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Journal of Alloys and Compounds, Volume 550, 15 February 2013, Pages 9-22.
M. Calvo-Dahlborg, P.S. Popel, M.J. Kramer, M. Besser, J.R. Morris, U. Dahlborg
GPM, UMR 6634, University of Rouen, BP 12, 76801 Saint-Etienne du Rouvray Cedex, France
Ural State Pedagogical Institute, Ekaterinburg, Russia
Ames Laboratory, Iowa State University, Ames, IA 50014, USA
Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6115, USA
Abstract
The microstructure of Al–Si alloys of hyper- (Al80Si20) hypo- (Al93Si7) and eutectic (Al87.8Si12.2) compositions have been investigated by Small Angle Neutron Scattering (SANS) during thermal cycles above liquidus temperature. Among the three investigated compositions, the eutectic one is the most homogeneous at first heating temperature, containing in the largest amounts three families of “particles” sizes. The results show that “particles” of different sizes exist in Al–Si melts of different compositions and that their distribution change during thermal cycles above the melting point. The microstructures can be well explained by the dissolution and branching temperatures extrapolated from density measurements. During heating up to maximum temperature large “particles” dissolve and recombine into smaller ones. For all compositions, the melt at the maximum temperature after heating is more homogeneous. There exist a temperature Td at which “particles” dissolve above melting and another temperature Tb at which a molten alloy can be considered as fully homogeneous, i.e. in a true equilibrium solution state. The presented results give the background for a complete understanding of the morphology and the physical properties of Al–Si alloys of different compositions and synthesized under different conditions.
Additional Information:
“It can be anticipated from the results presented in the paper that the high sensitivity to the thermal history found for Al-Si alloys (heating and cooling rates, heating and cooling modes, structural and microstructural state of the melt as well as highest temperature reached before quench or cooling, etc.) might explain the discrepancies in properties, structures and microstructures reported in the literature on alloys of other compositions, e.g. Al- or Fe-based alloys, amorphous alloys, etc..”
