Direct drive rotational friction welding of in-situ produced hybrid metal foam-filled tubes

In this work, unique hybrid metal foam-filled tubes incorporating low-cost ceramic fillers and sacrificial NaCl space holders were produced via a novel in-situ low-pressure AlSi12 infiltration and joined by direct drive rotational friction welding. The fabricated composite and hybrid foam-filled tubes (Ø25×160 mm, with 1.5 mm thick outer wall) achieved bulk densities of 1.68 ± 0.02 g/cm 3 and 1.71 ± 0.02 g/cm 3 , respectively, which increased by up to 7.6% post-weld due to friction welding induced compaction. Computed tomography and optical metallography revealed a coherent circular-patterned weld interface and, under moderate forge pressure (2500 kPa), a preserved open-cell architecture with narrow weld thickness (219 ± 176 µm) and minimal filler fragmentation. Three-point bend tests on Ø35 mm retained weld diameter, joined hybrid foam-filled tubes demonstrated an effective bend strength of 12.1 ± 0.39 MPa, corresponding to an average of 20.4 ± 5.0% improvement when retaining a larger weld-zone diameter, with fractures consistently propagating through the open-cell foam core rather than the weld line. These results confirm that direct drive rotational friction welding provides high-integrity bonds in hybrid foam-filled tubes, offering a scalable route to lightweight structural components. • A novel hybrid metal foam–filled tube (FFT) structure was developed. • Hybrid FFTs combine ceramic-filled and open-cell zones for tailored porosity. • Friction welding is viable for cohesively joining metal foam-filled tubes. • The joined composite and hybrid FFTs had a narrow (200–300 µm) hardened weld region. • Fractures propagate through the open-cell foam core instead of the weld line.