Abstract:Eutectic modification of A356 alloy with Li addition was investigated with scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). SEM micrograph results indicate that the transition of eutectic morphology, which is changed from flake-like to fibrous, is dramatically induced with the addition of 0.3% (mass fraction) Li. The larger microhardness corresponds to the modification morphology of the eutectic phase for A356 alloy with 0.3% Li addition. The modification effect is increased with increasing the cooling rate and degraded with prolonging the holding time of temperature. DSC results show that the eutectic solidification temperature of A356 alloy with Li addition is decreased and the eutectic temperature depression with 0.3% Li addition is decreased by 2.9 °C in cast-iron mold. The mixing enthalpies of Li with Si and Al in A356 alloy, which were calculated by the Miedema model, were used to study the mechanism of modification and ascertained its restricted growth theory.

Key words: A356 alloy; eutectic modification; lithium; DSC; mixing enthalpy