engleski

Thermodynamic consideration of Al-2, 2Mg-2, 1Li alloy behaviour

The mechanical properties of aluminum (Al) – magnesium (Mg) – lithium (Li) alloy are the result of microstructural constituent’s development during solidification [1, 2]. During solidification, development of microstructural constituents’ is influenced by chemical composition, thermodynamic parameters and processing parameters. This research was conducted in order to assess the influence of thermodynamic parameters on solidification of Al based alloy containing 2, 2 mass.% Mg and 2, 1 mass.% Li. Solidification under equilibrium and non-equilibrium conditions were comprehended, respectively. Equilibrium considerations were obtained using Computer Aided Thermodynamic Diagram Calculation (CALPHAD), while microstructural analysis under more realistic conditions required combination of Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD). Equilibrium solidification begins with transformation of αAl dendritic network at 640°C followed by precipitation of stabile δ phase at 380°C. Precipitation of δ phase is a result of reduced solubility of Li in αAl and high Li/Mg ratio (0, 95). The ternary T phase precipitates at 290°C from balked αAl’’ matrix reach in Mg. The solidification ends with precipitation of secondary eutectic β phase at 89°C. However, microstructural analysis under more realistic conditions indicated precipitation of metastable Al3Li (δ’) phase that was not covered by the predications. Metastable δ’ phase precipitates after transformation of αAl matrix as a result of reduced solubility of Li due to the Mg influence. The δ’ phase presents a main strengthening precipitate in Al-Mg-Li alloys.

AlMgLi, equilibrium and non-equilibrium solicification, microstructure

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