Most machine shops routinely work aluminum alloys, carbon and alloy steels, stainless steels, brass and copper alloys, and selected plastics for functional prototypes and production parts. Specialty alloys and hard metals may require slower cutting strategies and different tooling.
The “right” material is the one that meets strength, corrosion, weight, and cost targets as specified on the drawing. If a substitution is proposed, it should be reviewed for mechanical equivalence and any downstream finishing compatibility (anodize, weld, passivate).
For food, medical, or marine exposure, call out the governing standard or grade family so material certificates and traceability can match your quality plan.