Ablation resistance of partially infiltrated Al-20Si/graphite composite nozzle throats in a solid rocket motor

The ablation resistance of partially infiltrated Al-20Si/graphite composite (ASCG7) nozzle throats was evaluated using a Φ127 mm solid rocket motor (SRM). X-ray diffraction, scanning electron microscopy, three-dimensional topography reconstruction, and numerical simulation were used to investigate the ablation behavior. The results indicate that ASCG7 exhibits a thermal shock factor approximately 20% higher than that of the nearly fully infiltrated counterpart and remains structurally intact after oxyacetylene ablation. During SRM testing, the endothermic melting and possible evaporation of Al-20Si within the graphite matrix mitigate thermal loading. Molten Al-Si flowing from near-surface infiltrated pores transiently covers portions of the exposed graphite and participates in surface reactions, thereby reducing direct graphite exposure locally while being continuously depleted by high-velocity gas flow and Al₂O₃ particle erosion. In addition, the residual pores within the partially infiltrated structure provide local space for thermal deformation and mitigate thermal mismatch stresses. Owing to these synergistic effects, ASCG7 maintains structural integrity and exhibits a low unilateral linear ablation rate of 0.120 mm/s under a maximum chamber pressure of 13.68 MPa and an average pressure of 12.46 MPa over 3.16 s.