Can a diode laser engrave metal?

Coated metal, yes; bare metal, no. A diode happily marks anodized aluminum (bleaches the dye white) and blasts powder coating off tumblers to expose the steel underneath — two of the best-selling product lines in the hobby.

Bare stainless or brass reflects 455nm; no diode setting changes that. The upgrade path is a 2W IR module for light surface marks, or a fiber/MOPA machine for real metal engraving, depth, and color.