Microstructural and Hardness Changes during Isothermal Annealing of Nanostructured Al-11.6Fe-1.3V-2.3Si Alloy

Microstructural evolution and hardness change during isothermal annealing (300-550 °C, 30 min) of nanostructured Al-11.6Fe-1.3V-2.3Si alloy, prepared by mechanical alloying (MA) of elemental powders, were investigated using x-ray diffraction, transmission electron microscopy, and Vickers microhardness test. The results showed that the microstructure of the alloy after 60 h of MA consisted of a nanostructured Al-based solid solution with embedded Si. Annealing of the as-milled powders led to grain growth, internal strain release, and precipitation of the Al₁₂(Fe,V)₃Si compound above 400 °C. The grain growth of Al enhanced above the onset temperature for the precipitation of Al₁₂(Fe,V)₃Si phase. The grain size of Al after 30 min of annealing at 550 °C reached ~50 nm. Solute drag was responsible for retarding the grain growth below 400 °C, and above that temperature the grain growth was mainly limited by second-phase drag. The hardness (219 HV) of as-milled Al-11.6Fe-1.3V-2.3Si alloy decreased after annealing at 300 °C, but above that temperature the hardness increased with increasing the annealing temperature and reached ~250 HV after annealing at 550 °C for 30 min.