Diffusive-hardening alloys based on gallium and containing additional metallic components (powder fillers) can be used as metallic composite materials and lead-free solders which can be easily prepared, are hardening at room temperature and demonstrate high strength after hardening. The achievement of high mechanical characteristics of DHA is important and not fully solved problem. One of the important problems is the affording of high mechanical characteristics of such alloys. At the same time the materials mentioned above must show predefined structure and physic-chemical properties. Here, the rheological properties of powder mixes and gallium pastes have been studied. Also the influence of the fractional composition onto the material properties was investigated. The linear coefficients of thermal expansion were also studied for a number of compositions. The structure of alloys was studied by SEM (Carl Zeiss EVO 40) and EDX method (Oxford Instruments INCA X-Act spectrometer) and also by X-Ray diffraction (Shimadzu XRD 7000C diffractometer). Increase of dust-like fraction in the powders of 34-40 µm in size leads to the decreasing of initial hardening time fron 5 to 2 minutes. The conclusion is the following - the fraction of dust-like powders in filler mixes must not be higher than 13-15 wt.%. Only if this condition is completed the gallium paste hardening began after at least 4 min. Physico-chemical and mechanical properties of gallium pastes consisting of the Сu3Sn filler, gallium and tin meet to considerably high requirements for modern fusible solders.