Microstructure, mechanical properties and strengthening mechanisms of Mg matrix composites reinforced with in situ nanosized TiB₂ particles

In this work, Mg matrix composites reinforced with 2.5 wt% nanosized TiB₂ particles are fabricated by adding Al-TiB₂ master alloy prepared by the chemical reaction of Al-K₂TiF₆-KBF₄ system into molten magnesium. The size distribution of TiB₂ particles extracted from the master alloy and their effects on the microstructure and mechanical properties of AZ91 matrix are investigated. The results show that the TiB₂ particles display a dominant number of particles less than 100 nm and a uniform distribution in the composites. Also, the grain size of composites is decreased compared with AZ91 alloy. The high resolution TEM reveals that the interface between nanosized TiB₂ particles and matrix is clear and bonds well. Besides, the yield strength, ultimate tensile strength and elongation to fracture of composites are improved by 49.4%, 25.5% and 51.1% respectively. Among the strengthening mechanisms of nanosized particles reinforced Mg matrix composites, dislocation strengthening and Orowan strengthening play a more important role in increasing the strength. It is noteworthy that the elongation to fracture of the composites is higher than that of AZ91 matrix, which is contrary to other works.