Tailoring phase fractions of T' and η' phases in dual-phase strengthened Al-Zn-Mg-Cu alloy via ageing treatment

Hardness tests and transmission electron microscopy were used to investigate the strategy of tailoring the phase fraction of precipitates in an Al-Zn-Mg-Cu alloy strengthened by T' and eta' phases. Different phase fractions of T' and eta' phases are presented in samples subjected to either single or two stages of ageing treatments at 120 and 150 degrees C. For both types of ageing, the precipitation of eta' phase is found to be promoted by ageing at lower temperature and its phase fraction increases with prolonging ageing time at 120 degrees C; whereas the phase fractions of T' and eta' phases almost remain constant during ageing at 150 degrees C. Besides, the strain fields produced by T' and eta' phases were analyzed by using the geometric phase analysis technique, and on a macroscale the contributions of T' and eta' phases to precipitation strengthening have been quantitatively predicted by combining the size, phase fraction and number density of precipitates.

Automated summary

This study investigates the strategy of tailoring the phase fraction of precipitates in an Al-Zn-Mg-Cu alloy strengthened by T' and eta' phases. It is found that ageing at lower temperature promotes the precipitation of eta' phase, while ageing at higher temperature has little effect on the phase fractions of T' and eta' phases. The contributions of T' and eta' phases to precipitation strengthening can be predicted by analyzing the strain fields produced by them.