When Apple introduced the iPhone 6s on September 9, 2015 they pointed out in their press release and on their iPhone design page that they had upgraded the aluminum to that of the 7000 series aluminum, the same alloy used in the aerospace industry. Apple further noted that "It's created from a unique composition of elements that make it the strongest alloy we've ever used in an iPhone. On Thursday, one of Apple's patent applications covering this new aluminum series notes that the unique composition of the "7000 series aluminum alloys contains copper. The aluminum alloys have high yield strength, and in some aspects allow press quenchability and/or have extrusion speeds more rapid than conventional 7000 series Al alloys."

Apple's Patent Background

Commercial aluminum alloys, such as the 6063 aluminum (Al) alloy and 7000 series alloys, have been used for fabricating enclosures for electronic devices. However, the 6063 aluminum alloy has relatively low yield strength, for example, about 214 MPa, which may dent easily when used as an enclosure for electronic devices. Similarly, 7000 series aluminum alloys do not provide high yield strength. It may be desirable to produce alloys with high yield strength such that the alloys do not dent easily. The electronic devices may include mobile phones, tablet computers, notebook computers, instrument windows, appliance screens, and the like.

Many commercial 7000 series aluminum alloys have been developed for aerospace applications. Generally, 7000 series aluminum alloys have higher yield strengths than 6000 series aluminum alloys. However, such alloys still have lower than desired yield strengths. Further, typical commercial 7000 series aluminum alloys cannot be directly press-quenched, and instead must be solution heat treated and quenched, and have low extrusion speed.

There still remains a need to develop aluminum alloys with high strength, improved processing speed, and lower thermal conductivity.

Apple's Invention

Apple's invention, titled "7XXX Series Alloy with Cu Having High Yield Strength and Improved Extrudability," generally relates to aluminum alloys. More specifically, the embodiments relate to aluminum alloys with high strength and cosmetic appeal for applications including enclosures for electronic devices.

Apple notes in their filing that "7000 series aluminum alloys may provide aluminum alloys with high tensile yield strength, high extrusion speed, and/or low thermal conductivity. In certain variations, the alloys are press quenchable, allowing processing without additional subsequent solution heat treatment while not compromising the ability to form an aluminum alloy having a high tensile yield strength.

The compositions, elemental compositions, yield strength, press quenchability, and extrusion speed for examples of alloys and aluminum alloys of the present disclosure are depicted in Table 1 below. Table 1 lists example alloy compositions, tensile yield strengths, press quenchability, and extrusion speeds for examples of aluminum alloys in comparison to a 7003 alloy disclosed in U.S. Provisional Patent Application No. 61/884,860 (which is incorporated herein by reference in its entirety), and an example commercial 6063 Al alloy. The alloys have increased tensile yield strength, high extrusion speed, and can be press quenchable.

As depicted in Table 1 above, sample alloys 1, 2, and 3 have various amounts of elements including Fe, Si, Mg, Zn, Cu, and Al, along with an increased tensile strength of at least 450 MPa. Comparative alloys 6063 and 7003 have lower tensile yield strength than the presently disclosed alloys.

Sample alloys 1-3 have a yellow color due to the presence of Cu. Cu alloys have a yellow color that can be used to match existing dye colors. In various embodiments, the amount of Cu can be altered to match a desired dye color.

In further embodiments, the alloy may be optionally subjected to a stress-relief treatment between the solution heat-treatment and the aging heat-treatment. The stress-relief treatment can include stretching the alloy, compressing the alloy, or combinations thereof.

In some embodiments, the present alloys can be anodized. Anodizing is a surface treatment process for metal, most commonly used to protect aluminum alloys. Anodizing uses electrolytic passivation to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing may increase corrosion resistance and wear resistance, and may also provide better adhesion for paint primers and glues than bare metal. Anodized films may also be used for cosmetic effects, for example, it may add interference effects to reflected light.

In some embodiments, the present alloys can form enclosures for the electronic devices. The enclosures may be designed to have a blasted surface finish, or absence of streaky lines. Blasting is a surface finishing process, for example, smoothing a rough surface or roughening a smooth surface. Blasting may remove surface materials by forcibly propelling a stream of abrasive material against a surface under high pressure.

Apple's patent application 20150354045 was filed in June 2015. Apple also filed their invention in Europe. 

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