Eutectic reaction and microstructural characteristics of Al (Li)-Mg2Si alloys

Abstract

Thermal analysis, directional solidification and metallographic techniques were applied to investigate the pseudobinary eutectic reaction process and the microstructural characteristics of Al(Li)-Mg₂Si alloys. It was demonstrated that the eutectic reaction curve for L ⇔ Al(Li) + Mg₂Si in the Al(Li)-Mg-Si system moves to the Al-rich corner with the increase of Li additions. The pseudobinary eutectic point with the highest melting temperature and null temperature range of solidification (Δ T) and the ternary eutectic point for L ⇔ Al(Li) + Mg₂Si + Si all move towards the Si-rich direction. Li additions widen the range of yielding binary eutectic of Al(Li)-Mg₂Si and depress the appearing of ternary eutectic efficiently. Al(Li)-Mg₂Si eutectic alloys have the best aligned structure when the directional solidification occurs with a ΔT = 0. The Mg₂Si phase has a diversity of morphologies such as rod-like, crossed and rooftop-like. These various morphologies has the same preferred growth direction, i.e. [100].