Patently Apple was first to reveal Apple's patents on the future use of titanium in devices back in 2017. Since then we've covered a minimum of five additional titanium related patents covering a matte finish to titanium with chemically resistant compounds to anti-fingerprint coatings and more  (01, 02, 03, 04, 05 +).

Today the U.S. Patent and Trademark Office officially published a patent application from Apple that relates to anodized films and method for forming the same. More particularly, the present embodiments relate to a titanium-aluminum clad substrate and an anodic oxide coating disposed on the titanium-aluminum clad substrate having resistance to high temperature thermal processing.

In Apple's patent background they note that 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.

Apple's technical invention covers an enclosure for an electronic device that 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/cm.sup.3 and about 2.4 g/cm.sup.3, 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 ?m and about 10 ?m. 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 HV.sub.0.05 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/cm.sup.3 or a coating mass of about 24 mg/dm.sup.?2?m.sup.?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 HV.sub.0.05 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/dm.sup.2 and about 2.0 A/dm.sup.2 and an anodizing temperature of less than about 20? C. The anodic oxide can include a surface harness value between about 450 HV.sub.0.05 and about 550 HV.sub.0.05.

In some examples, the anodic oxide coating comprises a thickness between about 5 ?m and about 10 ?m. 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.

Review the patent figures below with notes. 

It would appear that this patent is out to improve the titanium finish on Apple devices when scratched or chipped in a drop event and even protect the titanium finish when exposed to salt water spray or in salt water in general and more. 

For full details of this technical patent, review patent application 20240229288.