Abstract
The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al–1.1Mg–0.5Cu–0.3Si at. pct alloy was investigated. Following solution heat treatment and natural aging, the alloys were analyzed in an undeformed, artificially aged condition and in a two-step deformed condition consisting of 80 pct deformation, artificial aging, 50 pct deformation and a final, short artificial aging. Using electron microscopy, it was found that both alloys contained similar amounts of primary Mg2Si particles, while the higher Fe level alloy produced roughly twice the number density and volume fraction of primary bcc α-AlFeSi particles. Lower volume fractions of hardening precipitates were measured in the high Fe level alloy, as attributed to the lower amount of Si available for precipitation. Using atomic resolution scanning transmission electron microscopy, a mix of L phases and structural elements of GPB zones was found in the undeformed conditions. In the deformed conditions, scanning precession electron diffraction revealed that the precipitates were nucleated both on and between deformation induced defects. The addition of Fe affected the relative ratio of these precipitates. Hardness measurements of conditions combining deformation and artificial aging were performed to investigate the hardening mechanisms at each processing step.