Influence of thermal stress relief parameters on crystallographic distortion and energy absorption behavior of closed-cell aluminium alloy foams

Aluminium foams offer lightweight structural advantages for energy absorption applications; however, residual stresses from foaming processes can degrade mechanical reliability and crystallographic integrity. This research addresses the problem by examining how thermal stress-relieving parameters affect the structural and energy-absorption performance of closed-cell aluminium alloy foams. The research contribution is the establishment of a clear correlation between lattice distortion, precipitate evolution, and compressive energy-absorption characteristics following low-temperature stress-relieving treatments. Three conditions were evaluated: as-received foam, stress relief at 500 °C for 60 min, and stress relief at 550 °C for 120 min. Mechanical behavior was examined through quasi-static compression tests, while crystallographic modifications were analyzed using X-ray diffraction and Williamson-Hall calculations. The 500 °C-60 min treatment improved compressive strength from 1.35 N/mm² to 2.88 N/mm² and enhanced energy absorption by 95%, attributed to refined and uniformly distributed precipitates that increased lattice integrity and reduced internal stresses. In contrast, excessive exposure at 550 °C for 120 min led to precipitate coarsening and a reduction in strength. XRD peak shifts confirmed changes in lattice strain resulting from thermal exposure. This study demonstrates that optimized thermal stress relief significantly improves mechanical reliability and provides insights for designing crash-resistant, load-bearing aluminium foam structures.