Mechanical properties and tribological behavior of AlSi11Cu alloy manufactured by additive friction stir deposition and subsequent T6 treatment

The AlSi11Cu alloy is widely applied in automotive components, favored for its inherent wear resistance contributed by the dispersion of hard Si particles. However, the needle-like silicon phase and coarse iron-rich intermetallic compounds formed by traditional casting methods severely limit the mechanical properties and wear performance of the material. To address this issue, this work proposes additive friction stir deposition (AFSD) followed by T6 heat treatment as a novel and targeted microstructural control approach. The adopted AFSD + T6 approach yields a refined microstructure with fine equiaxed grains and spheroidized second phases, thereby improving both mechanical properties and wear resistance. Compared with the cast alloy, the AFSD + T6 alloy exhibited a 58.3 % increase in yield strength, a 48.3 % increase in ultimate tensile strength, and a 66.6 % improvement in ductility. The AFSD + T6 alloy exhibited significantly reduced friction coefficient and wear rate at both 70 N and 140 N, with wear rates reaching only 7.5 % and 8.7 % of that of the cast alloy. All sliding wear tests were conducted under boundary lubrication regime using a GCr15 steel ball as the counterface material to simulate the piston ring-cylinder liner contact. This improvement is primarily attributed to microstructural refinement and enhanced particle/matrix bonding, which effectively suppresses fatigue crack initiation and propagation. As a result, fatigue wear is mitigated, allowing the formation and retention of a protective oxide tribo-layer that shifts the dominant wear mechanism to oxidative wear, thereby further enhancing wear resistance.