Non-destructive assessment of crystallographic texture and mechanical behaviour in AZ31 magnesium alloys via pulsed laser thermography

This paper investigates the use of pulsed laser spot thermography as a non-destructive technique to evaluate mechanical properties and crystallographic texture changes in AZ31 magnesium alloys after thermal treatment. Eight AZ31 specimens were studied in two metallurgical conditions: three as-received (H24 tempered) and five annealed at 450°C for 10,000 seconds. Thermal diffusivity was measured non-destructively using laser spot thermography, while standard destructive methods provided hardness and grain size values for reference. Results highlighted an unexpected reduction in thermal diffusivity (around 18%) after annealing, despite a notable increase in grain size (approximately 75%) and a corresponding decrease in hardness (13%). Statistical analysis showed a clear negative correlation between grain size and thermal diffusivity (R = –0.907, p < 0.01), along with a moderate positive correlation between hardness and diffusivity (R = 0.745, p < 0.05). Unlike in steels, where increased grain size usually corresponds to higher thermal conductivity, the observed diffusivity decrease in AZ31 is likely due to microstructural complexities such as texture evolution, lattice distortions, and secondary phases. The study demonstrates–for the first time–that pulsed laser thermography effectively captures microstructural changes related to mechanical behaviour and crystallographic orientation in magnesium alloys, offering a rapid, non-destructive, and reliable alternative to traditional characterisation methods.