Thermal stability and its effects on the mechanical properties of rapidly solidified Al-Ti alloys

Microstructure and mechanical properties of the rapidly solidified (RS) Al-Ti alloy after thermal exposure treatment have been investigated. It is revealed that the Al3Ti particle: which disperses homogeneously within the Al matrix, is coarsened via a volume diffusion controlled growth mechanism described by the LSW equation. The coarsening rate increases with increasing volume fraction of the particle. The Young's modulus of the Al-Ti alloy increases with increasing particle volume fraction, which can be predicted by the Halpin-Tsai equation and the Eshelby method. The modified shear lag model used to estimate Young's modulus of the particulate reinforced composite is hereby re-modified to give a more precise evaluation. The yield strength of the RS Al-Ti alloy is found to increase with increasing volume fraction and decreasing particle size of the reinforcement. It is indicated that the continuum strengthening mechanists (the modified shear lag model and the Eshelby model) fails to explain the increased yield strength. Therefore, strengthening mechanisms based on dislocation movement have been taken into account. Considering microstructure changes in the matrix due to the presence of the reinforcement. the Eshelby type model is believed to give the yield strength of the RS Al-Ti alloy quite accurately. (C) 2000 Elsevier Science S.A. All nights reserved.