Precipitation Sequence in Mg-Zn-Sn Based Alloys

Abstract

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.

Microstructural characterization and mechanical properties of a Mg–6Zn–3Sn–2Al alloy

“…However, the effect of Sn on the precipitation behavior of the Mg-Zn system remains unclear. In addition, previous researches have shown that the Mg-Sn-Zn alloys are susceptible to rapid over-ageing [11]. Therefore, the microstructural charac- teristics and mechanical properties of a Mg-6Zn-3Sn-2Al alloy in the different states (F, T4 and T6) were studied in the present paper.…”