Variation of age-hardening behavior of TM-addition Al-Mg-Si alloys

Microstructure and aging hardness variation of Al-Mg-Si-TM alloys (TM = Co, Ni, Cr, Mn and Fe) were investigated to reveal the effect of transition metals (TMs) on the age hardening behavior of Al-Mg-Si alloy using transmission electron microscopy. The peak hardness of Co-or Ni-addition alloys is higher than the base alloy; Fe-or Cr-addition alloys is similar to the base alloy but Mn-addition alloy is lower than the base alloy. It was found different TM formed the dispersoids with different amounts of Si, which results in the different densities of the precipitates in different alloys. Si is expensed to form the dispersoid of Al(TM) Si for Cr-, Mn-and Fe-addition alloys. The ratio of TM: Si calculated from the EDS result of the dispersoid is the largest for Fe-and smallest for Mn-addition alloys. On the other hand, 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. (C) 2011 Elsevier B.V. All rights reserved.