Molecular dynamics simulations of multiphase Al-Cu and Al-Cu-Mg alloys: Strengthening phases and laser irradiation

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Molecular dynamics simulations of multiphase Al-Cu and Al-Cu-Mg alloys: Strengthening phases and laser irradiation Alloys containing precipitates are used in many applications because of their high strength. Aluminium based Al-Cu and Al-Cu-Mg alloys are particularly popular in lightweight construction and aviation technology. Thermal aging of these alloys leads to precipitation of complex binary and ternary phases which form depending on temperature, aging time and concentrations of alloying elements. The strength of the alloy increases because these precipitates hinder dislocation motion effectively. Further improvement of the mechanical properties can be achieved by laser irradiation which can lead to phase transformations or generation of dislocations. As a result the strength can increase further and the propagation of fatigue cracks can be retarded. In this project molecular dynamics simulations are performed in order to gain insight into the underlying mechanisms of the improved material properties. For this purpose an interaction potential for Al-Cu-Mg is developed which takes into account electron temperature dependency as recommended for simulations of laser machining. The simulations focus on interactions of dislocations with complex precipitates, the investigation of effects resulting from laser irradiation, and improved modelling of precipitate phases using Monte Carlo / molecular dynamics hybrid simulations. The aim is to understand the influences of different factors as crystal structure of the precipitate, coherency strain or intensity and pulse duration of laser irradiation on the strength. It is intended to identify the main contributions of precipitation strengthening in Al-Cu and Al-Cu-Mg alloys. The absorption as well as electron and coupling parameters are positiondependent for laserirradiation of inhomogeneous materials. Furthermore, electron temperature dependent potentials developed in this project are applied in the simulations. Considering these dependencies requires substantial further development of the molecular dynamics software IMD. Furthermore, the implementation of the Monte Carlo molecular dynamics hybrid simulation in IMD will be extended in order to simulate the vacancy assisted formation of more realistic precipitates.