KR950013598B1 - Method for treating a surface of aluminum or aluminum alloy - Google Patents

Abstract

pretreating the surface of Al or Al alloy by dipping it in a mixing solution of NaOH and ZnO; arranging an electrolyte containing halide between an anodic plate and a cathodic plate facing each other in the electrolysis bath; and carrying out electrolytic corrosion of the surface of Al or Al alloy by supplying an electric power between the anodic plate and the cathodic plate. The method can coarsen the surface of Al or Al alloy.

Description

Surface treatment method of aluminum or aluminum alloy

1 is a cross-sectional view of the surface roughening treatment apparatus of aluminum or aluminum alloy according to the present invention.

2 is a cross-sectional view of the surface roughening treatment apparatus of aluminum or aluminum alloy according to the present invention that can adjust the size of the positive electrode plate by attaching a shielding frame to the positive electrode plate.

Figure 3a is a cross-sectional view of the surface roughening apparatus of the aluminum or aluminum alloy according to the present invention that can adjust the size of the positive electrode plate by attaching a shielding frame and an auxiliary negative electrode to the positive electrode plate.

Front view of the shielding frame and the auxiliary cathode of FIG. 3b or 3a.

4 is a graph showing the surface roughness of an aluminum substrate measured using a surface roughness shape measuring instrument before the roughening treatment according to the present invention.

5 to 10 are graphs showing the surface roughness of the aluminum substrate measured using the surface roughness shape measuring instrument after electrolytic corrosion in Examples 1 to 6, respectively, according to the present invention (an abbreviation indicated at the bottom of the graph is defined as follows). :)

RMS: Root Mean Square Roughness

Rt: Maximum Height of Roughness Profile

Rmax.D: Maximum Height of Roughness Profile: DIN

Rz.D: Ten Point Height of Irregularities: DIN

MAG. Magnification (the magnification of measurement and recording)

CUT OFF: Refers to the reference length selected by the frequency filter when directly measuring the roughness average using a tactile electric meter, usually given in mm.

TRAVERSING LENGTH: Designate length and cut off value (measuring length is 5 times cut off value).

* Explanation of symbols for main parts of the drawings

1: negative electrode plate 2: positive electrode plate

3: Mule to be processed 4: Electrolyzer

5: electrolytic solution 6: shielding frame

7: auxiliary cathode

The present invention relates to a method of surface roughening treatment of aluminum or aluminum alloy. More specifically, the present invention uniformly roughens the surface of the aluminum or aluminum alloy by using an electrolytic corrosion method in order to strengthen the adhesion between the aluminum substrate and the synthetic resin when the synthetic resin or paint is coated on the surface of the aluminum substrate. The present invention relates to a surface roughening treatment method of aluminum or aluminum alloy.

When coating synthetic resin, paint, or the like on aluminum or an aluminum alloy, the surface of the substrate must be roughened in order to strengthen the adhesion with the synthetic resin or the like. As the roughening method, a mechanical method using sand blast, etc., a chemical method such as an acid or an alkali, and an electrochemical method are used.

According to the mechanical method, since roughening is inadequate and the adhesive force of a base material and synthetic resin etc. becomes weak, there exists a fault which a coating film peels easily. In the chemical method, it is difficult to control the concentration, temperature, time, etc. of the treatment liquid, so that it is difficult to maintain a uniform roughening degree.

On the other hand, in the conventional electrochemical treatment method, since the electrical contacts are directly held on the aluminum substrate itself so that the aluminum substrate to be treated is an anode, and the metal material is used as the cathode to conduct electricity in the electrolyte, traces of the contacts remain on the workpiece. Also, it is easy to cause poor contact. In addition, in the case of processing a plurality of discontinuous workpieces, the automatic continuous processing cannot be performed because the contacts must be held at the individual workpieces. In some cases, only one surface of the aluminum substrate must be covered with a resin or the like depending on the application, and at this time, the roughening treatment should be performed only on one surface of the substrate. However, in the case of using the conventional electrochemical roughening method, there is a problem that the opposite surface must be completely covered with an insulator in order to prevent the opposite surface of the surface to be roughened from being roughened together by energization. In addition, in order to maintain the uniformity of roughening, a strict parallelism is required between the negative electrode plate and the workpiece, so that the shape of the workpiece must be perfectly flat, and if the complete parallelism between the workpiece and the negative electrode plate is not maintained, There are also problems in equipment operation such as spots on the degree of cotton.

In order to solve these problems, Korean Utility Model Publication No. 82-1142 discloses an improved electrolytic corrosion apparatus for electrochemically roughening only the entire surface or a specific range of one side of an aluminum or aluminum alloy material. According to this utility model notification, an aqueous solution of a halide is used as an electrolytic solution, and a workpiece is fixed to an electrolytic corrosion apparatus provided with an anode and a cathode, such as a metal or a carbon, separately from the workpiece, and the workpiece is fixed. It is described that fine irregularities can be formed only on the surface facing the negative electrode of the object by arranging the frame facing the negative electrode and energizing between the positive electrode and the negative electrode.

On the other hand, since aluminum is a highly active metal, it is easily oxidized in air or in water to form a stable oxide film on the surface. This natural oxide film serves to prevent corrosion in aqueous chloride solution. Therefore, when the aluminum substrate on which the oxide film is formed is corroded by immersing it in a chloride solution as it is, the weakest portion of the oxide film does not play a role in preventing corrosion, and as a result, local selective corrosion occurs. Therefore, uniform roughening suitable for resin coating cannot be achieved.

However, none of the above-mentioned utility model publications mentions the pretreatment of a treated aluminum substrate related to the formation of an aluminum oxide film, and also does not mention the correlation between the size of the treated surface of the treated aluminum substrate and the size of the positive electrode plate. The control of the distance between the treated aluminum substrate and the positive electrode is not described.

The present inventors have conducted research to improve the problem of the roughening method of the surface of the aluminum substrate by the conventional electrolytic corrosion method, as a result, to achieve a uniform surface roughening even if a natural oxide film on the surface of the aluminum substrate, Furthermore, by adjusting the size of the aluminum substrate to be processed, the size of the positive electrode plate and the distance therebetween, the present invention has developed a surface treatment method capable of uniform roughening to the end of the aluminum substrate to be processed without using an insulating frame. To complete.

It is an object of the present invention to provide an improved method for surface treatment of aluminum or aluminum alloy that can uniformly roughen only one side of the aluminum substrate to be treated by the electrolytic corrosion method even if an oxide film is present on the surface of the aluminum substrate.

Another object of the present invention is to adjust the size of the positive electrode plate according to the size of the aluminum substrate to be treated, the surface treatment method of the aluminum or aluminum alloy that can be roughened uniformly to the end of the aluminum substrate without using a fixing frame having an opening To provide.

Still another object of the present invention is to provide a surface treatment method of aluminum or an aluminum alloy that can be roughened uniformly to the end of the aluminum substrate by adjusting the distance between the aluminum substrate to be treated and the anode plate.

It is still another object of the present invention to provide a method for surface treatment of aluminum or aluminum alloy that can be uniformly roughened to the end of an aluminum substrate by adjusting the size of the anode plate by attaching a shielding frame and optionally an auxiliary electrode to the anode plate.

These and other objects and advantages of the present invention will become apparent from the following description.

According to the present invention, a step of pretreating the surface of aluminum or an aluminum alloy by immersing the treated aluminum or aluminum alloy in a mixed solution of sodium hydroxide and zinc oxide, wherein the pretreated aluminum or aluminum alloy is an aqueous solution of a halide as an electrolytic solution Electrochemical corrosion of the surface of the aluminum or aluminum alloy to be treated by disposing between two electrode plates in an electrolytic cell installed so that the positive electrode plate and the negative electrode plate face each other, and energizing between the two electrode plates on which the pretreated aluminum or aluminum alloy is disposed. A surface roughening treatment method of aluminum or an aluminum alloy is provided.

Aluminum is a highly active metal and is easily oxidized to form a stable oxide film on its surface. This oxide film prevents uniform roughening and should be removed. As a conventional method for removing this, mechanical methods such as sand blast, hairline, Scott brush, and the like have been used. However, when such a mechanical method is used, the aluminum substrate causes corrosion on the entire surface, resulting in a weak adhesive force with the resin, and a rise in labor costs, which has been a factor in the cost increase. In addition, even if the oxide film is removed by a mechanical method, the oxide film is re-formed during the surface treatment in the air or in the water. Therefore, uniform roughening cannot be expected without using strong acid or strong alkali chemicals. When used, there is a drawback that the natural corrosion occurs and the adhesion to the resin is weak.

According to the present invention, however, the oxide film formed on the surface is first removed by immersing the aluminum or aluminum alloy to be roughened in a mixed solution of sodium hydroxide and zinc oxide, and also on the surface of the aluminum to be treated in a subsequent electrolytic corrosion process. In order to prevent the oxide film from being reformed, a pretreatment process of coating zinc on the surface of the aluminum substrate from which the oxide film has been removed is performed. In this pretreatment process, the oxide film formed on the surface of the aluminum substrate to be dissolved and removed by sodium hydroxide, and zinc is deposited on the surface from which the oxide film is removed, thereby causing the surface of the aluminum substrate to be treated in a subsequent electrolytic corrosion step. By preventing the oxide film from being reformed, the surface of the aluminum substrate to be roughened can be maintained without the oxide film.

The mixed solution of sodium hydroxide and zinc oxide used in this pretreatment may contain 10 to 200 g / 1 of sodium hydroxide and 2 to 50 g / 1 of zinc oxide (ZnO). If the sodium hydroxide concentration is 200g / 1 or more, the washability is poor, and at 10g / 1 or less, the dissolution reaction to the aluminum oxide film is weak and the deposition of zinc becomes uneven, so the concentration of sodium hydroxide is appropriately 10 to 200g / 1. In addition, in the mixed solution of sodium hydroxide and zinc oxide, the zinc oxide concentration is 2g / 1 or less, so that the deposition of zinc is nonuniform, and the adhesion strength of zinc is weakened when the zinc oxide concentration is 50g / 1 or more, so the preferable zinc oxide concentration is 2-50g /. 1

The temperature of the pretreatment solution and the pretreatment time will vary depending on the concentration of the pretreatment solution, the degree to be roughened, and the size of the aluminum to be treated, but is generally performed at a temperature of 10 to 35 ° C. for 10 to 120 seconds. If the temperature of the pretreatment solution is 35 ° C. or higher, dissolution of aluminum having high activity may occur, and zinc is not uniform at 10 ° C. or lower, which is not preferable.

The aluminum substrate having zinc deposited on the surface obtained by the pretreatment as described above is then disposed between the two electrode plates of the electrolytic cell, which contain a halide solution as the electrolytic solution and are provided such that the positive electrode plate and the negative electrode plate face each other.

As the electrolytic solution used in the method of the present invention, an aqueous solution of a halide commonly used, for example sodium chloride, ammonium chloride and potassium chloride, is used at a concentration of 10 to 200 g / 1.

In the surface roughening apparatus of aluminum or aluminum alloy which concerns on this invention, metal, such as lead, aluminum, stainless steel, or graphite is used as an anode and a cathode. The two pole plates are disposed opposite each other, and the pretreated aluminum or aluminum alloy is disposed to face the two pole plates so that only the surface facing the cathode is electrochemically corroded and roughened.

According to the present invention, the electrolytic corrosion state of the aluminum to be treated can be adjusted by changing the size of the anode plate and the distance between the anode plate and the aluminum substrate to be treated. The area of the anode used in the surface roughening apparatus of aluminum or aluminum alloy according to the present invention should be smaller than the area of the aluminum substrate to be roughened. This is because if the area of the anode is larger than that of the aluminum substrate to be treated, the end portion of the aluminum substrate to be treated is negatively charged and does not corrode.

In the roughening apparatus according to the present invention, in order to make the area of the anode smaller than that of the aluminum substrate to be treated, an anode smaller than the aluminum to be treated is initially provided, or the anode is larger than the aluminum substrate to be treated. In this case, a method of offsetting the positive electrode may be adopted by attaching a shielding frame to the positive electrode or by adding an auxiliary negative electrode to the positive electrode with the shielding frame.

In the conventional roughening method using the electrolytic corrosion method, the aluminum substrate to be treated can be uniformly electrolytically corroded to the end of the aluminum substrate to be treated only when the aluminum substrate is fixed to the insulator frame. That is, when there is no insulated frame having one or more openings, there is a problem that the end of the corrosion surface of the object to be treated is difficult to be positively charged (+) and thus remains uncorroded. In this case, the end surface of the aluminum substrate to be treated is corroded, but the corroded opposite surface has a drawback in that corrosion occurs due to the opening of the insulating frame, thereby deteriorating the appearance. However, the present invention can uniformly corrode only one side of the workpiece with high efficiency without the insulation frame causing the above problems.

In addition, according to another embodiment of the present invention, an anode having an area larger than that of the aluminum substrate to be treated may be used. In this case, the size of the positive electrode plate is made smaller than the size of the surface to be treated of the aluminum substrate to be treated by attaching a shielding frame made of Bakelite or the like to the positive electrode plate to shield the electric field. I can regulate it. Therefore, when a shielding frame having an opening of which size is freely adjusted is attached to the positive electrode plate and subjected to electrolytic corrosion, the end of the aluminum base is not corroded as in the case where the size of the positive electrode plate is smaller than the size of the surface to be treated. Only one surface can be roughened uniformly without work.

Furthermore, if the auxiliary cathode having an opening having the same size as the opening of the shielding frame is freely adjusted to the shielding frame, the positive charge is canceled by the auxiliary cathode, thereby reducing the size of the anode. .

Subsequently, when the DC power is supplied and energized between the two electrode plates of the electrolytic cell, electrolytic corrosion occurs only on one side of the to-be-processed aluminum substrate facing the cathode, so that only one surface of the aluminum substrate is roughened uniformly.

In the method of the present invention, the electrolytic corrosion step of the pretreated aluminum surface is performed for 1 to 5 minutes at a voltage of 5 to 25V and a current density of 10 to 60 A / dm ² at an electrolyte solution temperature of 20 to 60 ° C.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 shows an apparatus for roughening the surface of aluminum or an aluminum alloy according to the present invention, in which an anode plate 1 and an anode plate 2 made of a metal such as lead, aluminum, stainless steel, etc. are disposed opposite to each other in an electrolytic cell 4. And an electrolytic solution 5 made of an aqueous solution of a halide such as sodium chloride, ammonium chloride or potassium chloride is filled. Further, an object to be processed 3 of aluminum or aluminum alloy is disposed between the two electrode plates so as to face the positive electrode plate. When the direct current is energized between the positive electrode plates 1 and 2 in the state arranged in this way, the surface of the workpiece 3 facing the negative electrode plate is positively charged and is electrolytically corroded by C1 ⁻ ions. The surface facing the positive electrode plate is negatively charged and does not corrode.

Unlike the prior art, the method of the present invention can adjust the portion to be positively charged by making the area of the positive electrode plate smaller than that of the object, so that even the end portion of the object can be uniformly corroded. However, if the positive electrode plate is larger than the workpiece, the end of the workpiece is not charged positively and does not corrode.

2 is another embodiment of the roughening apparatus for the aluminum surface according to the present invention, which can shield an electric field when the area of the positive electrode plate 2 is larger than the area of the object 3 to be treated with bakelite. By using the shield frame 6, etc., the exposed part of the positive electrode plate can be adjusted to be smaller than the area of the object to be processed. Therefore, when the shielding frame having an opening smaller than the size of the surface to be treated of the aluminum substrate to be treated is mounted on the positive electrode plate and subjected to electrolytic corrosion, even if the size of the positive electrode plate is larger than the size of the surface to be treated aluminum It is possible to roughen evenly to the edge part of to-be-processed aluminum.

3a shows another embodiment of an apparatus for roughing an aluminum surface according to the invention, in which an auxiliary cathode 7 is additionally attached to the anode of the electrolytic corrosion apparatus according to the invention shown in FIG. 3B is a front view of the auxiliary cathode 7, the center of which is provided with an opening having the same size as that of the opening of the shielding frame which can be freely adjusted in size. As a result, since the size of the anode can be selected to an appropriate size according to the electrolytic apparatus that performs electrolytic corrosion, its structure, and the size of the aluminum substrate to be treated, the limitation on the size of the anode is not important. In the absence of an auxiliary cathode, the size of the anode should always be smaller than the size of the workpiece, but not necessarily a small extent. If there is an auxiliary cathode, the size of the anode should be equal to or smaller than the size of the workpiece, but not limited to a small extent.

According to the present invention, not only the anode size but also the distance between the anode and the workpiece is used to obtain efficient electrolytic corrosion results. Even if the size of the anode is large, if the distance between the anode and the workpiece is far, the positive charge of the anode is reduced by that much. If the size of the anode is small, the distance between the anode and the workpiece should be narrowed. do. For example, as shown in Example 8, 430 When roughening an aluminum substrate having a size of mm x 1.2 mm, the size of the anode is 250 Even if it is as small as about mm, if the distance between the anode and the object is about 120 mm, the object cannot be uniformly electrolytically corroded. Preferably, the size of the anode is 250 mm to 430 mm and a uniform electrolytic corrosion of the aluminum to be treated can be obtained when the distance between the anode and the object is 80 to 20 mm.

When electrolytic corrosion of aluminum or an aluminum alloy is performed in accordance with the indirect energizing method of the present invention as described above, it is not necessary to hold an electrical contact on an individual to-be-processed aluminum substrate or to coat the opposite surface with an insulator beforehand. Even if the substrate is not shielded by an insulating frame having an opening, it can be uniformly electrolytically corroded to the ends. In addition, according to another aspect of the present invention, the trace of corrosion on the opposite side of the corrosion, which is a drawback of the conventional method of shielding a workpiece with an opening having an opening and electrolytic corrosion to the end, is also eliminated, and continuous processing is possible.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

350 in size 430 mm x 4 mm, with a purity of 99% or more, used as the anode plate, and the size is 430 An aluminum plate of mm x 1.2 mm was deposited in a mixed solution at 25 ° C. containing 10 g / 1 of sodium hydroxide and 2 g / 1 of zinc oxide for 30 seconds to deposit zinc on the aluminum to be treated. Subsequently, the zinc-deposited aluminum to be treated was washed with water, disposed in parallel between the two electrode plates, and subjected to electrolytic treatment in a 100 g / 1 ammonium chloride aqueous solution with a direct current flowing between the cathode and the anode. The temperature during the electrolytic treatment was 40 ° C., the current density was 30 A / dm ² , and the treatment time was 200 seconds. As a result, one side was not roughened at all, and the other side was roughened entirely. The roughening degree of the surface of the aluminum base material was measured using the surface roughness measuring instrument of Surfcom 110A by Tokyo Precision. The results are shown in Table 1.

Example 2

Anode plate size 300 As a result of the electrolytic treatment under the same conditions as in Example 1 except that it was mm x 4 mm, the aluminum to be treated was roughly roughened as in Example 1. The roughening degree was measured as in Example 1 and shown in Table 1.

Example 3

The aluminum plate to be treated was immersed in a mixed solution at 15 ° C. containing 100 g / 1 of sodium hydroxide and 20 g of zinc oxide for 1 minute to deposit zinc, followed by electrolytic treatment under the same conditions as in Example 1. Aluminum was roughened uniformly as in Example 1. The roughening degree was measured as in Example 1 and shown in Table 1.

Example 4

Except that the deposition time of zinc was only 10 seconds, zinc was deposited under the same conditions as in Example 3 and electrolytically treated under the same conditions as in Example 1, whereby the aluminum to be treated was roughly roughened as in Example 1. . The roughening degree was measured as in Example 1 and shown in Table 1.

Example 5

As a result of electrolytic treatment under the same conditions as in Example 1 except that the current density was set to 20 A / dm ² , the aluminum to be treated was roughly roughened as in Example 1. The roughening degree was measured as in Example 1 and shown in Table 1.

Example 6

Set the positive plate to 500mm x 500mm, 350 As a result of pretreatment under the same conditions as in Example 1, except that the shielding frame having an opening having a size of mm was attached to the positive electrode plate, the aluminum to be treated was roughly roughened as in Example 1. The roughening degree was measured as in Example 1 and shown in Table 1 below.

TABLE 1

In the table, Ra is an abbreviation for centerline roughness average.

Example 7

250 each for the size of the bipolar plate mm, 300 mm, 350 mm and 400 Except for changing to mm, the electrolytic treatment was carried out under the same conditions as in Example 1 to obtain roughening results as shown in Table 2 below.

[Table 2] Electrolytic Corrosion Status with Anode Size Change

As the size of the anode increased when the distance between the anode and the workpiece was constant, a portion of the circular plate as the workpiece was not etched. This is because the area charged negatively increases as the size of the anode increases.

Anode size 250-350 under the above conditions mm is suitable, 400 In the case of mm, since the anode was too large, the front and end portions of the workpiece were not partially etched.

Example 8

430 size of bipolar plate respectively mm, 400 mm, 250 mm and 250 The electrolytic treatment was carried out under the same conditions as in Example 1 except that the distance between the positive electrode and the workpiece was set to 20, 40, 80, and 120 mm, and the roughening results as shown in Table 3 below were obtained. .

[Table 3] Electrolytic Corrosion State with Variation of Anode Size and Distance between Anode and the Workpiece

Anode size is 250 mm to 430 mm and the workpiece can be uniformly etched when the distance between the anode and the workpiece is 80 to 20 mm.

Even if the anode plate is small (250 mm) If the distance between the anode and the workpiece is far (120 mm), the workpiece cannot be etched uniformly.

In addition, in Example 7, the anode size was 400 In the case of mm, the front and end of the workpiece were partially etched away. This occurs because the size of the anode and the distance between the anode and the workpiece are inadequate and can be etched uniformly by adjusting the distance.

Claims (6)

Immersing aluminum or an aluminum alloy in a mixed solution of sodium hydroxide and zinc oxide to pretreat the surface of the aluminum or aluminum alloy to be treated, wherein the pretreated aluminum or aluminum alloy contains a halide as an electrolyte and contains a positive electrode plate and a negative electrode plate. Electrolytic corrosion of the surface of the aluminum or aluminum alloy to be roughened by energizing between two electrode plates in the electrolytic cell disposed so as to face each other, the surface treatment method of aluminum or aluminum alloy. The method of claim 1, wherein the pretreatment step of the aluminum or aluminum alloy to be treated is immersed at a temperature of 10 to 35 ° C. in a mixed solution of sodium hydroxide at a concentration of 10 to 200 g / 1 and zinc oxide at a concentration of 2 to 50 g / 1. Surface treatment method is performed for 10 to 120 seconds. The surface treatment method according to claim 1, wherein the positive electrode plate has an area smaller than the area to be treated of the aluminum or aluminum alloy to be treated. The surface treatment method according to claim 1, wherein the size of the positive electrode plate can be adjusted by a shielding frame having an opening smaller than the size of the surface to be treated of the aluminum or aluminum alloy to be treated. 5. The surface treatment method according to claim 4, wherein the positive electrode plate can be adjusted in size by having an auxiliary negative electrode having an opening additionally mounted on the shielding frame. The surface treatment method according to claim 1, wherein the halide used as the electrolyte is selected from the group consisting of sodium chloride, ammonium chloride and potassium chloride, and the positive and negative plates are selected from the group consisting of lead, aluminum, stainless steel and graphite. .