Microstructural reconstruction, mechanical properties and wear behavior of a stir-cast SiCp/A356 composite processed by additive friction stir deposition

A stir-cast SiCp/A356 composite containing 24 vol% SiC was deposited onto an A356 substrate by additive friction stir deposition (AFSD) to investigate the solid-state reconstruction of casting defects, ceramic–matrix architecture, mechanical response, interfacial bonding, and wear resistance. X-ray micro-computed tomography, multiscale microscopy, electron backscatter diffraction, mechanical testing, and dry reciprocating sliding were employed. AFSD substantially reduced the population of large casting pores, with the maximum detected pore volume decreasing from approximately 5.16 × 10⁵ to 1.43 × 10⁵ μm³. The solidification-induced SiC-rich regions were disrupted, the eutectic Si phase was refined and redistributed, and part of the coarse SiC particles underwent fragmentation. Fine equiaxed aluminum-matrix grains were formed, with average grain sizes of 5.86 μm in the upper region and 4.93 μm near the deposit/substrate interface. The upper deposit exhibited a microhardness of approximately 100–118 HV_0.3, an ultimate tensile strength of approximately 275 MPa, and a fracture strain of approximately 2.8%, whereas the sub-top region showed lower strength but greater fracture strains of approximately 5.0–6.5%. In situ micro-CT revealed progressive damage accumulation before the formation of a dominant inclined crack. A continuous bonded interface was obtained, with a compression-shear strength of approximately 120–125 MPa. Under normal loads of 10, 20, and 30 N, the AFSD deposit exhibited wear volumes of approximately 0.13, 0.18, and 0.29 mm³, respectively, lower than the corresponding values of 0.15, 0.27, and 0.34 mm³ for the stir-cast feedstock. The largest reduction, approximately 33%, occurred at 20 N despite comparable friction coefficients. These results demonstrate that AFSD improves wear resistance primarily by enhancing microstructural continuity, surface strength, and damage accommodation rather than by universally reducing friction.