Steel is known for its machinability with great impact resistance and higher tensile strength. This material is typically used for parts that require better formability and stronger welds.
Aluminum was designed for machining with its high fatigue and improved strength. Aluminum also has increased resistance to corrosion due to a protective layer that forms when exposed to the atmosphere.
Cast Iron has good machinability due to the microstructures within that give cast iron increased lubrication and resistance to wear. However the strength can vary due to the natural composition in the microstructures which allow for fracturing.
There are quite a few plastics that can be machined with PVC, Nylon, and Delrin being the most popular. Plastics are lightweight with a relatively low cost. Delrin has increased machinability over Nylon.
Titanium has a high strength while being very lightweight with increased corrosion resistance. There are even alloys that are biocompatible for medical applications.
Inconel, nickel-chromium alloy 625, has high strength, excellent fabricability, and outstanding corrosion resistance. High tensile, creep, and rupture strength; out-standing fatigue and thermal-fatigue strength; oxidation resistance; and excellent weldability make Inconel a great choice for a wide number of industries and applications where increased durability is paramount.