KR960004783B1 - Aluminium alloy sheet for automotive body and method of manufacturing the same - Google Patents

Abstract

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Description

[Name of invention]

Aluminum alloy plate for automobile body and manufacturing method

Detailed description of the invention

[Field of Invention]

TECHNICAL FIELD The present invention relates to an aluminum (hereinafter referred to as A1) alloy plate used in automobiles, in particular in automobile bodies, and a method of manufacturing the same.

[Description of the Prior Art]

In recent years, it is desired to reduce the vehicle body weight for the purpose of improving fuel efficiency and improving performance of automobiles. Accordingly, the use of A1 materials having a specific gravity of about one third instead of steel materials conventionally used has increased. The A1 material is the most attention-oriented material for automobiles because it is not only lightweight but also excellent in corrosion resistance, workability, surface treatment, etc., and is easily regenerated. A1 materials are currently used in automobile bodies, wheels, bumpers, heat exchangers, engines, etc., and the scope of application is also expanding.

For example, when an A1 alloy plate is used for a vehicle body, moldability, weldability, adhesiveness, corrosion resistance after painting, and aesthetics are required. The method of manufacturing a vehicle body using an A1 alloy plate is basically the same as in the case of using a conventional steel plate, as shown below.

① molding

The A1 alloy plate of the coil shape or the A1 alloy plate cut | disconnected by predetermined dimension from the coil body is shape | molded to a predetermined shape.

② Junction

Join with the member installed in the vehicle body by welding and / or adhesion. In that case, it sends to the next process in combination with the member which consists of conventional steel materials.

③ Surface treatment

Iii) Degreasing using alkaline cleaner

Ii) defensive

Iii) surface adjustment by colloidal titanate treatment

Iii) chemical conversion by zinc phosphate treatment

Iii) defensive

(Here, "post-treatment" with chromic acid solution is performed as needed.)

Iii) drying

④ Painting

Ⅰ) First painting by electrodeposition coating

Ii) middle

Ⅲ) Finish

⑤ Chairman

Mount each part on the frame member.

Car bodies for automobiles are manufactured through the above steps (1) through (5).

The A1 alloy sheet as a raw material is manufactured by a process through casting, soaking, hot rolling, cold rolling, finishing annealing (annealing may be performed during cold rolling), and cut into coil shapes or predetermined dimensions. It is then provided for molding in the state of the plate.

However, the A1 alloy plate for automobile bodies obtained by the above method has the following problems.

First is the problem of machinability. The said A1 alloy material is bad in workability compared with the steel material which is mainstream as a material for automobile bodies. For this reason, when intense processing is performed, a crack, a surface roughness, etc. generate | occur | produce. Therefore, the member which can be used is limited.

Second is the problem of adhesion. When the endurance test is performed in a harsh environment, peeling occurs at the joint, or the adhesive strength at the joint is less than the desired value.

Therefore, there is a problem in safety or reliability.

Third is the problem of weldability. At the time of spot welding, the number of RBIs which can be welded continuously is small, and weldability is bad.

For this reason, the number of times of maintenance of a welding mechanism, especially an electrode increases, and productivity falls.

Fourth, it is a problem of coating film adhesion. If the endurance test is carried out in a harsh environment after coating, the coating film may be peeled off or swelling may damage the appearance.

Fifth is the problem of corrosion resistance. If the durability test is carried out in a harsh environment after coating, the corrosion of the form (Filiform Corrsoion) is likely to occur, and not only damages the appearance but also degrades the performance.

The material for automobile bodies may be used solely with A1 material, or with A1 material in combination with steel material. As described above, zinc phosphate treatment is often performed as the treatment of these coatings. do. In this case, coating film adhesiveness defect and corrosion resistance defect are especially related to this base material handling property.

[Overview of invention]

It is confirmed by the inventors that it is the oxide film formed on the A1 alloy plate as the cause of the various problems mentioned above. It was found that the structure of the oxide film of A1 greatly affected the A1 alloy composition. For example, in a material containing 0.3 to 10% by weight of Mg, such as an A1 alloy plate for an automobile body, an oxide film is present on the surface of the alloy plate, and the oxide film is magnesium oxide and / or hydroxide as well as A1 oxide and / or hydroxide. Or hydroxides coexist. It was confirmed that this magnesium oxide and / or hydroxide adversely affects weldability, adhesiveness, coating film adhesion, and corrosion resistance.

A1 oxide is largely divided two kinds, and one is an oxide film (A _l2 O _3), the other one of the amorphous state is the oxide film sex determination. The crystalline oxide film is composed of various phases depending on the production atmosphere, but representative phases are Gibbsite (r-A1 (OH) ₃ ), Bayerlite (α-Al (OH) ₃ ), Boehmite (r-AlOOH), etc. These two types of oxide films have different frictional resistances, and the frictional resistance of the crystalline oxide film is smaller than the frictional resistance of the oxide film in the amorphous state, so that the crystalline oxide film has better lubricity. Two kinds of such oxide films are mixed on the surface of the A1 alloy plate after rolling, and the crystalline oxide film is generated when exposed to high temperature in a wet atmosphere.

In the production of the A1 alloy plate, it has been found that such a crystalline oxide film is produced in the hot rolling process. This is considered to be because in a hot rolling process, it is generally rolled at 200 degreeC or more using aqueous rolling oil. Thereafter, the crystalline oxide film is crushed and rolled in the subsequent rolling process, but remains in the form of being buried in A1 substrate until the final sheet.

In addition, the inventors have found that weldability, adhesion, coating film adhesion, and corrosion resistance are affected by two kinds of oxides, A1 oxide and magnesium oxide, on the A1 alloy plate. In particular, the presence of a large amount of magnesium oxide was found to adversely affect the above properties.

An object of the present invention is to remove magnesium oxide on an A1 alloy plate as much as possible to improve the characteristics, and to prevent the formation of magnesium oxide even after leaving for a long time during the above-mentioned removal treatment to prevent the formation of magnesium oxide over time. A1 alloy plate is provided.

In order to achieve this object, the present invention provides a metal A1 substrate of an A1 alloy plate containing 2 to 10% by weight of Mg, a phosphate film of A1 formed on the substrate, and an A1 oxide film formed on the phosphate film. The present invention provides an A1 alloy plate for an automobile body provided with an oil film on the A1 film as needed.

Moreover, the objective of this invention is providing the manufacturing method of the A1 alloy plate for automobile bodies which can obtain the A1 alloy plate with few time-dependent changes of a characteristic efficiently.

In order to achieve this object, the present invention is to treat the surface of the A1 alloy plate containing 2 to 10% by weight of Mg with an acid of pH 4 or less to remove the magnesium oxide film in the oxide film on the surface of the plate, and the acid treated treatment Treating the plate with a phosphate solution to form a phosphate film of A1 between the metal A1 gas and the A1 film, and optionally, applying an oil on the A1 film to form an oil film. It provides a method of manufacturing an A1 alloy plate for an automobile body.

[Description of the Desirable Sun]

In the present invention, as the A1 alloy containing 2 to 10% by weight of Mg, for example, JISA5052 alloy, JISA5182 alloy, JISA5082 alloy, JISA5083 alloy, JISA5086 alloy, and A1-8% by weight Mg alloy can be used. The reason for limiting the amount of Mg to 2 to 10% by weight is that the strength is weak at less than 2% by weight, and when the content is more than 10% by weight, the production of the plate becomes difficult.

As described above, an oxide film of A1 oxide and magnesium oxide is present on the surface of the A1 alloy plate produced by the usual method.

In the present invention, only magnesium oxide is removed by acid treatment of A1 and magnesium oxide originally present on the metal A1 gas of the A1 alloy plate.

The pH of the acid used for this treatment is set to 4 or less. This is because if the pH is 4 or less, only magnesium oxide on the plate surface can be dissolved without dissolving A1 which is a base metal and A1 oxide on the plate surface. Thereby, crystalline A1 with high lubricity generated at the time of hot rolling can be left. As such an acid, 0.5-30 weight% nitric acid and 0.5-30 weight% sulfuric acid can be used.

In the present invention, the degree of removal of magnesium oxide is preferably 20% by weight or less based on the weight ratio of magnesium oxide in the total oxide on the metal gas. If the weight ratio of magnesium oxide in the total oxide exceeds 20% by weight, the magnesium oxide film itself acts as a fragile layer (peeling portion) at the time of adhesion, thereby lowering the adhesive strength. In addition, the electrical resistance increases at the time of welding, damaging the electrode of the welding mechanism, and at the time of continuous use, the welded portion called the nugget becomes small, and the desired strength cannot be obtained. In addition, the amount of zinc phosphate coating formed when the phosphate treatment, which is the coating material treatment, is small, and the zinc phosphate crystal coarsens, thereby reducing the adhesion and corrosion resistance after coating.

After the magnesium oxide is removed from the surface of the plate by the acid treatment, the Al oxide film, which is mostly present from the beginning, remains on the metal gas of the A1 alloy plate.

It is preferable that the thickness of this A1 oxide film is 10-200 GPa. This means that if the thickness of the A1 oxide film is less than 10 GPa, the electrical resistance is too small during spot welding and sufficient heat generation cannot be obtained, so that a nugget is not formed. If the thickness exceeds 200 GPa, the A1 oxide film itself acts as a weak layer during adhesion. This is because the adhesive strength is lowered. This is because, at the time of spot welding, the electrical resistance is so large that the number of electrodes that are damaged and can be continuously hitted is small.

The surface roughness of the A1 oxide film is preferably 0.1 to 2.5 µm in Ra (average roughness) and 0.5 to 40 µm in Rmax (maximum roughness). If Ra is less than 0.1 µm and Rmax is less than 0.5 µm, the lubricating oil supplied at the time of molding is poor, the moldability is lowered, and at the time of bonding, the adhesion area is small, and the adhesion is also lowered. On the other hand, when Ra exceeds 2.5 µm and Rmax exceeds 40 µm, the smoothness of the coated film surface after coating decreases, resulting in a decrease in product value.

As described above, after magnesium oxide is removed from the surface of the plate by acid treatment, the treated plate is then treated with a phosphate solution to form an A1 phosphate film between the metal gas of the A1 alloy plate and the A1 oxide film. do. The thickness of the phosphate film of A1 is about 1 kPa-5 kPa. In addition, even in the state of a monomolecular film, a sufficient effect can be obtained if the phosphate film of A1 exists. The film thickness of the phosphate film of A1 can be adjusted by setting conditions in the range of 0.01-5 weight% of phosphate solution, 20 degreeC or more of liquid temperature, and 2 second or more of treatment time.

As the treatment liquid used when forming the phosphate film of A1, a solution containing phosphate ion or phosphate can be used. As such a solution, the solution containing 0.01 weight% or more of at least 1 sort (s), such as sodium phosphate, sodium hypophosphite, sodium pyrophosphate, is mentioned.

In this way, by treating with the phosphate solution, it is possible to prevent the production of magnesium oxide by standing, thereby suppressing the time-dependent change in the characteristics of the A1 alloy plate. In addition, since the A1 oxide film originally formed on the gas phase is porous, the phosphate solution during the treatment passes through the A1 oxide film and reacts with A1, which is a gas, to form a strong A1 film between the metal A1 gas and the A1 oxide film. Phosphate film is formed.

In the present invention, it is preferable to apply oil on the A1 oxide film. Even when the A1 phosphate film is left for a long time from the treatment of the A1 alloy plate to the molding process, the formation of magnesium oxide can be sufficiently prevented, but the growth can be further prevented by applying oil. As this oil, rustproof oil of an emulsion zone or a wax system can be used. In addition, the application amount of oil can be sufficiently effective as long as it is an amount that uniformly covers the entire plate surface, but in practice, it is about 0.1 g / m 2 or more, preferably about 1 g / m 2.

In the production method of the present invention, the material may be cut out from the coil-shaped body to a predetermined dimension to form a plate-shaped body, and each treatment may be performed thereon, but the angle-processing may be performed continuously as it is. Particularly, the A1 alloy plate can be produced more efficiently and more productively by performing the treatment continuously.

Hereinafter, the Example performed in order to confirm the effect of this invention is demonstrated.

The present invention is not subject to the following limitations, and various changes, modifications, outlines, and the like can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention without departing from the spirit of the present invention. You may add it.

Example 1

Ingot is made by melting and casting to JIS A5182 alloy (A1-0.3 wt% Mn-4.5 wt% Mg alloy) material, and then homogenizing, hot rolling, cold rolling and finishing annealing are performed sequentially. The board | plate material of thickness 1.0mm was produced.

Subsequently, this plate was treated with a spraying method using 5 wt% nitric acid for 10 seconds, and the plate was washed with water to remove the magnesium oxide film from the oxide film on the surface of the plate and dried. Subsequently, a 0.1 wt% sodium pyrophosphate solution was used and treated at a temperature of 40 ° C. and a processing time of 300 seconds to form a phosphate film having a thickness of 5 kPa between the metal A1 gas and the A1 oxide film formed thereon. To obtain an A1 alloy plate (this invention material (1)).

About the obtained this invention material (1), the thickness (total film thickness of a magnesium oxide film and an A1 film | membrane) of a total oxide film, the weight ratio of magnesium oxide in a total oxide film, shaping | molding immediately after processing (after leaving for about 1 week) The properties, adhesion, weldability, coating adhesion, and corrosion resistance were examined. The results are shown in Table 1 below. Moreover, this invention material (1) was left to stand in a constant temperature / humidity tank with a temperature of 40 degreeC, and a relative humidity of 95% for 90 days, and the time-dependent change of the said characteristic of this invention material (1) after leaving to stand was investigated. The results are written together in Table 1 below. In addition, each evaluation was performed in this way.

(1) The thickness of the total oxide film and the weight ratio of magnesium oxide in the total oxide film were determined by ESCA (X-ray photoelectron spectroscopy device).

② Formability

JIS Z2247 Eriksen test A method was performed about this invention material (1), and the Eriksen centimeter (mm) was measured.

③ Adhesive

The present invention material (1) was cut into 25 x 100 mm, and the two sheets were pasted together with a commercial epoxy adhesive at a stacking width of 13 mm and baked at 170 ° C for 30 minutes.

Thereafter, a salt spray test in accordance with JIS Z2371 was conducted for 90 days, the tensile shear strength before and after the salt spray test was measured, and the residual ratio of the strength determined by the following formula was calculated.

Strength Retention Rate (%) = (Shear Strength after Test / Shear Strength before Test) × 100

④ weldability

The continuous score (spot score until the electrode was damaged and no nugget was formed) by spot welding was examined.

⑤ Film adhesion

A 70 x 150 mm plate is cut out from the present invention material 1, degreased at 45 ° C. for 30 seconds using a weak alkali degreasing agent, washed with water, and then surface-conditioned for 30 seconds at room temperature with a colloidal titanium solution. In this state, a chemical treatment of commercial zinc phosphate is performed at 45 ° C. for 2 minutes. Thereafter, this is washed with water, dried, and subjected to priming painting by cationic electrodeposition coating, intermediate coating by spraying, and finishing coating to prepare a sample.

The sample was immersed in hot water at 50 ° C. for 20 days, and then subjected to a checkerboard test (100 sheets of 2mm × 2mm bottom plates, peeled test by tape) in accordance with JIS D0202. The number was expressed as follows.

Remaining count / test count (100)

⑥ Corrosion resistance

Samples were prepared in the same manner as in the coating adhesion test, a cross cut (x mark) reaching the substrate was placed on the sample surface, and a salt spray test in accordance with JIS Z2371 was performed for 24 hours. Thereafter, the relative humidity was 95% at 50 ° C. After being left for 2000 hours in a humid atmosphere of, the maximum length of the actual corrosion from the crosscut was measured.

Example 2

0.05% by weight sodium phosphate instead of forming a 5 ° thick A1 phosphate film between the metal A1 gas and the A1 oxide film by using 0.1% by weight sodium pyrophosphate and treating it at a temperature of 40 ° C. and a processing time of 300 seconds. A1 alloy plate (Inventive Material (2)) was obtained in the same manner as in Example 1 except that the solution was treated at a temperature of 90 ° C. and a treatment time of 10 seconds to form an A1 phosphate coating having a thickness of 2 kPa.

The obtained inventive material (2) was investigated in the same manner as in Example 1 with respect to the thickness of the total oxide film, the weight ratio of magnesium oxide in the total oxide film, formability, adhesion, weldability, coating film adhesion, corrosion resistance, and the change with time. It was. The results are written together in Table 1 below.

Example 3

3 wt% fatigue instead of using a 0.1 wt% sodium pyrophosphate solution at a temperature of 40 ° C. and a treatment time of 300 seconds to form a phosphate coating having a thickness of 5 kPa between the metal A1 gas and the A1 oxide film. Treatment with a sodium phosphate solution at a temperature of 50 ° C. and a treatment time of 120 seconds to form an A1 phosphate coating having a thickness of 5 kPa, and an emulsion-type rust-prevented oil having a viscosity of 3 cst on the A1 oxide film (top layer) at an oil coating rate of 1 g / m 2. A1 alloy plate (this invention material (3)) was obtained like Example 1 except having apply | coated.

With respect to the obtained inventive material (3), the thickness of the total oxide film, the weight ratio of magnesium oxide in the total oxide film, the moldability, the adhesiveness, the weldability, the coating film adhesion, the corrosion resistance, and the aging change thereof were examined in the same manner as in Example 1. . The results are shown in Table 1 below.

[Prior Example 1]

Ingots were prepared by melting and casting in an alloy material of JIS A5182, and then, ingots were homogenized, hot rolled, cold rolled, and finished annealed in order to produce 1.0 mm thick plates.

Subsequently, this plate was treated with a spraying method using 5 wt% nitric acid for 10 seconds, and the plate was washed with water to remove the magnesium oxide film from the oxide film on the surface of the plate and dried.

Next, on the remaining A1 oxide film, an emulsion zone antirust oil having a viscosity of 5 cst was applied at a coating amount of 1 g / m 2 to obtain an A1 alloy plate (conventional material (1)).

With respect to the obtained conventional material (1), the thickness of the total oxide film, the weight ratio of magnesium oxide in the total oxide film, the moldability, the adhesion, the weldability, the coating film adhesion, the corrosion resistance, and the aging change thereof were investigated in the same manner as in Example 1. . The results are written together in the table below.

[Conventional Example 2]

An A1 alloy plate (conventional material (2)) was obtained in the same manner as in Example 1 except that a wax-based rust preventive oil was used instead of an emulsion zone rust preventive oil having a viscosity of 5 cst.

With respect to the obtained conventional material (2), the thickness of the total oxide film, the weight ratio of magnesium oxide in the total oxide film, the moldability, the adhesion, the weldability, the coating film adhesion, the corrosion resistance, and the aging change thereof were investigated in the same manner as in Example 1. . The results are shown in Table 1 below.

[Prior Example 3]

Ingots were prepared by melting and casting in an alloy material of JIS A5182, and homogenizing treatment, hot rolling, cold rolling, and finish annealing were carried out on these ingots to produce a 1.0 mm thick sheet.

Subsequently, this board is treated with a spraying method using 5 wt% nitric acid for 10 seconds, and the board is washed with water to remove the magnesium oxide film in the oxide film on the surface of the board, followed by drying, thereby drying the A1 alloy plate (the conventional material (3)). Got it.

With respect to the obtained conventional material (3), the weight ratio of the total oxide film, the weight ratio of the magnesium oxide in the total oxide film, the moldability, the adhesiveness, the weldability, the coating film adhesion, the corrosion resistance, and the aging change thereof were examined in the same manner as in Example 1. The results are written together in Table 1 below.

* 1 Magnesium oxide weight ratio is with respect to a total oxide film (A1 film + magnesium oxide film).

* 2 A: Immediately after treatment (after 1 week incubation)

B: After 90 days at 40 ° C and 95% humidity

As is apparent from the first table, the A1 alloy plates (Invention Materials (1) to (3)) of the present invention had little change over time in characteristics. On the other hand, in the conventional A1 alloy plates (prior materials (1) to (3)), the thickness of the oxide film after standing is increasing, and the change with the characteristic with time is large.

As described above, in the A1 alloy plate for automobile body of the present invention, the surface of the plate removes magnesium oxide, forms a phosphate film of A1 between the metal A1 gas and the A1 oxide film, and the top layer is oxidized as necessary. By forming an oil film on the A1 film, properties (forming, adhesion, weldability) are improved, and subsequent generation of magnesium oxide is prevented as much as possible, thereby minimizing the change in properties over time. In addition, in the A1 alloy plate for automobile body of the present invention, the formation rate of the chemical conversion film during the chemical conversion treatment in the coating step is increased, and the elution of A1 ions into the liquid flow is suppressed, whereby the chemical film is coated on the A1 alloy plate. Can be formed uniformly, and as a result, coating-film adhesiveness and corrosion resistance improve. Thereby, a chemical conversion film can be formed uniformly on A1 alloy plate, As a result, coating-film adhesiveness and corrosion resistance improve. Moreover, the manufacturing method of the A1 alloy plate for automobile bodies of this invention can obtain the A1 alloy plate with little change with time-dependent characteristic efficiently.

Claims (4)

An A1 alloy plate for a motor vehicle body comprising a metal A1 gas of an A1 alloy plate containing 2 to 10% by weight of Mg, a phosphate film of A1 formed on the substrate, and an A1 film formed on the phosphate film. A metal A1 gas of an A1 alloy plate containing 2 to 10% by weight of Mg, a phosphate film of A1 formed on the substrate, an A1 oxide film formed on the phosphate film, and an oil film formed on the A1 film A1 alloy plate for automobile body. Treating the A1 alloy plate containing 2 to 10% by weight of Mg with an acid having a pH of 4 or less to remove the magnesium oxide film from the oxide film composed of the A1 oxide film and the magnesium oxide film on the surface of the alloy plate; A process for producing an A1 alloy plate for an automobile body, comprising the step of forming a phosphate film of A1 between a metal A1 gas and an A1 film by treating the treated plate with a phosphate solution. 4. The method of manufacturing an A1 alloy plate for an automobile body according to claim 3, further comprising the step of applying oil on the A1 oxide film to form an oil film.