The Microstructures and Mechanical Properties of Low-Cost Ti Particles Reinforced AZ81 Composites

Compared to conventional ceramic particle-reinforced Mg composites, incorporating Ti particles into the Mg molten melt poses greater difficulty due to their significantly higher density compared to Mg. To develop a feasible and effective method for incorporating Ti particles, the water flow visualization experiment was used to reveal the optimum parameters of the stirring velocity, the height of the stirrer, and the angle of the stirrer to the horizon. Based on the results, the Ti/AZ81 composite was successfully fabricated at a variable speed (100–950 rpm/min) and height (4–10 cm) with an angle of 75° via nearly semi-solid stirring casting and followed by hot extrusion. The distribution of Ti particles in the Mg matrix was more homogenous, exhibiting fewer flaws and a higher recovery rate. The tensile results indicated that the Ti/AZ81 composite exhibited excellent comprehensive mechanical properties with an ultimate strength (UTS), yield strength (YS), and elongation of 374.5 MPa, 263.5 MPa, and 11.5%, respectively, which were superior to other Ti particle-reinforced AZ alloys. The characterizations revealed that the interfacial product AlTi phase was additionally formed and the Ti/Mg interface showed a strong bonding strength. The dynamic recrystallization (DRX) was significantly promoted due to the particle-stimulated nucleation (PSN) and Ti particles weakened the precipitation of Mg17Al12. Based on the quantitative calculations, the increased strength was mainly attributed to grain refinement, the mismatch coefficient of thermal expansion (CTE), and the heterogeneous microstructures of Ti/AZ81 composite, in which heterogeneous deformation-induced (HDI) strengthening is dominant.