The suppression effect of expandable graphites (EGs) on 5 mu m aluminum dust explosions was systematically studied in an open-space dust apparatus. Flame propagation behaviors showed that flame structures became more discrete and more irregular after the addition of EGs. The flame propagation velocities declined variously owing to the suppression effect of EGs. Meanwhile, the optimum suppression concentration for each EG was determined. It was proved that the suppression effect was improved remarkably by increasing the expandable ratios of EGs. Moreover, expandable ratios of EGs had a preferable influence on the suppression effect in comparison with size distributions. Scanning electron microscopy demonstrated that the volumes of EGs increased by several hundred times when encountered with high temperature and the surface got fluffy and multihole. Based on above results, the suppression mechanism of EG for aluminum dust explosions was summarized in this paper in detail. (C) 2020 Elsevier B.V. All rights reserved.