Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-07-03
2003-05-27
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S254000, C148S260000, C148S274000, C148S275000, C106S014120, C106S014130, C106S014140, C106S014160, C106S014170, C252S388000, C252S390000, C252S396000
Reexamination Certificate
active
06569264
ABSTRACT:
This application is the National Stage Application of PCT/JP00/00019 filed Jan. 6, 2000.
TECHNICAL FIELD
The present invention relates to corrosion inhibitor compositions for magnesium or magnesium alloys and a process for inhibiting the corrosion of such metals with use of the composition.
The present invention relates also to surface treating agents and a surface treating process for shaped articles of magnesium and/or magnesium alloy, and a process for producing components made from magnesium and/or magnesium alloy.
BACKGROUND ART
Magnesium is the most lightweight of all the metals for use as practically useful structural materials, has a high specific strength, is easy to machine and therefore has found wide use for motor vehicle components, electric products such as computers and acoustic devices, aircraft components, etc. Generally, magnesium and magnesium alloys are made into shaped articles mainly by die casting, extrusion or rolling, while the so-called thixomolding process with use of an injection molding machine has been established technically in recent years. This process assures the freedom of shape of moldings, the productivity thereof and improved properties, rendering the moldings useful for wider application.
However, magnesium is the basest of all the metals for use as practically useful structural materials, therefore has the drawback of being susceptible to oxidation and needs to be inhibited from corroding as an important problem.
Magnesium or magnesium alloys are generally treated with chromates for corrosion inhibition (for example, JP-B No. 17911/1986, etc.). The chromate treatment nevertheless involves difficulty in setting the conditions for the treatment, so that it has been desired to provide more convenient corrosion inhibiting processes. Furthermore, the chromate treatment has the drawback that when conducted, the treatment discolors the surface of the metal, depriving the metal of its luster. Since the treatment uses a chromium compound, processes are more desirable which are less likely to burden the environment.
Although magnesium and/or magnesium alloys are not very costly as materials, the shaped products of magnesium and/or magnesium alloys prepared by thixomolding, extrusion, rollingor die casting have a highly active surface, which therefore becomes corroded at a high rate, necessitating a cumbersome surface treatment. The cost of this treatment inevitably makes the product two to three times as expensive as resin molding conventionally in use.
Castings or molding obtained by die casting or thixomolding are made into magnesium alloy products generally by the following steps.
1. Mechanical Pretreating Step
Polishing step with use of a polishing belt, abrasive paper or brush or by barrel finishing, buffing, blasting or the like for removing surface roughness or extraneous matter such as burrs, tough oxides, extrusion lubricant, mold releasing agent, casting sand, cutting oil or common soil.
2. Degreasing Step
(1) Degreasing with solvent: Preliminary degreasing or cleaning for removing cutting oil, grease or the like with a petroleum, aromatic, hydrocarbon or chlorine solvent.
(2) Degreasing with alkali: Degreasing or cleaning with use of caustic soda or like alkali solution for removing common soil, scorched lubricant or cutting oil, etc.
(3) Degreasing with emulsion: Cleaning for removing soil from the metal surface by emulsification.
3. Pickling Step
The step of cleaning with a solution of single acid such as hydrofluoric acid, nitric acid, phosphoric acid or chromic acid or a solution of a mixture of such acids for removing oxide film, corrosion product, scorched lubricant, lodged abrasive agent, shot, casting sand or other soil which remains unremoved by the degreasing step, activating the surface of the casting or molding, or removing segregated layer.
4. Step of Chemical Conversion Treatment
The step of forming a chromate film over the surface of the casting or molding generally with use of a chromic acid agent to give corrosion resistance.
5. Drying Step
6. Coating or Plating Step
7. Assembling Step
Since magnesium is the basest of all the practically useful structural materials and has properties susceptible to oxidation, the magnesium casting or molding obtained by die casting or thixomolding requires many steps when to be made into a product for use as a component of magnesium alloy, necessitating equipment, chemical agents, labor, etc. for the steps and consequently leading to reduced productivity and an increased cost.
These steps each have drawbacks as will be described below.
1. The mechanical pretreating step produces cut chips or fine particles of magnesium due to polishing, involving the hazard of ignition or explosion and necessitating utmost care for the work.
2. The degreasing step requires good care for the disposal of waste liquid or waste water in view of the influence on the environment. Especially the release of solvents, such as chlorine solvents, which are likely to be toxic to the environment must be avoided, hence the need for a limitation on use.
3. The pickling step produces marked dimensional variations in the casting or molding.
4. The step of chemical conversion treatment, especially of chromate treatment, (1) is likely to exert an influence on the environment, (2) discolors the treated surface, depriving the surface of the metallic luster, and (3) reduces the purity of magnesium owing to contamination with chromium when the product is recycled.
The coating step has a problem as to the adhesion between the magnesium or magnesium alloy substrate and the coating formed thereon. Although the chromate film gives improved adhesion to the coating, chemical conversion treating agents of the nonchromate type are desired because of the reasons given above and the worldwide trend to impose a limitation on the use of hexavalent chromium. Presently manganese phosphate is proposed as a chemical conversion treating agent of the nonchromate type, whereas the presence of manganese in this agent is not desirable from the viewpoint that this impurity metal becomes incorporated into magnesium recycled, and manganese adversely affects the electromagnetic wave shielding properties of magnesium or magnesium alloy which are characteristic thereof although the proposed compound is almost satisfactory with respect to the adhesion of the coating.
An object of the present invention is to provide a corrosion inhibitor composition which is convenient for use in the anticorrosion treatment of magnesium or magnesium alloy while permitting the metal to retain its metallic luster despite the treatment, and which is less likely to involve environmental problems, and to also provide a process for inhibiting corrosion with use of the corrosion inhibitor composition.
Another object of the invention is to provide a surface treating agent and a surface treating process for shaped products of magnesium and/or magnesium alloy which can be used or practiced with a reduced number of steps and smaller equipment, decreased amounts of chemical agents and diminished labor to achieve improved productivity and a greater cost reduction, and also a process for producing magnesium and/or magnesium alloy components.
Still another object of the invention is to provide a surface treating agent which gives improved adhesion to coatings and produces high corrosion inhibitory effects without resulting in impaired properties to shield electromagnetic waves.
DISCLOSURE OF THE INVENTION
The present invention provides a corrosion inhibitor composition for magnesium or magnesium alloys which contains at least one compound selected from among aromatic carboxylic acids and salts thereof as an effective component.
The invention further provides a corrosion inhibitor composition for magnesium or magnesium alloys which contains at least one compound selected from among aromatic carboxylic acids and salts thereof, and at least one compound selected from among pyrazole compounds and triazole compounds.
The invention further provides a process for inhibiting corrosion of shap
Fukumura Kazunori
Shiraishi Takahiko
Kubovcik & Kubovcik
Oltmans Andrew L.
Otsuka Kagaku Kabushiki Kaisha
Sheehan John
LandOfFree
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