A rumor from The Information back in late November 2024, claimed that Apple would return to using an aluminum frame for high-end iPhones in the future, away from titanium frames. While that sounds like a step backwards, a new patent application published today details an all-new aluminum finish has been developed supporting this rumor. The patent relate to systems and methods for applying coatings that improve the cosmetics and enhance physical characteristics of aluminum substrates.

In Apple's patent background they note that physical vapor deposition (PVD) is a method of providing a coating on a metal substrate, often used in industry to provide a protective and sometimes cosmetically appealing coating to metal parts. Generally during PVD, a solid material is vaporized in a vacuum and deposited onto the surface of a part. The nature of the PVD coating can depend on a number of factors, including the metal substrates and the process parameters used in the PVD processes. In some applications, a PVD coating is also colored, giving the metal part an attractive colored finish.

Unfortunately, when certain metal alloy substrates are used, the PVD coating can peel, chip or otherwise delaminate from their metal substrates when exposed to scratching or scraping forces during normal use of the part, or even during certain manufacturing operations such as drilling or machining which might be performed after applying a PVD coating. This delamination can cause the underlying metal substrate to be exposed at chipped or peeled regions of the anodic oxide coating, leaving visible chip marks and rendering the metal substrate more susceptible to corrosion. This delamination can be at least partially attributed to poor adhesion of the PVD coating to the metal substrate.

In addition to making the anodic oxide coating more susceptible to delamination, the PVD process itself requires conditions that can cause less durable aluminum alloys to crack, which can further result in corrosion or detract from the aesthetic appeal of the part.

New Cosmetic Finish for Aluminum Allows

Apple's invention relates to processes for providing cosmetically appealing and durable physical vapor deposition (“PVD”) coatings on aluminum alloy substrates. Conventional PVD methods when applied to some aluminum alloys can result in corrosion of the substrate and a coating that has cosmetic defects or that is predisposed to delamination. Methods described herein involve application treatments that can be used to eliminate or reduce these cosmetic defects and to provide a well-adhered PVD coating.

In a particular embodiment, the methods and processes include forming or applying a barrier layer or an underlayer on the substrate. The barrier layer protects the substrate from the conditions of the PVD process to prevent and/or minimize corrosions. Additionally, the underlayer can improve the adhesion of the PVD coating to the substrate. Further, the processes and methods described herein can be used to create a cosmetically attractive surface on less refined and/or less cosmetic substrates.

Consequently, a much wider possibility of aluminum alloy substrates for external enclosures and small parts of electronic devices can be utilized upon application of the processes disclosed herein. For example, substrates that can incorporate the present systems and methods can include die-cast alloys, very high strength alloys with significant second phase particles, welded enclosure structures, highly recycled alloys with more impurity content, and other alloys manufactured in different methods beyond extrusion and/or computer numerical control (CNC) machining.

While certain aluminum alloy substrates, such a 6000 series aluminum or 7000 series aluminum alloy substrates using the new process is the focus of the patent, Apple points out that the methods described in the patent can be applicable to the treatment of any of a number of other suitable metal alloys, including aluminum alloy substrates that contain various alloying elements.

In addition, aluminum alloy substrates where the metal matrix is formed of recycled metals or manufacturing processes that form alloys, such as die-casting aluminum, can also be used. In some examples, the metal matrix includes more than one type of alloy material. As used herein, the terms PVD film, PVD layer, and PVD coating can be used interchangeably and can refer to any suitable PVD process used in the manufacturing of the part or enclosure, unless otherwise specified.

Most of Apple's Inventors

• Lee Hooton: iPhone Product Design Engineer
• Zack Feinberg: Manager | Product Design
• James Curran: Anodising research and development
• Shinjita Acharya, PhD: Product Design Materials Engineer
• Elizabeth Nicometo: Materials Product Design Engineer
• Brian Tryon: Product Design Materials Engineer
• Isabel Yang: Materials Product Design Engineer