Surface layer characteristics of CNT/Al-Mg-Si alloy composites treated by stress peening

To determine the effect of carbon nanotubes (CNTs) on the characteristics of CNT/Al composites treated by stress peening, a 1.5 wt% CNT/Al-Mg-Si alloy composite and an Al-Mg-Si alloy were fabricated via flake powder metallurgy process. The evolution of residual stress fields, surface topography, and microhardness of peened layers were explored before and after the peening treatments. The differences in microstructure, including domain size, microstrain, and dislocation density, were determined via Rietveld refinement. After stress peening, the maximum residual stress values of CNT/Al-Mg-Si composite and Al-Mg-Si alloy were improved by 101 MPa, 83 MPa, respectively, compared with traditional shot peening. Meanwhile, the magnitude of the residual stress of CNT/Al-Mg-Si composite was generally higher than that of Al-Mg-Si alloy. Results also reveal that pre-stress and CNTs addition could improve the compressive residual stress fields treated by stress peening. Nevertheless, in the peened layers, the domain sizes were further refined (12%) and the microstrain was increased by applying prestress and CNTs. The difference in microhardness of peened layers was consistent with the change law of surface layer characteristics.