Enhanced Strength and Ductility of AZ31 Magnesium Matrix Composites Reinforced with Titanium Particles via Friction Stir Processing

Abstract

Magnesium Matrix Composites (MMCs) have garnered significant attention due to their low density and excellent specific strength, making them attractive candidates for structural applications. However, a marked deterioration of ductility is typically observed upon the incorporation of conventional ceramic reinforcements (e.g., SiC, Al2O3, or B4C). To overcome this limitation, the use of Titanium (Ti), a metallic reinforcement with superior mechanical and chemical compatibility with magnesium alloys, has emerged as a viable alternative. In this study, AZ31/Ti MMCs were fabricated at varying volume fractions (0%, 7%, 14% and 21%) using Friction Stir Processing (FSP), an optimal solid-state technique that prevents undesirable phase formation. Microstructural investigations confirmed that Ti particles were uniformly distributed throughout the stir zone, forming a sound metallurgical interface regardless of volume percentage. Crucially, the absence of detrimental intermetallic compounds (TiAl3 or TiMg2) was confirmed by XRD and EDS, validating the superiority of FSP thermal profile. A remarkable grain refinement was achieved, reducing the grain size from approximately 93 μm in the base alloy to 4.3μm in the 21 vol. % Ti composites, due to Dynamic Recrystallisation (DRX) and the Particle-Stimulated Nucleation (PSN) mechanism. Significant enhancement in properties was demonstrated by mechanical testing. Ultimate Tensile Strength (UTS) was increased from 226 MPa to 283 MPa and Yield Strength (YS) was nearly doubled (from 98 MPa to 193 MPa) with the 21 vol. % Ti addition. A quantitative analysis confirmed that this YS enhancement was primarily driven by grain refinement (≈60% contribution) and high-density dislocation hardening (≈27% contribution), validating the synergistic strengthening mechanisms activated by FSP and Ti reinforcement. Notably, considerable ductility was maintained (reducing from 14.5% to 9.4%), which is significantly better than that of typical ceramic-reinforced MMCs. Ductile fracture features were revealed by fractographic analysis, validating the strong matrix-particle synergy and integrity.