Optimizing the Peak-Ageing Conditions for Microalloyed 2219Al Alloys

Abstract

The 2219Al alloy system microalloyed with varying contents (0–0.1 wt%) of Sn and Cd was separately processed through casting route. Overall age-hardening behaviour of cast and solutionized alloy with trace contents of Sn and Cd was individually studied, by generating the age-hardening curves at given precipitation temperature of 170 °C. Independent influences of elemental Sn and Cd on the peak-hardness, peak-ageing time, and thermal stability were investigated. For all investigated alloys, hardness increased with ageing time up to peak-hardness corresponding to peak-ageing time. Hardness dropped during over-ageing. Peak-ageing times of 2219Al alloy were evaluated to be 24 h and 40 h, when microalloyed, respectively, with Sn and Cd. The peak-hardness was achieved more steadily and faster, when microalloyed with Sn, indicating an accelerated precipitation kinetics. Trace contents of either Sn or Cd had no appreciable effect on peak-ageing time. But, trace additions of both Sn and Cd can potentially induce a higher thermal stability on the strengthening effect at elevated temperatures. For a constant peak-ageing time, the peak-hardness increased with adding either Sn or Cd up to 0.06 wt%, while further contents of the microalloying elements decreased the peak-hardness. Peak-ageing conditions to achieve best possible hardness or mechanical strength could be optimized for 2219Al alloys microalloyed with Sn and Cd. The influences of the individual microalloying elements Sn and Cd on the peak-ageing characteristics of the alloy were compared and correlated with available literature.