Investigation of mechanical properties and microstructural evolution in Cu─Al alloys with gradient structure

Abstract

Gradient structured (GS) materials have been reported to exhibit an outstanding mechanical properties. However, the influence of processing parameters on the GS specimens with different stacking fault energies (SFEs) and microstructural evolution during tensile are not very clear. In the present work, GS Cu─Al alloys with different SFEs of 28, 12 and 6 mJ/m2 were prepared by surface mechanical attrition treatment (SMAT) for different processing times. Results revealed that the SFE of 6 mJ/m2 specimen for SMAT 15 min exhibited a superior combination of strength and ductility, which had a significant hetero-deformation induced (HDI) stress originating from the accumulation of geometrically necessary dislocations (GNDs). Microstructure observations showed that deformation twins in the SFE of 6 mJ/m2 specimens formed in the gradient layer owing to its lower SFE. Moreover, in-situ electron backscatter diffraction (EBSD) revealed that the GNDs of the SFE of 6 mJ/m2 specimen initially formed at the grain boundaries with gradient grain size. Then, the formation of GNDs gradually migrated to the coarse grain region with increasing strain, which resulted in the HDI strain hardening and HDI stress strengthening. This work provide strategies to optimize properties and an understanding of deformation mechanisms in the GS materials during tensile test.