1989 Volume 53 Issue 2 Pages 157-163
Hardness measurements, and optical and transmission electron microscopic observations were made on Al-8%Mg alloy specimens subjected to two kinds of thermomechanical treatments: either cold-worked in a large range up to 75% just after quenching and then aged (Process I), or else pre-aged for various times after quenching, cold-worked and finally aged (Process II). After Process I, the hardness increased with increasing cold reduction, although the precipitate density in the cold-worked specimens was lower than that in the specimen without cold-work: the precipitate density initially decreased markedly and then gradually increased with increasing cold reduction. This variation was attributed to the loss in the precipitation that required quenched-in excess vacancies and to the gain in the preferential precipitation on deformation bands revealed by TEM observations. The pre-aging treatment before cold-working in Process II resulted in a greater increase in hardness than in Process I owing to dislocation hardening without any loss in precipitate density.
