Microstructural Evolution and Solidification Behavior of Functionally Graded In Situ Al–Cr Composites During Centrifugal Casting

Functionally graded Al-based composite tubes, reinforced by Al–Cr intermetallic particles, were prepared using horizontal centrifugal casting. A liquid Al–Cr alloy containing 1, 3, and 6 wt% chromium was poured into the centrifugally rotating mold. The present study focused on the effectiveness of process parameters, including mold temperature and rotational speed, on the graded profile of in situ formed particles during centrifugal casting of Al–Cr alloys. Detailed microstructure analysis revealed that the Al–Cr intermetallic compounds formed in situ in the Al-matrix, and segregated onto the outer surface of the tube. Identified intermetallic particles were Al11Cr2 and Al7Cr, with more accumulation of the former near the outer surface. The impacts of the process parameters on the thickness of the particle segregation region were found to be dependent on the initial Cr content. At higher Cr content, the resulted gradient was steeper. Brinell hardness test showed an increasing trend of hardness corresponding with the increment of the area fraction of the intermetallic particles. The maximum hardness (54 HB) was achieved at the outermost region of the centrifugally cast Al-6wt%Cr composite at a mold temperature of 600 °C and a rotational speed of 1800 rpm.