Enhancing microstructure, mechanical strength, and electrical conductivity in Cu–W composites through multi-pass friction stir processing and pre-strain techniques

In this study, tungsten-reinforced copper matrix composites were fabricated using submerged friction stir processing (FSP). The effects of pre-strain and multiple FSP passes on the microstructure, mechanical properties, and electrical conductivity were systematically analyzed. The average grain size in the stir zone (SZ) decreased from 12.1 ± 1.2 μm in a single-pass processed sample on rolled copper to 5.4 ± 0.9 μm after three passes. Similarly, for fully annealed copper, the grain size reduced from 15.4 ± 1.4 μm after one pass to 10.2 ± 1.2 μm after three passes, highlighting the combined influence of dynamic recrystallization and particle-stimulated nucleation. Hardness measurements revealed a maximum of 174.6 ± 3.3 HV0.1 in the three-pass processed sample on rolled copper, marking a 34 % increase compared to the single-pass processed sample, primarily due to grain refinement and tungsten dispersion. The ultimate tensile strength (UTS) increased from 256.4 ± 10.4 MPa after one pass to 310.8 ± 11.2 MPa after three passes, with a corresponding improvement in elongation from 19.1 ± 1.2 % to 26.3 ± 1.3 %, attributed to grain boundary strengthening and load transfer effects. Electrical conductivity also improved with successive passes, reaching 89.1 ± 0.3 % IACS in the three-pass processed sample on rolled copper, due to reduced dislocation density and enhanced tungsten dispersion.