Effect of ultrasound power on residual stress and compressive performance in low-density die compaction of sulfur molding powder

This study investigates how different ultrasound power levels affect mechanical properties and the distribution of residual stress during low-density die compaction of sulfur molding powder. Specimens were compacted on a hydraulic press to a forming density of 1.4 g·cm-3 and then examined by X-ray inspection, microstructural analysis, residual-stress mapping, and compressive-performance testing. The results show that ultrasonic assistance markedly improves densification and microstructural uniformity. For U1, the maximum residual stress and variance were 12.87 MPa and 10.90 MPa2, whereas those for U2, U3, and U4 were reduced to 8.97, 8.93, and 7.48 MPa, yielding stress-homogenization rates of 54.86%, 57.52%, and 67.98%. The compressive strength increased from 19.7 MPa for U1 to 22.1, 22.3, and 23.0 MPa for U2, U3, and U4. Ultrasound effectively reduces compaction-induced residual stress and enhances load-bearing capacity. U2 and U3 provide the best balance between microstructural uniformity and mechanical performance. U4 achieves the highest strength but shows a risk of microstructural layering.