Effect of Ti addition on the thermal stability of nanocrystalline AZ61 Mg alloy

Nanostructured alloys possess exceptional desirable properties but suffer from low thermal stability, as a consequence of a high content of grain boundaries where the atoms are in non-equilibrium lattice positions. Here nanocrystalline Ti/AZ61 magnesium matrix composite (AZ61Mg-Ti) was annealed isothermally be-tween 573 K and 723 K. Subsequently, the thermal stability was analyzed, taking nanocrystalline AZ61 alloy as the comparative object. After annealing at 723 K for 600 min, the average grain size of AZ61Mg-Ti was approximately 95 nm, much less than that for the annealed AZ61 alloy (-450 nm). And Ti particles with size of -410 nm and nano scale Ti3Al particles with size of -8 nm were uniformly distributed in magnesium matrix. The kinetics of magnesium grain growth for nanocrystalline AZ61Mg-Ti, was well interpreted by generalized parabolic grain growth model, D-8 - D-0(8) = kt . The activation energy (E-g) for grain growth was calculated to be 134 kJ/mol, being 42 kJ/mol higher than that for pure Mg. For E-g, the contribution rates of drag effect and pinning effect to improve thermal stability were calculated to be 62% and 38%, respectively. Hardness evolution of annealed samples was studied and with raising annealing temperature the down -trend for AZ61Mg-Ti was more gradual than for AZ61 alloy due to the effect of the non-thermal sensitive Ti particles and the restricted Mg grain growth. After annealing treatment at 723 K for 600 min, the hardness was 1.27 GPa, higher than that for the annealed AZ61 (1.13 GPa). (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the thermal stability and hardness evolution of nanocrystalline AZ61Mg-Ti magnesium matrix composite. The results show that after annealing, AZ61Mg-Ti has smaller grain size with uniformly distributed Ti particles and nano scale Ti3Al particles in the magnesium matrix. The kinetics of grain growth follows a generalized parabolic model, and the drag effect and pinning effect contribute to the improved thermal stability. Additionally, the annealed AZ61Mg-Ti exhibits higher hardness.