Experimental study of the ternary magnesium-aluminium-strontium system

The phase diagram of the ternary magnesium-aluminium-strontium (Mg-Al-Sr) system has been investigated with 22 different alloys by DSC, XRD and metallography. Liquidus temperature and enthalpy were determined. Al4Sr and (Mg) were found to be the dominating phases in the investigated alloys. Four new phase fields have been identified; the new phases were tentatively designated as τ1, τ2, τ3 and τ4 and may be ternary intermetallics or solid solutions. Some peak positions of τ1 corresponded well with the newly reported ternary compound Al3Mg13Sr. The identified phases in the as-cast condition were found consistent and thermodynamically stable with the post-DSC sample (25 ↔ 700 °C) in the investigated alloys. Two ternary eutectic transformations have been observed. The experimental results were compared with the pertinent thermodynamic findings. A considerable discrepancy in the solid-phase transformation temperature was observed. Predicted phases by the thermodynamic calculation do not agree with the present XRD results for nine samples, which suggests that this system should be remodeled.