JP3255625B2 - Composite material with excellent phosphatability and electric corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite material in which a steel material and an aluminum alloy material are joined together and subjected to a phosphate treatment and then painted.

[0002]

2. Description of the Related Art In recent years, with respect to global environmental problems due to exhaust gas and the like, improvement in fuel efficiency by reducing the weight of transport vehicles such as vehicles, ships, aircraft, motorcycles, and automobiles has been pursued. For this reason, the use of Al alloy materials for structural materials, panels, frame materials, etc. of transport vehicle bodies is also increasing.

[0003] An Al alloy has the characteristics that its specific gravity is one-third that of steel, that it has excellent energy absorption, and that it has a high degree of freedom in its cross-sectional shape. Therefore, it is possible to comply with safety standards and improve vehicle performance without increasing the vehicle weight.

For this reason, Al-Mg-based materials are used for door beams and side members as vehicle door reinforcing members, body reinforcing members (vehicle protection members) such as bumpers and bumper stays, and the like.
Si-based AA 6000 series Al alloy, Al-Zn-Mg-based AA 7000 series Al
Extruded shapes such as alloys are used.

In addition, structural materials having complicated shapes and thick portions, such as motorcycles, automobile wheels, suspension parts such as knuckles, lower arms, and upper arms, include:
Since it is inexpensive and has the necessary strength and toughness, cast materials and forged materials of Al alloy (these are collectively referred to as cast forged materials in the present invention) are used. As casting material, 6.5
Up to 7.5% (mass%, the same applies hereinafter), JIS to AA AC4CH
Al-Si-Mg-based Al alloys are typical. In addition, as a forging material, Al-Si-
Typical examples include Mg-based JIS to AA 6000-based Al alloys.

[0006] Further, as a member of a vehicle such as a panel material such as a door, a fender or a bonnet of an automobile or a wheel, Al-Si-Mg-based JIS to AA6000-based Al alloy is representative. The 6000 series Al alloy has a low yield strength during press forming and can secure the formability, age hardens during baking coating after press forming to improve proof strength, and can secure the strength required for panel materials. Also, scrap
When reused as an Al alloy melting raw material, there is also an advantage that the amount of alloy is relatively small and an original 6000 series Al alloy ingot can be easily obtained.

However, for example, when an Al alloy material is used for an automobile body, most of the automobile body except for a part of an all-aluminum vehicle or the like is composed of a conventional steel material such as a steel plate and an Al alloy material. It is used after being converted. Examples of this composite material include a door beam made of an extruded aluminum alloy, and a steel plate member such as an inner or outer door and an aluminum alloy door beam are welded or mechanically joined by bolting or the like, It is attached to the body as a composite door.

[0008] Usually, in the production line of automobile transports, the body after molding and assembly is subjected to a coating base treatment such as a zinc phosphate treatment and a cationic electrodeposition coating treatment, and is then subjected to baking-hardening intermediate coating and top coating. Such as painted. Each process condition in this production line basically matches the condition of the steel material used so far. Therefore, used for car bodies
Al alloy materials, either as composite materials or as individual members, together with steel, in other words, under the same conditions as steel, are subjected to a surface treatment such as zinc phosphate treatment and cationic electrodeposition coating. Will be.

(Problem of zinc phosphate treatability on steel side in composite material) However, in the case of Al alloy material, zinc phosphate treatability is inferior to steel material. There is a problem that it is difficult to secure a zinc phosphate film. If the phosphatability is poor, the adhesion of a coating film formed by coating afterwards is reduced. And as a result,
There is a problem that after coating, rust-like corrosion and swelling of the coating film occur, thereby deteriorating the corrosion resistance and appearance of the automobile.

[0010] Therefore, in order to improve the phosphatability of the Al alloy material, the phosphating bath has been conventionally improved. As a typical example, a high concentration of free fluorine (F) ions of several tens to several hundreds ppm is added to a phosphating bath.

[0011] To solve the problem of phosphatability of Al alloy material,
The addition of the free fluorine (F) ions certainly improves the phosphatability of the Al alloy material. However, the formation of a phosphate film on the surface of the Al alloy material is promoted by the elution of Al ions from the surface of the Al alloy material. Al
The elution amount of ions increases. When the elution of Al ions increases, a new problem arises in that the phosphatability of the important steel material is impaired.

For example, usually, when a steel material is subjected to a phosphate treatment, phosphoferrite having granular crystals is formed on the surface of the steel material. This phosphoferrite has good subsequent electrodeposition coating properties as a coating base, and can guarantee corrosion resistance such as coating film adhesion and appearance. However, when a large amount of Al ions is contained in the phosphate bath, a whipite having plate-like crystals is formed on the surface of the steel material. The Hopite has poor electrodeposition coating properties, and cannot guarantee corrosion resistance such as coating film adhesion and appearance.

(Electrical corrosion problem on the side of Al alloy material in the composite material) On the other hand, the composite material of the steel member and the Al alloy material is not only a problem at the time of manufacturing such as the zinc phosphate treatment described above, but also a problem. In addition, when used as a composite material for a transport machine, there is a problem that corrosion, that is, so-called electrolytic corrosion, easily occurs on the side of the Al alloy material. This is because the Al alloy is a metal that is more noble than steel, so when the steel member and the Al alloy material come into contact, a battery is formed between the two metals, and the corrosion current easily flows through the Al alloy material,
This is because it causes electrolytic corrosion.

[0014] Further, the transport machine is often used in a salt water corrosive environment such as seawater, and the composite material is often used under a certain stress load state or a state where stress is easily concentrated. . The use in such a corrosive environment remarkably promotes the occurrence of electrolytic corrosion (reduces the electrolytic corrosion resistance).

[0015] Further, even when a high-strength element such as Zn or Cu is added in order to further increase the maximum load and bending stiffness of the Al alloy material, the electrolytic corrosion sensitivity of the Al alloy material is also increased.

In the case of a composite material in which a steel material and an Al alloy material are joined by a fastener made of an Al alloy, the portion where the electrolytic corrosion occurs is made of Al.
Alloy fasteners and the surface of Al alloy material near the fasteners, steel
In the case of a composite material obtained by joining an Al alloy material with a steel fastener, the composite material is a surface portion of the Al alloy material in contact with the fastener.

In a composite material, an Al alloy fastener and Al
In the case of improving the electrolytic corrosion resistance of the alloy material surface, there is a limit to means for improving the chemical composition and structure of the Al alloy material from the material side. Al alloy materials and Al alloy fastener chemical components and structures are each determined from mechanical requirements such as strength, and from the viewpoint of corrosion resistance, when controlling these chemical components and structures, the mechanical This is because a contradiction occurs in which the required characteristics are sacrificed.

Therefore, in order to improve the electrolytic corrosion resistance of the surface of these Al alloy materials, the surfaces of these Al alloys are surface-treated to be electrically insulated from the steel material, and the steel material and the Al
It is conceivable to make it difficult to form a battery with the alloy material.

[0019]

(Problem to be Solved by Zinc Phosphate on the Side of Steel in Composite Material) In order to improve the zinc phosphate treatability of the steel material in the composite material, of course, a phosphate treatment bath is used. The accumulated Al ions may be positively removed. However, loss of phosphate bath due to this removal,
This is not a practical solution for automobile manufacturing lines where the cost of processing equipment is large and energy saving and efficiency are strictly pursued.

(Problem of electrolytic corrosion on Al alloy side in composite material) On the other hand, to solve the problem of electrolytic corrosion resistance on the surface of Al alloy material, the problem of Al alloy material that can electrically insulate steel and Al alloy material is considered. As is well known, there are various methods for surface treatment. For example, Al oxide film by anodizing or surface oxidation, zinc plating film by electroplating or displacement plating, so-called dacro film treatment combining zinc and chromium, chromate film by chromate treatment, resin film
(Including vinyl sheets, etc.), films of lithium salt, magnesium salt, cerium salt, calcium salt, etc., and potassium permanganate film. However, there are various problems in applying these conventional surface treatments or surface coatings to Al alloy fasteners or composites targeted by the present invention.

Among them, the galvanized film or dacro film formed by electricity or substitution has the effect of sacrificial corrosion protection, but is conductive, and not only has the effect of not electrically insulating the steel material and the Al alloy material, but on the contrary. In addition, the formation of a battery between both metals is promoted, and the electrolytic corrosion is promoted.

Although the Al oxide film is effective as an electrical insulating film, it inhibits the phosphatability of the Al alloy material when the Al alloy material is subjected to phosphating and painting. In addition, the adhesion of the coating film is inferior, hindering the throwing power of the coating film, and the coating film is easily blistered,
There is a problem that the corrosion resistance after painting is reduced. Furthermore,
Due to its insulating property, when the composite material is welded, there is also a problem that the weldability of the Al alloy material is hindered.

Although the resin film has an insulating effect, the coating process is complicated and the cost is high. In addition, during phosphating and coating, as in the case of the Al oxide film, the phosphating property, electrodeposition coating property, and adhesion of the coating film are low, and the coating cannot be performed substantially.

Further, the other films do not have electrical insulating film properties as much as Al oxide films, and also have problems such as adhesion of the films when provided on the surface of the Al alloy material. In addition, the cost of coating treatment (chemicals etc.) generally increases, and although chromate coatings and the like are actually widely used as coating base treatments, there is also the problem of waste treatment of treatment liquids, which raises the cost. is there.

Therefore, in a composite material of a steel material and an Al alloy material, the elution of Al is prevented to improve the phosphatability of the steel material, and the electric corrosion resistance of the Al alloy material and the fastener made of the Al alloy is effectively improved. At present, there is no effective surface treatment or surface treatment film that can be improved.

The present invention has been made in view of such circumstances, and an object of the present invention is to solve the problems of the conventional Al alloy material for transport vehicles and to provide a composite material of steel and Al alloy material. Even if it is phosphated, it suppresses the elution of Al ions from the surface of the Al alloy material, improves the phosphatability of the steel material, and effectively improves the electrolytic corrosion resistance of Al alloy materials and Al alloy fasteners It is an object of the present invention to provide a composite material which can be improved.

[0027]

In order to achieve this object, the gist of the composite material of the present invention is a composite material in which a steel material and an aluminum alloy material are joined together and subjected to a phosphate treatment and then painted. That is, a hydrated oxide film of aluminum is previously provided on the surface of the aluminum alloy material before the phosphate treatment .

According to the present invention, a hydrated oxide film of Al is provided on one Al alloy material surface of the composite material to insulate the Al alloy material surface from the phosphating bath, and to prevent Al from the Al alloy material surface. Prevent elution. And as a result, the phosphatability of the other steel material of the composite material is improved.

Further, by providing a hydrated oxide film of Al on the outer surface of an Al alloy material or a fastener made of an Al alloy, the steel material is electrically insulated from the steel material, thereby fastening the steel material to an Al alloy material or an Al alloy fastener. To make the battery difficult to form
Improves the electrical corrosion resistance of the surface of the Al alloy material.

The hydrated oxide film of Al has no reactivity or low reactivity with the phosphating bath. Therefore, the above effects can be achieved. The hydrated oxide film of Al itself refers to a film provided in advance before the phosphate treatment, and may be provided immediately before the phosphate treatment or during the phosphate treatment step, or may be an Al alloy material. It may be provided after manufacturing itself and before forming into a product.

In addition to being non-reactive with the phosphating bath, the coating provided on the surface of the Al alloy material is used for coating. It is necessary to have good adhesion to a resin coating film (resin paint or resin coating film), but a hydrated oxide film of Al satisfies this condition. In other words, the Al alloy material provided with the hydrated oxide film of Al can ensure good adhesion to the resin film in the subsequent coating process even if the phosphate film cannot be identified. is there.

The hydrated oxide film of Al also has characteristics that it does not impair press formability and weldability and that the film itself has excellent corrosion resistance. For example, in an Al alloy material for a transport machine, a hydrated oxide film of Al is provided before forming, and in this pre-coated state, forming such as press forming or bending may be performed. In such a case, the precoat film needs to have press formability or not to impair press formability. Also,
Since the members are welded or joined by an adhesive after the forming process, in such a case, it is necessary to have weldability or not hinder weldability. In addition, assuming use in a corrosive environment, it is necessary to have a thread rust resistance or not to impair the thread rust resistance as corrosion resistance after coating.

Further, the hydrated oxide of Al has a higher adhesiveness of the coating, or a press formability and a weldability, when provided on the surface of the Al alloy material, as compared with other surface-treated coatings. There is also the advantage of being superior. In addition, the hydrated oxide of Al can be inexpensively formed by a method of directly contacting high-temperature water or water vapor, which will be described later, as compared with other surface-treated films. Better than other coatings.

Therefore, the hydrated oxide film of Al according to the present invention is a main object of the present invention, which is the Al alloy material at the time of phosphate treatment, compared with the surface treatment or the pre-coat film of the Al alloy material. It is also excellent in that it can achieve the effect of suppressing the elution of Al ions from the surface, the effect of improving the phosphatability of the steel material side, and the effect of improving the electrical corrosion resistance of the Al alloy material without newly occurring adverse effects. .

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Hydrated oxide film of Al)
Therefore, the hydrated oxide film of Al provided on the surface of the Al alloy material is
General formula, Al _TwoO_Three・ XH_TwoHydration reaction of Al oxide represented by O
Refers to a film of a hydrated oxide of Al generated by the above method. And
The hydrated oxide of Al in the present invention refers to the degree of hydration (X
Value, etc.), morphology, crystal structure,
There is no particular limitation on crystallinity and the like. Just Al
Among the hydrated oxides, the pseudo-base in which the value of X is about 1.5 to 1.9.
-Mite is generally called boehmite film.
ing.

The film structure of these hydrated oxides of Al can be identified by infrared spectroscopy (FT-IR) in addition to the morphological observation by the scanning electron microscope. That is, by FT-IR, AlO found in the vicinity 3000~3700cm ^-1 ← → absorption spectrum due to stretching vibration of H, and 1000~1050cm are found in the vicinity of ^-1 Al ← → absorption spectrum due to stretching vibrations of OH, further 800 Absorption spectrum due to stretching vibration of OAl ← → O observed around ~ 600 cm ^-1
Any one or more are recognized, the Al of the present invention
The presence of a hydrated oxide film is confirmed. The thickness of the hydrated oxide film of Al is determined by observing a fracture surface of an Al alloy material (for example, a fracture surface of an Al alloy extruded material by bending at 180 °) by a scanning electron microscope at a magnification of 20,000 or more. be able to.

The hydrated oxide film of Al in the present invention means not only a film composed of pure Al hydrated oxide of Al ₂ O ₃ .XH ₂ O but also a hydrated oxide of Al. As long as it is mainly composed of a material film, it may be a mixture, that is, a material containing an impurity element which may possibly be mixed in or form an Al hydrated oxide film.

For example, a hydrated oxide of Al, Fe, Ni, Co,
A composite film with one or more metal compounds selected from Zn (metal salts of these metals, for example, sulfates, carbonates,
Oxides and hydroxides are contained in the composite film in an amount of at least 1.0 at% in terms of the metal element in terms of the metal element).
Alternatively, a composite or mixed film containing a metal compound such as Si or Mn, which is a metal compound that is lower in potential than the natural potential of Al, in a total amount and an average content in the film of 1 at% or more (these metal materials). Metal salts such as sulfates, carbonates, oxides, and hydroxides are contained in the composite coating in an amount of 1.0 at% or more in terms of the metal element in terms of the metal element). In these cases, the water resistance, the thread rust resistance, and the corrosion resistance such as overall corrosion are more excellent than the case of a film of a hydrated oxide of Al alone. However, the permissible amounts of these metal compounds or impurity elements are within a range that does not impair the properties such as corrosion resistance and adhesion of the hydrated oxide film of Al.

The thickness of the hydrated oxide film of Al such as boehmite impairs the lower limit of the film thickness necessary for preventing the elution of Al into the phosphate bath and other properties such as press formability and weldability. It is determined in terms of the upper limit of the film thickness that is not used. The optimum film thickness varies depending on the specific conditions, so it is generally difficult to determine the optimum film thickness. However, the optimum film thickness is preferably in the range of 100 to 8000 ° (angstrom).

The hydrated oxide film of Al is formed by forming a composite material of a steel material and an Al alloy material into a member for a transport machine, for example.
It may be performed after welding or welding, or after grinding the whole or part of the Al alloy material, or may be performed prior to these processes. Before the formation of the hydrated oxide film of Al, an appropriate pretreatment for degrease or washing the surface of the Al alloy material or the Al alloy of the molding material with an organic solvent, an alkaline solution or an acidic solution is performed. Among these pretreatments, when pretreatment with an aqueous nitric acid solution, the effect of improving the denseness of the hydrated oxide film of Al formed in a later step, suppressing the penetration of moisture, and further improving the water resistance. Have. The hydrated oxide film of Al may not necessarily be formed on the entire surface of the Al alloy material, but is provided at least on the surface portion of the Al alloy material where corrosion resistance after coating is a problem.

After this pretreatment, the surface of the Al alloy material is brought into direct contact with high-temperature water or steam,
Hydration reaction after providing Al oxide layer on the alloy material surface
A method of converting into a hydrated oxide film of Al, further, a method of adjusting the hydration amount by heating after providing these hydrated oxide films of Al, or as described in JP-A-05-70969 A method of contacting with a high-temperature neutral or weak alkaline bath (pure water, tap water, an aqueous solution of triethanolamine or ammonia) or the like is appropriately selected, and the two-layer method of the present invention is used.
Create a hydrated oxide film of Al. In the case of an extruded material, particularly, immediately after the hot extrusion of the Al alloy, it is water-cooled online by a shower, a spray, or the like, and is kept for a certain period of time in the presence of high-temperature steam or moisture to oxidize the generated Al. It is also possible to include a substantial amount of hydrated oxide of Al in the coating so as to have the same function as the layer of only hydrated oxide of Al.

Then, the Al alloy material provided with the hydrated oxide film of Al is subjected to a coating base treatment such as a phosphate treatment together with a steel material according to a current automobile coating line, and then subjected to cationic electrodeposition coating. And finish coating of middle coat and top coat. Note that phosphating with a steel material in the present invention means not only a case where a composite material of a steel material and an Al alloy material is simultaneously phosphating, but also a line where the steel material is processed under the same conditions as the steel material. This includes the case where only the Al alloy material is subjected to the phosphate treatment.

Next, the Al alloy to which the present invention is applied is from AA to
Al alloys of JIS 3000 series, 5000 series, 6000 series, and 7000 series component standards can be appropriately applied. Even Al alloys other than these standards satisfy the required characteristics of applications such as the transport aircraft of the present invention.
All alloys are subject to the present invention. For example, it is permissible to appropriately change the component composition in order to further improve the characteristics or add other characteristics. In this regard, depending on the change of the component range of the above elements, and more specific applications and required characteristics, in addition, appropriately include nonstandard elements such as Ni, V, Zr, Sc, Ag, and impurities such as H. Is acceptable.

The Al alloy material according to the present invention is produced as a sheet material or an extruded material by rolling, extruding, or the like according to a conventional method. That is, the molten aluminum alloy melt-adjusted within the component standard range is cast by appropriately selecting a normal melting casting method such as a continuous casting rolling method and a semi-continuous casting method (DC casting method). Next, the ingot is subjected to a homogenizing heat treatment, and hot rolling-cold rolling-tempering treatment (solution treatment and quenching treatment and age hardening treatment), extrusion processing-tempering treatment, hot forging-
By tempering treatment or a combination of these,
An Al alloy material having a desired cross-sectional shape such as a shaped material or a forged material is used.

Further, as for the steel material, ordinary low carbon steel, low alloy steel, high strength (high tensile) steel, and the like used in this kind of field can be basically used. Also, P, Cu,
Weather resistant steel containing Cr, Ni, etc. may be used. And the steel material can be manufactured by a normal steel plate manufacturing method. That is, the steel is produced by continuous casting or ingot-making method, and then subjected to cold rolling after hot working such as slab rolling, hot forging, and thick plate rolling, thereby producing a predetermined product sheet thickness. These processing conditions and conditions for cooling and heat treatment after the processing are appropriately determined according to requirements and specifications of mechanical properties such as strength of the steel material.

The Al alloy material and the steel material are formed, for example, as members or parts of a transport machine, respectively.
The steel member and the Al alloy member are made into a composite material by mechanical joining such as welding or bolting, and attached to the transport as a transport composite material member or composite part.

[0047]

[Embodiment 1] Next, an embodiment relating to improvement of phosphatability of a steel material in the composite material of the present invention will be described. According to the conventional method, an extruded material of an Al alloy having a composition of A to E shown in Table 1
A test piece of a composite material in which the (profile) and the plate were bolted to steel plates having the compositions of F and G shown in Table 2 was produced. And
The surface of the Al alloy material of these composite test pieces was
Under the conditions shown in (1), a hydrated oxide film of Al was formed. The method of forming the hydrated oxide film of Al is as follows: each test piece is immersed in 30% nitric acid at 40 ° C for 2 minutes, washed with water, and then 0.5% triethanolamine (T
EA) The hydrated oxide film of Al was formed by immersion in an aqueous solution for 10 to 50 seconds, and the thickness of the hydrated oxide film of Al was controlled by changing the temperature and immersion time of the TEA aqueous solution.

For comparison, as shown in Table 3, the comparative examples
For No. 7, a test piece of a composite material of an Al alloy material and a steel material provided with a zinc plating film on a surface thereof and provided with a zinc plating film was prepared. In addition, No. 8 has a normal Al oxide film
A test piece of a composite material of an Al alloy material and a steel material was prepared. Furthermore,
For No. 9, a test piece of a composite material of an Al alloy material and a steel material from which an oxide film was removed by alkali etching just before the zinc phosphate treatment was prepared.

(Conversion conditions) Test pieces of each composite material (test material)
The bent part (R part) of the molded material obtained by bending the U was sampled as a corrosion resistance test piece after coating, the lubricant on the surface was degreased completely, and then the phosphoric acid in both the invention and comparative examples was Colloidal dispersion of titanium colloidal liquid (Colloidal titanium solution: Nippon Parker Rising Co., Ltd., trade name PB
L3020 system, temperature 25 ° C, immersion 1 minute) treatment and zinc phosphate treatment (free fluorine ion content 50ppm, temperature 42 ° C,
(Immersion for 2 minutes). At this time, the elution amount of Al from the Al test piece was determined by measuring the total amount (mg) of Al in the zinc phosphate solution by the atomic absorption method and converting it to the unit area of the test piece (1 m ² ). Was.

The zinc phosphate adhesion of the steel material was measured, and the adhesion of 1.5 to 2.0 g / m ² or more was evaluated as ○, and 1.5 g to 1.0 /
The adhesion amount of m ² △, was evaluated as × adhesion amount of less than 1.0 / m ^2.
Furthermore, the form of the zinc phosphate film on the steel surface was observed with a 1000-fold SEM, and when granular phosphoferrite with excellent electrodeposition coatability was generated, ○, leaf-like hopitete with poor electrodeposition coatability was observed. Was evaluated as x when the occurrence of. Table 4 shows the results.

(Coating conditions) After performing these chemical conversion treatments, cationic electrodeposition coating was performed.
As a bake coating, more specifically, a polyester melamine-based coating film having a thickness of 30 μm was provided as an intermediate coating. 170 ° C for bake hardening (bake hardening)
X 20 minutes.

(Corrosion Resistance Test after Painting) Then, the coated test pieces of the invention examples and the comparative examples were all subjected to a yarn rust evaluation test under the same conditions. Table 4 also shows the results of these evaluations. The rust resistance evaluation test was performed by applying a 7 cm cross-cut to the surface of a painted test piece of Al alloy and steel, and then applying 3% HCl at 35 ° C.
After immersion in an aqueous solution for 2 minutes, then left in an atmosphere of constant temperature and humidity of 40 ° C and 85% RH for 200 hours, and then the maximum length L of thread rust generated on the surface (painted surface) of Al alloy material and steel material (The distance in the vertical direction from the cross cut) was measured. Then, when the maximum length L of the thread rust is L ≤ 1 mm, ○, 1 mm <L ≤
Those with 3 mm were evaluated as Δ, and those with L> 3 mm were evaluated as x.
At the same time, the coating was evaluated for blistering (peeling).
When the coating film did not bulge, it was evaluated as ○, and when the coating film did not bulge, it was evaluated as x.

As is clear from the results in Table 4, the Al of the present invention
Invention example No. 1 ~ with Al hydrated oxide film provided on the alloy material surface
No. 6 has a small amount of Al eluted in the zinc phosphate treatment and has excellent corrosion resistance such as yarn rust resistance after coating. The zinc phosphate film on the surface of the steel material adheres uniformly, and the amount of adhesion is large.

On the other hand, Comparative Example No. 7 which had been subjected to zinc substitution plating and Comparative Example No. 8 which was a normal Al alloy material having a natural oxide film, and alkali etching was performed immediately before zinc phosphate treatment. Comparative example No. 9 which is an example of the Al alloy material from which the oxide film was removed, the comparative example No. 7 has some corrosion resistance such as thread rust resistance after painting on the Al alloy material side, but In general, the elution amount of Al in zinc phosphate treatment is large,
The zinc phosphate coating on the steel surface is non-uniform and the amount of adhesion is small. For this reason, coating film swelling occurred on the steel material side including the Al alloy material (Comparative Examples Nos. 8 and 9).

Accordingly, the above facts support the critical significance and the preferred conditions of the present invention.

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

[Table 3]

[0059]

[Table 4]

[0060]

Embodiment 2 Next, an embodiment of the composite material of the present invention with respect to electric corrosion resistance will be described. As in Example 1, A shown in Table 1
Specimens of steel alloy and bolts made of JIS 5N02 (T6 treated) Al alloy were prepared on steel sheets having the compositions of F and G shown in Table 2 by using the Al alloy materials having the compositions of -E. Then, a hydrated oxide film of Al was previously formed on the surface of the Al alloy material and / or Al alloy bolt of these composite materials under the conditions shown in Table 5. The method of forming the hydrated oxide film of Al is as follows: each extruded material is immersed in 30% nitric acid at 40 ° C for 2 minutes, washed with water, and then heated to 70-90 ° C.
Immersion in 0.5% triethanolamine (TEA) aqueous solution for 10 to 50 seconds
The thickness of the hydrated oxide film of Al was controlled by changing the temperature and the immersion time of the TEA aqueous solution while forming the hydrated oxide film.

As for Invention Example No. 11 in Table 5, each test piece was immersed in 30% nitric acid at 40 ° C. for 2 minutes, washed with water, and then treated with a 90 ° C. aqueous solution containing 4 g / l of nickel acetate for 30 minutes. Then, a composite film with a hydrated oxide of Al containing 5.7 at% of nickel was provided on the surface of the Al alloy. Further, for Invention Example No. 16 in Table 5,
Each test piece was immersed in 30% nitric acid at 40 ° C for 2 minutes, washed with water, and treated with a 90 ° C aqueous solution containing 7 g / l of lithium carbonate for 20 minutes.
A composite film with a hydrated oxide of Al containing 11 at% of lithium was provided on the surface of the alloy.

(Identification of hydrated oxide film of Al) As in Example 1, the hydrated oxide film of Al was identified by the FT-IR method. As a result, at least one or more of the specific absorption spectra was recognized. As a result, the presence of a hydrated oxide film of Al was confirmed.

For comparison, as shown in Table 5,
Comparative Examples Nos. 13 and 20 were provided with a zinc plating film by zinc displacement plating on the surface of the Al alloy material (No. 20 also provided a zinc plating film on the Al alloy bolt), Nos. 14 and 21 In
Example of providing a natural oxide film of Al on the surface of Al alloy material (No. 21 is Al
(Al natural oxide film is also provided on alloy bolts.)
In Nos. 15 and 22, examples where the alkaline oxide film was once removed from the surface of the Al alloy material by alkali etching before the electrolytic corrosion test (N
o.22 also removed the natural oxide film on the surface of the aluminum alloy bolt).

(Electrolytic Corrosion Test) A salt water spray test was performed on a composite material having a structure in which steel and an Al alloy material came into contact with each other via bolts to easily cause electrolytic corrosion. The electrolytic corrosion of the bolts was evaluated. The electrolytic corrosion test conditions are JI
According to SZ 2371, 35 ° C for composite material kept at 35 ° C atmosphere
5% aqueous sodium chloride solution for 1000 hours, and after this test, corrosion products on the composite surface were removed by washing with nitric acid,
By measuring the mass change of the Al alloy material and the Al alloy bolt before and after the test, the weight loss (g / m ² ) due to corrosion was measured, and the electrolytic corrosion property was evaluated. In addition, in this test, although corrosion other than electrolytic corrosion naturally occurs in the Al alloy material and the bolts made of Al alloy, the total corrosion weight loss including these corrosions was evaluated as electrolytic corrosion. Table 6 shows the results.

As is clear from Tables 5 and 6, in the comparison between the steel bolts and the steel bolts, the invention examples Nos. 10 to 12 in which the Al hydrated oxide film was provided on the surface of the Al alloy material were the Al alloys. Comparative Example No. 13 with zinc displacement plating on the surface of the material, Comparative Example No. 14 with a natural oxide film on the surface of the Al alloy material, and alkali etching was performed immediately before zinc phosphate treatment to oxidize the surface of the Al alloy material Compared with Comparative Example No.15 from which the film was removed, the corrosion weight loss due to electrolytic corrosion and the number of corrosion points were smaller. By the way, usually
Corrosion test under similar conditions without combining with steel
5082, 606 (when electric corrosion does not occur and normal corrosion occurs)
Corrosion weight loss of Al alloy material, such as 1 is the level of 12~13 g / m ^2. Therefore, the corrosion weight loss of Invention Examples Nos. 10 to 12 was 14 to
From the level of 18 g / m ² , it can be seen that the hydrated oxide film of Al has the effect of suppressing electrolytic corrosion.

Further, in comparison between the bolts made of Al alloy and the bolts made of Al alloy, Invention Examples Nos. 16 and 17 in which Al hydrated oxide films were provided on both surfaces of the Al alloy material and the bolt, water was applied only to the bolt surface. Inventive Example No. 18 in which a hydrated oxide film was provided and Inventive Example No. 19 in which a hydrated oxide film was provided only on the surface of an Al alloy material, Comparative Example No. 20 in which a zinc displacement plating was applied to the surface of the Al alloy material , Compared to Comparative Example No. 21 having a natural oxide film on the surface of the Al alloy material, and Comparative Example No. 22 in which alkali etching was performed immediately before the zinc phosphate treatment to remove the oxide film on the surface of the Al alloy material. Less corrosion weight loss due to electrolytic corrosion. However, Invention Example No. 18 in which the hydrated oxide film was provided only on the bolt surface, and Invention Example No. 19 in which the hydrated oxide film was provided only on the surface of the Al alloy material, were Invention Examples No. Compared with 16 and 17, the corrosion resistance is inferior.

Therefore, these results support the fact that the hydrated oxide film of Al has an effect of suppressing electrolytic corrosion, and the significance of the critical and prescribed conditions defined in the present invention.

[0068]

[Table 5]

[0069]

[Table 6]

[0070]

According to the present invention, the elution of Al ions from the surface of the Al alloy material can be suppressed even if the composite material of the steel material and the Al alloy material is subjected to phosphate treatment. It is possible to provide a composite material that improves the corrosion resistance of the Al alloy material after coating as well as the processability. Further, the electrolytic corrosion resistance of the Al alloy material when used as a composite material of a steel material and an Al alloy material can be improved. Therefore, Al alloy car,
It is of great industrial value in that it can be used for a variety of transportation equipment such as vehicles and ships.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 B05D 3/10 B05D 7/14

Claims (5)

(57) [Claims] 1. A steel material and an aluminum alloy material are joined,
And a composite material to be coated after being subjected to a phosphate treatment, wherein a hydrated oxide film of aluminum is previously provided on the surface of the aluminum alloy material before the phosphate treatment. Composite material with excellent resistance and corrosion resistance. 2. The composite material according to claim 1, wherein the composite material is joined by an aluminum alloy fastener, and a hydrated oxide film of aluminum is provided on a surface of the fastener. Composite material with excellent phosphatability and electric corrosion resistance. 3. The composite material according to claim 1, wherein the composite material is joined by a steel fastener, and a hydrated oxide film of aluminum is provided on at least a surface portion of the aluminum alloy material in contact with the fastener. The composite material excellent in phosphatability and electric corrosion resistance described in 1. 4. The composite material according to claim 1, wherein the composite material is used for a transport machine. 5. The composite material according to claim 1, wherein the composite material is used for an automobile.