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The evolution of strontium (Sr) containing intermetallic phase in the eutectic reaction of Sr-modified Al-Si hypoeutectic alloy was studied with high energy synchrotron beam source for nano-diffraction experiments and x-ray fluorescence elemental mapping. Contrary to popular belief, Sr does not seem to interfere with the Twin Plane Re-entrant Edge (TPRE) growth mechanism of eutectic Si, but evolves as the Al2Si2Sr phase during the eutectic reaction at the boundary between the eutectic Si and Al grains.

Extensive experimental research work has been carried out to investigate precipitation peculiarities in Mg-Zn-Sn-based alloys during aging at different temperatures. This in-depth research was conducted on Mg-4.4wt%Zn-4.0wt%Sn-0.6wt%Y and Mg-4.4wt%Zn-4.4wt%Sn-1.1wt%Sb using x-ray diffraction (XRD), transmission electron microscopy (TEM) including high-resolution TEM, and scanning electron microscopy (SEM) equipped with an energy-dispersive x-ray spectrometer (EDS). It was found that, first, a hexagonal close-packed (hcp)-MgZn 2 phase nucleates and grows in the form of needles having coherent interphase boundaries with ␣-Mg matrix. Then the face-centered cubic (fcc)-Mg 2 Sn-phase nucleates heterogeneously, mainly at the tips of MgZn 2 needles. A very certain mutual orientation of crystal lattices of MgZn 2 , Mg 2 Sn, and ␣-Mg matrix was revealed. The orientation of Mg 2 Sn precipitates is perpendicular to that of MgZn 2 needles. They grow in the form of plates parallel to the basal planes of ␣-Mg matrix. Two-phase T-like particles are very typical of alloys aged for 1 to 16 days at 175 to 225°C. The width/length ratio of MgZn 2 needles inside T-like particles differs substantially from that found in single needles. The elastic/surface energy balance of needles and its influence on the morphology and coarsening behavior has been analyzed.

Extensive experimental research work has been carried out in order to develop an Mg-Zn-Sn based creep resistant alloy. It was found that the addition of Y improves the structural stability of this alloy. The main goal of this work was to investigate precipitation sequence in Mg-Zn-Sn-Y alloys during aging at different temperatures. In order to elucidate the sequence of phase formation, XRD, TEM, SEM and EDS analyses were applied. It was found that, firstly, an hcp-MgZn2 phase nucleates homogeneously, and grows in the form of needles having coherent interphase boundaries with Mg-matrix. High-resolution TEM images in combination with Fourier transformed images reveal a topotaxial orientation relationship which is given by {110}MgZn2 <100>MgZn2∥(002)α-Mg<110>α-Mg. The cubic fcc Mg2Sn-phase nucleates heterogeneously, mainly at the tips of MgZn2-needles when the needle's width reaches a certain critical value. The orientation of Mg2Sn-precipitates is usually perpendicular to the one of MgZn2-needles. Two-phase T-like particles are very typical of alloys aged for 1-16 days at 175-225C. The width/length ratio of MgZn2-needles inside T-like particles differs substantially from the one found in single needles. The elastic/surface energy balance of needles and its influence on the morphology and coarsening behaviour has been analyzed.