US20140116883A1

US20140116883A1 - Surface treatment process for aluminum alloy and aluminum alloy article thereof

Info

Publication number: US20140116883A1
Application number: US13/865,634
Authority: US
Inventors: Cheng-Yang XIONG; Shu-Xiang Zhou; Kai-Rong Liao
Original assignee: Shenzhen Futaihong Precision Industry Co Ltd; FIH Hong Kong Ltd
Current assignee: Shenzhen Futaihong Precision Industry Co Ltd; FIH Hong Kong Ltd
Priority date: 2012-10-31
Filing date: 2013-04-18
Publication date: 2014-05-01
Also published as: CN103789808A; TW201416494A; CN103789808B; TWI573898B

Abstract

A surface treatment process for aluminum alloy includes the steps of: providing an aluminum alloy substrate containing silicon element; evenly distributing the silicon element in the substrate by solution treating the substrate; removing the silicon element at/near the surface of the substrate by acid treating the substrate; forming a porous aluminum oxide film on the substrate by anodizing the substrate; and staining the aluminum oxide film. An aluminum alloy article treated by the process is also described.

Description

BACKGROUND

1. Technical Field
The present disclosure relates to a surface treatment process for aluminum alloy and an aluminum alloy article treated by the process.
2. Description of Related Art
Aluminum alloys are widely used to manufacture housings of electronic devices. The aluminum alloys are usually anodized and stained to present colorful appearances. However, the color of the aluminum alloy may not be uniform due to the silicon element contained in the aluminum alloy. So, the silicon element is necessary to be removed from the aluminum alloy.
The current method to remove the silicon element is to treat the aluminum alloy using acid. However, treating the aluminum alloy using acid can remove silicon element at/near the surface of the aluminum alloy, but not all the silicon element in the aluminum alloy. Commonly, the silicon element at/near the surface of the aluminum alloy has a lower density than that of in the inner of the aluminum alloy. As a result, despite removing the silicon element at/near the surface, most of the silicon element in the inner would transmit to the surface of the aluminum alloy to affect the uniformity of the color.
Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the disclosure can be better understood with reference to the following figure. The components in the figure are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure.

The figure is a cross-sectional view of an aluminum alloy article in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

A surface treatment process for an aluminum alloy may include the following steps.
Referring to the figure, an aluminum alloy substrate 10 is provided. The substrate 10 contains silicon element.
The substrate 10 is ultrasonically cleaned using absolute ethanol for about 25 minutes (min) to about 35 min. Then the substrate 10 is air-dried for about 2 min to about 3 min.
The substrate 10 is solution treated. A chamber type electrical resistance furnace (not shown) is provided and set to have an inner temperature of about 495° C. to about 525° C. The substrate 10 is positioned in the furnace to be solution treated for about 8 hours to about 10 hours. During the solution treatment, the silicon element in the substrate 10 takes place a transmission to evenly distribute in the substrate 10 along the thickness. That is, the solution treatment makes the density of the silicon element in the substrate 10 consistent. Thus, the density of the silicon element at/near the surface of the substrate 10 is greater than the density of the aluminum alloy which is not solution treated.
The substrate 10 is removed from the furnace to be quenched in 5 seconds. The quenching process is carried out by dipping the substrate 10 in water for about 3 min to about 5 min. The water has a temperature of about 20° C. to about 25° C.
The substrate 10 is acid treated to remove silicon element at/near the surface of the substrate 10. The substrate 10 is dipped in an acid solution for about 5 min to about 10 min The acid solution contains nitric acid and hydrofluoric acid in a volume ratio of about 8-10 : 1-1.5. During dipping, the silicon element at/near the surface of the substrate 10 chemically reacts with the hydrofluoric acid to produce silicon tetrafluoride that can be dissolved in the acid solution, thereby the silicon element at/near the surface of the substrate 10 is removed. After the acid treatment, the substrate 10, from the surface to the depth of about 15 micrometers (pm) to about 25 μm, contains no silicon element. The total content of the silicon element contained in the substrate 10 decreases about 1.3% to about 1.65% after the acid treatment. Since the silicon element has been evenly distributed in the substrate 10 after the solution treatment, the acid treatment in the embodiment can remove much more silicon element compared to the conventional acid treatment.
The substrate 10 is chemically polished to smoothen the surface and enhance the glossiness of the substrate 10. The chemical polishing process may include the following steps:
The substrate 10 is dipped in a first polishing solution having a temperature of about 70° C. to about 90° C. for about 20 seconds to about 30 seconds. The first polishing solution contains sulfuric acid and phosphoric acid in a volume ratio of about 1-1.5 : 3-5. The sulfuric acid and the phosphoric acid ionize H⁺ to chemically react with the aluminum oxide that may formed on the surface of the substrate 10 in air to produce Al³⁺and H₂O, thereby removing the aluminum oxide and smoothening the surface of the substrate 10.
The substrate 10 is dipped in a second polishing solution having a temperature of about 60° C. to about 80° C. for about 20 seconds to about 30 seconds. The second polishing solution contains nitric acid and phosphoric acid in a volume ratio of about 1-1.5 : 1-3. The phosphoric acid can chemically react with the aluminum contained in the substrate 10 to produce an aluminum phosphate on the surface of the substrate 10, the aluminum phosphate then dissolves in the nitric acid, thereby enhancing the glossy of the substrate 10.
The substrate 10 is anodized. The anodizing process is carried out in a sulfuric solution having a concentration of about 120 g/L to about 210 g/L for about 5 min to about 65 min. The substrate 10 acts as an anode, a stainless steel is provided to act as a cathode. A voltage of about 20 V to about 60 V is applied to the anode and cathode, producing an electric current of about 2 A/dm²to about 6.5 A/dm²in the sulfuric solution. During the anodizing process, the sulfuric acid is kept at a temperature of about 3° C. to about 30° C. After the anodizing process, an aluminum oxide film 12 is formed on the substrate 10 (see the figure). The aluminum oxide film 12 has a thickness of about 5 μm to about 12 μm, and contains no silicon element which would affect to the substantially staining to the aluminum oxide film 12. Further, the solution treatment applied to the substrate 10 can also prevent the transmission of the silicon element in the inner of the substrate 10 to the surface of the substrate 10 to affect the substantial staining process. The aluminum oxide film 12 defines a plurality of micro-pores 121.
The aluminum oxide film 12 is stained using a colorant having a concentration of about 0.2 g/L to about 4 g/L and a pH value of about 4-10. The colorant may be xanthene dyes, methane dyes, coumarins dyes, cyanine dyes, stilbene dyes, or oxazine dyes. The pH value of the colorant can be adjusted using an acetic acid, ammonia water, or sodium hydroxide. The colorant has a temperature of about 30° C. to about 60° C. Staining the aluminum oxide film 12 may last for about 5 min to about 20 min, allowing the micro-pores 121 to be completely filled by the colorant.
A sealing treatment is applied to the aluminum oxide film 12, using boiling water, vapor, nickel acetate, nickel sulfate, potassium dichromate, or stearic acid. In the embodiment, boiling water is selected. The sealing treatment lasts for about 30 min to about 45 min. After the sealing treatment, a hydrated aluminum oxide film 14 is formed on the aluminum oxide film 12.
Referring to the figure, an aluminum alloy article 100 made by the method above includes the aluminum alloy substrate 10, the aluminum oxide film 12, and the hydrated aluminum oxide film 14. The aluminum oxide film 12 is an anodic layer, and defines a plurality of micro-pores 121 therein. The aluminum oxide film 12 has a thickness of about 5 μm to about 12 μm. The aluminum oxide film 12 contains no silicon element, thus the aluminum oxide film 12 has a uniform color after being stained.
Specific examples of the surface treatment process are described below. The ultrasonic cleaning in these specific examples is as described above and always the same.

Example 1

In air drying the substrate 10: the substrate 10 was dried by a dryer (not shown) for 2 min.
In solution treating the substrate 10: the furnace had an inner temperature of about 525° C., the substrate 10 was positioned in the furnace to be solution treated for about 8 hours.
In quenching the substrate 10: the substrate 10 was dipped in water having a temperature of about 20° C. for 5 min.
In acid treating the substrate 10: the substrate 10 was dipped in the acid solution for 5 min The acid solution contained nitric acid and hydrofluoric acid in a volume ratio of 8:1. After the acid treatment, the total content of the silicon element contained in the substrate 10 decreased about 1.3%.
In polishing the substrate 10: the substrate 10 was dipped in a first polishing solution having a temperature of about 70° C. for 20 seconds. The first polishing solution contained sulfuric acid and phosphoric acid in a volume ratio of 1:3. Then the substrate 10 was dipped in a second polishing solution having a temperature of about 60° C. for 20 seconds. The second polishing solution contained nitric acid and phosphoric acid in a volume ratio of about 1 : 1.
In anodizing the substrate 10: the anodizing process was carried out in a sulfuric solution having a concentration of about 130 g/L for about 15 min. The substrate 10 acted as an anode, a stainless steel was provided to act as a cathode. A voltage of about 22 V was applied to the anode and cathode, producing an electric current of about 2.3 A/dm²in the sulfuric solution. During the anodizing process, the sulfuric acid was kept at a temperature of about 20° C.
In staining the aluminum oxide film 12: the aluminum oxide film 12 was stained using a xanthene dye having a concentration of about 4 g/L and a pH value of about 5. The xanthene dye had a temperature of about 30° C. Staining the aluminum oxide film 12 lasted 5 min
In sealing the aluminum oxide film 12: boiling water was selected to seal the micro-pores of the aluminum oxide film 12 for 30 min.

Example 2

In air drying the substrate 10: the substrate 10 was dried by a dryer for 2 min.
In solution treating the substrate 10: the furnace had an inner temperature of about 510° C., the substrate 10 was positioned in the furnace to be solution treated for about 9 hours.
In quenching the substrate 10: the substrate 10 was dipped in water having a temperature of about 15° C. for 5 min.
In acid treating the substrate 10: the substrate 10 was dipped in the acid solution for 5 min The acid solution contained nitric acid and hydrofluoric acid in a volume ratio of 10:1.5. After the acid treatment, the total content of the silicon element contained in the substrate 10 decreased about 1.5%.
In polishing the substrate 10: the substrate 10 was dipped in a first polishing solution having a temperature of about 75° C. for 20 seconds. The first polishing solution contained sulfuric acid and phosphoric acid in a volume ratio of about 1:5. Then the substrate 10 was dipped in a second polishing solution having a temperature of about 70° C. for 30 seconds. The second polishing solution contained nitric acid and phosphoric acid in a volume ratio of about 1:1.
In anodizing the substrate 10: the anodizing process was carried out in a sulfuric solution having a concentration of about 180 g/L for about 20 min. The substrate 10 acted as an anode, a stainless steel was provided to act as a cathode. A voltage of about 30 V was applied to the anode and cathode, producing an electric current of about 3 A/dm²in the sulfuric solution. During the anodizing process, the sulfuric acid was kept at a temperature of about 20° C.
In staining the aluminum oxide film 12: the aluminum oxide film 12 was stained using a xanthene dye having a concentration of about 3 g/L and a pH value of about 6. The xanthene dye had a temperature of about 40° C. Staining of the aluminum oxide film 12 lasted 10 min.
In sealing the aluminum oxide film 12: boiling water was selected to seal the micro-pores of the aluminum oxide film 12 for 40 min.

Example 3

In air drying the substrate 10: the substrate 10 was dried by a dryer for 3 min.
In solution treating the substrate 10: the furnace had an inner temperature of about 495° C., the substrate 10 was positioned in the furnace to be solution treated for about 10 hours.
In quenching the substrate 10: the substrate 10 was dipped in water having a temperature of about 20° C. for 5 min.
In acid treating the substrate 10: the substrate 10 was dipped in the acid solution for 10 min The acid solution contained nitric acid and hydrofluoric acid in a volume ratio of 9:1. After the acid treatment, the total content of the silicon element contained in the substrate 10 decreased about 1.65%.
In polishing the substrate 10: the substrate 10 was dipped in a first polishing solution having a temperature of about 80° C. for 30 seconds. The first polishing solution contained sulfuric acid and phosphoric acid in a volume ratio of about 1:4. Then the substrate 10 was dipped in a second polishing solution having a temperature of about 80° C. for 30 seconds. The second polishing solution contained nitric acid and phosphoric acid in a volume ratio of about 1:2.
In anodizing the substrate 10: the anodizing process was carried out in a sulfuric solution having a concentration of about 200 g/L for about 60 min. The substrate 10 acted as an anode, a stainless steel was provided to act as a cathode. A voltage of about 55 V was applied to the anode and cathode, producing an electric current of about 5.5 A/dm²in the sulfuric solution. During the anodizing process, the sulfuric acid was kept at a temperature of about 5° C.
In staining the aluminum oxide film 12: the aluminum oxide film 12 was stained using a xanthene dye having a concentration of about 1 g/L and a pH value of about 5. The xanthene dye had a temperature of about 60° C. Staining the aluminum oxide film 12 lasted 20 min.
In sealing the aluminum oxide film 12: boiling water was selected to seal the micro-pores of the aluminum oxide film 12 for 35 min.
It is believed that the exemplary embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its advantages, the examples hereinbefore described merely being preferred or exemplary embodiment of the disclosure.

Claims

What is claimed is:

1. A surface treatment process for aluminum alloy, comprising:

providing an aluminum alloy substrate comprising silicon element;

evenly distributing the silicon element in the substrate by solution treating the substrate;

removing the silicon element at/near the surface of the substrate by acid treating the substrate;

forming a porous aluminum oxide film on the substrate by anodizing the substrate; and

staining the aluminum oxide film.

2. The process as claimed in claim 1, wherein solution treating the substrate is carried out by positioning the substrate in a chamber type electrical resistance furnace having an inner temperature of about 495° C. to about 525° C. for about 8 hours to about 10 hours.

3. The process as claimed in claim 1, wherein acid treating the substrate is carried out by dipping the substrate in an acid solution for about 5 min to about 10 min, the acid solution comprises nitric acid and hydrofluoric acid in a volume ratio of about 8-10:1-1.5.

4. The process as claimed in claim 3, wherein after the acid treatment, the substrate comprises no silicon element from the surface of the substrate to the depth of about 15 μm to about 25 μm of the substrate, the total content of the silicon element contained in the substrate decreases about 1.3% to about 1.65%.

5. The process as claimed in claim 1, wherein anodizing the substrate is carried out in a sulfuric solution having a concentration of about 120 g/L to about 210 g/L for about 5 min to about 65 min, the substrate acts as an anode, a stainless steel is provided and acts as a cathode, a voltage of about 20 V to about 60V is applied to the anode and cathode, producing an electric current of about 2 A/dm²to about 6.5 A/dm²in the sulfuric solution; wherein during the anodizing process, the sulfuric solution is kept at a temperature of about 3° C. to about 30° C.

6. The process as claimed in claim 5, wherein the aluminum oxide film has a thickness of about 5 μm to about 12 μm, the aluminum oxide film defines a plurality of micro-pores, and comprises no silicon element.

7. The process as claimed in claim 1, wherein staining the aluminum oxide film is carried out using a colorant having a concentration of about 0.2 g/L to about 4 g/L and a pH value of about 4-10, the colorant has a temperature of about 30° C. to about 60° C., staining the aluminum oxide film last about 5 min to about 20 min.

8. The process as claimed in claim 7, wherein the colorant is xanthene dyes, methane dyes, coumarins dyes, cyanine dyes, stilbene dyes, or oxazine dyes.

9. The process as claimed in claim 7, wherein the pH value of the colorant is adjusted using an acetic acid, ammonia water, or a sodium hydroxide.

10. The process as claimed in claim 1, further comprising a sealing treatment to the aluminum oxide film using boiling water, vapor, nickel acetate, nickel sulfate, potassium dichromate, or stearic acid.

11. The process as claimed in claim 10, wherein a hydrated aluminum oxide film is formed on the aluminum oxide film after the sealing treatment.

12. The process as claimed in claim 1, further comprising a step of quenching the substrate after the substrate being solution treated, the quenching process is carried by dipping the substrate in water having a temperature of about 20° C. to about 25° C. for about 3 min to about 5 min.

13. The process as claimed in claim 1, further comprising a step of chemical polishing the substrate before the substrate being anodized.

14. The process as claimed in claim 13, wherein the chemical polishing process comprises the following steps: the substrate is dipped in a first polishing solution having a temperature of about 70° C. to about 90° C. for about 20 seconds to about 30 seconds, the first polishing solution comprises sulfuric acid and phosphoric acid in a volume ratio of about 1-1.5:3-5; the substrate is dipped in a second polishing solution having a temperature of about 60° C. to about 80° C. for about 20 seconds to about 30 seconds, the second polishing solution comprises nitric acid and phosphoric acid in a volume ratio of about 1-1.5:3-5.

15. An aluminum alloy article, comprising:

an aluminum alloy substrate, the substrate comprising no silicon element from the surface of the substrate to the depth of about 15 μm to about 25 μm of the substrate;

an porous aluminum oxide film disposed on the substrate, the aluminum oxide film comprising no silicon element, and defining a plurality of micro-pores; and

a hydrated aluminum oxide film disposed on the aluminum oxide film.

16. The aluminum alloy article as claimed in claim 15, wherein the aluminum oxide film has a thickness of about 5 μm to about 12 μm.