Al–Ga–Sn, Al–Ga–In and Al–Ga–In–Sn alloys were prepared using arc melting technique. Their microstructures were investigated by X-ray diffraction and scanning electron microscopy with energy dispersed X-ray. Based on microstructure analysis, the phase constituents of alloys at Al grain boundaries were identi?ed. The melting points of Al grain boundary phases were measured using differential scanning calorimeter.The reactivities of Al–water at different water temperatures indicate that liquid Al grain boundary phases promote Al–water reactions of alloys. The melting points of Al grain boundary phases affect the reaction temperatures of Al–water, leading to different reaction temperatures of alloys. The measured H2 generation rate and yields of alloys are related to the compositions of alloys. The theory of microgalvanic cell is used to explain the observed different H2 generation rates of alloys. Al-Ga-Sn, Al-Ga-In and Al-Ga-In-Sn alloys were prepared using arc melting technique. Their microstructures were investigated by X-ray diffraction and scanning electron microscopy with energy dispersed X-ray. analysis, the phase constituents of alloys at Al grain boundary were identi? ed. The melting points of Al grain boundary phases were measured using differential scanning calorimeter. reactivities of Al-water at different water temperatures indicate that liquid Al grain boundary phases promote Al The water points of Al grain boundary phases affect the reaction temperatures of Al-water, leading to different reaction temperatures of alloys. The measured H2 generation rate and yields of alloys are related to the compositions of alloys. The theory of microgalvanic cell is used to explain the observed different H2 generation rates of alloys.