Strengthening Mechanisms of the β′ Nano-phase in Al-Mg-Si Alloy

Al-Mg-Si alloy is a typical heat-treatable strengthening alloy that can significantly improve its strength through precipitation hardening during heat treatment. Additionally, the alloy exhibits a certain level of plastic flow ability in the solid state, making it suitable for the production of complex and diverse profiles using the hot extrusion process. During the hot extrusion process of Al-Mg-Si alloy, a large number of dislocations are introduced, which have a significant impact on various properties of the alloy and the formation of precipitates. This study utilized high-resolution transmission electron microscopy (HRTEM) to investigate the interaction between unannihilated residual dislocations and semi-coherent nanoscale β′ phase in the extruded Al-Mg-Si alloy. The research results demonstrate the presence of a significant number of unannihilated residual dislocations within and around the nanoscale β′ phase. Moreover, the nanoscale β′ phase precipitates along the dislocation lines, reducing the lattice distortion energy (dislocation energy) and generating a pinning effect on dislocations, thereby increasing the energy required for dislocation motion initiation. Additionally, there is an atomic mismatch between the β′ phase and the α-Al matrix, resulting in a transition region of 2-5 nm, which enhances the interaction among dislocations and requires additional energy for dislocations to overcome this area.