Effect of aging time and temperature on microstructure and microhardness of nano-SiC/Al-Zn-Mg-Cu composites

Nano-SiC/Al-Zn-Mg-Cu composites are prepared by high-energy ball milling combined with spark plasma sintering （SPS） and hot extrusion. The precipitation hardening characteristics， aging precipitation behavior， and microhardness of nano-SiC/Al-Zn-Mg-Cu composites are studied by differential scanning calorimetry （DSC）， synchrotron radiation X-ray diffraction（SR-XRD）， transmission electron microscopy （TEM） analysis and microhardness test. Results show that the addition of nano-SiC particles increases the thermal diffusion activation energy of η'and η phases， and inhibits the growth of the precipitated phase in the composites. Moreover， adding SiC particles increases the concentration of η' phase and refines the η phase at the grain boundaries， which enhances the precipitate-strengthening effect. With the increase of aging time， the density and size of η' phase within the grain increases， and gradually transforms into η phase. Meanwhile， the η phase precipitated along the grain boundary coarsens. Increasing the aging temperature can increase the free energy of the composite system and the diffusion rate of the solute atoms， promoting the growth of η' phase and η phase and the transformation of η' to η phase. The addition of 3%（volume fraction）SiC nanoparticles increases the microhardness by about 50%， and the peak aging time decreases from 64 h to 16 h with the aging temperature increasing from 100 ℃ to 140 ℃， but the aging temperature change has little effect on the hardness value of peak aging.