Thermodynamic calculated and TEM observed microstructure of Al-Li-Mg-Si alloys

The microstructures of two AI-Li-Mg-Si alloys have been studied by thermodynamic calculation and TEN observation in this paper. The results show that the addition of lithium changes the precipitation behavior of Al-Mg-Si alloys. The calculated AI-Li-Mg-Si phase diagrams are used to investigate the equilibrium phase distribution as a function of temperature for the Al-1.8Li-1.8Mg-0.8Si alloy and Al-1.8Li-2.8Mg-0.8Si alloy. According to calculation, delta' phase (Al3Li) becomes the mayor precipitate in Al-1.8Li-1.8Mg-0.8Si alloy while a few amount of beta'(Mg2Si) phase and AlLiSi phase precipitate. TEM observation show that delta' phase and AlLiSi phase are precipitated in Al-1.8Li-1.8Mg-0.8Si and heterogeneous rod Mg2Si phase is also observed. Calculation on Al-1.8Li-2.8Mg-0.8Si show that both delta' phase and Mg2Si phase precipitate on aging temperature. Experimental results are in agreement with calculation. Published by Elsevier Science S.A.