JP4124761B2 - Mg or Mg alloy casing and manufacturing method thereof - Google Patents

Description

  The present invention relates to a Mg or Mg alloy casing for easily forming a chemical conversion treatment film on the surface of a molded body made of Mg or Mg alloy and improving the yield of coating, and a method for manufacturing the same.

  In recent years, mobile devices such as notebook computers and PDAs have been increasingly carried and used outdoors. Along with this, there is a demand for smaller, lighter and thinner devices, and it is necessary to reduce the thickness of the housing, which accounts for 30% of the total mass of the device. However, when the thickness is reduced, it has become difficult to maintain sufficient strength with the resin casing. Furthermore, the amount of heat generated by the MPU of the notebook personal computer is increasing. In the future, the amount of heat generated during AC drive is scheduled to be 13 to 16 W, and it is an urgent task to develop a casing with high cooling performance.

  As a solution to this problem, light metals such as Al, Mg, or Mg alloys having high specific strength, low specific gravity, and high thermal conductivity are attracting attention as housing materials. In particular, Mg or Mg alloy has a specific gravity as light as about 70% of that of Al, and is excellent in recyclability. As Mg or Mg alloy, Mg-Al-Zn system, Mg-Al-Mn system, Mg or Mg-Al-Si system, Mg-Al-rare earth element (RE) system, etc. have already been put into practical use. Molding is performed by means such as die casting, thixo molding, sheet metal processing, and the like. Subsequently, the molded product is subjected to a chemical conversion treatment, and then the chemical conversion treatment product is subjected to a coating treatment to produce a product. In the above, die casting is a method in which molten metal is pressurized and poured into a mold and cast, and thixomolding is a mold at a temperature of about 250 ° C. from an extruder at about 600 ° C. in a semi-molten or molten state. Refers to the method of extrusion molding.

The chemical conversion treatment is a treatment for forming a chemical conversion coating having an anticorrosive function on the surface of Mg or Mg alloy, such as a chromic acid solution containing a hexavalent chromium solution as a main component or a non-chromic acid solution containing no hexavalent chromium. By immersing the Mg alloy, a chromium chromate complex salt coating (generally xCrO ₃ · yCr ₂ O ₃ · 2H ₂ O or Cr (OH) ₂ · HCrO ₄ · 2H ₂ O Etc.). After this chemical conversion treatment, a coating treatment is performed. The following patent documents 1 and 2 are proposed as a chemical conversion treatment method.

  There are the following problems when manufacturing products using Mg or Mg alloys as raw materials. A molded product obtained by molding means such as die casting or thixo mold has burrs. In order to remove the burrs, at present, the burrs are punched out by press, removed by machining such as cutting, or removed by hand finishing, but both methods are troublesome work. . There is also a method of removing burrs by shot blasting in which abrasive grains are blown with air on molded products. However, Mg or Mg alloys and abrasive grains are easily generated and scattered, resulting in poor workability and dust explosion. There is a problem that the risk of is high.

  Moreover, when performing the said chemical conversion treatment, pre-processing is required. In the usual chemical conversion treatment step, the molded product is degreased and then further washed with an acid, followed by etching to remove the mold release agent used at the time of molding from the molded product, The surface of the molded product is subjected to a surface conditioning treatment so that a chromium chromate complex film can be easily formed (the above treatment is a pretreatment for the chemical conversion treatment), and then the molding is performed. A chemical conversion treatment is performed by immersing the processed product in the chromic acid solution, non-chromic acid solution, or the like, and then the chemical conversion treatment product is washed with water and further dried at around 70 ° C. to cure the chemical conversion film. In this way, the pretreatment of the chemical conversion treatment has to be carried out in several steps such as degreasing treatment, cleaning treatment and etching treatment surface adjustment treatment, which is cumbersome, complicated processing equipment, and high processing cost. Become.

Molded products manufactured by molding such as die casting or thixo mold have molding defects such as shrinkage, voids, and hot water flow marks. At the time of inspecting this molding defect (shrinkage, void, flow, etc.), in order to make the molded product easier to see, partly buffed manually and then visually inspected. Since it is carried out by work, there are problems that the inspection is troublesome and that dust is generated when buffing. As means for performing surface adjustment such as buffing, Patent Document 3 that performs wet blasting has been proposed. Further, Patent Document 4 has been proposed as a method of continuously performing the wet blasting as a pretreatment for chemical conversion treatment.
JP-A-11-131255 JP 2000-96255 A JP 2003-284457 A JP 2000-263442 A

  Each of the conventional techniques is a method using wet blasting as a pretreatment for chemical conversion treatment, and the number of steps is the same as the treatment using conventional chemical treatment, and the effect of improving the cost and the like is small. Further, defective molding requires correction by putty coating before chemical conversion treatment, which causes a decrease in yield and an increase in cost.

  The present invention provides a Mg or Mg alloy casing capable of easily forming a chemical conversion treatment film on the surface of a molded body made of Mg alloy, reducing correction by putty coating, improving coating yield, and reducing costs. A manufacturing method is provided.

Mg or Mg alloy housing of the present invention, by wet blasting using a solution obtained by adding and the Mg or Mg alloy casing surface a chemical conversion treatment liquid abrasive, calcium phosphate Mg or Mg alloy casing surface -A chemical film formed of a composite film of magnesium phosphate is formed.

The manufacturing method of the Mg or Mg alloy casing of the present invention is a surface treatment method of Mg or Mg alloy , and a chemical conversion treatment liquid containing calcium ions, manganese ions and phosphate ions on the surface of Mg or Mg alloy, and an abrasive. By performing wet blasting using a solution to which is added, an uneven film formed by blasting and a composite film composed of a composite coating of calcium phosphate-magnesium phosphate are simultaneously formed on the surface of the Mg or Mg alloy casing.

  According to the present invention, the surface of the Mg or Mg alloy casing is wet blasted with the chemical conversion solution and the liquid added with the abrasive, and the surface of the Mg or Mg alloy casing is unevenly formed and the film is formed simultaneously. Thus, it is possible to form a chemical conversion treatment film, reduce the repair by putty coating, reduce the yield, and improve the cost. In other words, when a mixture of the chemical conversion treatment liquid and the abrasive is sprayed onto the surface of the Mg or Mg alloy casing by wet blasting, the surface is scraped off by the abrasive and at the same time the Mg and the chemical conversion treatment liquid have an appropriate film thickness due to the reaction. A dense calcium phosphate-magnesium phosphate composite coating is produced. Therefore, calcium and phosphorus are formed on the surface of Mg or Mg alloy without forming an oxide or hydroxide film that degrades the bare corrosion resistance, rust prevention, coating film adhesion and coating film corrosion resistance. Improvement of corrosion resistance, and manganese can form a composite coating of calcium phosphate-magnesium phosphate that contributes to improvement of coating film adhesion. Furthermore, there is no shrinkage, voids, flow, etc. on the surface of the chemical product, so there is no need to correct putty before painting, and cost can be reduced.

  As a result of diligent research to solve the above-mentioned problems, the inventors of the present invention have made Mg or Mg alloy a chemical conversion treatment and wet blasting as a pretreatment for, for example, rust prevention treatment and coating of a casing made of Mg or Mg alloy. We found a way to solve the above problem by processing at the same time. Here, the wet blast treatment refers to a treatment in which a liquid and an abrasive are mixed and sprayed at a pressure in the range of 0.1 to 0.3 MPa.

  The chemical conversion liquid used in the present invention preferably contains calcium ions, manganese ions and phosphate ions, and is further wet-blasted using a liquid in which an aqueous liquid containing an oxidation accelerator and an abrasive such as alumina are added. Is preferred. In the wet blast treatment, the surface polishing of the casing and the chemical conversion coating are simultaneously performed, so that the formed coating is also polished. However, a sufficient coating can be obtained by satisfying the above conditions.

  As the abrasive, it is preferable to use at least one particle selected from alumina, zirconium, glass and resin. As the resin, melamine resin, urea resin, polyester resin, phenol resin, epoxy resin, urethane resin and the like can be used. The average particle diameter of the abrasive particles is preferably in the range of 10 to 300 μm.

  As a calcium ion source used for the chemical conversion treatment liquid to be sprayed, one or more of calcium nitrate, calcium nitrite, calcium thiosulfate, calcium dihydrogen phosphate and the like can be blended. Moreover, 1 type, or 2 or more types, such as manganese carbonate, manganese nitrate, manganese hydrogen phosphate, manganese biphosphate, manganese borofluoride, can be mix | blended as a manganese ion source. Moreover, 1 type, or 2 or more types, such as orthophosphoric acid, condensed phosphoric acid, phosphorous acid, hypophosphorous acid, can be mix | blended as a phosphate ion source.

  Moreover, sodium chlorate, sodium hypochlorite, etc. can be used as an oxidation accelerator. This oxidation accelerator can increase the reactivity between Mg or Mg alloy and each of the above component ions during the chemical conversion treatment, and more conveniently form a chemical conversion film having good bare corrosion resistance and the like. Moreover, the preferable compounding quantity of this oxidation accelerator is a ratio of the range of 0.02-2g / L, in order to obtain the chemical conversion film of said performance stably.

In the present invention, when the liquid mixture of the chemical conversion treatment liquid and the abrasive is sprayed onto the surface of the Mg or Mg alloy by wet blasting, the surface is scraped by the abrasive and at the same time, the Mg or Mg and the chemical conversion treatment liquid are appropriately reacted. A dense composite film of calcium phosphate-manganese phosphate with a film thickness is formed. Therefore, a composite coating of calcium phosphate-manganese phosphate can be formed without forming an oxide or hydroxide film on the Mg or Mg surface. Adhesion of the composite coating film formed by the chemical conversion treatment, Ca weight at 5 mg / m ² or more 50 mg / m ² or less, Mn weight at 3 mg / m ² or more 25 mg / m ² or less, phosphorus weight 30 mg / m ² or more It is preferably 100 mg / m ² or less.

  Moreover, it is preferable to make the ratio of a chemical conversion liquid and an abrasives into the range of 70-90 mass% of chemical conversion liquid, and 10-30 mass% of abrasives.

  By forming a chemical conversion coating on the surface of Mg or Mg alloy so as to contain the above-mentioned predetermined amounts of calcium, manganese and phosphorus, a chemical conversion that maintains a certain level of bare corrosion resistance, rust prevention, coating adhesion and coating corrosion resistance A film is obtained. In particular, calcium and phosphorus are considered to contribute to improving the bare corrosion resistance of the chemical conversion film, and manganese contributes to improving the adhesion of the coating film.

  Further, by polishing the Mg or Mg surface with an abrasive, there is no shrinkage, voids, flow, etc. on the surface of the Mg or Mg housing manufactured product, and there is no need for putty correction before painting, and cost reduction is possible. . Due to the polishing action of the abrasive contained in the wet blast liquid, the surface roughness of the Mg or Mg alloy casing is preferably in the range of 0.5 μm to 100 μm in terms of 10-point average surface roughness.

  Subsequent to the above treatment step, it is preferable to wash with water and dry. Furthermore, after wet blasting and rinsing, the coating film thickness is reduced by shower spraying an aqueous solution containing calcium ions, manganese ions and phosphate ions equivalent to the chemical conversion treatment solution used during wet blasting, and further containing an oxidation accelerator. The thickness can be increased, and the corrosion resistance is improved.

  Thereafter, a coating process can be performed. As this coating treatment, a paint such as an epoxy resin can be undercoated by a method such as spray coating or electrodeposition coating, and a paint such as a melamine resin can be further applied thereon. In addition, it is possible to electrostatically paint powder coatings made of various resins.

  Hereinafter, the present invention will be described more specifically based on examples and comparative examples.

(Example 1)
A notebook PC case (width: 329 mm, height: 274 mm, height: 2 mm) manufactured by Chixso molding of Mg or Mg alloy of ASTM AZ91D was used as a processing target member. In thixomolding, Mg or Mg alloy was extruded from an extruder at about 600 ° C. into a mold at about 250 ° C. in a semi-molten or molten state. The surface treatment process is shown in FIG.

  80% by mass of an aqueous solution containing “Grandafiner MC1000” (product name, manufactured by Million Chemical Co., Ltd., phosphoric acid 15 to 25% by mass, manganese compound 10 to 15% by mass, calcium compound 10 to 20% by mass) as a chemical conversion treatment liquid; As an abrasive, 20% by mass of alumina having an average particle diameter of 40 μm (Mako Co., Ltd., Macorundum A # 320) was mixed and used. As the wet blast, a Macau lambda was used, the compressed air pressure was 0.2 MPa, the pump pressure was 0.12 MPa, the distance between the casing and the nozzle was 30 mm, and the casing was sequentially fed at 40 mm / s. It was washed with water to remove the chemical conversion treatment liquid and the abrasive, further washed with deionized water, and then dried.

(Comparative Example 1)
As a comparative example, FIG. 2 shows a process of chemical conversion after etching. Surface adjustments 1 and 2 in FIG. 2 indicate an etching process.

  Using “GFMG15SX” (trade name, manufactured by Million Chemical Co., Ltd.) as a degreasing agent, maintaining the liquid temperature at 70 ° C., immersing the Mg or Mg alloy casing described above for 5 minutes in the degreasing treatment, Thereafter, it was washed with water. "Grandafiner MG104S" (trade name, manufactured by Million Chemical Co., Ltd., phosphoric acid 30 to 40% by mass, surfactant less than 0.1% by mass, remaining water) is maintained at a concentration of 5% and a liquid temperature of 60 ° C as an etching agent. The film was immersed for 60 seconds for etching, and then washed with water. Thereafter, the etched member was immersed in the “GFMG15SX” (trade name, manufactured by Million Chemical Co., Ltd.) maintained at a liquid temperature of 60 ° C. for 7 minutes, and then washed with water. “Grandafiner MC1000” (trade name, manufactured by Million Chemical Co., Ltd., phosphoric acid 15 to 25% by mass, manganese compound 10 to 15% by mass, calcium compound 10 to 20% by mass) is used as a chemical conversion treatment liquid and maintained at 35 ° C. The Mg or Mg alloy case treated as described above was immersed for 40 seconds for chemical conversion treatment, washed with water, further washed with deionized water, and then dried.

  The appearance of Example 1 and Comparative Example 1 were evaluated, and the amount of element adhesion on the surface of the Mg or Mg alloy casing was measured by a quantitative method using fluorescent X-rays. Assuming five locations on the surface of the housing, the variation was investigated. The electrical resistivity was measured by “Lorestar MP” (4-terminal 2-probe method) manufactured by Dia Instruments Co., Ltd. The results are shown in Table 1 and FIGS. FIG. 3 is a photograph showing the appearance of Comparative Example 1, and FIG. 4 is a photograph showing the appearance of Example 1. The appearance of Example 1 was a uniform surface, but the appearance of Comparative Example 1 was uneven.

  In addition, a two-coat epoxy coating (baked at 150 ° C) on the Mg or Mg alloy housing was held in a high-temperature, high-humidity environment (60 ° C, relative humidity of 95% RH) for 100 hours, followed by a cross-cut test (a grid pattern on the sample surface). Draw a pattern and divide it into 100 parts, count the number of remaining lattices after tape-up, and judge according to the following criteria: That is, when the remaining number is 100, it passes, and when it is less, it is rejected It was.

  The results are shown in the appearance photograph of FIGS. 5A-C for Example 1, and the appearance photograph of FIGS. 6A-C for Comparative Example 1. 5 to 6, “OH” indicates a size before the test, and “2 mm” and “1 mm” indicate the size of the grid, respectively.

  Further, a salt spray test (SST) according to JIS Z 2371 was conducted for 8 hours and 24 hours to evaluate the corrosion resistance. The results are shown in the appearance photograph of FIGS. 7A-C for Example 1, and the appearance photograph of FIGS. 8A-C for Comparative Example 1. 7 to 8, “OH” indicates a pre-test time, and “8H” and “24H” indicate test processing times, respectively.

  From the above results, it was confirmed that Example 1 obtained a uniform color tone and was smooth as compared with Comparative Example 1. Furthermore, there was no shrinkage, voids, flow, etc. on the surface of the molded product. As a result, the yield of the coating performed after the treatment is improved, and it is not necessary to repair the putty before coating, thereby reducing the cost.

  In Example 1, the amount of coating adhered was small compared to the comparative example. Other film properties, such as resistance, paintability, and corrosion resistance, showed the same values in the examples and comparative examples.

  Further, in Example 1, since the total number of steps is small, coating treatment can be easily performed, and the cost can be reduced.

Process drawing which shows the flow in Example 1 of this invention. Process drawing which shows the flow in the comparative example 1. FIG. The surface observation photograph of the notebook computer housing | casing in Example 1 of this invention. The surface observation photograph of the notebook computer case in Comparative Example 1. AC is the surface observation photograph which shows the result of the cross cut test in Example 1 of this invention. AC is a surface observation photograph showing the results of the cross cut test in Comparative Example 1. AC is the surface observation photograph which evaluated the corrosion resistance by the salt spray test (SST) in Example 1 of this invention. AC is the surface observation photograph which evaluated the corrosion resistance by the salt spray test (SST) in the comparative example 1. FIG.

Claims (5)

The Mg or Mg alloy casing surface is made of a composite coating containing calcium phosphate-magnesium phosphate on the Mg or Mg alloy casing surface by wet blasting using a solution obtained by adding a chemical conversion treatment liquid and an abrasive. A Mg or Mg alloy casing characterized by forming a film. Adhesion of the composite coating film formed by the chemical conversion treatment, Ca weight at 5 mg / m ² or more 50 mg / m ² or less, Mn weight at 3 mg / m ² or more 25 mg / m ² or less, phosphorus weight 30 mg / m ² or more The Mg or Mg alloy casing according to claim 1, which is in a range of 100 mg / m ² or less.   The Mg or Mg alloy casing according to claim 1, wherein the chemical film formation includes calcium, manganese, and phosphorus. A surface treatment method of Mg or Mg alloy,
Unevenness due to blasting on the Mg or Mg alloy housing surface by wet blasting using a solution obtained by adding a chemical conversion treatment solution containing calcium ions, manganese ions and phosphate ions to the Mg or Mg alloy surface and an abrasive. A method for producing a Mg or Mg alloy casing, wherein a chemical film formed of a composite coating containing calcium phosphate-magnesium phosphate and magnesium phosphate is simultaneously formed.   5. The method for producing an Mg or Mg alloy casing according to claim 4, wherein the surface roughness of the Mg or Mg alloy casing is in a range of 0.5 μm to 100 μm in terms of 10-point average surface roughness.

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