Controlling externally solidified crystals and porosity for enhancing mechanical properties of a die-casting aluminum-silicon alloy

• Ceramic shot sleeves and higher slow shot speeds significantly reduce porosity and externally solidified crystals (ESCs) in HPDC Al-Si alloys. • Increasing slow shot speed from 0.05 to 0.1 m/s reduces pore volume fraction by 67.1% in ceramic-shot-sleeve samples versus 10.2% in steel-shot-sleeve samples. • At 0.1 m/s slow shot speed, ceramic shot sleeve castings show 8.3% higher yield strength, 17.4% higher tensile strength, and 81.4% higher elongation than steel shot sleeve. • The findings offer practical guidance for minimizing defects and enhancing mechanical properties in automotive die-cast components.