JP2006200007A - Aluminum alloy sheet for automobile body sheet having excellent water wettability after degreasing and adhesive property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for an automobile body sheet formed after the application of rust-preventive lubricating oil, having excellent adhesive properties when being joined and assembled with an adhesive, and having excellent water wettability after the subsequent alkali degreasing treatment. <P>SOLUTION: In the surface of an Al-Mg based or Al-Mg-Si based aluminum alloy material, the maximum luminescence intensity at the time when the luminescence intensity of Mg in the depth direction is measured with a GDS and OH absorbency by OH stretching vibration when being measured by a polarization reflection method in a flat sheet with FT-IR lie in the relation of (the Mg maximum luminescence intensity)+0.438×(the OH absorbency)≤3.5, and also, satisfy the regions within the Mg maximum luminescence intensity>0 and the OH absorbency>0. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an aluminum alloy sheet for automobile body sheets (hereinafter referred to as aluminum) that is formed after application of a rust-preventive lubricating oil and has excellent adhesion when bonded and assembled with an adhesive, and excellent water wettability after subsequent alkaline degreasing treatment. Is simply referred to as Al).

In recent years, exhaust gas regulations for automobiles and the like have been strengthened due to environmental problems such as global warming, and improvement in fuel consumption due to weight reduction is inevitable. For this reason, Al alloy materials are beginning to be used for hoods, fenders, doors, etc., instead of steel plates conventionally used in automobiles and the like. In particular, 5000 series alloys and 6000 series alloys to which magnesium (hereinafter, magnesium is referred to as Mg) are mainly used as automobile materials.
Usually, an automobile production line is coated with a lubricating rust-preventive oil and then molded and then joined by an adhesive, spot welding, or the like in an assembly process to become an alkali degreasing, chemical conversion treatment, or coating process.
As performance requirements for automotive materials, in addition to material performance, there are surface treatment performance (degreasing, chemical conversion, yarn rust resistance, coating film adhesion, adhesion).
As a chemical conversion treatment improvement, for example, as disclosed in Japanese Patent Application Laid-Open No. 2001-348670, a method of generating a 0.1 to 1.5 g / m ² zincate film on an aluminum surface has been proposed.
Japanese Patent Application Laid-Open No. 2000-239778 discloses a method for suppressing a hydroxyl group so that a spectral peak height of 3500 cm ^{−1 in} an FT-IR analysis using an aluminum oxide film of 100 angstroms or less is parallel polarization, is 0.007 or less. Proposed. Further, Japanese Patent Application Laid-Open No. 2003-013253 proposes an aluminum structural material characterized in that it is an aluminum hydroxide film having a thickness of 1500 to 10000 angstroms and a water contact angle ≦ 20 °.
Furthermore, in order to improve the degreasing property, Japanese Patent Publication No. 7-116629 discloses that an oxide film rich in MgO is chemically dissolved, the oxide film thickness is 45 angstroms or less, and the Mg / Al ratio of the surface layer is 0.5 or less. A method to make it is proposed.
However, since any of these methods has focused attention on oxides or hydroxides, problems that cause poor adhesion or poor wetting after degreasing have not been sufficiently solved.
JP 2001-348670 A JP 2000-239778 A JP 2003-013253 A Japanese Patent Publication No.7-116629

The oxide film formed on the surface of the aluminum alloy material has changed in quality after storage after production, and there has been a problem that the adhesiveness between the aluminum alloy plates or between the aluminum alloy plate and the steel plate is lowered when assembling into an automobile body sheet.
In addition, when the aluminum alloy material is molded and alkali degreased after it is assembled, there is a problem that water wettability is lowered, and as a result, chemical spots are generated.
An object of the present invention is to provide an aluminum alloy sheet for an automobile body sheet that improves the water wettability after degreasing and also has good adhesion.
Another object of the present invention is to provide a low-cost and environmentally friendly method as a method for producing an aluminum alloy sheet having excellent water wettability and adhesion after degreasing.

In order to solve the purpose of the previous term, the present inventor studied the investigation and countermeasures of the factors that reduce the adhesion of the surface treatment performance and the wettability after degreasing.
As a result, it was found that the amount of Mg and OH of the surface film produced in the softening and solution treatment process of the Al alloy plate that is normally produced affects the wettability after adhesion and degreasing, and the surface Mg and The amount of OH is {(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} ≦ 3.5, and it is important to adjust the surface condition so that the surface coating amount is 250 mg / m ² or less. As a result, the present invention was reached.

That is, according to the present invention, the Al—Mg-based and Al—Mg—Si-based aluminum alloy material surfaces have the maximum emission intensity when the Mg emission intensity in the depth direction is measured by GDS, and the polarization reflection method of the flat plate by FT-IR. OH absorption rate due to OH stretching vibration when measured by the following relationship: {(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} ≦ 3.5, and Mg maximum emission intensity> 0, OH It is an aluminum material for automobile body sheets excellent in water wettability and adhesiveness after degreasing, characterized by being in the region of absorption rate> 0.
The total amount of the oxide film, oxyhydroxide film, hydroxide film or hydrated film obtained from the weight reduction when immersed in the chromic acid phosphate mixture is 250 mg / m ² or less. Item 2. The aluminum material for automobile body sheets according to Item 1, having excellent water wettability and adhesion after degreasing.
Further, after the final annealing of the Al—Mg and Al—Mg—Si aluminum alloy materials, immediately contact with water of temperature ≧ 40 ° C., electrical conductivity ≦ 200 ms / m, 4 ≦ pH ≦ 9 for 2 to 30 seconds. Then, it is dried and stored in an atmosphere of room temperature ≦ 40 ° C. and relative humidity ≦ 70%, and the surface of the aluminum alloy material is applied by applying 0.2 to ² g / m ² of rust preventive oil within 14 days. The maximum luminescence intensity when measuring the Mg luminescence intensity in the depth direction by GDS and the OH absorption rate due to OH stretching vibration when measured by the FT-IR flat plate reflection method is {(Mg maximal luminescence). Intensity) + 0.438 × (OH absorption rate)} ≦ 3.5, and is in the range of Mg maximum emission intensity> 0, OH absorption rate> 0, Aluminum for car body sheets with excellent adhesion It is a manufacturing method of chloride material.

  ADVANTAGE OF THE INVENTION According to this invention, the body sheet material for motor vehicles excellent in adhesiveness and water wettability after degreasing | defatting can be provided by making the relationship between Mg amount concentrated on the Al surface and OH absorption rate into a specific relationship.

In general, Al alloy sheets for automobiles are manufactured by homogenizing, hot rolling, and cold rolling Al alloy ingots, and heat treatment of softening and solution treatment is performed in the final process to satisfy material performance. Then, it is manufactured in the process of cutting and oiling.
In other words, automotive Al materials are usually softened and solution treated at high temperatures at the end of the manufacturing process. Generally, when an Mg-containing Al alloy is heat-treated in the atmosphere, Mg in the alloy diffuses to the surface. Thus, rich MgO is formed in the outermost surface layer by combining with oxygen. Therefore, an oxide film in which MgO and Al ₂ O ₃ are mixed is formed on the Al alloy surface.
As described in the background art, the deterioration of the surface characteristics due to the oxide film has been paid attention to in the past, but conventionally, the method of removing the surface film is generally performed because it has been vaguely focused on oxides or hydroxides. As a result, sufficient wettability after degreasing was not obtained.
When the present inventors performed softening and solution treatment at a high temperature at the end of the manufacturing process in the surface coating, Mg concentrates on the surface and combines with oxygen to become MgO, which cools to room temperature. After the production, the moisture in the atmosphere is absorbed with the passage of time, and it becomes hydrate MgO. (H ₂ O) _n and hydroxide Mg (OH) ₂ , which inhibits adhesion and is also molded and assembled. Rust preventive oil is not removed by alkaline degreasing, and subsequent water washing results in poor water wetting. As a result, Ti colloid that nucleates the formation of the surface-adjusted chemical film does not adhere to the surface and causes abnormal formation of the coating surface. Found to cause.
Therefore, by specifying the amount of hydrated oxide and hydroxide of Mg, the adhesion and water wettability after degreasing can be improved.
However, aluminum hydrated oxides and hydroxides also exist on the surface of the aluminum alloy, and therefore it is difficult to individually measure MgO. (H ₂ O) _n and Mg (OH) ₂ . Therefore, in the present invention, the Mg amount is defined by the Mg maximum emission intensity, and the (OH) amount is defined by the OH absorption rate.
That is, when there are a large amount of MgO. (H ₂ O) _n and hydroxide Mg (OH) ₂ , the surface maximum Mg emission intensity is large and the OH absorption rate is also large. And OH amount: {(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} ≦ 3.5 by adjusting the surface condition so that both wettability and wettability after degreasing A good surface that satisfies the above can be obtained.
When the value of {(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} exceeds 3.5, Mg concentrated on the surface is MgO. (H ₂ O) _n and hydroxide Mg (OH ) It becomes the form of ₂ , and these reduce adhesiveness and water wettability after degreasing.
However, even if the maximum Mg emission intensity is large, if the OH absorption rate is small and within the range of the above formula, the Mg on the surface is in the state of MgO, and in this case, the adhesive strength is not directly reduced.
On the other hand, even if the OH absorption rate is large, if the Mg maximum emission intensity is small and within the range of the above formula, the surface is mainly covered with aluminum hydrated oxide, hydroxide, Mg hydrated oxide, This means that the amount of hydroxide is small. In this case as well, there is no problem because the wettability and adhesion after degreasing are not adversely affected.
The reason why Mg maximum emission intensity> 0 is that Mg contained in the material itself exists on the plate surface and is measured.
Furthermore, the reason why the OH absorption rate is greater than 0 is that OH groups are generated on the surface and measured by alkali degreasing and hot water washing treatment.

Next, the total amount regulation of oxide films and the like will be described.
Al oxides and Al hydroxides present in addition to Mg hydrated oxides and hydroxides will not cause water wetting after degreasing and decrease in adhesion if the amount is below a certain level. Since the thermal expansion coefficient of the product and the Al hydroxide is smaller than that of the aluminum material, the residual stress due to the thermal expansion and thermal shrinkage generated during the baking and cooling of the adhesive is easily broken and the adhesive strength is reduced. In addition, the water wettability after degreasing is good, but the hydrated oxide is not removed by alkali degreasing after molding, and a subsequent chemical conversion film is not formed.
Therefore, the total amount of the oxide film, oxyhydroxide film, hydroxide film or hydrated film determined from the weight reduction when immersed in the phosphoric acid chromic acid mixed solution is 250 mg / m ² or less.

Next, a manufacturing method will be described.
As a method of adjusting to the range of the above formula, it is conceivable to suppress precipitation of Mg on the surface layer from the beginning, remove the surface Mg, and prevent hydration (hydroxylation) of the surface film.
Precipitation of Mg on the surface layer increases as the Mg content in the alloy increases and the heat treatment temperature increases, so it is effective to lower the annealing temperature (specifically, 510 ° C. or less) or shorten the treatment time. It is. Moreover, Mg diffusion can be suppressed by increasing the rolling reduction of cold rolling after hot rolling. However, it may be difficult to take measures such as lowering the rolling reduction or heat treatment temperature in order to maintain the material performance.
As a method for removing the surface film, alkali and acid treatments are usually performed, but the equipment is large and increases costs. Further, if alkali and acid components remain on the aluminum surface due to safety of work and lack of rinsing, it is not preferable because it causes corrosion.
Therefore, the present inventor conducted an investigation to find a means that does not increase the cost and does not lower the adhesiveness and the water wettability after degreasing. It was found that the amount of Mg and (OH) in the surface film can be reduced so as to satisfy the above formula by immersing in water or spraying for 2 to 30 seconds by washing.
If the water temperature used for cleaning is less than 40 ° C., the amount of Mg and (OH) in the surface film cannot be reduced sufficiently. In addition, the electrical conductivity is an indicator of the purity of water, but the purity of water does not directly affect the surface Mg removal, but if the amount of impurities is large, Cl, Ca, etc. remaining on the surface is the starting point of corrosion occurrence. Electrical conductivity ≦ 200 ms / m.
In addition, if the pH is in the range of 4 ≦ pH ≦ 9, if it exceeds this range, acid or alkali components remain on the aluminum plate surface, which deteriorates surface performance such as deterioration of corrosion resistance. It is to be done.
As a method of contacting with water, it is performed by dipping or spraying, which is a normal cleaning method. If the contact time is less than 2 seconds, the amount of Mg and (OH) in the surface film cannot be sufficiently removed, and if the contact time exceeds 30 seconds, no further effect can be obtained.
Even if the surface is adjusted in this way, since Mg exists in the surface layer, when it is stored after treatment and after a long time, the surface film changes due to changes in the temperature and humidity of the atmosphere, and the surface hydrates Mg. Progression of water and hydroxylation reduces the wettability after adhesion and degreasing. For this reason, it is necessary to store in an atmosphere having an indoor temperature of 40 ° C. or less and a relative humidity of 70% or less, and to protect the surface by applying rust preventive oil within 14 days after the surface adjustment by washing.
If the storage temperature exceeds 40 ° C. or the relative humidity exceeds 70%, surface hydration and hydroxylation proceed rapidly, and the adhesiveness and water wettability after degreasing deteriorate. Therefore, storage is performed in an atmosphere having a room temperature of 40 ° C. or less and a relative humidity of 70% or less.
Even if stored under these conditions, hydration / hydroxylation proceeds in the same manner after 14 days from the above washing, and there is no oil coating effect. Therefore, rust preventive oil should be applied within 14 days. Incidentally, the coating amount of oil has no effect is less than 0.2 g / m ^2, the upper limit does not affect the performance, and 0.2 to 2 g / m ² since it increases the cost and the coating amount of oil is large. The effect of the present invention can be obtained within 14 days, but it is desirable to apply oil immediately after the surface adjustment.

A final heat-treated plate made of 5182 alloy (contains 4.5% by mass of Mg) and 6022 (contains 0.6% by mass of Mg) used for automobile body sheets is heated at 40 ° C. (pH = 7.3, conductivity 50 ms / m) After cleaning for 6 sec at a spray pressure of 1.5 kg / cm ² to adjust the amount of surface Mg, it was exposed to a constant temperature and humidity chamber (40 ° C. RH 40-80% × 1 to 14 days), and OH in the surface oxide film Specimens with varying amounts were prepared.
Then, using a structural adhesive for automotive hemming (manufactured by Sunstar Giken), after bonding at an adhesive thickness of 0.15 mm, baking was performed at 175 ° C. for 20 minutes, and shear strength and cohesive failure in a shear tensile test were performed. The rate was evaluated.
Adhesiveness evaluation 80% ≤ cohesive failure rate ... ◎ ⇒ pass 70% ≤ cohesive failure rate <80% ... ○ ⇒ pass
Cohesive failure rate <70% .................. ⇒ Fail
In addition, as an evaluation test of water wettability after degreasing, a commercially available alkaline degreasing agent (manufactured by Nihon Parkerizing Co., Ltd.) is deteriorated after immersing and applying a commercially available rust-preventive lubricating oil to the surface of the Al plate and leaving it in the room for 1 to 15 days. After being immersed in a liquid (pH ₂ adjustment with CO ₂ gas, addition of 3000 ppm of rust preventive oil) at 40 ° C. for 2 min, washed with tap water for 30 sec, the water wetted area when vertically held for 30 sec was visually evaluated.
Evaluation of water wettability after degreasing 80% <Water wetted area ............ ◎ ⇒Pass 60 ≦ Wet wet area ≦ 80% ... ○ ⇒Pass water wetted area <60% ... ...... x ⇒ rejected The surface OH amount was measured by measuring the OH absorption rate of 3500 cm ⁻¹ in the polarization reflection method of FT-IR (manufactured by Perkikin Elma).
Further, the surface Mg amount was measured by GDOES (Glow Discharge Emission Spectroscopy: JY5000RF manufactured by HORIBA, Ltd.) at a pressure of 775 Pa and an output of 40 W with Mg sensitivity = 900 V, and the maximum peak height of Mg was obtained.

1 to 5 of the present invention and 11 of the comparative example are Al-Mg-based, and 6 to 10 and Comparative Example 12 are the adhesiveness when changing the OH amount of the Al-Mg-Si-based, and water wettability after degreasing. .
The present invention examples No. 1 to 10 satisfy the range of {(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} ≦ 3.5, and have good results in both adhesiveness and water wettability after degreasing. It is.
On the other hand, the Al—Mg and Al—Mg—Si based alloys of the comparative examples increase in the amount of OH and deviate from the range of the formula, and the adhesion performance and the water wettability after degreasing decrease.

The final heat treatment plate made of 5182 alloy (contains 4.5% by weight Mg) and 6022 (contains 0.6% by weight Mg) is used to change the hot water treatment conditions (conductivity, temperature) and spray pressure 1.5 kg / cm ^2. Sample materials were prepared and evaluated by the wettability test of Example 1 after adhesion and degreasing.
The electric conductivity of hot water was adjusted by adding industrial water to pure water, and the pH was adjusted by adding dilute sulfuric acid on the acidic side and sodium carbonate on the alkaline side.
The surface coating amount was determined from the weight difference before and after film removal. The film removal solution was prepared by dissolving 20 g / LCrO ₃ and 50 g / L phosphoric acid in pure water, immersing them at 80 ° C. for 5 minutes, washing and drying.

In the present inventions 1 to 9, when the electric conductivity, pH, surface coating amount, and Mg + 0.438 × OH ≦ 3.5 are satisfied, both the adhesiveness and water wettability are good.
Comparative Examples 10 and 11 are as manufactured, but Comparative Example 10 is poor in adhesion and water wettability after degreasing, and Comparative Example 11 has low OH content, so that the adhesiveness is good, but the water wettability after degreasing. Inferior.
Comparative Example 12 has a short hot water washing time and poor adhesion and water wettability after degreasing. Comparative Example 13 has a long hot water washing time to form a boehmite film and has good water wettability after degreasing. Inferior.
In Comparative Examples 14 and 15, since the hot water pH is high (alkaline), the Mg component of the surface layer cannot be removed, so that the adhesiveness and water wettability after degreasing are poor.

  A final heat-treated plate made of 5182 alloy (containing 4.5% by weight of Mg) and 6022 (containing 0.6% by weight of Mg) is subjected to a hot water washing treatment at 60 ° C. (pH = 6.1, conductivity = 20 ms / m) for 6 seconds. The material with the surface Mg amount adjusted was changed in the amount of rust-preventive oil and the amount of oil applied, and after exposure for 14 days to an atmosphere in which the temperature and humidity of the constant temperature and humidity chamber were changed, the wettability after degreasing was evaluated.

Examples 1 to 3 are 5182 alloy, Examples 7 and 8 are invention examples of storage conditions in a temperature and humidity atmosphere with 6022 non-oiled oil, and Examples 12 and 13 are 5182 alloy under oil-free storage conditions. Comparative examples, Examples 15 and 16 show comparative examples of the 6022 alloy oil-free storage conditions. Examples 4 to 6 are 5182 alloy, Examples 10 and 11 are invention examples of oil storage amount storage conditions of 6022 alloy, Example 14 is 5182 alloy, Example 17 is a comparative example of oil storage amount storage of 6022 alloy Indicates.
In storage without rust-preventive lubricant, the higher the temperature, the lower the wettability after taking out at lower humidity. The performance maintenance limit is 14 days in an atmosphere of 40 ° C. and RH 70%. If it is stored at a humidity of 70% or more, the water-wetting performance cannot be maintained after degreasing.
If the rust preventive lubricating oil is stored in a high humidity environment after coating, if the amount of coating is 0.2 g / m ² or more, surface alteration does not occur and water wettability after degreasing is maintained. When the oil coating amount is 2 g / m ² or less, the wettability after degreasing decreases due to surface alteration in a high humidity environment.

It is explanatory drawing which showed the OH absorption rate measurement of FT-IR. It is explanatory drawing which showed Mg maximum height measurement of GDOES.

Claims (3)

When the surface of Al-Mg and Al-Mg-Si-based aluminum alloy materials is measured by GDS and the maximum emission intensity when measuring the Mg emission intensity in the depth direction, and by FT-IR with a flat plate polarization reflection method OH absorption rate due to OH stretching vibration of
{(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} ≦ 3.5
And the maximum emission intensity of Mg> 0
OH absorption rate> 0
An aluminum material for automobile body sheets excellent in water wettability and adhesion after degreasing, characterized in that it falls within the range of 2. The total amount of an oxide film, an oxyhydroxide film, a hydroxide film or a hydrated film obtained from a weight reduction when immersed in a phosphoric acid chromic acid mixture is 250 mg / m ² or less. The aluminum material for automobile body sheets having excellent water wettability and adhesion after degreasing as described in 1. After the final annealing of the Al—Mg-based and Al—Mg—Si-based aluminum alloy materials, they were immediately brought into contact with water of temperature ≧ 40 ° C., electrical conductivity ≦ 200 ms / m, 4 ≦ pH ≦ 9 for 2 to 30 seconds. After drying, storing in an atmosphere of room temperature ≦ 40 ° C. and relative humidity ≦ 70%, and applying 0.2 to ² g / m ² of rust preventive oil within 14 days, the surface of the aluminum alloy material The maximum emission intensity when measuring the Mg emission intensity in the depth direction by GDS, and the OH absorption rate due to the OH stretching vibration when measured by FT-IR using a flat plate polarization reflection method,
{(Mg maximum emission intensity) + 0.438 × (OH absorption rate)} ≦ 3.5
And the maximum emission intensity of Mg> 0
OH absorption rate> 0
A method for producing an aluminum material for an automobile body sheet, which is excellent in water wettability and adhesion after degreasing.

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