Papers by Keyword: Mg₂Si

Abstract: The effect of extrusion ratios and solution heat treatment on microstructure and tensile properties of extruded Al-15%Mg₂Si-1.0%Gd composite was investigated. The as-cast composite was hot extruded using three different dies and solution heat treated. After conducting heat treatment on extruded samples, microstructure alteration was examined using scanning electron microscope (SEM). Furthermore, mechanical properties of the composites were studied with tensile test. The results demonstrated that extruded and heat treated composite possesses higher strength and ductility compared to as-extruded composites. It was also found that the extrusion and heat treatment processes altered the morphology of primary Mg₂Si particles as well as reduction in their size especially when the extrusion ratio increases. Fracture surface examination revealed a transition from ductile fracture in as-extruded samples to more ductile fracture in extruded and heat treated ones. This can be attributed to the change in size and morphology of primary Mg₂Si particles as well as fragmentation of Gd intermetallic compounds.

Abstract: Magnesium alloys, in which the in-situ Mg2Si particles were dispersed, were fabricated by a casting process, and the dry sliding wear behavior of the alloys was investigated. Optical microscopy revealed that the polygonal Mg2Si particles were homogeneously dispersed in the alloys. Mg2Si particle volume fractions in the alloys were 7 and 11 vol%. Although the wear loss of the alloy decreased due to the particle-dispersion, there was no difference in the wear loss between the alloys with different volume fractions. The worn surfaces of the particle-dispersed alloys were covered with the crumbled Mg2Si particles, which would prevent seizure between the alloy and the steel counterpart, leading to an improvement in the wear resistance of the alloy. The particle-dispersion slightly decreased the scatter of the coefficient of friction during the wear for the low sliding speed and load, but the effect of the dispersion was not clearly observed for the high speed and load.

Abstract: We report on preparation of Mg₂(Si,Ge,Sn)-based thermoelectric materials by a direct induction melting method in Al₂O₃ crucible. A 40 g ingot of Mg₂Si_0.8Sn_0.1Ge_0.1 was prepared after addition to the batch 10 wt% of Mg excess. Evolution of crystal structure of the induction melted sample upon annealing and spark plasma sintering (SPS) was tracked by room-temperature X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. An evidence for the formation of Mg₂(Si,Ge,Sn) solid solution was obtained from the crystal lattice parameter of this phase which was found to be larger than that of undoped Mg₂Si. XRD and SEM indicated that alongside with the main phase of the Mg₂(Si,Ge,Sn) solid solution, an impurity phase of Mg₂Sn exists in the sample. Amount of the Mg₂Sn impurity phase is significantly reduced in spark plasma sintered sample.

Abstract: Supersaturation behavior of Al solid solutions and its effect on tensile property in Al-7Si-0.4Mg and Al-7Si-0.8Mg alloys during solution heat treatment were investigated in this study. As a result of Mg solubility measurement for Al solid solitions after solution heat treatment for 6 hrs by electron probe micro analyzer (EPMA)-wavelength-dispersive X-ray spectroscopy (WDS), Al-7Si-0.8Mg alloy had the higher Mg solubility, about 0.55 mass%, corresponding to that of Al-Si-Mg ternary phase diagram. From the tensile test, Al-7Si-0.8Mg alloy showed the improved strength and similar elongation to that of Al-7Si-0.4Mg alloy.

Abstract: Recrystallization control over the whole process route is strictly needed in order to achieve the required texture and properties. An important factor for this is the different type of particles formed in the material, their size and volume fractions. This study addresses the role of the Mn-bearing dispersoids and the Mg-Si (-Cu) particles, forming during different phases of the sheet processing, thus significantly influencing the recrystallization. It will be shown that, when present, the latter ones are playing an important role in the recrystallization control, not only in promoting the recrystallization by means of Particle Stimulated Nucleation, but also retarding it, if the particle size is sufficiently fine. Moreover, they can completely block the recrystallization, if concurrently precipitating during it. The Mn-dispersoids is comparable in its pinning effect, but takes over only when the Mg & Si atoms are in solid solution. Additionally, an update of the Diagram of Humphreys on the effect of particles on the recrystallization of 6xxx alloys is proposed and discussed.

Abstract: Mg₂Si which is composed of less toxic and naturally abundant elements,has attracted more attention for its potential application to thermoelectric devices. In this paper, the basic performance and preparation technique of Mg₂Si thermoelectric materials are introduced. reviewed the current research progress of Mg₂Si thermoelectricity. And the paper points out the existing problems and the trend of study in the future.

Abstract: The Mg₂Si compound was synthesized by the solid state reaction method. The powder precursors of Mg and Si were thoroughly mixed in ballmilling for 24 hr in an argon atmosphere. Mixed powder was pressed at 170MPa and sintered at 800 °C for 6 hr in an argon atmosphere. The sinter powder was crushed in mortar for 1 hr. The crystal structure and microstructure were measured and observed by using XRD and SEM. The microstructure and the crystal structure were analyzed. TheMg₂Si shows single phase, cubic structure and particle size about 1-10 mm.

Abstract: The metallurgy reactions in the weld pool were analyzed with the application of reaction kinetics. Furthermore a formula to quantificationally calculate the amount of Mg2Si was generated. By means of calculating the thermodynamic condition of the reaction and combined with the verification testing, this article indicates that the metallurgical product Mg2Si was created in the liquid weld pool but not separated out from the arborescent crystal during its solid state. This thesis summarizes the precipitation mechanism of Mg2Si and explains the configuration, amount and location where Mg2Si was separated out by analyzing the phase diagrams and constitution diagrams. Relevant data suggests that: the content of Mg2Si is slightly less than Mg.

Abstract: The microstructural evolution behavior of Mg-3Si-1.70Sn alloys during semisolid isothermal heat treatment was investigated by optical microscopy observations in the present study. With the holding time increasing, the grains evolve to be more spheroidal and 15min is adequate for the alloy to be spheroidized, after this coarsening begins to happen. The amount of the liquid islands inside α-Mg grains decreases and that of the liquid phase at the grain boundaries increases with the prolonged holding time. Moreover, the morphology of eutectic Mg₂Si phases changes from the Chinese script and/or long-fiber shape to short fiber or spherical shapes during semisolid isothermal heat treatment, which can be attributed to the Rayleigh shape instability.

Abstract: Mg2Si particle reinforced hypereutectic Al-Si composite was prepared by casting, and the microstructure and wear resistance of the composite were researched. The results indicated that the morphology of Mg2Si obviously changed with Mg2Si contents increasing, in which the morphology of Mg2Si in the composite had changed from polygon block to characters like and finally became coarse dendrite. There were effects of Mg2Si content and morphology on the wear resistance in the composite, which had the higher hardness and better wear resistance at the suitable Mg2Si content.