1985 Volume 49 Issue 1 Pages 59-63
Al-Si alloys with compositions in the range from 0 at% to 30 at%Si were rapidly solidified from the melt by the single roller method. The lattice parameter of aluminum decreased with increasing silicon content up to about 16 at%, indicating the extended solid solubility, but increased again for much higher silicon content. Examination by a scanning electron microscope (SEM) revealed that the eutectic structure appeared at about 25 at%Si, whereas the equilibrium eutectic composition was 12 at%Si.
The exothermal heat of the ribbons measured by differential scanning calorimetry (DSC) was as large as about 150 kJ/kg for 16-30 at%Si samples. It was mainly caused by the decomposition of supersaturated solid solution for samples with relatively low silicon contents and by the reduction of surface area of finely branched eutectic silicon during coarsening for samples with higher silicon contents. The measurement of electrical resistivity (standard four-probe technique) showed that the solid solution was stable up to about 450 K at the continuous heating of 0.33 K/s.
Spheroidization and subsequent dispersion of the fibrous silicon phase took place at far lower temperatures and shorter annealing times in comparison with the conventionally solidified sample. The reason for such an enhancement of the structural change can be attributed to the highly unstable fine net work structure of the silicon phase and the high supersaturation of silicon in the aluminum matrix.
