Size Of Mg2Si Research Articles

From sol\u2013gel prepared porous silica to monolithic porous Mg2Si/MgO composite materials

Mg2Si is apart from its conductivity properties expected to be a promising candidate for thermoelectric applications due to its low toxicity, low costs, and the high abundance of its precursor chemicals. Through the addition of a homogeneous distribution of nanoparticles (e.g. MgO) and by reducing the size of Mg2Si to the nanometer regime, it is possible to decrease the thermal conductivity by increasing phonon-interface scattering and, as a result, improve the thermoelectric properties. However, classical approaches do not allow for the synthesis of nanocomposites from Mg2Si and MgO. In this work, a straightforward route is presented towards homogeneously mixed Mg2Si/MgO via a two-step magnesiothermic reduction process starting from sol–gel derived hierarchically organized porous silica. Monolithic materials composed of Mg2Si and MgO in variable molar ratios are built up from a macroporous network of Mg2Si with homogeneously distributed MgO particles exhibiting a crystallite size in the range of 24–37 nm.

Laser cladding of a Mg based Mg–Gd–Y–Zr alloy with Al–Si powders

In the present work, a Mg based Mg–Gd–Y–Zr alloy was subjected to laser cladding with Al–Si powders at different laser scanning speeds in order to improve its surface properties. It is observed that the laser clad layer mainly contains Mg2Si, Mg17Al12 and Al2(Gd,Y) phases distributed in the Mg matrix. The depth of the laser clad layer increases with decreasing the scanning speed. The clad layer has graded microstructures and compositions. Both the volume fraction and size of Mg2Si, Mg17Al12 and Al2(Gd,Y) phases decreases with the increasing depth. Due to the formation of these hardening phases, the hardness of clad layer reached a maximum value of HV440 when the laser scanning speed is 2mm/s, more than 5 times of the substrate (HV75). Besides, the corrosion properties of the untreated and laser treated samples were all measured in a NaCl (3.5wt.%) aqueous solution. The corrosion potential was increased from −1.77V for the untreated alloy to −1.13V for the laser clad alloy with scanning rate of 2mm/s, while the corrosion current density was reduced from 2.10×10−5Acm−2 to 1.64×10−6Acm−2. The results show that laser cladding is an efficient method to improve surface properties of Mg–Rare earth alloys.

Wear properties of squeeze cast in situ Mg2Si–A380 alloy

In situ composites have been studied mainly to eliminate wettability, porosity and non-uniform distribution of particulate problems in composite materials. Al–Mg2Si alloy are preferred choice of such group of alloys owing to the combination of light weight and improved mechanical properties. The morphology of Mg2Si is one of the key parameters for the wear properties. In this work, squeezed casting method was used to produce samples where porosity was aimed to be reduced and morphology of Mg2Si was altered. In addition, the wear properties of in situ A380–Mg2Si were investigated. It was found that as squeeze pressure was increased, porosity and size of Mg2Si was decreased and wear rate was increased.

Effect of Isothermal Holding in Solid-Liquid Phase Region on Mg<sub>2</sub>Si Morphology in Hypereutectic Al-Si <i>In Situ</i> Composite

Mg2Si reinforced hypereutectic Al-Si in-situ composite was prepared and the effects of the isothermal holding temperature and time on Mg2Si in the composite were researched. The results showed that there were the important effects of holding temperature and time in the solid-liquid phase region of the Al-Si alloy on the size and morphology of Mg2Si. The size and morphology of Mg2Si became smaller and round with the rising of the holding temperature and prolonging of the holding time. The suitable technology in the test was obtained, in which when being held at 615°C for 300s, the size of Mg2Si decreased to 20.54μm and the shape factor of Mg2Si reached about 0.67.

Influences of Morphology and Size of Mg2Si on Microstructural Evolution of Mg–6.2Si Alloys during Partial Remelting

After isothermally treated at 660°C for 20 min, both dendritic Mg2Si in unmodified alloys and polyhedral ones in KBF4-modified alloys transformed to nearly globular morphology, while the degree of spheroidization in KBF4-modified alloy was lower than that in unmodified alloy. This result might be attributed to both restriction effect of boron and stability of octahedral primary Mg2Si crystals. After isothermal treatment at 660°C for 20 min, however, the initial grain sizes of dendritic Mg2Si crystals in unmodified alloy or polyhedral ones in modified alloy obtained by different cooling rates (copper mold with the holes of φ20 and φ6 mm) only caused a little effect on the partial remelting microstructure. The fine primary Mg2Si particles obtained from φ6 mm hole, however, were more readily to evolve to globular crystals, which might be attributed to the more active Ostwald ripening and/or coalescence.