The microstructural changes in the matrix and grain boundary have been investigated using the transmission electron microscope. Alloys were made by RSP (rapid solidification process) to obtain the supersatured solid solution. All of the experiments were made in the vaccum or under an inert gas condition to prevent the oxidation. The preaging was conducted at 500℃ for one hour to suppress the formation of the cellular phase which may have a bad effect on the mechanical properties, and then they were aged to observe the coarsening behavior of the metastable precipitates at 425℃ for 125 hr, 200hr and 400hr. The coarsening rates of cubic $Al_3(Ti_0.1V_0.2Zr_0.5)$ and $Al_3(Ti_0.2V_0.4ZR_0.4)$ precipitates were measured and the behavior of PFZ was observed, too. Most of the spherical $Ll_2Al_3X$ precipitates are found to be coherent with the matrix. The coarsening rate of the $Ll_2Al_3X$ particles obey the LSW behaviour in both alloys well. The cubic $Al_3(Ti_0.2V_0.4Zr_0.4)$ particles is 4 times as fast as that of the cubic $Al_3(Ti_0.1V_0.4Zr_0.5)$ ones. In calculating the overall lattice misfit by the application of the Vegard's law, the former have a lattice misfit larger than that of the latter. The coarsening behavior in the Al-Ti-V-Zr alloys was similar to that of Al-V-Zr alloys made by RSP, but very sluggish in comparison with that of the Al-V-Zr alloy maded by IM (ingot metallurgy). After an exposure of 400 hours at 425℃, the average radius of the $Ll_2$ spherical particles is only 5 to 7 nm. Half width of $Ll_2Al_3X$ PFZ increased linearly with the square root of the aging time. There is a systematic increase in the mean PFZ width with aging time but the scatter in the data also increases with aging time. Due to the low coarsening rate and the thermal stability and the high volume fraction of the dispersed phase, the Al-Ti-V-Zr system shows a promise as a basis for a high temperature high strength Al alloys.
