joining between dissimilar materials (different in thermal conductivity etc.) and in resistance spot welding where the polarity of the opposing electrodes is constant such as in an inverter welder. Without adversely affecting the electrode deterioration due to excessive melting.

Therefore, in order to solve the problem of the quality deterioration peculiar to the resistance spot welding described above, the electrode tip has been improved, the surface oxide film has been removed (see Japanese Patent Laid-Open No. 4-358094), the electrode side and the plate side. Improvement measures have been taken by inserting a metal plating film into the metal (see Japanese Patent Laid-Open No. 4-344877). However, regarding the welding quality, electrode wear, etc. due to the deviation of the nugget, no effective improvement measures have been proposed so far.

[0006]

The removal of the oxide film greatly contributes to prolonging the life of the electrode, but there are some problems in the following points.

If the oxide film on the electrode contact surface is completely removed by mechanical means such as brushing, resistance heat generation does not occur between the electrode and the plate, and the heat of fusion necessary for nugget formation is diffused to the electrode side. Therefore, the nugget is not melted in the electrode direction, and it is difficult to obtain a normal joint. Since the surface from which the oxide film has been completely removed is activated, welding or the like due to diffusion bonding between the electrode and the plate occurs during welding.

Further, the removal of the oxide film on the contact surface between the plates is carried out in order to satisfy the required strength in resistance spot welding in which a weld is formed by the heat energy of I ² R (I: current, R: resistance). Has a problem in terms of cost such as high heat input. Also, regarding the insertion of inclusions (metal plating film, etc.) between the plates, it is extremely difficult to put them into practical use in terms of cost and work efficiency, and regarding electrode chips, there is no one that dramatically improves the service life. Not yet developed.

The present invention has been made to solve the above problems, and in resistance spot welding of plates having different plate thicknesses and thermal conductivities, welding quality is improved by extending the service life of electrodes and normalizing the nugget shape. It is an object of the present invention to provide a resistance spot welding method for Al and Al alloys, which enables improvement of heat resistance and energy saving.

[0010]

Means for Solving the Problems The inventors of the present invention, in resistance spot welding, determine the thickness of the oxide film on the surface of the plate that contacts the electrode according to the plate thickness, the thermal conductivity of the plate and the polarity of the electrode. The present invention has been made based on the finding that it is possible to prolong the service life of the electrode and normalize the shape of the nugget by controlling it by controlling it.

The gist of the invention is that, when resistance spot welding of two Al or Al alloy plates having a thickness of T ₁ and T ₂ is performed, the thickness of the oxide film on the side of the plate having a thickness of T ₁ that comes into contact with the electrodes. t ₁
And the ratio (t ₁ / t ₂ ) of the oxide film thickness t ₂ on the side of the plate whose thickness is T ₂ to the electrode is (1) T ₁ ≧ T ₂ ,
(1.5 × T ₁ / T ₂ −0.5) ⁻¹ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁
And (2) if T ₁ ≤T ₂ , then T ₂ / T ₁ ≤t ₁ / t ₂ ≤
This is a resistance spot welding method for Al and Al alloys in which the resistance spot welding is performed at 1.5 × T ₂ / T ₁ -0.5 and the oxide film thicknesses t ₁ and t ₂ are controlled in the range of 2.5 nm to 7.0 nm.

In resistance spot welding of two Al or Al alloy plates having thermal conductivity of K ₁ and K ₂ , the oxide film thickness t ₁ on the side of the plate having thermal conductivity of K ₁ in contact with the electrode. If the ratio (t ₁ / t ₂ ) between the oxide film thickness t ₂ on the side of the plate having a thermal conductivity of K ₂ and contacting the electrode is (1) K ₁ ≧ K ₂ , then K
₁ / K ₂ ≦ t ₁ / t ₂ ≦ 1.6 × K ₁ / K ₂ −0.6,
(2) In the case of K ₁ ≦ K ₂ , (1.6 × K ₂ / K ₁ −0.6) ⁻¹ ≦ t
₁ / t ₂ ≦ K ₁ / K ₂ and the oxide film thicknesses t ₁ and t
_This is a resistance spot welding method for Al and Al alloys in which resistance spot welding is performed by controlling ₂ in the range of 2.5 nm to 7.0 nm.

When performing resistance spot welding of two Al or Al alloy plates using a rectifying type welding machine in which the polarities of the opposing electrodes are unchanged, the oxide film thickness t ₁ on the side contacting the + side electrode of the plates and The ratio (t ₁ / t ₂ ) of the plate to the oxide film thickness t ₂ on the side in contact with the negative electrode is 0.7 ≦ t ₁ / t ₂ ≦ 1.0.
(However, except when t1 / t2 is 1.0) , and Al and Al alloys which perform resistance spot welding by controlling the oxide film thicknesses t ₁ and t ₂ in the range of 2.5 nm to 7.0 nm. Resistance spot welding method.

When resistance spot welding two Al or Al alloy plates using a rectifying type welding machine in which the polarities of opposing electrodes are unchanged, a plate having a thickness of T ₁ and a thermal conductivity of K ₁ is used. Of the oxide film thickness t ₁ on the side in contact with the + side electrode of the plate and the oxide film thickness t ₂ on the side in contact with the − side electrode of the plate having a plate thickness T ₂ and a thermal conductivity of K ₂ (t ₁ / T ₂ ) is (1) T ₁ ≧ T
₂ , when K ₁ ≧ K ₂ , 0.7 × (1.5 × T ₁ / T ₂ −0.5)
^-1 × K ₁ / K ₂ ≤t ₁ / t ₂ ≤T ₂ / T ₁ × (1.6 × K ₁
/ K ₂ −0.6) and (2) T ₁ ≧ T ₂ and K ₁ ≦ K ₂ ,
_{0.7 × (1.5 × T 1 /} T 2 -0.5) -1 × (1.6 × K 2 / K 1 -
0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁ × K ₁ / K ₂ , and (3)
When T ₁ ≦ T ₂ and K ₁ ≧ K ₂ , 0.7 × T ₂ / T ₁ × K
₁ / K ₂ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × (1.6
× K ₁ / K ₂ −0.6), and (4) T ₁ ≦ T ₂ and K ₁ ≦ K ₂ , 0.7 × T ₂ / T ₁ × (1.6 × K ₂ / K ₁ −0.6) ⁻¹ ≦
t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × K ₁ / K ₂ ,
Further, it is a resistance spot welding method for Al and Al alloys in which resistance spot welding is performed by controlling the oxide film thicknesses t ₁ and t ₂ in the range of 2.5 nm to 7.0 nm.

In resistance spot welding of two Al or Al alloy plates using an AC welding machine in which the polarities of the electrodes facing each other are varied, a plate having a thickness of T ₁ and a thermal conductivity of K ₁ is used. The oxide film thickness t ₁ on the side in contact with the electrode and the oxide film thickness t on the side in contact with the electrode of the plate whose plate thickness is T ₂ and thermal conductivity is K _2.
The ratio of ₂ (t ₁ / t _{2) is, (1) T 1 ≧ T} 2, K 1 ≧ K 2
In the case of, (1.5 × T ₁ / T ₂ −0.5) ⁻¹ × K ₁ / K ₂ ≦ t ₁
/ T ₂ ≦ T ₂ / T ₁ × (1.6 × K ₁ / K ₂ −0.6), (2)
When T ₁ ≧ T ₂ and K ₁ ≦ K ₂ , (1.5 × T ₁ / T ₂ −0.
5) ^-1 × (1.6 × K ₂ / K ₁ -0.6) ^-1 ≤t ₁ / t ₂ ≤T ₂ /
If T ₁ × K ₁ / K ₂ and (3) T ₁ ≦ T ₂ and K ₁ ≧ K ₂ , then T ₂ / T ₁ × K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂
/ T ₁ −0.5) × (1.6 × K ₁ / K ₂ −0.6), (4) T ₁ ≦
If T ₂ and K ₁ ≦ K ₂ , then T ₂ / T ₁ × (1.6 × K ₂ / K
₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × K
₁ / K ₂ and the oxide film thicknesses t ₁ and t ₂ are 2.5 nm
This is a resistance spot welding method for Al and Al alloys in which resistance spot welding is performed in the range of 7.0 nm.

[0016]

In the present invention, it is only the thickness of the oxide film on the side of the Al and Al alloy plate that comes into contact with the electrode that is specified, and the thickness of the oxide film on the opposite side that comes into contact with the bonding interface, that is, the electrode is not particularly specified. A chemical method is recommended for controlling the oxide film thickness. Specifically, the oxide film thickness can be effectively reduced and controlled by an etching type alkaline cleaner (sodium phosphate, caustic soda, etc.), acid (nitric acid, sulfuric acid, etc.) and the like.

The reasons for limiting the thickness of the oxide film will be described below. According to the research conducted by the present inventor, the thickness of the oxide film that exhibits the effect of preventing electrode wear due to resistance heating between the electrode and the plate is
It was found to be 7.0 nm or less. As mentioned above, the electrode life of Al and Al alloy plates is greatly affected by the thickness of the oxide film on the side in contact with the electrode.
When the thickness exceeds nm, the resistance heating value at the electrode tip reaches a region where electrode wear is promoted at the time of continuous hitting. Therefore,
The thickness of the oxide film on the side that contacts the electrode is limited to 7.0 nm or less.

The thickness of the oxide film on the side contacting the electrode is
If it is less than 2.5 nm, the electrode wear due to resistance heating is eliminated at the electrode tip, but conversely the heat conduction loss of the fusion heat from the joint to the electrode becomes remarkable due to the cooling action of the electrode,
The penetration of the melted portion in the plate thickness direction, where strength is exerted, becomes insufficient, causing strength deterioration. Further, since it is cooled more rapidly than usual, solidification cracking inside is also likely to occur. Therefore, the thickness of the oxide film on the side that contacts the electrode is limited to 2.5 nm or more.

Next, the reason for limiting the thickness of the oxide film based on the difference between the plates will be described. When the plate thickness is different, the cause of insufficient melting into the fusion zone on the thin plate side is that on the thin plate side where the bonding interface is close to the electrode, the loss of melting heat due to heat conduction loss due to cooling is more pronounced on the thin plate side Insufficient blending into the side. Also, in the initial stage of energization, resistance heat generation between both plates forms a fusion zone, but after that, heat transfer due to volume resistance at the central part between both electrodes due to fringing phenomenon etc., and melting on the thin plate side is insufficient. . There are two possible causes.

Although the strength of the welded portion deteriorates due to insufficient penetration on the thin plate side due to the above phenomenon, the strength deterioration can be reduced by controlling the thickness of the oxide film on the side in contact with the electrode. That is, the surface heat generation of the electrode and the plate is a cause of electrode wear, but at the same time, it exerts an effect of preventing heat loss from the fusion zone toward the electrode. Therefore, by controlling the oxide film thickness ratio (t ₁ / t ₂ ) with respect to the plate thickness ratio within the range of the following formula, it is possible to heat the thin plate surface and reduce the loss of the heat of fusion to secure the penetration. Become.

When T ₁ ≧ T ₂ , (1.5 × T ₁ / T ₂ −0.
5) In the case of ^-1 ≤t ₁ / t ₂ ≤T ₂ / T ₁ and T ₁ ≤T ₂ , T
₂ / T ₁ ≦ t ₁ / t ₂ ≦ 1.5 × T ₂ / T ₁ −0.5, where T ₁ and T _{2 are the} plate thickness, t _{1 is the} thickness of the oxide film on the side in contact with the electrode of the plate thickness T ₁ , t ₂ : Thickness of the oxide film on the side of the plate thickness T ₂ that contacts the electrode.

Where t₁/ T₂The above ranges respectively
The reason for limiting like₁/ T ₂Is less than the left side
And the above effect is not exhibited, and if the right side is exceeded, conversely the thick plate side
This is because the penetration depth of is insufficient.

In the case of joining dissimilar materials, it is the difference in the thermal conductivity or the electrical conductivity between the dissimilar materials that causes the defective fusion between the dissimilar materials. The present invention is a measure for improving defective penetration due to the difference in thermal conductivity.

Regarding materials having different thermal conductivities, those having a high thermal conductivity receive heat loss due to cooling from the electrode side, and therefore, those having a high thermal conductivity need to have a thick oxide film. That is, the oxide film thickness ratio (t
_{By controlling 1} / t ₂ ) within the range of the following formula, it is possible to generate heat on the surface of the material having high thermal conductivity, reduce the loss of the heat of fusion, and secure the penetration.

When K ₁ ≧ K ₂ , K ₁ / K ₂ ≦ t ₁ / t
_{If 2} ≤ 1.6 × K ₁ / K ₂ -0.6, K ₁ ≤ K ₂ , then (1.6
× K ₂ / K ₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ K ₁ / K ₂ , where K ₁ and K _{2 are} thermal conductivity, and t ₁ is contact with an electrode made of a material having thermal conductivity K _1. Thickness of the oxide film on the side to be heated, t ₂ : Thermal conductivity K ₂
Thickness of the oxide film on the side of the material that contacts the electrode.

Where t₁/ T₂The above ranges respectively
The reason for limiting like₁/ T ₂Is less than the left side
And the above effect is not exhibited, and if the right side is exceeded, heat conduction will be reversed.
This is because the penetration depth of the low-rate material is insufficient.

Polarized (polarity of the electrode is unchanged)
When resistance spot welding is performed using a welding machine, a rectifying type welding machine such as an inverter welding machine has a constant polarity, and the nugget tends to deviate to the + side due to the polarity effect. Further, as a result, the + side electrode is more worn at the time of continuous hitting. Therefore, in this case, the polarity effect can be reduced by making the thickness of the oxide film on the side in contact with the negative electrode larger than that on the positive side.

That is, the oxide film thickness t ₁ on the side contacting the + side electrode and the oxide film thickness t ₂ on the side contacting the − side electrode.
By controlling the ratio (t ₁ / t ₂ ) with the ratio within the range of the following formula, it becomes possible to reduce the polarity effect and secure the penetration.

0.7 ≦ (t ₁ / t ₂ ) ≦ 1.0 (however,
(Except when t1 / t2 is 1.0) Here, the reason why the coefficient on the left side is 0.7 and the coefficient on the right side is 1.0 is that the above effect is obtained when the coefficient on the right side exceeds 1.0. This is because if it is not exhibited and the coefficient on the left side is less than 0.7, the penetration depth on the + side is insufficient.

Furthermore, when resistance spot welding is performed on materials having different plate thicknesses and different thermal conductivities using a welding machine in which the polarities of the electrodes do not change, the oxide film thickness t ₁ on the side in contact with the + side electrode
The ratio of the oxide film thickness t ₂ on the side in contact with the negative electrode to the negative electrode (t
_{By controlling 1} / t ₂ ) within the range of the product of the right side and the product of the left side of each of the above equations, it is possible to reduce the polarity effect and secure the melt. That is, the oxide film thicknesses t ₁ and t
The ratio of ₂ (t ₁ / t ₂₎ is controlled within the range of the following formula.

When T ₁ ≧ T ₂ and K ₁ ≧ K ₂ , 0.7 × (1.
5 × T ₁ / T ₂ −0.5) ⁻¹ × K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ T
₂ / T ₁ × (1.6 × K ₁ / K ₂ −0.6), T ₁ ≧ T ₂ , K ₁
If ≤ K ₂ , 0.7 x (1.5 x T ₁ / T ₂ -0.5) ^-1 x (1.6
× K ₂ / K ₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁ × K ₁
/ K ₂ , T ₁ ≦ T ₂ , K ₁ ≧ K ₂ , 0.7 × T ₂ /
T ₁ × K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.
5) × (1.6 × K ₁ / K ₂ −0.6), T ₁ ≦ T ₂ , K ₁ ≦ K ₂
In the case of, 0.7 × T ₂ / T ₁ × (1.6 × K ₂ / K ₁ −0.6) ⁻¹
≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × K ₁ / K ₂ ,

When resistance spot welding is performed on materials having different plate thicknesses and different thermal conductivities by using an AC welding machine whose polarity varies, it is not necessary to consider the polarity effect, and the oxide film thicknesses t ₁ and t ₂ It is possible to secure the penetration by controlling the ratio (t ₁ / t ₂ ) within the range of the product of the right side and the product of the left side of each equation when the plate thickness is different and the thermal conductivity is different. Becomes That is, the ratio of the oxide film thickness t ₁ to t ₂ (t
₁ / t ₂ ) is controlled within the range of the following formula.

When T ₁ ≧ T ₂ and K ₁ ≧ K ₂ , (1.5 × T
₁ / T ₂ −0.5) ⁻¹ × K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ T ₂ / T
_{1 × (1.6 × K 1 /} K 2 -0.6), T 1 ≧ T 2, K 1 ≦ K 2
In the case of, (1.5 × T ₁ / T ₂ −0.5) ⁻¹ × (1.6 × K ₂ / K ₁
−0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁ × K ₁ / K ₂ , T ₁
When ≦ T ₂ and K ₁ ≧ K ₂ , T ₂ / T ₁ × K ₁ / K ₂ ≦
t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × (1.6 × K ₁ / K
₂ -0.6), if the _{T 1 ≦ T 2, K 1} ≦ K 2, T 2 / T 1
× (1.6 × K ₂ / K ₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂
/ T ₁ −0.5) × K ₁ / K ₂ ,

In all of the above, the thickness of the oxide film on the side in contact with the electrode is adjusted in the range of 2.5 nm to 7.0 nm in consideration of the effect on electrode wear.

[0035]

EXAMPLES The present invention will be described below with reference to examples. The materials used in the examples are shown in Table 1. These materials are listed in Table 2.
Welding was performed under the resistance spot welding conditions shown in, and each welded joint was evaluated. Table 3 shows the relationship between the oxide film thickness ratio, the plate thickness, and the thermal conductivity, which are the main points of the present invention, on the left side of the above equation.
The value on the right side is shown. The evaluation method is (1) variation in joint strength,
It was based on four items: (2) continuous hitting property, (3) penetration depth of the nugget, and (4) electrode wear expansion rate, which was finally judged by comprehensive evaluation. The results are shown in Table 4. The evaluation criteria are as follows.

(1) Variation in joint strength Evaluated by standard deviation of total tensile strength at 100 continuous spots ◎: 80N or less, ○: 80 to 130N, △: 130 to 180N, ×: 18
0N or more

(2) Continuous Dotting Property Evaluated by the number of dotting points divided by the minimum value of JIS A class ◎: 3000 points or more, ○: 3000 to 1500 points, △: 1500 to 1000
Points, ×: less than 1000 points

(3) Penetration depth of nugget Evaluated by t / T in FIG. 2 ◎: 0.9 or more, ○: 0.9 to 0.7, △: 0.7 to 0.5, ×:
Less than 0.5

(4) Electrode wear expansion rate The pressure-sensitive diameter between the electrode tip and the plate was measured by pressure-sensitive paper at the time of continuous hitting, and evaluated by the ratio of the initial pressure-sensitive diameter and the pressure-sensitive diameter at 1000 hitting ◎: 1.2 Below, ○: 1.2 to 1.4, △: 1.4 to 1.8, ×:
1.8 or more

Comprehensive evaluation Evaluation is made by the results of the above (1) to (4) ◎: ◎ in all evaluations, ○○: (1) and (2) are ◎, all more than ○, ○: all more than ○, △: All above △, ×: (1)
There is × in the evaluation of ~ (4), × ×: ○ in the evaluation of (1) to (4)
There is no above and all are x and △

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

As is apparent from Tables 3 and 4, in Test Nos. 1 to 3 of the method of the present invention, the oxide film thickness was adjusted to the range of 2.5 nm to 7.0 nm which is the limited range of the present invention. Good joint characteristics are obtained and electrode wear is small. Exam N
o.4 to 6 are examples in which the plate thicknesses are different, and the oxide film thickness ratio is within the limited range determined by the plate thickness of the present invention, and thus good evaluation is obtained. Test Nos. 7 and 8 are examples in which the thermal conductivity is different, and the oxide film thickness ratio is within the limited range determined by the thermal conductivity of the present invention, and thus good evaluation is obtained. Test No. 11 is an example in which the plate thickness and the thermal conductivity are different, and the oxide film thickness ratio is within the limited range of the present invention, and thus a good evaluation is obtained.

Test Nos. 9 and 10 are examples in which a welding machine having polarity is used. Since the oxide film thickness ratio is 0.78 to 0.79 and is within the range of 0.7 to 1.0 which is the limited range of the present invention, Good evaluation has been obtained. Test No. 12 is an example in which a welding machine having polarity is used and the plate thickness and the thermal conductivity are different, and the oxide film thickness ratio is within the limited range determined by the plate thickness and the thermal conductivity of the present invention. Therefore, a good evaluation is obtained.

On the other hand, in Test Nos. 13 and 14 of the comparative example, the oxide film thicknesses were 1.0 nm and 9.0 nm, respectively, which were outside the range of 2.5 nm to 7.0 nm, which is the limited range of the present invention, and therefore were evaluated as good. Not obtained. Test Nos. 15 and 16 are examples in which the plate thicknesses are different, and the oxide film thickness ratio is out of the limited range determined by the plate thickness of the present invention, and therefore a good evaluation has not been obtained. Also, test
No. 16 has one oxide film thickness of 7.0 nm or more. Exam N
o.17 and 18 are examples in which the thermal conductivity is different, and the oxide film thickness ratio is out of the limited range determined by the thermal conductivity of the present invention, and therefore a good evaluation has not been obtained. In both tests, the thickness of one oxide film is 7.0 nm or more.

Test Nos. 19 and 20 are examples of using a welding machine having polarity. Since the oxide film thickness ratio is outside the range of 0.7 to 1.0 which is the limit range of the present invention, good evaluation is obtained. Not obtained. Test No. 20 has one oxide film thickness of 7.
It is 0 nm or more.

[0049]

As is clear from the above description, according to the present invention, in resistance spot welding of Al and Al alloy materials having different thicknesses and thermal conductivities, the electrode life is extended and the nugget shape is normalized. Therefore, it is possible to improve welding quality and save energy. Therefore, the resistance spot welding method according to the present invention can be used in the field of transportation equipment such as automobiles.
And the use of Al alloy materials can be expanded.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a resistance spot welding method.

FIG. 2 is an explanatory diagram of a method for evaluating a penetration depth of a nugget in an example.

[Explanation of symbols]

1 ... Electrode tip, 2 ... Electrode tip, 3 ... Oxide film, 4 ...
Oxide film, 5 ... Al or Al alloy, 6 ... Al or Al alloy,
7 ... Nugget.

Claims (5)

(57) [Claims] 1. When resistance spot welding two Al or Al alloy plates having plate thicknesses of T ₁ and T ₂ , the plate thickness is T 1.
The ratio of the oxide film thickness t ₂ of the _{side 1} a is oxide film thickness t ₁ and the thickness of the side in contact with the electrode plate is in contact with the electrode plate is T ₂ (t 1 _{/ t 2)} is, ( 1) In the case of T ₁ ≧ T ₂ , (1.5 × T ₁ / T ₂ −0.5) ⁻¹ ≦ t ₁ / t ₂ ≦ T
₂ / T ₁ and (2) when T ₁ ≦ T ₂ , T ₂ / T ₁ ≦ t ₁ / t ₂ ≦ 1.5 × T ₂ / T ₁ −0.5
And the oxide film thicknesses t ₁ and t ₂ are 2.5 nm to 7.0 n.
A resistance spot welding method for Al and Al alloys, characterized in that the resistance spot welding is performed in a range of m. _2. Two pieces of Al having thermal conductivities K ₁ and K _2.
Alternatively, in resistance spot welding of an Al alloy plate, the oxide film thickness t on the side in contact with the electrode of the plate having a thermal conductivity of K _1
If the ratio (t ₁ / t ₂ ) between ₁ and the oxide film thickness t ₂ on the side of the plate having a thermal conductivity of K ₂ that contacts the electrode is (1) K ₁ ≧ K ₂ , then K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ 1.6 × K ₁ / K ₂ −0.6
(2) In the case of K ₁ ≦ K ₂ , (1.6 × K ₂ / K ₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ K
₁ / K ₂ and the oxide film thicknesses t ₁ and t ₂ are 2.5 nm to 7.0 n.
A resistance spot welding method for Al and Al alloys, characterized in that the resistance spot welding is performed in a range of m. 3. When performing resistance spot welding of two Al or Al alloy plates using a rectifying type welding machine in which the polarities of opposing electrodes are unchanged, the oxide film thickness t on the side contacting the + side electrode of the plates ₁ and the oxide film thickness t ₂ on the side in contact with the negative electrode of the plate (t ₁ / t ₂ ) is 0.7 ≦ t ₁ / t ₂ ≦ 1.0 (where t1 / t2 is 1.
(Excluding the case of 0) , and the oxide film thicknesses t ₁ and t ₂ are 2.5 nm to 7.0 n.
A resistance spot welding method for Al and Al alloys, characterized in that the resistance spot welding is performed in a range of m. 4. When performing resistance spot welding of two Al or Al alloy plates using a rectifying type welding machine in which the polarities of the opposing electrodes are unchanged, the plate thickness is T ₁ and the thermal conductivity is K ₁ . and oxide film thickness t ₁ of the side in contact with the + side electrode of a plate, the plate thickness T _2, the thermal conductivity of the plate is K ₂ - the ratio of the oxide film thickness t ₂ of the side in contact with the side electrode ( When t ₁ / t ₂ ) is (1) T ₁ ≧ T ₂ and K ₁ ≧ K ₂ , 0.7 × (1.5 × T ₁ / T ₂ −0.5) ⁻¹ × K ₁ /
K ₂ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁ × (1.6 × K ₁ / K ₂ −0.6), and (2) 0 if T ₁ ≧ T ₂ and K ₁ ≦ K ₂ 0.7 × (1.5 × T ₁ / T ₂ −0.5) ⁻¹ × (1.
6 × K ₂ / K ₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁ × K ₁ / K ₂ , and (3) when T ₁ ≦ T ₂ and K ₁ ≧ K ₂ , 0.7 × T ₂ / T ₁ × K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × (1.6 × K ₁ / K
In _{2 -0.6), (4) T} 1 ≦ T 2, if the _{K 1 ≦ K 2, 0.7 ×} T 2 / T 1 × (1.6 × K 2 / K 1 -0.6)
⁻¹ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × K ₁ / K ₂ , and the oxide film thicknesses t ₁ and t ₂ are 2.5 nm to 7.0 n.
A resistance spot welding method for Al and Al alloys, characterized in that the resistance spot welding is performed in a range of m. 5. When performing resistance spot welding of two Al or Al alloy plates using an AC welding machine in which the polarities of opposing electrodes are changed, the plate thickness is T ₁ and the thermal conductivity is K ₁ . The oxide film thickness t ₁ on the side of the plate that contacts the electrode, and the plate thickness T ₂ ,
When the ratio (t ₁ / t ₂ ) to the oxide film thickness t ₂ on the side of the plate having the thermal conductivity of K ₂ that contacts the electrode is (1) T ₁ ≧ T ₂ and K ₁ ≧ K ₂ , _{(1.5 × T 1 / T 2} -0.5) -1 × K 1 / K 2 ≦ t
₁ / t ₂ ≦ T ₂ / T ₁ × (1.6 × K ₁ / K ₂ −0.6), (2) In the case of T ₁ ≧ T ₂ and K ₁ ≦ K ₂ , (1.5 × ^{_{T 1 / T 2 -0.5) -1}} × (1.6 × K 2
/ K ₁ −0.6) ⁻¹ ≦ t ₁ / t ₂ ≦ T ₂ / T ₁ × K ₁ / K ₂ , and (3) In the case of T ₁ ≦ T ₂ and K ₁ ≧ K ₂ , T ₂ / T ₁ × K ₁ / K ₂ ≦ t ₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × (1.6 × K ₁ / K
_{2 -0.6), (4) T 1} ≦ T 2, if the _{K 1 ≦ K 2, T 2} / T 1 × (1.6 × K 2 / K 1 -0.6) -1 ≦ t
₁ / t ₂ ≦ (1.5 × T ₂ / T ₁ −0.5) × K ₁ / K ₂ , and the oxide film thicknesses t ₁ and t ₂ are 2.5 nm to 7.0 n.
A resistance spot welding method for Al and Al alloys, characterized in that the resistance spot welding is performed in a range of m.