Effect of quenching rates on the artificial aging response of an AlMgSiCu 6061 wrought alloy

The influence of quenching rate on the precipitation behavior and age-hardening response of a wrought Al–Mg–Si–Cu (AA6061) alloy was investigated using differential scanning calorimetry (DSC), scanning transmission electron microscopy (STEM/EDX), kinetic analysis, and microhardness measurements. Rapid and slow quenching conditions were employed following solution heat treatment to evaluate the effect of cooling rate on subsequent artificial aging. Rapid quenching preserved a highly supersaturated solid solution and promoted the formation of a dense distribution of fine metastable precipitates during aging, resulting in a strong age-hardening response. In contrast, slow quenching induced significant precipitation during cooling, leading to solute depletion and the formation of coarse precipitates that reduced the availability of strengthening elements during subsequent aging. Microstructural observations revealed pronounced precipitate coarsening and lower precipitate number densities after slow quenching, while DSC analysis showed suppression of early-stage precipitation reactions. Kinetic analysis further indicated that prior precipitation during slow cooling altered the transformation behavior during subsequent heating. The results demonstrate that quench-induced precipitation and the associated loss of matrix supersaturation are the primary factors governing quench sensitivity and age-hardening performance in AA6061 alloy.