Thermal Stability of Nanocrystalline AZ31/TiB2 Magnesium Matrix Composites Prepared via Mechanical Milling

In this work, the thermal stability of nanocrystalline (NC) AZ31/TiB2 magnesium matrix composites was investigated, while the microstructure evolution and mechanical properties were analyzed. The results indicated the AZ31/TiB2 still maintained NC structure after annealing at 350 degrees C for 180 min. Even at the high annealing temperature of 400 degrees C and 450 degrees C for 180 min, their average grain size just reached about 124 nm and 155 nm, indicating excellent thermal stability. The TiB2 particles with sub-micron size uniformly distributed in Mg matrix had no change in size and no reaction with matrix during the annealing treatment. Due to the strong Zener pinning effect of TiB2 particles, the grain growth of Mg matrix at high temperature was effectively inhibited. Meanwhile, the solution and precipitation behavior of Al atoms were completed in a short time, due to the existence of many grain boundaries and structural defects. By calculation, the grain growth kinetics was described by the kinetics equation D-8 - D-0(8) = kt and the activation energy E-g for grain growth was 131.6 kJ/mol, which was much higher than that of pure Mg (92 kJ/mol). Due to their excellent thermal stability, the decrease in both compressive yield strength and ultimate compressive strength was no more than 12.2% after annealing treatment. Even annealing at 450 degrees C for 180 min, the CYS and UCS of the samples were still above 283 MPa and 295 MPa, respectively.

Automated summary

The research showed that the nanocrystalline AZ31/TiB2 magnesium matrix composites exhibit excellent thermal stability, maintaining small grain sizes even after annealing at high temperatures. This leads to a minimal decrease in compressive yield strength and ultimate compressive strength, showcasing the effectiveness of the TiB2 particles in inhibiting grain growth at high temperatures.