Effects of Cooling Rate and Supercooling Degree on Solidified Structures of Al–Mn, Al–Cr and Al–Zr Alloys in Rapid Solidification

Abstract

Effects of supercooling and cooling rate on the solidified structures of Al–Mn, Al–Cr and Al–Zr alloys, which had a strong tendency to form metastable solid solution by rapid cooling of the molten alloys, were investigated by means of thermal analysis and microscopic observation. The results obtained were as follows:(1) The square of the degree of supercooling was proportional to the cooling rate on the solidification of the alloys having a solute concentration up to the maximum solid solubility limit at equilibrium (Ce). At solute concentrations higher than Ce, this relation was satisfied under the conditions that the primary crystals were a super-saturated solid solution.(2) The minimum cooling rate to form the super-saturated solid solutions containing more solute atoms than Ce was 115, 175 and 190°C/sec for Al–Mn, Al–Cr and Al–Zr respectively.(3) Metastable phase diagrams were proposed under varying conditions of composition, temperature and cooling rate in the Al–Mn, Al–Cr and Al–Zr systems.