Stronger and harder than carbon steel, alloy steel is preferred for high-stress applications, such as axles, torsion bars, and drive shafts. It includes alloys 4130, 4140, 4340, ES2100, and 8620.

With strength that’s comparable to carbon steel at a fraction of the weight, these aluminum alloys are widely used to make structures, shafts, and molds. High-strength aluminum includes 2000- and 7000-series alloys, QC-10, and Metapor.

Especially suited for corrosive applications, such as those involving salt water, chemicals, and acids. Highly corrosion-resistant stainless steel includes 316, 2205, Alloy 20, and Nitronic 50.