The Relation between Damping Behaviour and Constitution of Quenched Aluminium-Copper-Magnesium-Silicon Alloys

Abstract

Further support has been obtained for a suggestion previously made (J. Inst. Metals, 1956–7, 85, 425) that the height of the damping maximum, δ _p , which develops in quench-ageing Al-Cu-Mg-Si alloys is related to the composition of the α phase at the quenching temperature. Parallel measurements are reported of δ _p and of the as-quenched electrical resistivity as a function of quenching temperature and of alloy composition. Discontinuities in the damping and resistivity variations showed close agreement and are claimed to coincide with the attainment of the limit of solubility of the α phase at the quenching temperature. A preliminary investigation of the feasibility of using the damping discontinuity to determine the composition limits of the α phase has led to the conclusion that the α/(α + Mg₂Si) boundary at 460° C for alloys with 0.85 at.- % copper is close to that estimated by Axon (J. Inst. Metals, 1954–55, 83, 490). The method also confirmed the expected position of the α/(α + θ) boundary but showed unexpected damping behaviour in the two-phase (α + θ) region.