The diffusion and phase precipitation processes in welded joints of pure Al-Cr-Ni system and low alloyed Al-Cr-Ni-X systems (where X means Co, W, or Ti) were simulated using CALPHAD method and DICTRA software focusing on the gama/gama' phase transformation. The equilibrium calculations allowed to predict phase diagram cross-sections for the Al-Cr-Ni-X systems. The performed simulations based on local equilibrium condition in diffusion couple enabled to describe the phase transformation process and obtain redistribution of alloying species, activity profiles, and other time-distance dependences for other relevant values in diffusion-affected zone of the Al-Cr-Ni / Al-Cr-Ni-X weldments.