Processing Method for Forming an Aluminum Alloy Surface Having Fine Texture and Matte Appearance

This application claims the benefit of priority to Taiwan Patent Application No. 113114846, filed on Apr. 22, 2024. The entire content of the above identified application is incorporated herein by reference.

Some references, which may include patents, patent applications and various publications, may be cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.

The present disclosure relates to a processing method of an aluminum alloy surface, and more particularly to a processing method for forming an aluminum alloy surface having a fine texture and a matte appearance, which is adapted for processing of an aluminum alloy article, so as to add a ceramic texture to the aluminum alloy surface for enhancement in appearance quality and allow an appearance thereof to be adjustable in color.

Currently, portable electronic products available on the market are developed toward being light, thin, short, and small. Aluminum alloy has become a popular material for manufacturing housings or other mechanical components of the portable electronic products due to its excellent mechanical properties and light weight. In order to improve aesthetic appearance and durability, aluminum alloy parts usually undergo a surface treatment (such as an anodizing treatment).

CN 102312263 A discloses an oxidation method for ceramizing an aluminum part, in which an oxidation solution that includes chromic acid, citric acid, and nickel sulfate is used to form a ceramic film on a surface of the aluminum part. However, the chromic acid in the oxidation solution is disadvantageous for environmental protection, and the ceramic film is silvery gray and cannot effectively exhibit bright colors through dyeing.

CN 102834551 A discloses a method for producing substantially white anodized aluminum oxide, in which two or more solutions flow into pores of an anodized layer and react with each other to form a white precipitate in a soaking treatment. However, the method requires a long period of time, and is complicated to operate.

CN 104428454 B discloses a method for forming a white anodized film, in which a laser beam is used to scan an anodized film, so as to form an array of uniformly spaced light diffusing portions (i.e., micro-cracks) in the anodized film. However, the method requires high equipment and operation costs, and is disadvantageous for a large-area treatment.

A high-voltage micro-arc treatment process is usually used for the surface treatment of the aluminum alloy to produce a ceramic texture.

However, high operation voltages may result in high operation costs, and the process is relatively complex and has the problem of difficulty in dyeing due to a high pore density.

In the relevant industry, surface treatment technology that can be practically used to process large-area aluminum alloy parts with complex structures for producing an aluminum alloy surface having a white ceramic texture is yet to be developed.

In response to the above-referenced technical inadequacies, the present disclosure provides a processing method for forming an aluminum alloy surface having a fine texture and a matte appearance, which is adapted for processing of an aluminum alloy article. After processing, the aluminum alloy surface can exhibit a fine matte texture and have a ceramic-like aesthetic appearance.

In order to solve the above-mentioned problems, one of the technical aspects adopted by the present disclosure is to provide a processing method for forming an aluminum alloy surface having a fine texture and a matte appearance, which includes: chemically polishing an aluminum alloy surface to have a 60-degree gloss between 10GU and 1000GU; performing an electrolytic treatment on the chemically polished aluminum alloy surface; and performing a first anodizing treatment on the aluminum alloy surface that undergoes the electrolytic treatment. The electrolytic treatment is operated at a current density between 0.01 A/dmand 1.5 A/dmand a gradually increasing voltage from 0V to 50V for 3 minutes to 30 minutes. The first anodizing treatment is operated at a current density between 0.1 A/dmand 2.5 A/dmand a voltage between 10V and 20V for 30 minutes to 120 minutes. Based on the CIEL*a*b color system, the aluminum alloy surface that undergoes the first anodizing treatment has an L*value from 77 to 85, an a*value from −0.55 to −0.40, and a b*value from −0.7 to 0.3.

In one of the possible or preferred embodiments, the electrolytic treatment is performed in a first treatment solution having a temperature between 20° C. and 80° C. and a pH value between 8 and 11. Based on a total weight of the first treatment solution being 100 wt %, the first treatment solution includes 3 wt % to 15 wt % of sodium carbonate and 1 wt % to 15 wt % of at least one fluoride. The at least one fluoride is selected from the group consisting of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and hydrofluoric acid.

In one of the possible or preferred embodiments, the first treatment solution further includes 5 wt % to 50 wt % of glycerol, 0.1 wt % to 10 wt % of a chelating agent, and 0.1 wt % to 10 wt % of an additive. The chelating agent is selected from the consisting of sodium gluconate, group ethylenediaminetetraacetic acid, citric acid, and potassium sodium tartrate, and the additive is selected from the group consisting of boric acid, sodium citrate, and triethanolamine.

In one of the possible or preferred embodiments, the first anodizing treatment is performed in a second treatment solution having a temperature between 5° C. and 20° C. Based on a total weight of the second treatment solution being 100 wt %, the second treatment solution includes 5% to 25% of sulfuric acid, 5 wt % to 20 wt % of oxalic acid, or a combination thereof.

In one of the possible or preferred embodiments, after the step of performing the first anodizing treatment, the processing method further includes: performing a pore sealing treatment on the aluminum alloy surface that undergoes the first anodizing treatment.

In one of the possible or preferred embodiments, the pore sealing treatment is a nickel sealing treatment, a hot-water sealing treatment, or a coating and sealing treatment. A sealing material used in the coating and sealing treatment is a UV curing or thermal curing material that includes a polyurethane polymer, a polycarbonate polymer, aminosiloxane, epoxy siloxane, a nanosilicon compound, or any combination thereof.

In one of the possible or preferred embodiments, between the step of performing the first anodizing treatment and the step of performing the pore sealing treatment, the processing method further includes: performing a first dyeing treatment on the aluminum alloy surface that undergoes the first anodizing treatment. The first anodizing treatment includes forming a porous aluminum oxide layer on the aluminum alloy surface, and the first dyeing treatment includes filling at least one dye into pores of the porous aluminum oxide layer.

In one of the possible or preferred embodiments, after the step of performing the pore sealing treatment, the processing method further includes: forming a diamond cut surface on the aluminum alloy surface that undergoes the pore sealing treatment.

In one of the possible or preferred embodiments, after the step of forming the diamond cut surface, the processing method further includes: performing a second anodizing treatment on the diamond cut surface. The second anodizing treatment is operated at a current density between 0.1 A/dmand 1.5 A/dmand a voltage between 10V and 20V for 10 minutes to 60 minutes. Furthermore, the second anodizing treatment is performed in a third treatment solution having a temperature between 5° C. and 20° C. Based on a total weight of the third treatment solution being 100 wt %, the third treatment solution includes 5% to 20% of sulfuric acid, 5 wt % to 20 wt % of oxalic acid, or a combination thereof.

In one of the possible or preferred embodiments, after the step of performing the second anodizing treatment, the processing method further includes: performing a second dyeing treatment on the diamond cut surface that undergoes the second anodizing treatment.

Therefore, in the processing method for forming the aluminum alloy surface having the fine texture and the matte appearance provided by the present disclosure, by virtue of “chemically polishing an aluminum alloy surface (which can be pre-treated by, for example, sandblasting or uniform polishing) to have a 60-degree gloss between 10 GU and 1,000 GU (which is measured at a 60-degree angle),” “performing an electrolytic treatment (under special conditions) on the chemically polished aluminum alloy surface,” and “performing a first anodizing treatment (under special conditions) on the aluminum alloy surface that undergoes the electrolytic treatment,” an aluminum alloy surface having a unique white ceramic texture can be produced. A white color difference can be controlled by adjusting operating condition parameters, and an appearance color of the aluminum alloy surface can also be changed according to requirements. Furthermore, the processing method of the present disclosure can be practically adapted for large-area processing of aluminum alloy parts with complex structures, and a processed product can directly satisfy product testing specifications due to having high reliability.

These and other aspects of the present disclosure will become apparent from the following description of the embodiment taken in conjunction with the following drawings and their captions, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure.

The present disclosure is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Like numbers in the drawings indicate like components throughout the views. As used in the description herein and throughout the claims that follow, unless the context clearly dictates otherwise, the meaning of “a,” “an” and “the” includes plural reference, and the meaning of “in” includes “in” and “on.” Titles or subtitles can be used herein for the convenience of a reader, which shall have no influence on the scope of the present disclosure.

The terms used herein generally have their ordinary meanings in the art. In the case of conflict, the present document, including any definitions given herein, will prevail. The same thing can be expressed in more than one way. Alternative language and synonyms can be used for any term(s) discussed herein, and no special significance is to be placed upon whether a term is elaborated or discussed herein. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms is illustrative only, and in no way limits the scope and meaning of the present disclosure or of any exemplified term. Likewise, the present disclosure is not limited to various embodiments given herein. Numbering terms such as “first,” “second” or “third” can be used to describe various components, signals or the like, which are for distinguishing one component/signal from another one only, and are not intended to, nor should be construed to impose any substantive limitations on the components, signals or the like.

Unless otherwise stated, the material(s) used in any described embodiment is/are commercially available material(s) or may be prepared by methods known in the art, and the process(es) or method(s) used in any described embodiment is/are conventional process(es) or method(s) commonly used in the related art.

In the present disclosure, although multiple steps shown in a flowchart are described in a specific order, the steps are not required or implied to be executed in said specific order or all executed to achieve desired results. In practice, two or more steps can be optionally combined into one step, or one step can be optionally divided into two or more steps.

Referring to, an embodiment of the present disclosure provides a processing method for forming an aluminum alloy surface having a fine texture and a matte appearance, which mainly includes: chemically polishing an aluminum alloy surface (step S); performing an electrolytic treatment on the chemically polished aluminum alloy surface (step S); and performing a first anodizing treatment on the aluminum alloy surface that undergoes the electrolytic treatment (step S). More specifically, the processing method is a surface treatment method of an aluminum alloy article, and mainly adopts a combination of the electrolytic treatment under special conditions and an anodizing treatment, so as to add a ceramic texture to the aluminum alloy surface and allow an appearance thereof to be adjustable in color.

The aluminum alloy article can be made of an aluminum alloy selected from 5000 series (e.g., 5052), 6000 series (e.g., 6063), and 7000 series (e.g., 7075) aluminum alloys. However, such examples are not meant to limit the scope of the present disclosure. Furthermore, the aluminum alloy article can have a desired shape (e.g., a sheeted shape) by casting, extruding, forging, or cutting, so as to be applicable for appearance parts of electronic products.

Referring toto, each step of the processing method will be described in detail below.

In step S, the aluminum alloy article can be placed in a chemical polishing solution that is used to remove wrinkles on an aluminum alloy surface, thereby allowing the aluminum alloy surface to be smoother and brighter. In the embodiment of the present disclosure, the chemically polished aluminum alloy surface has a 60-degree gloss between 10GU and 1000GU, which is measured at a 60-degree angle. The chemical polishing solution can include phosphoric acid or a combination of phosphoric acid and sulfuric acid, but is not limited thereto.

In practice, the processing method of the present disclosure can further include pre-treatment steps, i.e., pre-treating the aluminum alloy surface before the step of chemical polishing. The pre-treatment steps may vary with different purposes, and can include, for example, sandblasting, degreasing, acid washing, and alkaline washing steps that can be executed in sequence.

More specifically, the material used for sandblasting can be rounded steel grits, iron sand, or zircon sand. In the degreasing step, the aluminum alloy article can be placed in a degreasing agent-containing solution having a temperature of 50° C. for 1 minute to 3 minutes. In the acid washing step, the aluminum alloy article can be placed in an acid agent-containing solution having a temperature from 20° C. to 40° C. for 1 minute to 3 minutes. In the alkaline washing step, the aluminum alloy article can be placed in an alkaline agent-containing solution having a temperature from 40° C. to 60° C. for 0.5 minutes to 2 minutes. However, the above description is for exemplary purposes only, and is not meant to limit the scope of the present disclosure.

In step S, the aluminum alloy article can be placed in a first treatment solution that includes alkaline chemicals and undergo the electrolytic treatment under special conditions. The first treatment solution has a temperature between 20° C. and 80° C. and a pH value between 8 and 11. Based on a total weight of the first treatment solution being 100 wt %, the first treatment solution includes 3 wt % to 15 wt % of sodium carbonate and 1 wt % to 15 wt % of at least one fluoride. The at least one fluoride can be selected from the group consisting of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and hydrofluoric acid. In the embodiment of the present disclosure, the first treatment solution can further include 0.1 wt % to 10 wt % of a chelating agent and 0.1 wt % to 10 wt % of an additive. The chelating agent can be selected from the group consisting of sodium gluconate, ethylenediaminetetraacetic acid, citric acid, and potassium sodium tartrate, and the additive can be selected from the group consisting of boric acid, sodium citrate, and triethanolamine. If necessary, the first treatment solution can further include 5 wt % to 50 wt % of glycerol. However, such examples are not meant to limit the scope of the present disclosure.

Reference is made toand. In the electrolytic treatment, an aluminum alloy articleto be treated serves as an anode, and a cathode is made of a corrosion-resistant material (such as a stainless steel plate, a carbon plate, a titanium plate, or a lead-antimony plate). A first porous aluminum oxide layeris formed and well adhered onto an aluminum alloy surfaceby the application of a predetermined current and a gradually increasing voltage. More specifically, the electrolytic treatment is operated at a current density between 0.01 A/dmand 1.5 A/dmand a gradually increasing voltage from 0V to a target voltage Vt for 3 minutes to 30 minutes. The target voltage can be from 10V to 50V.

In the embodiment of the present disclosure, the current density of the electrolytic treatment can be 0.01 A/dm, 0.05 A/dm, 0.1 A/dm, 0.5 A/dm, 1.0 A/dm, or 1.5 A/dm. The treatment time of the electrolytic treatment can be 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

In step S, the aluminum alloy article can be placed in a second treatment solution that includes acid chemicals and undergo the first anodizing treatment under special conditions. The second treatment solution has a temperature between 5° C. and 20° C. Based on a total weight of the second treatment solution being 100 wt %, the second treatment solution includes 5% to 25% of sulfuric acid, 5 wt % to 20 wt % of oxalic acid, or a combination thereof.

As shown in, in the first anodizing treatment, the aluminum alloy articleto be treated serves as an anode, and a cathode is made of a corrosion-resistant material (such as a stainless steel plate, a carbon plate, a titanium plate, or a lead-antimony plate). A second porous aluminum oxide layeris formed and well adhered onto the aluminum alloy surfaceby the application of a predetermined current and a predetermined voltage. More specifically, the first anodizing treatment is operated at a current density between 0.1 A/dmand 2.5 A/dmand a voltage between 10V and 20V for 30 minutes to 120 minutes.

In the embodiment of the present disclosure, the current density of the first anodizing treatment can be 0.01 A/dm, 0.05 A/dm, 0.1 A/dm, 0.5 A/dm, 1.0 A/dm, 1.5 A/dm, 2.0 A/dm, or 2.5 A/dm. The voltage of the first anodizing treatment can be 10V, 11V, 12V, 13V, 14V, 15V, 16V, 17V, 18V, 19V, or 20V. The treatment time of the first anodizing treatment can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, 90 minutes, 95 minutes, 100 minutes, 105 minutes, 110 minutes, 115 minutes, or 120 minutes.

More specifically, the second porous aluminum oxide layeris located between the aluminum alloy surfaceand the first porous aluminum oxide layer. The first porous aluminum oxide layerhas a thinner thickness than the second porous aluminum oxide layer. Furthermore, the first porous aluminum oxide layerand the second porous aluminum oxide layerare different in pore structure (e.g., the shape, size or aspect ratio of pores), pore arrangement, and porosity. It is worth mentioning that the aluminum alloy surfacethat undergoes the first anodizing treatment can have a unique white ceramic texture. That is, the aluminum alloy surfacethat undergoes the first anodizing treatment and is not dyed has an L*value from 77 to 85, an a*value from −0.55 to −0.40, and a b*value from −0.7 to 0.3, based on the CIEL*a*b color system.

Referring to, the processing method of the present disclosure can further include: performing a dyeing treatment on the aluminum alloy surface that undergoes the first anodizing treatment (step S); and performing a pore sealing treatment on the aluminum alloy surface that undergoes the first anodizing treatment (step S). The dyeing treatment can change an appearance color of the aluminum alloy surface. The pore sealing treatment can not only provide sufficient protection for the aluminum alloy surface, but also ensure that the dyed aluminum alloy surface will not fade or change in color.

In step S, the aluminum alloy article can be placed in a dyeing solution that includes a dye, so as to colorize the aluminum alloy surface that undergoes the first anodizing treatment. Afterwards, a water washing process can be used to remove the excessive dye from the aluminum alloy surface. The dye suitable for step Scan be an Okuno dye, but is not limited thereto.

As shown in, in the dyeing treatment, the dye in the dyeing solution can be deposited into pores of the first porous aluminum oxide layeror the second porous aluminum oxide layer, so as to produce a color change on the aluminum alloy surface. A part of the dye remaining outside the pores of the first porous alumina layercan be easily carried away by washing water.

In step S, the aluminum alloy surface that undergoes the dyeing treatment is in contact with a sealing material that includes a pore sealing agent to undergo the pore sealing treatment. Here, the contact time can be controlled. The pore sealing treatment can be a nickel sealing treatment, a hot-water sealing treatment, or a coating and sealing treatment. The coating and sealing treatment can include curing the sealing material under UV irradiation or heating conditions, so that the dye is firmly attached to the aluminum alloy surface and will not fall off. More specifically, the sealing material used in the coating and sealing treatment is a UV curing or thermal curing material that includes a polyurethane polymer, a polycarbonate polymer (e.g., polycarbonate), aminosiloxane, epoxy siloxane, a nanosilicon compound, or any combination thereof. Suitable ways for applying the sealing material in step Sinclude coating. However, such examples are not meant to limit the scope of the present disclosure.

As shown in, in the pore sealing treatment, the sealing material can be in contact with the aluminum alloy surfaceby coating, so as to form a transparent sealing layeron the first porous aluminum oxide layerand seal the pores. In the presence of the transparent sealing layer, the dye can be stably retained in the pores of the first porous aluminum oxide layerfor a long period of time.

According to requirements of product appearance, after the first anodizing treatment (step S) is completed, the processing method can skip the dyeing treatment (step S) and directly proceed to the pore sealing treatment (step S).

As shown in, a processed product Z can be obtained after the above steps are completed, and the processed product Z includes the aluminum alloy article, the first porous aluminum oxide layer, the second porous aluminum oxide layer, and the transparent sealing layer. The aluminum alloy articlehas the aluminum alloy surface, and the first porous aluminum oxide layer, the second porous aluminum oxide layer, and the transparent sealing layerare formed on the aluminum alloy surface. The second porous aluminum oxide layeris formed between the aluminum alloy surfaceand the first porous aluminum oxide layer, and the transparent sealing layercovers the first porous aluminum oxide layer.

Referring to, the processing method can further include post-treatment steps, i.e., post-treating the aluminum alloy surface after the step of performing the pore sealing treatment. In the embodiment of the present disclosure, the processing method can further include: forming a diamond cut surface on the aluminum alloy surface that undergoes the pore sealing treatment (step S); performing a second anodizing treatment on the diamond cut surface (step S); and performing a second dyeing treatment on the diamond cut surface that undergoes the second anodizing treatment (step S).

Reference is made to. In step S, diamond cutting is performed with a cutting oil to cut a portion (e.g., an edge portion) of the processed product Z, so as to form a diamond cut surface CE having a 60-degree gloss between 200 GU and 1,000 GU (which is measured at a 60-degree angle).

In step S, a treatment solution and operation conditions used in the second anodizing treatment are substantially the same as those used in the first anodizing treatment. The only difference is that, in the second anodizing treatment, the treatment solution includes a lower concentration of sulfuric acid and the treatment time is shorter. More specifically, the treatment solution of the second anodizing treatment can include 5% to 25% of sulfuric acid, 5 wt % to 20 wt % of oxalic acid, or a combination thereof. The treatment time of the second anodizing treatment ranges from 10 minutes to 60 minutes. Furthermore, the second anodizing treatment is operated at a current density between 0.1 A/dmand 1.5 A/dmand a voltage between 10V and 20V.