Abstract: The present study aims to clarify the influence of Mo addition on α-dispersoids precipitation, associated recrystallization resistance and mechanical performance of Mn-containing Al-Mg-Si-Cu alloys. Results reveal that joint addition of Mn and Mo as dispersoid-forming elements dramatically enhances α-dispersoids precipitation, achieving a fivefold increment in number density and a 26.5 % reduction in size compared to the alloy containing only Mn addition. Additionally, the width of dispersoid-free zones is reduced from appropriately 5 µm to <1 µm. A portion of the α-Al(Mn, Mo, Fe)Si dispersoids exhibits the quasicrystal characteristics, forming coherent interfaces with the aluminum matrix. In compassion, α-Al(Mn, Fe)Si dispersoids transformed entirely into a simple cubic structure, being partially coherent with the matrix. The improvements in α-dispersoids precipitation contribute to higher pinning force on moving boundaries, resulting in superior resistance to recrystallization of the alloy. Consequently, an ideal fibrous microstructure is retained in alloy co-alloyed with Mn and Mo after solution treatment. Whereas, alloys containing only Mn or Mo show complete recrystallization. A superior balance between strength and ductility is achieved for 0.7Mn0.3Mo alloy, attributed to the increased work hardening capacity and suppression of dynamic recovery.

Key words: Al-Mg-Si-Cu-Mn alloy, Dispersoids, Recrystallization resistance, Mechanical property, Mo addition