Abstract
It is well known that ultrafine grained and nanocrystalline materials show enhanced strength, while they are susceptible to thermally induced grain coarsening. The present work aims to enhance the thermal stability of ultrafine Al grains produced by equal channel angular pressing (ECAP) via dynamically precipitation. Detailed characterization by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) has been carried out to reveal the microstructural evolution during both ECAP and post-ECAP annealing. After five passes of ECAP, both Al-8Zn and Al-6Bi-8Zn alloys show an ultrafine grain structure together with dynamic precipitated nanoscale Zn particles along grain boundaries. Upon annealing at 200 °C, ultrafine grains in the Al-8Zn and Al-6Bi-8Zn alloys show a remarkable thermal stability compared to the Al-8Bi alloy, which is mainly due to the presence of nanoscale Zn precipitates along grain boundaries. The present work reveals that nanoscale Zn particles have a positive effect on preserving the ultrafine grains during annealing, which is useful for the design of UFG Al alloys with improved thermal stability.
Highlights
Al alloys have received great interest for lightweighting in automobile and aerospace industries due to their high specific strength [1,2]
It is well known that grain refinement is effective in strengthening Al alloys
Severe plastic deformation (SPD) processes have been developed for producing ultrafine grained or nanocrystalline Al alloys [3,4,5,6] with improved strengths in comparison to their coarsegrained counterparts [3,4,7]
Summary
Al alloys have received great interest for lightweighting in automobile and aerospace industries due to their high specific strength [1,2]. It is well known that grain refinement is effective in strengthening Al alloys. Severe plastic deformation (SPD) processes have been developed for producing ultrafine grained (submicrometer) or nanocrystalline Al alloys [3,4,5,6] with improved strengths in comparison to their coarsegrained counterparts [3,4,7]. The poor ductility is attributed to the low work-hardening rate of the materials, which is a result of the low dislocation accumulation capability of the ultrafine grains [8]. A suitable annealing treatment can lead to better ductility for wrought Al alloys. Annealing on SPD-processed materials has been extensively studied to optimize its strength and ductility [3]
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