Characterisation of microstructure and thermal stability of rapidly solidified Al–8·5Fe–1·3V–1·7Si alloy during prolonged exposure at 625°C

Abstract

Al–8·5Fe–1·3V–1·7Si (wt-%) alloy consolidated and rolled into sheet from pulverised planar flow cast material has been subjected to exposure times up to 575 h at 625°C. Both as received and exposed samples were investigated to reveal the effect of the exposure on microstructural stability, including dispersoid size. Microstructural characterisation was performed by a combination of X-ray diffraction, differential thermal analysis, and scanning and transmission electron microscopy. The results showed the presence of coarse plate shaped Al₁₃Fe₄ particles after 2 h at 625°C and additional polyhedral shaped Al₁₃(Fe,V)₃Si particles were observed evenly distributed within the matrix after exposure at 625°C for 290 h. Even after 575 h at 625°C, the silicide phase in the material retained the same bcc structure as in the as received condition but with a slightly increased lattice parameter. The experimentally determined coarsening rates of silicides in the material were a factor of 2 to 3 lower than predictions based on control by volume diffusion of V in the α-Al matrix.