Alloying

Alloying is the practice of combining two or more elements to produce a material with properties different from its components. Most alloys are metals or metal-like; adding elements can alter hardness, strength, ductility, corrosion resistance, and thermal or electrical behavior. Alloying is achieved by melting the constituent elements and permitting them to mix, or by solid-state diffusion through high-temperature treatment or aging processes.

Common mechanisms include substitutional solid solutions, where atoms substitute for host atoms in a crystal lattice, and interstitial solid solutions, where small atoms occupy gaps between larger atoms. Phase formation, precipitation hardening, and the development of intermetallic compounds also contribute to property changes. Heat treatment can further modify microstructure to tune performance.

Notable examples: steel, an alloy of iron and carbon (and often chromium, nickel, vanadium, or molybdenum to tailor properties); bronze, copper with tin; brass, copper with zinc; aluminum alloys, which mix aluminum with magnesium, silicon, or others; and nickel-based superalloys used in high-temperature engines. Alloys are chosen for balance of strength, hardness, toughness, weight, and corrosion resistance.

Historically, alloying began in antiquity with bronze and brass; modern alloying supports extensive aerospace, automotive, construction, and electronics applications. The field continues to evolve with new alloy systems and processing techniques such as additive manufacturing and advanced heat treatments.