Precipitation hardening

Precipitation hardening is a heat-treatment process that strengthens an alloy by forming finely dispersed particles that impede dislocation motion.

Solid-solution treatment: Heating an alloy to dissolve soluble constituents into a uniform solid solution. This first stage dissolves the alloying elements needed to form later precipitates.
Supersaturated solid solution: A solid solution containing more dissolved solute than is stable at equilibrium. Quenching creates the metastable starting state for precipitation.
Aluminium alloy: An alloy whose principal metallic element is aluminium. Many high-strength aluminium alloys gain strength through precipitation hardening.
Work hardening: Strengthening caused by plastic deformation that increases dislocation density. It strengthens through accumulated defects, rather than dispersed precipitates.
Quenching: Rapid cooling that suppresses diffusion and retains a high-temperature material structure. It traps dissolved solute in a supersaturated solid solution before precipitation begins.
Phase diagram: A map showing stable phases of a material as temperature and composition vary. It identifies compositions and temperatures that permit solution treatment and precipitation.
Duralumin: An early age-hardenable aluminium alloy based primarily on aluminium, copper, and magnesium. Its discovery helped establish precipitation hardening as a practical strengthening method.
Solid-solution strengthening: Strengthening caused by solute atoms that distort a host crystal lattice. It relies on dissolved atoms, whereas precipitation hardening relies on a separate particle phase.
Artificial aging: Heat treatment at a controlled temperature that accelerates microstructural changes after quenching. Aging controls the size, spacing, and distribution of strengthening precipitates.
Nucleation: The initial formation of a stable new phase within a parent phase. Precipitate formation begins when stable nuclei emerge from the supersaturated matrix.

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