JP5328013B2 - Method for forming magnesium oxide film - Google Patents

Description

  The present invention relates to a novel method for forming a high-hardness magnesium oxide film on the surface of magnesium or an alloy thereof.

  Magnesium and its alloys have a small specific gravity, and a beautiful metallic luster can be obtained by polishing. For example, in the electronic equipment field, it is used for notebook PC cases by utilizing its light weight, metal physical properties, and precision workability, and in the automobile and its parts field, steering wheel core and cylinder head cover that take advantage of lightness. It is used for steering lock housings.

  However, magnesium and its alloys have the property of being easily oxidized in the atmosphere, so that they are easily combusted and have the disadvantages of low corrosion resistance and heat resistance and low hardness compared to aluminum alloys.

Therefore, in order to remedy these drawbacks, various surface treatment methods have been attempted, and so far, for example, in an electrolytic solution containing a mixed solvent composed of tertiary amine and aliphatic alcohol and water, magnesium or an alloy thereof can be used. A method of forming a transparent film having heat resistance and corrosion resistance by anodizing the surface (see Patent Document 1), Al, Si, Ti, Mn, Zr, Ni, V, Nb, Ta on a magnesium substrate , Fe, Co, B and C, a coating layer comprising a composite of an oxide of at least one element selected from Mg and an oxide having a thickness of 20 μm or more and excellent in adhesion, corrosion resistance, and wear resistance A high corrosion-resistant oxide film is formed by anodizing magnesium or an alloy base material thereof in an electrolyte solution containing an insoluble fine particle and an alkali metal hydroxide (see Patent Document 2). Method (see Patent Document 3), base material made of magnesium or an alloy thereof, magnesium hydroxide 60 to 99.9%, magnesium oxide 0.1 to 40%, Mn, Ti, Mo, Si, W, Zr, V , Cr, Co, Pd, P, S, Br, F, I, B, C, N or a surface of these compounds or a chain or cyclic hydrocarbon having an OH group, a CHO group, a CO group or an NH ₂ group A metal material having good metallic luster, coating film adhesion and colorability (see Patent Document 4), including a anodic oxide film composed of a substantially non-porous barrier layer, and a magnesium-containing metal product, Ti, Zr Corrosion resistance, heat resistance and wear resistance by anodizing in an electrolyte containing water-soluble or water-dispersible complex fluoride or oxyfluoride of an element selected from Hf, Si, Sn, Al, Ge and B For forming a conductive film (patented) Document reference 5), the magnesium or the surface of the alloy, the general formula _{MgO · (A n O m)} x ( however, A is Al, Mn, Si, B, Ca, Ti, V, W, Mo, Zr or Zn , N is 1 to 5, m is 1 to 15, and x is 1 to 5), and a porous material having a thickness of 1 to 80 μm including fine pores having an average pore diameter of 50 nm to 25 μm Magnesium metal material (see Patent Document 6) having a porous anodized film and excellent in corrosion resistance, and adding a silicon compound to a solvent mixed with water and an organic solvent, and adjusting the basicity to magnesium or its A method of forming an anodic oxide film having extremely high corrosion resistance by anodizing an alloy (see Patent Document 7) has been proposed.

  However, anodized films formed by methods known so far are insufficient in improvement in heat resistance and corrosion resistance and insufficient in hardness, and are not necessarily satisfactory in practice.

JP 2003-301297 A (Claims and others) JP 2004-18981 A (Claims and others) JP 2004-91852 A (Claims and others) JP 2005-68555 A (Claims and others) JP 2005-504883 A (Claims and others) JP 2006-291278 A (Claims and others) JP 2008-13803 A (Claims and others)

  The present invention has been made for the purpose of providing a method for forming an anodic oxide film on the surface of magnesium or an alloy thereof having high resistance to combustion, good heat resistance and corrosion resistance, and significantly improved hardness. Is.

  In forming a magnesium oxide film by anodic oxidation treatment on the surface of magnesium or an alloy thereof, the inventors have added flame retardant and corrosion resistance by adding a predetermined amount of alkali metal oxalate to the electrolyte. The present inventors have found that an oxide film having a high hardness is formed well, and based on this finding, the present invention has been made.

That is, the present invention is for anodizing magnesium or an alloy thereof in an electrolytic solution containing 50 to 300 g / liter of sodium hydroxide or potassium hydroxide and 0.5 to 200 g / liter of a glycol compound as basic compositions. The present invention provides a method for forming a magnesium oxide film having flame resistance and corrosion resistance, characterized in that potassium oxalate is added to the electrolytic solution at a concentration of 7.5 to 25 g / liter.

  In the method of the present invention, the magnesium base material to be anodized may be magnesium alone or an alloy of magnesium and at least one metal selected from titanium, zirconium, hafnium, tin, aluminum and germanium. May be. As for the magnesium content rate in this magnesium alloy, 50 mass% or more is preferable. If the magnesium content is lower than this, the specific gravity is small, and the advantage of the magnesium alloy that a beautiful metallic luster can be obtained by polishing is lost.

  As the electrolytic solution in the method of the present invention, an aqueous solution containing an alkali metal hydroxide or a water-soluble salt is used. The alkali metal hydroxide includes sodium hydroxide, potassium hydroxide, and lithium hydroxide, and sodium hydroxide and potassium hydroxide are particularly preferable.

  Water-soluble salts of alkali metals include sodium, potassium and lithium carbonates, bicarbonates, silicates, hydrohalides, hydrofluorosilicates, and particularly sodium or potassium carbonates. Salts or bicarbonates are preferred.

  The concentration of these alkali metal hydroxides or water-soluble salts in the electrolytic solution is selected in the range of 50 to 300 g / liter, preferably 100 to 250 g / liter. If this concentration is less than 50 g / liter, it takes a long time to obtain a film having a desired thickness, and if it exceeds 300 g / liter, a uniform film cannot be obtained.

  Next, in order to maintain stability, a glycol compound is blended in the electrolytic solution. As the glycol compound, for example, lower alkylene glycol such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and the like is used. These glycol compounds are used at a concentration in the range of 0.5 to 200 g / liter, preferably 10 to 100 g / liter. If the amount of the glycol compound is less than this, the stability of the electrolytic solution becomes insufficient, and if it is more than this, fogging, unevenness and the like occur.

In the method of the present invention, it is necessary to add an alkali metal oxalate to the electrolytic solution. As the alkali metal oxalate, it is preferable to use the same alkali metal as the alkali metal in the alkali metal hydroxide or water-soluble salt used together, but if desired, use a salt with a different alkali metal. You can also.
A preferred alkali metal oxalate is sodium oxalate or potassium oxalate.

  This alkali metal oxalate must be used at a concentration of 7.5 to 25 g / liter. Outside this range, the hardness of the resulting magnesium oxide film cannot be sufficiently increased.

  In the method of the present invention, for the purpose of improving the physical properties of the resulting magnesium oxide film, a water-soluble salt of at least one metal selected from silicon, titanium and zirconium is blended in the electrolyte as desired. Can do.

  When anodized using an electrolytic solution containing a water-soluble salt of these metals, the produced magnesium oxide film can contain at least one selected from silicon oxide, titanium oxide and zirconium oxide. . The amount of water-soluble salt of these metals is suitably in the range of 1-50 g / liter.

  If desired, ammonia, an amine, an organic solvent, etc. can be added to the electrolytic solution used in the method of the present invention in an amount that does not hinder anodic oxidation.

Next, in order to form a high hardness magnesium oxide film having flame resistance and corrosion resistance according to the method of the present invention, magnesium or a magnesium alloy is used as one electrode and magnesium or platinum as the other electrode in a predetermined electrolyte. Immersion and current density of 1-5 A / dm ² , preferably 2-2.5 A / dm ² , voltage 2-15 v, preferably 5-10 V, bath temperature 20-80 ° C., preferably 25-50 ° C., 10 Electrolytic treatment is performed for -50 minutes, preferably 20-40 minutes. The film forming speed at this time is suitably 0.3 to 2.0 μm / min.
In this way, a magnesium oxide film having a thickness of 20 to 60 μm and a Vickers hardness (Hv) of 150 to 500 is obtained.

  The magnesium oxide film thus obtained is composed of 0.5 to 40% by mass of magnesium oxide and 60 to 99.5% by mass of magnesium hydroxide. Magnesium hydroxide lacks corrosion resistance in an acidic atmosphere. Therefore, if necessary, it is dehydrated by heating to 390 ° C. or higher, and it is stabilized by changing to magnesium oxide.

  According to the method of the present invention, a magnesium oxide film having high hardness can be formed by simply adding an alkali metal oxalate to the electrolyte without increasing the film thickness.

  Next, the best mode for carrying out the present invention will be described by way of examples, but the present invention is not limited thereby.

Six types of electrolytes were prepared by adding different amounts of potassium oxalate to a basic composition consisting of 230 g / liter potassium hydroxide and 80 g / liter ethylene glycol, and a magnesium plate (as an anode for each electrolyte solution) 20 × 50 × 1 mm) using a platinum plate (10 × 50 × 0.1 mm) as a cathode, an anode for 20 minutes under conditions of a liquid temperature of 50 to 55 ° C., a current density of 7.5 A / dm ² , and an AC voltage of 10 V Oxidation treatment was performed.
By this treatment, a magnesium oxide film having a film thickness of about 20 μm was formed on the anode surface. The Vickers hardness (Hv) of the obtained magnesium oxide film was measured, and the relationship with the amount of potassium oxalate added (g / liter) is shown as a graph in FIG.
As can be seen from this graph, the hardness becomes remarkably high when the amount of potassium oxalate added is 7.5 to 25 g / liter.

An electrolyte having a basic composition of potassium hydroxide 230 g / liter, ethylene glycol 80 g / liter, potassium oxalate 7.5 g / liter, silicic acid 10 g / liter, titanium tetrachloride 5 g / liter or zirconium tetrachloride 12.4 g / liter To prepare three types of electrolytes, and each of the electrolytes uses a magnesium plate as an anode and a cathode, each having a liquid temperature of 25 to 30 ° C., a current density of 2.8 A / dm ² , and an AC voltage of 7 V. Under conditions, anodization was performed for 40 minutes to form a magnesium oxide film containing SiO ₂ (A), TiO ₂ (B) or ZrO ₂ (C) having a thickness of about 20 μm on the anode surface. The Vickers hardness of these magnesium oxide films was 232 Hv for (A), 245 Hv for (B), and 255 Hv for (C).
For comparison, when the Vickers hardness was measured in the same manner for a magnesium oxide film obtained by anodizing under the same conditions using an electrolytic solution to which potassium oxalate was not added, (A) was 75 Hv, (B) was 85 Hv and (C) was 88 Hv.

  The method of the present invention can be used for producing a magnesium-based lightweight material having good flame resistance and corrosion resistance and high hardness.

The graph which shows the relationship between the potassium oxalate addition amount in Example 1, and the hardness of the obtained magnesium oxide membrane | film | coat.

Claims (1)

When anodizing magnesium or an alloy thereof in an electrolytic solution containing 50 to 300 g / liter of sodium hydroxide or potassium hydroxide and 0.5 to 200 g / liter of a glycol compound as basic compositions , A method for forming a magnesium oxide film having flame resistance and corrosion resistance, wherein potassium oxalate is added at a concentration of 7.5 to 25 g / liter.

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