Effect of Mn or fe addition on age-hardening behaviour of AlMg ₂Si alloys

Microstructure and aging hardness variation of AlMgSi alloys with different Mn or Fe content were investigated to reveal the effect of Mn or Fe on the age hardening behavior of AlMgSi alloy using transmission electron microscopy. The peak hardness of the alloys with small content of Mn or Fe is higher than that of the base alloy; the peak hardness of the alloy with 0.2 at%Fe is similar to that of the base alloy but the peak hardness of the alloy with 0.25 at%Mn is lower than that of the base alloy. Si is expensed to form the dispersoid of AlMnSi or AlFeSi in the alloy with 0.25 at%Mn or 0.2 at%Fe. On the other hand, small Mn or Fe addition enhances the formation of βAA phase which is similar to Co- or Ni-addition alloys because Si is not expensed to form such dispersoid in Co- and Ni-addition alloys. It is thought that this will result in the difference of Si in the matrix for the formation of the precipitate.