Free Energy Calculation of Al-Li-Mg Alloy from Electron Level
Based on Thomas-Fermi model£¬the calculation method of free energy for atom cluster with electric field had been found. The change trend of free energy of Al-Li-Mg alloy under the effect of electric field had been calculated systemically and quantitatively. And following results had been given: mostly the free energy of Al3Li andMg5Al8 at aging temperature is lower than that of free energy at solid solution temperature, but once the negative electric field increased to certain degree there will be opposite result. At aging temperature, the free energy ofAl3Li and Mg5Al8 are lower than that of Al-2.14wt.%Li andAl-2.6wt.%Mg. And comparing with 1420 alloy, the electric field promotes the precipitation of Al3Li and restrains the precipitation of Mg5Al8.
The effect of an electric field on the mechanical properties and microstructure of Al–Li alloy containing Ce
Abstract The influence of an electric field on the tensile properties and microstructure of Al–Li alloy containing Ce is investigated. The ductility of the alloy is improved, but the strength has no change under the effect of an electric field (electric field treatment). Scanning Electron Microscopy (SEM) and TEM results show that the fracture mode is changed by the applied electric field; the subgrains become larger with the increase of the strength of the electric field, the volume fraction of δ ′ phase increases and its distribution is more random with an electric filed. The relation between the mechanical properties, and the microstructure of those alloys is analyzed. On the basis of experiment results, the mechanism of the effect of an electric field is discussed.
The nucleation and growth of S' precipitates in an aluminium - 2.5% copper - 1.2% magnesium alloy
Abstract The nucleation and growth of S' precipitates in an aluminium-2.5% copper-1.2% magnesium alloy aged at 190°C have been examined by transmission electron microscopy. The S' precipitates have been shown to be heterogeneously nucleated at dislocations, and to grow as laths on {210} planes in a 〈001〉 direction. The shape of the laths is consistent with the degree of mismatch of the matrix and precipitate planes at the precipitate-matrix interfaces. Precipitate sheets are formed at dislocations by the growth of these laths on {210} planes with a common 〈001〉 growth direction; the growth planes conform to the strain energy requirement that the misfit vector of the precipitate should lie approximately parallel to the Burgers vector of the dislocation, and are those expected from consideration of the effect of the line tension of the dislocation. The possibility of refining the precipitate distribution is discussed, and an increase in the density of sites for heterogeneous nucleation (e.g. by prestrain prior to ageing) or a modification of the interfacial energy (e.g. by addition of silicon) are both shown to result in refinement of the S' precipitate distribution.