Apple has filed a patent application for a new anodizing process it says will help reduce crazing or cracks when temperatures hit over 300°F.
The application was filed with the U.S. Patent Office in May 2023 and was published in July 2024. The application describes an enclosure for an electronic device that includes a titanium-aluminum clad substrate and an anodic oxide coating disposed on the titanium-aluminum clad substrate.
The application says that the anodic oxide coating includes a density of between about 2.1 g/cm3 and about 2.4 g/cm3 or includes a maximum porosity between about 21% and about 31% and can be exposed to a temperature of over 150°C (302°F) without cracking or crazing.
The patent inventors are: James A. Curran from Sunnyvale, CA; Kar-Wai Hon from Taipei City; Todd S. Mintz from San Jose, CA; and Isabel Yang from San Jose, CA.
From the Application:
Background
The surfaces of many products in the commercial and consumer industries can be treated by any number of processes to alter the surface and create a desired effect, either functional, cosmetic, or both. One example of such a surface treatment is the anodizing of a metal substrate. Anodizing converts a portion of the metal substrate into a metal oxide, thereby creating a metal oxide layer, which is generally harder than the underlying metal substrate and can act as a protective layer. An anodizing method, often referred to as “Type II” anodizing, has been found to provide metal oxide layers with good corrosion and wear resistance for many consumer products.
While Type II anodic oxides are cosmetically appealing and can be dyed a wide range of colors, typical sealed Type II anodic oxides can develop cracks when exposed to temperatures of about 80°C. or higher, an effect known as “crazing.” In other words, “Crazing” is visually perceptible cracking of an anodic oxide coating. After an exposure to about 150°C. the Type II oxides can be crazed and the high density of the cracks can result in poor corrosion protection for the underlying substrate, particularly in corrosive environmental exposures. Consequently, a more robust anodic oxide is needed.
Summary
In some examples, an enclosure for an electronic device can include a titanium-aluminum clad substrate and an anodic oxide coating disposed on the titanium-aluminum clad substrate. The anodic oxide can include a density of between about 2.1 g/cm3 and about 2.4 g/cm3, or can include a maximum porosity between about 21% and about 31%. In some examples, the anodic oxide coating can include a thickness between about 5 μm and about 10 μm. The anodic oxide coating can be sealed with nickel acetate. In some examples, the anodic oxide coating can include a nickel concentration no greater than 0.08% by weight. The titanium-aluminum clad substrate can include a 6000-series or 7000-series aluminum alloy. In some examples, the anodic oxide coating can include a hardness value of 400 HV0.05 or greater. The anodic oxide coating can be free of crazing after a thermal exposure of at least 150°C. In some examples, the enclosure can further include a vapor deposition coating deposited on the anodic oxide coating. In some examples, the anodic oxide can include a density of about 2.3 g/cm3 or a coating mass of about 24 mg/dm−2μm−1.
According to some examples, a housing can include a substrate having aluminum and an anodic oxide disposed on the substrate, the anodic oxide including a hardness value of 450 HV0.05 or greater. In some examples, the anodic oxide can include a dye. The anodic oxide can be sealed with nickel acetate. In some examples, the anodic oxide has a color of −1<a*<1 and −1<b*<1 as measured in accordance with CIE 1976 L*a*b* color space.
According to some examples, a method for forming an oxide coating includes forming an anodic oxide coating by anodizing a substrate comprising aluminum in an electrolyte using a current density between about 1.0 A/dm2 and about 2.0 A/dm2 and an anodizing temperature of less than about 20° C. The anodic oxide can include a surface harness value between about 450 HV0.05 and about 550 HV0.05. In some examples, the anodic oxide coating comprises a thickness between about 5 μm and about 10 μm. The electrolyte can include about 5-250 g/L of sulfuric acid. In some examples, the electrolyte can include about 5-100 g/L of organic acid. The organic acid can include at least one of oxalic acid, glycolic acid, tartaric acid, malic acid, citric acid, or malonic acid. In some examples, the electrolyte can include a mixture of about 100 g/L sulfuric acid and about 20 g/L of an organic acid. In some examples, the method also includes sealing the anodic oxide coating with nickel acetate.
Detailed Description
Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims.
The following disclosure relates to anodizing processes that result in cosmetically appealing and durable anodic oxide films. The anodizing processes described herein can be used as alternatives to conventional Type II anodizing processes, which have been found to cause certain defects when exposed to elevated temperatures. Typical or conventional Type II anodic oxides that are sealed are known to develop cracks that extend through the entire thickness of the oxide film coating when exposed to temperatures of about 80° C. or higher, which is known as crazing. After exposure to about 150° C., the coatings are typically severely crazed and the high density of the cracks extending through the oxide can result in poor corrosion protection for the underlying substrate. In some examples, the cracks can be about 1 μm wide.
In some examples, the degree of crazing can be minimized by reducing the thickness of the anodic oxide. However, lower oxide coating thickness can provide less corrosion protection to the aluminum substrate. A thickness of at least 5 microns (μm), and preferably between about 5 μm and about 10 μm can provide sufficient corrosion protection of an aluminum alloy in an expected in-service environmental exposure. For a titanium-aluminum clad enclosure, the galvanic coupling with the titanium emphasizes the need for good corrosion protection of the aluminum, and hence for a relatively thick, un-crazed, and defect-free oxide coating.
However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. Furthermore, as used herein, a system, a method, an article, a component, a feature, or a sub-feature including at least one of a first option, a second option, or a third option should be understood as referring to a system, a method, an article, a component, a feature, or a sub-feature that can include one of each listed option (e.g., only one of the first option, only one of the second option, or only one of the third option), multiple of a single listed option (e.g., two or more of the first option), two options simultaneously (e.g., one of the first option and one of the second option), or combination thereof (e.g., two of the first option and one of the second option).
The full patent application can be reviewed at https://patents.justia.com/patent/20240229288
