Microstructure Optimization and Strengthening Mechanisms of in-situ TiB2/Al-Cu Composite after Six-Passes Multi-directional Forging

The in-situ TiB2/Al-Cu composite was processed by a six-passes multi-directional forging (MDF). The microstructure evolution of the forged workpiece was examined across different regions. A comparison of the mechanical properties between the as-cast and MDFed composites was conducted, alongside an analysis of the strengthening mechanisms. The results indicate that the grain refinement achieved through the MDF process is primarily due to the subdivision of the original grains via mechanical geometric fragmentation and the occurrence of dynamic recrystallization (DRX). DRX grains are formed through discontinuous recrystallization (DDRX), continuous recrystallization (CDRX), and recrystallization induced by particle-stimulated nucleation (PSN). An increase in accumulated equivalent strain (ΣΔε) leads to finer α-Al grains and a more uniform distribution of TiB2 particles, enhancing the Vickers hardness of the composite. Additionally, the tensile properties of the MDFed composite exhibit significant improvement compared to the as-cast composites, with ultimate tensile strength (UTS) and yield strength (YS) increasing by 51.2% and 54%, respectively. This enhancement is primarily attributed to grain refinement strengthening and dislocation strengthening resulting from the MDF process.