Abstract
This paper discusses the effect of deep cryogenic treatment (DCT) on the evolution of natural and artificial aging of Al-Mg-Si alloy EN AW 6026. This study provides the first research and evidence of DCT effect on dispersoids and their development in aluminum alloys. DCT induces reformation and regrowth of dispersoids during natural aging from a preferential cuboidal shape to spherical, which is also distinguishable by the change in chemical composition. Additionally, with DCT the dispersoids form in a denser manner, which consequently influences the hardness evolution with aging time. The study also reveals that the exposure duration to DCT (from 24 to 48 h) increases the DCT impact on the hardness evolution during natural aging of selected alloy. The influence of homogenization temperature on the DCT performance is also researched in connection to modified natural aging, which is correlated to the presence and formation of secondary phases during homogenization. Furthermore, DCT also promotes the formation of β'' precipitates and at the same time retards the formation of larger β' precipitates during artificial aging. After artificial aging, both dispersoids and precipitates display a denser population and more elongated shape aligned along the< 100 > axis of the aluminum matrix with DCT compared to conventionally heat-treated samples without DCT. The microstructural changes during DCT application are strongly linked to the modification of dispersoids with homogenization and artificial aging that influence the content of alloying elements in the matrix.
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