FORMATION OF ULTRAFINE GRAINS DURING INTENSE PLASTIC STRAINING IN AN Al-Li ALLOY AT 400 deg C

摘要

Microstructural evolution of 1421 aluminum alloy belonging to Al-Mg-Li-Sc system has been studied at T = 400 deg C and at a strain rate of about 10~(-2) s~(-1). The 1421 alloy was subjected to equal-channel angular extrusion (ECAE) up to a true strain of 12. It was shown that continuous dynamic recrystallization occurs in the 1421 alloy and results in the formation of ultrafine grains. After epsilon = 1, the arrays of low-angle boundaries are evolved. Al_3(Zr,Sc) dispersoids provide high stability of such subgrain structure. As a result, gradual transformation of low-angle boundaries into high-angle boundaries takes place with increasing strain. Firstly, recrystallization grains with an average size of about 1 mum were revealed after epsilon = 2. Following deformation leads to an increase in volume fraction of recrystallized grains which attends about 80 pct at e = 12. An the same time, the deformation induced microstructure is non-uniform. At e >= 8, the bands of recrystallized grains alternate with bands of elongated subgrains. Mechanisms of ultrafine grain formation are discussed.