Influence of solution treatment on surface recrystallization and age-hardening response of extruded 2196 Al-Li alloy

This study investigated the local non-uniformity of extruded 2196 Al-Li alloy and the influence of solution treatment on surface recrystallization and age-hardening response of the alloy. Microstructural analysis revealed that in the extruded alloy before solution treatment, a sub-grain layer with low dislocation density is formed at the sample edge due to the activation of dynamic recovery controlled by the refined second phase distribution at this region, give rise to decreasing hardness from the center to the edge of the extruded sample. During follow solution treatment above 440 degrees C, the increased solution treatment temperature leading to a gradual dissolution of the second phases and a growth of the peripheral coarse grain (PCG) layer thickness. A notable reversal in hardness distribution occurred at the cross-section of the rod, with higher hardness value within the PCG layer. This phenomenon can be attributed to the formation of finer and uniform distribution of T1 phase particles in the sample edge after heat treatment, the second phase particles in the sample edge are more readily to dissolve during solution treatment and thus increase the age hardening response of the alloy. The asynchronous relationship between the dissolution kinetics of second phase and the recrystallization kinetics with the solution treatment temperature gives space for simultaneously regulating the age hardness response and the PCG layer.