How does quenching create a supersaturated solid solution in aluminum?

In the context of metallurgy, quenching creates a supersaturated solid solution in aluminum by leveraging temperature-dependent solubility.1

The process begins by heating the aluminum alloy to a high temperature—such as 540° C (1,000° F) for an aluminum-copper alloy—where the alloying elements dissolve completely into the metal matrix to form a single-phase solid solution.1

By rapidly cooling the metal through quenching, the atoms of the alloying elements are "frozen" in their positions within the matrix. This rapid cooling prevents the atoms from diffusing and forming a separate solute-rich precipitate, which would naturally occur during slow cooling as solubility decreases at lower temperatures. Consequently, the resulting structure retains a higher concentration of solute atoms than is thermodynamically stable at room temperature, creating a supersaturated solid solution. This state is a critical precursor to precipitation hardening, where subsequent aging allows for the controlled formation of fine precipitates that strengthen the material.21