The knowledge of the microstructure, hence properties can be found from an understanding phase equilibria. Such an approach has been adopted in the present study to design Al-$Al_3$(Ti,V,Zr) composite systems. Phase boundaries of the quasi-ternary section of $Al_3Ti-Al_3V-Al_3Zr$ system (75at% Al) in quaternary Al-Ti-V-Zr phase diagram were first investigated by EDX and XRD analysis at 1173°K, 1273°K and 1373°K, and then thermodynamically optimized by the Thermo-Calc program. Relevant thermodynamic parameters were obtained, and isothermal and vertical sections were calculated. Using these obtained parameters, quasi-ternary Ti-V-Zr systems of Al-2at%(Ti,V,Zr), Al-4at%(Ti,V,Zr) and Al-6at%(Ti,V,Zr) were calculated in the temperature range 698°K~873°K. At 425℃ that is thought to be the maximum temperature at which Al alloy resist the degradation of mechanical strength, site fractions of Ti, V and Zr in each $D0_{22}$ and $D0_{23}$ phase were calculated and property diagrams were constructed. On the basis of site fractions, lattice parameters, a and c, overall lattice misfits, volume fractions and coarsening rate constants of $D0_{22}$ and $D0_{23}$ phase were calculated and property diagrams were constructed with a hope to find out optimum composition which maximize the precipitation-hardened strengthening effect.
