Influence of equal-channel angular pressing on 6061 Al matrix composites reinforced with NiTi particles

In this study, the effects of equal-channel angular pressing (ECAP) on the microstructure and properties of NiTip/ 6061 Al matrix composites are investigated, with an analysis of the underlying mechanisms. The results indicate that the grain size of the composites progressively decreases with an increasing number of ECAP passes. Specifically, the average grain size of the composite after 7 ECAP passes is reduced to 0.35 mu m, which is approximately 15 % of the grain size observed in composites that were not subjected to ECAP. Furthermore, the composite that was not processed by ECAP exhibits a silk texture. It is noted that both the texture content and texture strength of the composite significantly diminish following ECAP treatment. The tensile strength of the composite initially increases and subsequently stabilizes as the number of ECAP passes increases. The tensile strength of the composite without ECAP is measured at 179 MPa, while the tensile strengths of the composites subjected to 4-pass and 7-pass ECAP are enhanced to 264 MPa and 269 MPa, respectively. This enhancement can be attributed to the increase in accumulated strain and deformation resistance within the composite. However, the formation of fine new grains in the composites processed by 7-pass ECAP consumes a portion of the distortion energy, leading to a reduction in the degree of tensile strength enhancement. As the number of ECAP passes increases, the elongation of the composites initially rises and then declines. The maximum elongation observed in the composite processed by 4-pass ECAP is 12.9 %. It is hypothesized that a portion of the distortion energy is utilized to enhance the bonding between the matrix and the NiTi particles.