Formation of hypoeutectic microstructure in a rapidly solidified Al–5 wt-%Sr alloy

Abstract

The microstructure and thermal analysis of the melt spun Al-5 wt-%Sr alloy have been investigated using X-ray diffraction, TEM, and differential scanning calorimetry (DSC). The experimental results show that rapid solidification makes the eutectic composition shift to a higher Sr content exceeding 5 wt-%Sr. The microstructure of the melt spun Al-5Sr alloy is hypoeutectic and composed of primary α-Al cells and the α-Al/Al₄Sr eutectic; quite different from that of the ingot like alloy comprising coarse primary Al₄Sr phase embedded in the eutectic. In the melt spun Al-5Sr alloy, some areas comprise equiaxed or elongated α-Al cells with intercellular irregular α-Al/Al₄Sr eutectic. Moreover, some areas fully comprise coupled α-Al/Al₄Sr eutectic. The eutectic Al₄Sr phase is lamellar strip like or vermiform in morphology. The size of the eutectic Al₄Sr phase is less than 50 nm in width. Furthermore, the very fine microstructure of the melt spun Al-5Sr alloy has a marked effect on the DSC trace in heating process.