Solidification and precipitation in Mg alloys

July 8, 2009

[1] Phase-Field Simulations of the Dendrite Morphologies and Selected Evolution of Primary Alpha-Mg Phases during the Solidification of Mg-rich Mg-Al Based Alloys

M Wang et al

A formulation of solid-liquid interfacial thermodynamic and kinetic anisotropic characteristics for hexagonal close-packed metals is proposed. The two- and three-dimensional dendritic growth of primary Mg in undercooled Mg-Al alloy melts are modeled using the phase-field method, with consideration of the integration of crystallographic lattice symmetry and experimental observations. The morphologies of three-dimensional dendrites are obtained and the calculated results have shown intricately hierarchical branched structures. The excess free energy of solution system is based on the Redlich-Kister model.

[2] Phase transformations in QE22 Mg alloy

G Barucca et al

The precipitation sequence in a QE22 Mg alloy is followed by differential scanning calorimetry, microhardness, electrical resistivity, positron annihilation spectroscopy and transmission electron microscopy (TEM) observations, after different thermal treatments. The decomposition of the supersaturated solid solution occurs via the formation of nanosized coherent structures (GP zones) followed by the co-precipitation of two metastable phases responsible for the peak ageing condition. The stable phase (Mg, Ag)12Nd appears at the highest annealing times, leading to over-ageing and hardness reduction. TEM observations provide information on the crystallographic structure of the forming phases, allowing some inconsistencies present in the literature to be clarified. Activation energies are derived from both calorimetric and resistometric measurements at different scanning rates.

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