Phase diagrams and ternary compounds of the Al-Mg-Cr and the Al-Mg-Mn systems in Al-rich side

Abstract

Phase diagrams in the Al-rich side of solid state Al-Mg-Cr and Al-Mg-Mn alloys were reconfirmed. In addition, crystal structures of ternary compounds in these alloys were studied by an X-ray analysis with Cu-Kα radiation. Following results were obtained:(1) In the Al-rich side of the Al-Mg-Cr system, the α solid solution, θ (CrAl7), β (Mg2Al3) and the ternary compound E were identified. The shape of the phase diagram was almost the same as that previously reported. However, it was found that the solid solubility of Cr in Al was reduced as the Mg content increased.(2) In the Al-rich side of the Al-Mg-Mn system, the α solid solution, MnAl6, β (Mg2Al3) and the ternary compound T were identified. The shape of the phase diagram was nearly the same as that previously reported, except the region of (α + T). This region existed at the lower Mg content side as a whole.(3) A complete analysis of the crystal structure of the E phase was difficult because satisfactory electrolytic separation of the compounds was not possible. However, it was fbund that the diffraction intensities of the E phase in the present study was satisfactorily explained by the parameters given by S. Samson. Thus, it was confirmed that the E phase was face centered cubic with the space group Fd3m, had the basic composition of Mg3Cr2Al18 and had the Iattice parameter of 14.545±0.001Å.(4) It was found that the diffraction pattern of the T phase was very similar to that of the E phase. Since this fact suggested that the T phase had the same structure as the E phase, the computation based on the parameter of the E phase was performed. The computed diffraction intensity was in close agreement with the observed value. Thus, it was concluded that the T phase was also face centered cubic with the space group Fd3m and had the basic composition of Mg3Mn2Al18. The lattice parameter was 14.529±0.001Å.