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.
A study on the ageing treatment of 2091 Al-Li alloy with an electric field
Our previous studies [1–3] have revealed that the diffusion and the phase transformation of Al–Li alloy can be influenced by applying an electric field. The experimental results showed the phenomenon of accelerating diffusion of the alloying elements, thereby inducing a phase transformation. The direct effect of electric field on the phase transformation of 2091 Al–Li alloy is investigated in this paper by means of an ageing treatment. The 2091 Al–Li alloy was melted under an argon atmosphere. Table I gives the chemical composition of the alloy. The ingots were hotand cold-rolled to 2 mm thickness. The specimens were given solid solution treatment at 530 8C for 20 min, and then aged at various temperatures and times both with (E  4 kV cmy1) and without an electric field. The mechanical properties were measured using an INSTRON electron tensile machine to investigate the ageing kinetics. The microstructure was observed by means of transmission electron microscopy (TEM). Fig. 1 shows the relationship between the yield strengths and the ageing times (16 h, 24 h, 32 h, 40 h, 48 h, 56 h, 64 h) at different temperatures (150 8C. 160 8C, 170 8C). The ageing treatment in the presence of an electric field retards the ageing kinetics and gives a lower peak strength. Similar phenomena take place at the other ageing temperatures. The times to reach the peak strength tp are fitted to the rate equation for ageing based on the coarsening of precipitate particles [4]:
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.