Structure of MgLiAl alloys after various routes of severe plastic deformation studied by TEM

Abstract

Two MgLiAl alloys consisting either of alpha (hcp) + beta (bcc) phases or only beta phase were subjected to twist channel angular pressing TCAP (with helical component) or cyclic compression to a total strain of epsilon = 5 in order to study the effectiveness of various deformation modes on grain refinement. After the first TCAP pass grains of alpha phase were refined from 30 mu m down to about 6 mu m and of beta phase from initial 200 mu m down to 8 mu m. MAXStrain cycling led to much finer grains of alpha and beta phases in the range 200-300 nm causing higher hardening and indicating higher effectiveness of the process. The Li2MgAl precipitates were refined during severe plastic deformation (SPD) processes and in addition fine particles of hexagonal alpha phase of size below 100 nm were observed within the beta phase showing orientation relationship (0001) alpha parallel to (011) beta. Two-phase material after SPD showed deviation of about 1.5 degrees from the ideal Burgers orientation relationship (0001) alpha parallel to (011) beta.