The kinetics of liquid Ga penetration along grain boundaries in pure Al, Al-Mn (50 ppm Mn) and Al-Ga alloys (with concentration 0.7, 1 and 3% mass. Ga) was studied. It was shown that crack-like channels filled by liquid Ga were formed along all grain boundaries. Their width was about 1-3 µm. Investigation of quenched state showed that in all samples, channels had grown with linear kinetics, and that the propagation rate depended on impurity concentration in alloys: 35µm/s for Al-Mn alloy, 14 µm/s for pure Al and 9±1 µm/s for Al with (0.7-3) % Ga alloys. The difference in penetration rates of pure Al and Al based alloys are discussed in terms of internal stress and mechanical properties.