Comparison of substructures in high temperature deformed aluminium alloys by polarised optical, scanning and transmission electron microscopes

Abstract

Microstructural investigation on Al, Al-11Zn and Al-5Mg alloys deformed at high temperatures in torsion were conducted using POM, SEM with EBSI and EBSP as well as TEM. The results indicate that POM can be used to reveal subgrain structure for Al and Al-11Zn, but mainly grain structure for Al-5Mg. For Al-5Mg, the real grain size with misorientation θ > 10°C. which is determined by EBSP, is smaller than that measured by POM. This suggests that POM may not reveal all large angle grain boundaries for strongly solution hardened alloys. In the order POM, SEM and TEM, they can be applied to reveal more information about subgrain structures for Al alloys. Inadequate observation by POM of subgrain structures for Al-5Mg may be explained by smaller subgrain size and higher internal dislocation density than those for Al, which arises from the solution hardening by Mg atoms.