Abstract
The formation of the Guinier-Preston zones in aluminium alloys is closely linked with the excess vacancies. Traces of tin added to an Al-Ag alloy exert an influence on the Guinier-Preston zones precipitation. Due to their high binding energy with vacancies, tin atoms trap some of these available to promote the diffusion of silver atoms for the formation of the Guinier-Preston zones. At 125°C, tin microalloying slows down the reaction of the Guinier-Preston zones precipitation. The diffusion coefficient of the solute atoms in the Sn free alloy and in the Sn added alloy are determined during the coarsening regime which obeys to the Lifshitz, Slyosov and Wagner theory.
Highlights
Al-Ag supersaturated solid solution evolves towards the equilibrium state following the sequence [1,2,3,4]: Supersaturated solid solution → Guinier-Preston (GP) zones → metastable γ‘ phase → equilibrium γ phase
Precipitation starts from the formation of GP zones, which are isomorphous with the matrix and, have a lower interfacial energy than intermediate or equilibrium precipitate phases that possess a distinct crystal structure
It is well known that the formation of the GP zones in aluminium alloys is closely linked with the excess vacancies
Summary
Al-Ag supersaturated solid solution evolves towards the equilibrium state following the sequence [1,2,3,4]: Supersaturated solid solution → Guinier-Preston (GP) zones → metastable γ‘ phase → equilibrium γ phase. The Guinier-Preston zones (GP), consisting of silver atom clusters, are coherent with the matrix. Precipitation starts from the formation of GP zones, which are isomorphous with the matrix and, have a lower interfacial energy than intermediate or equilibrium precipitate phases that possess a distinct crystal structure. Most trace element effects arise because they modify the nucleation and the growth characteristics of the phases which form during precipitation [5,6,7,8,9]. GP zones formation is governed by a transport mechanism of solute atoms by solute atom-vacancy complexes. The high binding energy between tin atoms and vacancies leads to the formation of vacancy-tin atom pairs and silver atom-vacancy-tin atom complexes
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