Aluminum plating substance for anodizing

Abstract: An aluminum plating material to be anodized comprising a substrate (1), a metal layer (2) formed on the substrate, the metal layer being electro­ chemically nobler than aluminum and an aluminum alloy, and an aluminum layer (3) formed on the metal layer. The aluminum plating material prevents peeling of an aluminum layer from the substrate upon anodizing, which allows formation of uniform pores of the anodizing film, and which provides good coloring and anitiwear pro­ perties of the anodized film.

Description: The present invention relates to an aluminum plating material for anodizing, and an anodized material used for particularly, a colored medium and an antiwear material. Anodizing of aluminum or an aluminum alloy in an electrolytic solution such nitric acid, sulfuric acid, or chromic acid is known to those skilled in the art. An application of an anodized film for, e.g., aircraft, automobile, and optical components is also known. Various types of tools utilizing antiwear properties of hard anodized films are further known. The reference, Chemical Abstracts, Vol. 88, No. 14, Abstract No. 96659n, April 3, 1978, page 468, discloses the anodic oxidation of thin metal layers. Patterns for semiconductors are made by localized anodic oxidation of Al or Ti metal layers on another metal layer having a thickness of about < 0.1 µm. The reference discloses an example of an Si plate coated with Ti. An aluminum layer thereon of 1.5 µm thickness was anodized to give a porous Al₂0₃ layer. The United States patent US-A-4,681,666 discloses a method of planarization of a layer of metal and anodic aluminum in a multi-layered interconnect system. The substrate may be a semiconductor, insulating or metal waver. An aluminum coating provided on the substrate is anodized from the top to almost the bottom, leaving a small thickness of unanodized aluminum at the bottom. The thickness of the anodized aluminum is in the range of 1 to 150 µm. An undercoat of another anodizable metal may be provided between the coating of aluminum and the substrate, the undercoat provided to complete the anodizing of the unanodizable aluminum. The undercoat layer may be niobium, tantalum, titanium, molybdenum or vanadium. The present inventors have made extensive studies for a variety of applications of anodized materials which are produced by steps of plating a substrate of a metal except for aluminum or an aluminum alloy, a ceramic substrate, or a plastic substrate with aluminum or an aluminum alloy, and anodizing the plated aluminum film. The present inventors assume that an anodizing reaction of an Aℓ film progresses in accordance with the following mechanism. Aℓ dissolution: Aℓ → Aℓ³⁺, Aℓ³⁺ + H₂O → Aℓ(OH)₃ → Aℓ₂O₃·H₂O Anionic discharge and Aℓ₂O₃ Production: 2OH⁻ → H₂O + O (nascent oxygen atom) Aℓ + O → Aℓ₂O₃ (insulating film) According to the studies of the present inventors, when a composite substrate obtained by directly aluminum-plating a metal substrate except for an aluminum or aluminum alloy substrate is anodized, dissolution of aluminum layer progresses. At the same time, the metal substrate is locally dissolved to result in an anodized aluminum film having nonuniform pores. In particular, when a metal substrate has low resistance to chemicals, it is found that an interface between the substrate and the aluminum layer is undesirably dissolved, and the resultant anodized film may peel from the substrate. When a composite substrate obtained by directly aluminum-plating a nonconductive plastic or ceramic substrate is anodized, it is found that the anodized film tends to peel from the substrate if adhesion strength between the nonconductive substrate and the aluminum plating layer is low. In addition, since the material becomes insulative as a whole upon anodizing, coloring by electrolysis or electrolysis in pores cannot be performed. It is a first object of the present invention to provide an aluminum plating material for allowing high anodizing performance and a method of anodizing. It is a second object of the present invention to provide an anodized aluminum plating material which can prevent peeling of an aluminum layer from a substrate upon anodizing, which allows formation of uniform pores of the anodized film, and which provides good coloring and antiwear properties of the anodized film. According to the invention, an aluminum plating material and a method of anodizing the material are provided as defined in claims 1 and 7. The present invention further provides an anodized aluminum plating as defined in claims 14 and 20. The metal layer may be exemplified as: (1) a metal layer containing a component selected from the group consisting of Ti, Ni, Nb, Ta and W, and preferably Ti or Ni, (2) a metal layer of an alloy consisting of at least two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, e.g., an Ni-Ti alloy, or (3) a metal layer of an alloy consisting of at least one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu, e.g., an Ni-Zn alloy. The thickness of the metal layer must be 0.3 to 2 µm to protect the substrate from electrochemical or chemical treatments. The maximum thickness of the metal layer is 2 µm since it is electrochemically nobler than aluminum and chemically stable. The presence of the metal layer prevents local damage to the substrate caused by dissolution of the aluminum layer. The metal layer also prevents the Aℓ layer from peeling and facilitates production of an anodized film having uniform pores. Since the aluminum layer performs electrolytic precipitation for coloring of the anodized layer, the thickness of the aluminum layer must be generally 0.1 µm or more. However, the economical maximum thickness of the aluminum layer is 30 µm. An example of the aluminum alloy is an Aℓ-Mg alloy. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic sectional view of an aluminum plating material to be anodized according to an embodiment of the present invention; Figs. 2 and 3 are schematic sectional views showing aluminum plating materials as embodiments of the present invention after anodizing, respectively; and Figs. 4 to 5 are graphs showing changes in currents as a function of time when aluminum plating materials are anodized at a constant voltage. A preferred embodiment of the present invention will be described below. Referring to Figs. 1 and 2, reference numeral 1 denotes a substrate; 2, a metal layer; and 3, an aluminum layer. Referring to Figs. 2 and 3, reference numeral 4 denotes an anodized film. In each embodiment, a structure (Fig. 2) in which an aluminum layer is partly anodized to form an anodized film on the aluminum layer or a structure (Fig. 3) in which an aluminum layer is completely anodized is obtained. Example 1 Anodizing Aluminum Plating Substrate for Coloring A 0.3-µm thick Ni film was formed on a 0.8-mm thick cold-rolled steel plate 1 by arc discharge type ion plating to form a metal layer 2. 10-µm thick Aℓ was deposited on the metal layer 2 by vacuum deposition to form an aluminum layer 3. The plated substrate prepared as described above was anodized in a sulfuric acid bath under conditions indicated below to form a porous anodized film 4. Electrolytic Bath Composition: 15 wt% aqueous solution of sulfuric acid Electrolytic Bath Temperature: 20°C Current Density: 1 to 3 A/dm² Electrolysis Time: 10 to 30 minutes Anodized Film Thickness: 5 to 10 µm Changes in current density in anodizing at a constant voltage of 15 V are shown in Fig. 4. A solid line represents changes in current of Example 1. A broken line represents changes in current density in anodizing following the same procedures as in Example 1 in a comparative example using a plating material having an Aℓ layer formed on a substrate following the same procedures as in Example 1 except that a metal layer was not formed. In Example 1, the current density was decreased to 1/2 after about 30 minutes. This indicates that anodizing of the aluminum layer 3 has progressed and the Ni metal layer 2 was exposed. That is to say, it indicates that a uniform anodized film which reached the Ni layer after Aℓ anodizing is obtained. The end time was determined to be a timing at which the current was reduced to 1/2. In the comparative example indicated by the broken line, close to the end of the electrolysis time, the current density largely varies. This indicates that the substrate is locally dissolved. The current is not greatly reduced because the cold-rolled steel plate is used as the substrate. Coloring of the anodized film was performed by using the following electrolytic coloring bath: Electrolytic Bath Composition: 20 g/ℓ, CoSO₄ 25 g/ℓ, H₃BO₃ 15 g/ℓ, (NH₄)₂SO₄ Electrolytic Condition: 15 V (AC), 3 minutes By using the substrate of Example 1, a beautiful black colored film was obtained after electrolysis. That is, no black defects or cracks were found, and pores having a uniform pore size (diameters: about 100 to about 200 Å), a uniform depth, and a uniform distribution were produced. Example 2 (not part of the present invention). Antiwear Anodizing Aluminum Plating Substrate A 0.1-µm thick Ni-Zn alloy (Ni: 18 wt%; Zn: 82 wt%) film was formed on a 0.8-mm thick cold-rolled steel plate 1 by electroplating to obtain a metal layer 2. 15-µm thick Aℓ was deposited on the metal layer 2 by vacuum deposition to form an aluminum layer 3. The resultant substrate was anodized in an oxalic acid bath under the conditions indicated below to form a porous film 4. Electrolytic Bath Composition: 27 g/ℓ, (COOH)₂ Electrolytic Bath Temperature: 20°C Current Density: 1 to 3 A/dm² Electrolysis Time: 10 to 30 minutes Anodized Film Tkickness: 5 to µm Changes in current in anodizing at a constant voltage of 30 V are shown in Fig. 5. A solid line represents changes in current of Example 2. A broken line represents changes in current in anodizing following the same procedures as in Example 2 in a comparative example using a plating material having an Aℓ layer formed on a substrate following the same procedures as in Example 2 except that a metal layer was not formed. In Example 2, a current density was decreased to 1/2 after about 25 minutes. This indicates that anodizing of the aluminum layer 3 has progressed and the Ni-Zn alloy was exposed. That is to say, it indicates that a uniform anodized film which reached the Ni-Zn alloy layer after Aℓ anodizing is obtained. In the comparative example indicated by the broken line, close to the end of the electrolysis time, the current density largely varies. This indicates that the substrate is locally dissolved. The current is not greatly reduced because the cold-rolled steel plate is used as the substrate. The resultant porous film 4 had a Vicker's hardness (HV) value of 550 and was found to be an anodized film having excellent antiwear properties. In the above examples, Ni, Ti, Ni-Zn, and Ni-Ti are exemplified as the materials for the metal layers. A material for the metal layer may be any material which is electrochemically nobler than the material of the aluminum layer and chemically stable. For example, Nb, Ta, or W, or its alloy with Fe, P, Mn or Cu may be used to obtain the same effect as in the above examples.

Claims: An aluminum plating material for anodizing, comprising: a substrate (1), which is made of one of steel and stainless steel; an aluminum layer (3) serving as an outermost layer consisting of aluminum or an aluminum alloy; and a metal layer (2) sandwiched between the substrate and the aluminum layer, the metal layer being electrochemically nobler than the aluminum layer and chemically stable, and the metal layer having a thickness of 0.3 µm to 2 µm. A material according to claim 1, characterized in that the metal layer is a layer selected from the group consisting of: (1) a metal layer containing a component selected from the group consisting of Ti, Ni, Nb, Ta and W, (2) a metal layer of an alloy consisting of at least two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, or (3) a metal layer of an alloy consisting of at least one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu. A material according to claim 1, characterized in that the metal layer is at least one layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and the aluminum layer has a thickness of 0.1 µm to 30 µm. A material according to claim 1, characterized in that the metal layer is at least one layer consisting of two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, and the aluminum layer has a thickness of 0.1 µm to 30 µm. A material according to claim 1, characterized in that the metal layer is at least one layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and one component selected from the group consisting of Zn, Fe, P, Mn, and Cu, and the aluminum layer has a thickness of 0.1 µm to 30 µm. A material according to claim 1, characterized in that the substrate is made of one of a cold-rolled steel plate and a stainless steel plate. A method of anodizing an aluminum plating material, characterized by comprising the steps of: preparing a substrate (1), which is made of one of steel and stainless steel; forming at least one metal layer (2) which is electrochemically nobler than aluminum or an aluminum alloy and chemically stable, and the metal layer having a thickness of 0.3 µm to 2 µm; forming an aluminum layer (3) of aluminum or an aluminum alloy on the substrate, the aluminum layer constituting an outermost layer, thereby obtaining an aluminum plating material; and anodizing the aluminum plating material. A method according to claim 7, characterized in that the aluminum film has a thickness falling within a range of 0.1 µm to 30 µm. A method according to claim 7, characterized in that the metal layer is a layer selected from the group consisting of: (1) a metal layer containing a component selected from the group consisting of Ti, Ni, Nb, Ta, and W, (2) a metal layer of an alloy having at least two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, and (3) a metal layer of an alloy consisting of at least one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu. A method according to claim 7, characterized by comprising the steps of: preparing the substrate; forming at least one metal layer on a surface of the substrate, the metal layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W; forming an aluminum layer of aluminum or an aluminum alloy on the metal layer, the aluminum layer having a thickness of 0.1 µm to 30 µm and constituting an outermost layer, thereby obtaining an aluminum plating material; and anodizing the aluminum plating material. A method according to claim 7, characterized by comprising the steps of: preparing the substrate; forming at least one metal layer on a surface of the substrate, the metal layer consisting of two components selected from the group consisting of Ti, Ni, Nb, Ta, and W; forming an aluminum layer of aluminum or an aluminum alloy on the metal layer, the aluminum layer having a thickness of 0.1 µm to 30 µm and constituting an outermost layer, thereby obtaining an aluminum plating material; and anodizing the aluminum plating material. A method according to claim 7, characterized by comprising the steps of: preparing the substrate; forming at least one metal layer on a surface of the substrate, the metal layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P Mn, and Cu; forming an aluminum layer of aluminum or an aluminum alloy on the metal layer, the aluminum layer having a thickness of 0.1 µm to 30 µm and constituting an outermost layer, thereby obtaining an aluminum plating material; and anodizing the aluminum plating material. A method according to claim 7, characterized by further comprising the step of anodizing the aluminum layer to form an anodized film and thereafter coloring the anodized film. An anodized aluminum plating material comprising: a substrate (1), which is made of one of steel and stainless steel; at least one metal layer (2) formed on the substrate, the metal layer being electrochemically nobler than aluminum or an aluminum alloy and chemically stable; and the metal layer having a thickness of 0.3 µm to 2 µm; an aluminum layer (3) formed on the metal layer and consisting of aluminum or an aluminum alloy; and an anodized film layer (4) formed on the aluminum layer. A material according to claim 14, characterized in that a total thickness of the aluminum layer and the anodized film layer falls within a range of 0.1 µm to 30 µm. A material according to claim 14, characterized in that the metal layer is a layer selected from the group consisting of (1) a metal layer containing a component selected from the group consisting of Ti, Ni, Nb, Ta, and W, (2) a metal layer of an alloy consisting of at least two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, and (3) a metal layer of an alloy consisting of at least one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu. A material according to claim 14, characterized in that the metal layer is at least one layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W, and the total thickness of the aluminum layer and the anodized film layer falls within a range of 0.1 µm to 30 µm. A material according to claim 14, characterized in that the metal layer is at least one layer consisting of two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, and a total thickness of the aluminum layer and the anodized film layer falls within a range of 0.1 µm to 30 µm. A material according to claim 14, characterized in that the metal layer is at least one layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu, and a total thickness of the aluminum layer and anodized film layer falls within a range of 0.1 µm to 30 µm. An anodized aluminum plating material comprising: a substrate (1), which is made of one of steel and stainless steel; at least one metal layer (2) formed on the substrate, the metal layer being electrochemically nobler and more stable than aluminum or an aluminum alloy; and the metal layer having a thickness of 0.3 µm to 2 µm; and an anodized film layer (4) formed on the metal layer. A material according to claim 20, characterized in that the anodized film layer has a thickness falling within a range of 0.1 µm to 30 µm. A material according to claim 20, characterized in that the metal layer is a layer selected from the group consisting of: (1) a metal layer containing a component selected from the group consisting of Ti, Ni, Nb, Ta, and W, (2) a metal layer of an alloy consisting of at least two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, and (3) a metal layer of an alloy consisting of at least one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu. A material according to claim 20, characterized in that the metal layer is at least one layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W, and the anodized film layer has a thickness of 0.1 µm to 30 µm. A material according to claim 20, characterized in that the metal layer is at least one layer consisting of two components selected from the group consisting of Ti, Ni, Nb, Ta, and W, and the anodized film layer has a thickness of 0.1 µm to 30 µm. A material according to claim 20, characterized in that the metal layer is at least one layer consisting of one component selected from the group consisting of Ti, Ni, Nb, Ta, and W and at least one component selected from the group consisting of Zn, Fe, P, Mn, and Cu, and the anodized film layer has a thickness of 0.1 µm to 30 µm.

Inventors: KAGECHIKA HIROSHI, YASUE YOSHIHIKO, KAGECHIKA, HIROSHI, YASUE, YOSHIHIKO, Kagechika, Hiroshi c/o Patent &amp; License Dept., Yasue, Yoshihiko c/o Patent &amp; License Dept.
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1989
Main classification: C25D11
IPC codes: C23C14, C23C30, C25D11, C23C28, B32B15