Abstract: An electronic device such as a wristwatch may include a conductive housing. A corrosion-resistant coating may be deposited on the conductive housing. The coating may include transition layers and an uppermost alloy layer. The transition layers may include a chromium seed layer on the conductive housing and a chromium nitride layer on the chromium seed layer. The uppermost alloy layer may include TiCrCN or other alloys and may provide the coating with desired optical reflection and absorption characteristics. The transition layers may include a minimal number of coating defects, thereby eliminating potential sites at which visible defects could form when exposed to salt water. This may allow the electronic device to exhibit a desired color and to be submerged in salt water without producing undesirable visible defects on the conductive housing structures.

Abstract: This application relates to a part for a portable electronic device. The part includes a titanium alloy substrate including a network of branching channels. The branching channels include a first channel and a second channel, where the first channel is defined by a first channel wall that extends away from a first opening in the exterior surface, and the second channel is defined by a second channel wall that extends away from a second opening in the first channel wall.

Abstract: An electronic device such as a wristwatch may include a conductive housing. A corrosion-resistant coating may be deposited on the conductive housing. The coating may include transition layers and an uppermost alloy layer. The transition layers may include a chromium seed layer on the conductive housing and a chromium nitride layer on the chromium seed layer. The uppermost alloy layer may include TiCrCN or other alloys and may provide the coating with desired optical reflection and absorption characteristics. The transition layers may include a minimal number of coating defects, thereby eliminating potential sites at which visible defects could form when exposed to salt water. This may allow the electronic device to exhibit a desired color and to be submerged in salt water without producing undesirable visible defects on the conductive housing structures.

Abstract: This application relates to a multi-piece enclosure for a portable electronic device. The enclosure includes a metal part including a metal substrate and a metal oxide layer overlaying the metal substrate, the metal oxide layer having an external surface that includes openings that lead into undercut regions. The openings are characterized as having a first width, and the undercut regions are characterized as having a second width that is greater than the first width. The enclosure further includes a non-metallic bulk layer including protruding portions that extend into the undercut regions such that the non-metallic bulk layer is interlocked with the metal part.