Influence of fraction of high angle boundaries on the mechanical behavior of an ultrafine grained Al-Mg alloy

The mechanical behavior of ultrafine grained AA5052 processed through different techniques-rolled, annealed, friction stir processed (FSP) and equal channel angular pressed (ECAP)-were compared and correlated with microstructure. The microstructure was characterized using electron back scattered diffraction to obtain the boundary spacing, the fraction of high angle boundaries and to estimate the dislocation density from local misorientations. Both FSP and ECAP conditions had ultrafine boundary spacing, but the fraction of high angle boundaries was larger for the FSP condition. Tensile deformation carried out at 297 K and 10−3 s−1 showed a lower work-hardening rate and recovery rate for FSP as compared to the ECAP condition. It was inferred that low angle boundaries are more effective sinks for dislocations. When comparing differently processed materials, the strength, ductility and work-hardening behavior correlate better with the fraction of high angle boundaries than the boundary spacing.