This invention relates to micro-arc oxidation (MAO) treatment process with surface coloration on magnesium (Mg) alloys and/or aluminum (Al) alloys.
Micro-arc oxidation (MAO) treatment is promising and efficient to form thick ceramic layers with good adhesion to the substrate, which is also environmental friendly with good cost efficiency. Manufacturers, however, are often not satisfied with the MAO process since it generates an unwanted color on the treated surface. Current methods attempt to modify the surface color but require additional processes that are inefficient and time consuming.
Therefore, there is a need to provide a surface color treatment method with the MAO process on alloys.
One example embodiment is a method of treating a surface of an aluminum (Al) alloy, which includes immersing the Al alloy into an electrolyte; and applying an electric current with a current density of 0.03-0.17 A/cm2 and a pulse frequency of 500-2,600 Hz on the Al alloy for a time duration of 100-720 seconds. The Al alloy includes at least 90 weight percent of Al. The electrolyte is a mixture of 10-30 g/L silicate, 3-6 g/L hydroxide, and 8-40 g/L tungstate in deionized (DI) water. A color of the surface of the Al alloy that is treated by the method is uniformly enhanced.
Another example embodiment is a method of treating the surface of magnesium (Mg) alloy, which includes immersing the Mg alloy into an electrolyte; and applying an electric current with current density of 0.03-0.17 A/cm2 and a pulse frequency of 500-2,600 Hz on the Mg alloy for a time duration of 100-720 seconds. The Mg alloy comprises at least 90 weight percent of Mg. The electrolyte is a mixture of 20-30 g/L silicates, 5-20 g/L phosphate, 3-6 g/L hydroxide, 5-10 g/L glycerol, 0.5-2 g/L tungstate, and 5-15 g/L titanium dioxide (TiO2) nanoparticles in deionized (DI) water. A color of the surface of the Mg alloy that is treated by the method is uniformly enhanced.
Other example embodiments are discussed herein.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
As used herein and in the claims, “comprising” means including the following elements but not excluding others.
Samples made of commercial grade Al alloy 7075 are used in these experiments. By way of example, Table 600 in
The Al alloy samples are treated with a micro-arc oxidation (MAO) method. First, an electrolyte for MAO treatment is prepared by dissolving 10-30 g/L silicates and 3-6 g/L hydroxide into deionized (DI) water in a stainless steel bath. Then, an additive 8-40 g/L tungstate is added into the electrolyte. An electric current with a current density of 0.03-0.17 A/cm2 is applied on the Al alloy immersed in the electrolyte with a pulse frequency of 500-2,600 Hz for a time duration of 100-720 seconds. Chemically and mechanically protective Al based ceramic layer is formed on a surface of the Al alloy samples during the process to obtain MAO treated Al alloy. A coating thickness of the Al based ceramic layer is 5-40 um. A color of the MAO treated Al alloy surface is uniformly enhanced.
In an example embodiment, the silicate is sodium metasilicate nonahydrate, the hydroxide is sodium hydroxide, and the tungstate is sodium tungstate.
In an example embodiment, the electrolyte is a mixture of 15 g/L sodium metasilicate nonahydrate, 3 g/L sodium hydroxide and 40 g/L sodium tungstate in DI water; an electric current with a current density of 0.08 A/cm2 and a pulse frequency of 2,600 Hz is applied on the Al alloy for a time duration of 540 seconds. The color of the Al alloy surface is uniformly enhanced to match with the standard color code PANTONE 19-0823 TCX.
The Al alloy is provided in box 700.
The Al alloy is immersed into an electrolyte in box 702.
An electric current with a current density of 0.03-0.17 A/cm2 and a pulse frequency of 500-2,600 Hz is applied on the Al alloy for a time duration of 100-720 seconds is applied in box 704.
In another example embodiment, the color of the MAO treated Al alloy can be controlled by the MAO treatment time.
In another example embodiment, no additional step, such as an annealing step, is required to obtain a MAO treated Al alloy with an enhanced surface coloration.
In one example embodiment, a MAO treated Al alloy with a standard color code of PANTONE 19-0823 TCX can be obtained when 40 g/L sodium tungstate is added into the electrolyte for MAO treatment, as shown in
Samples made of commercial grade Mg alloy AZ31B or AZ91D are used in these experiments. By way of example, Table 602 in
The Mg alloy samples are treated with a MAO method. First, an electrolyte for MAO treatment is prepared by dissolving 20-30 g/L silicates, 5-20 g/L phosphates, and 3-6 g/L hydroxide into DI water in a stainless steel bath. Then, additives of 5-10 g/L glycerol, 0.5-2 g/L tungstate, and 5-15 g/L TiO2 nanoparticles are added into the electrolyte. By way of example, the TiO2 nanoparticles added are rutile titanium dioxide with a particle size of 30 nm. An electric current with a current density of 0.03-0.17 A/cm2 and a pulse frequency of 500-2,600 Hz is applied on the Mg alloy samples immersed in the electrolyte for a time duration of 100-720 seconds. Chemically and mechanically protective Mg based ceramic layer is formed on a surface of the Mg alloy samples during the process to obtain MAO treated Mg alloy. A coating thickness of the Mg based ceramic layer is 5-40 um. A color of the MAO treated Mg alloy surface is uniformly enhanced.
In an example embodiment, the silicate is sodium metasilicate nonahydrate, the phosphate is sodium pyrophosphate decahydrate, the hydroxide is sodium hydroxide, and the tungstate is sodium tungstate.
In an example embodiment, Mg alloy AZ31B is used. The electrolyte is a mixture of 30 g/L sodium metasilicate nonahydrate, 10 g/L sodium pyrophosphate decahydrate, 3 g/L sodium hydroxide, 5 g/L glycerol, 0.5 g/L sodium tungstate, and 10 g/L rutile titanium dioxide with a particle size of 30 nm in DI water; an electric current with a current density of 0.17 A/cm2 and a pulse frequency of 2,600 Hz is applied on the Mg alloy sample for a time duration of 150 seconds. The color of the Mg alloy surface is uniformly enhanced to match with the standard color code PANTONE 7540C.
The Mg alloy is provided in box 800.
The Mg alloy is immersed into an electrolyte in box 802.
An electric current with a current density of 0.03-0.17 A/cm2 and a pulse frequency of 500-2,600 Hz on the Mg alloy for a time duration of 100-720 seconds is applied in box 804.
In another example embodiment, no additional step, such as an annealing step, is required to obtain a MAO treated Mg alloy with an enhanced surface coloration.
In one example embodiment, a MAO treated Mg alloy with a standard color code PANTONE 7540 C can be obtained when 10 g/L TiO2 nanoparticles are added into the electrolyte for MAO treatment, as shown in
As used herein, the term “uniformly enhanced” means color of a MAO coating formed in this invention is darker than the conventional white MAO color, in which the sRGB values of the color of the MAO coating formed in this invention is lower than the sRGB values of the conventional white MAO color. The color of the MAO coating formed in this invention is uniform such that the results of the measured PANTONE color code by color meter can be repeated in the same MAO sample.
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