The effect of the chromium or the manganese addition on the precipitation behavior in the Al–7%Mg alloy was experimentally investigated. The solution treatment was conducted at various temperatures in order to reveal the influences of concentration of solute atoms, size of crystal grains and size and morphology of Al
6Mn or Mg
3Cr
2Al
18 phase on the precipitation of metastable β′ and stable β phases. The precipitation of the β′ and the β phases in the chromium or the manganese added specimen was greatly accelerated by a refinement of the crystal grain. In addition, these precipitates were formed in the interface between the matrix and the coarse second phases (Al
6Mn or Mg
3Cr
2Al
18). In the manganese added specimen, the precipitation of the β′ and the β phases was slowed down as solutionizing temperature was raised. No clear relationship was obtained between the formation of the β′ and the β phases and the precipitates of Al
6Mn and Mg
3Cr
2Al
18.
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