ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

Precipitation and deformation in Al-alloys

Aluminium alloys importance on the broad fields of engineering is unbroken and therefore the research of scientific backgrounds is still of significant interest. The understanding of complex processing routes and deformation mechanisms of material microstructure are fundamental for guaranteeing required mechanical properties and applications.

The aim of this project is to focus on the evolution of strengthening phase and matrix and on shearing processes in Al alloys under service temperature and load. During precipitation hardening a single-phase alloy decompose in the miscibility gap into secondary phases which pass through different metastable states into a stable phase and provide additional strength. We make use of a recently developed dissipation model for interface to simulate 3D precipitation processes in Al alloys. The evolution of precipitates and response of the matrix and precipitates as a whole under creep conditions will be investigated.

During shear load at high temperature grain boundary sliding is the rate- controlling mechanism of deformation. Sliding consists of two main processes (Fig. 2), a flattening of the grain boundary due to the compression and tension of shearing and a sequence of localised shear transformation which creates a sliding displacement at the end of the boundary.

Volume free energy of the Ag-Cu system at 750°C with miscibility gap and three microstructures (cCu = 0.3, cCu = 0.5, cCu = 0.7) after spinodal decomposition.

Recent progress:
I: We have succeeded to implement the spinodal decomposition procedure into open source phase-field software, OpenPhase. We have examined our code for well-known example of Ag-Cu.
II: So far we have analysed the influence of a shear load on triple junctions of grains with different grain orientations (rotation of elastic constants) and triple junctions at equilibrium. The angles at the triple junction remain constant. The variation of interface energy does not have a sufficient flattening effect because of a limiting factor to guarantee thermodynamic stability.

Ongoing and future work:
I: We transfer the well-known Ag-Cu example to technical Al alloys to investigate the influence of external parameter and to predict material behaviour during the early stages of precipitation.
II: We make use of a vacancy model to nucleate voids to create plane grain boundaries using our phase-field software, OpenPhase. Furthermore we simulate the sliding process at the flattened grain boundary.

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