Mg2Si Composite Research Articles

The effect of Zr on the microstructure and tensile properties of hot-extruded Al–Mg2Si composite

This work was carried out to investigate the effect of different amounts of Zr on the microstructure and tensile properties of homogenized and hot extruded Al-15% Mg2Si composite using optical microscopy and scanning electron microscopy (SEM). The results showed that Zr addition has no significant effect on the morphology of both primary and eutectic Mg2Si phase in as-cast condition. But, applying homogenizing and extrusion processes changed the morphology of Mg2Si phases from irregular to a more spherical shape. Further results demonstrated that the average size of primary Mg2Si decreases with the addition of Zr up to 0.1% from 56μm to 24μm in hot-extruded condition. As the mount of Zr increased up to 0.1wt.%, ultimate tensile strength (UTS) and elongation values were also increased from 160MPa and 3.2% to 292MPa and 9.5%, respectively. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in hot-extruded Zr-modified specimens. This can be attributed to the changes in size and morphology of Mg2Si intermetallic and porosity content.

Study on fracture behaviour of Al–15%Mg2Si metal matrix composite with and without beryllium additions

In this study, the influence of Beryllium (Be) content on the fracture behaviour of Al–15%Mg2Si composite was investigated. The results showed an increase in mechanical properties with increasing of Be content. The stress–strain curves of samples showed a same category of serrations reflecting non-uniform deformation. Scanning electron microscopy was employed to examine the crack nucleation and fracture model. The results indicate that Al–15%Mg2Si composite shows different behaviours of crack initiation and fracture for samples with and without Be. Differences observed in the fracture behaviour were attributed to microstructural changes as well as morphological aspects of primary Mg2Si particles.

Synthesis kinetics of Mg2Si and solid-state formation of Mg–Mg2Si composite

The synthesis kinetics of Mg2Si intermetallic compounds (IMC) from the elemental mixture of Mg–Si powders was studied by using differential thermal analysis (DTA). The exothermic peaks were at 818K, which indicated the synthesis reaction of 2Mg+Si→Mg2Si. The synthesis kinetics of Mg2Si was evaluated by the Ozawa method and KAS method, and its activation energy was calculated as 377.53KJ/mol. Based on the data from DTA curves, the bulky materials of Mg–Mg2Si composite were prepared through solid-state reaction by using SPS consolidation process. From the results of XRD and SEM-EDS analysis on the composite materials, it was clarified that at low temperatures of 813K and 833K, Mg and Si powders never react completely, and the suitable temperature of solid-state synthesis by SPS should be about 853K.

Thermoelectric properties and oxidation behaviour of Magnesium Silicide

We study the oxidation behaviour of Mg2Si and the thermoelectric properties of Mg2Si composites. Above 723 K, Mg2Si reacts with O2 in air to yield MgO and Si. Using the Johnson-Mehl-Avrami (JMA) equation, the Avrami exponent (n) is equal to ~0.5, and it depends on the reaction temperature and time; this indicates that the oxidation is controlled by the diffusion-controlled reaction. In order to improve the oxidation-resistance of Mg2Si, β-FeSi2 films were fabricated on sintered Mg2Si samples by RF magnetron-sputtering deposition at RT followed by post-annealing at 873 K in vacuum. The β-FeSi2 layer effectively prevented the diffusion of oxygen at 873 K and improved the oxidation resistance of Mg2Si. The thermoelectric properties of impurity-doped Mg2Si composites fabricated using the reduction method of metal oxide / carbonate / hydroxide additives (Al2O3, Sb2O3, Bi2O3, Li2CO3, CuO, Ag2O, In2O3, La(OH)3, Ga2O3, Na2CO3, and Y2O3) have been characterized. The maximum values of ZT for impurity-doped Mg2Si composites fabricated using the reduction method of Al2O3, Bi2O3, Sb2O3, and La(OH)3 additives show 0.58 at 862 K, 0.68 at 864 K, 0.63 at 863 K, and 0.06 at 865 K, respectively.

Microstructure and Tensile Properties of Al-15wt%Mg<sub>2</sub>Si Composite after Hot Extrusion and Heat Treatment

In this study, the relationship between microstructures and mechanical properties of the extrusion processed Al-15wt.%Mg2Si composite was investigated after applying various extrusion ratios (6:1, 12:1 and 18:1) and solution treatment. Various techniques including metallography, tensile testing and SEM fractography were utilized to characterize the mechanical behavior of the MMC. Results demonstrated that extruded and heat treated composite possesses considerably higher strength and enhanced ductility in comparison with the as-cast samples. It was also found that heat treatment and extrusion processes do not change the primary Mg2Si morphology considerably, but its size increases as extrusion ratio decreased. Heat treatment and extrusion ratio effects on tensile strength, elongation of extruded specimens were also studied in this work.

Enhanced ductility in an Al–Mg2Si in situ composite processed by ECAP using a modified BC route

A modified BC route, noted as BC-m, was designed and employed to process an Al–Mg2Si composite in an effort to improve the ductility of the composite. The modification was implemented to improve the effectiveness of particle redistribution of the conventional BC route while maintaining its high grain refinement efficiency. The experimental results demonstrated that route BC-m was strongly effective in redistributing particles while maintaining a comparable microstructural refinement efficiency relative to route BC, which led to an increase in ultimate tensile strength and much higher ductility in the composite. Additionally, the use of route BC resulted in higher yield strength because of its stronger work-hardening effect compared to route BC-m.

Modification of Cast Al-Mg2Si Metal Matrix Composite by Li

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15 pct Mg2Si composite were investigated. Adding 0.3 pct Li reduced the average size of Mg2Si primary particles from ~30 to ~6 μm. The effect of cooling rate was investigated by the use of a mold with different section thicknesses from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and cooling rate increases, and their effects are additive. Similarly, both effects increased ultimate tensile stress (UTS) and elongation values. The thin sections show somewhat unexpectedly low and scattered tensile results attributed to the casting defects observed in fracture surfaces. The Li-modified alloy displays serrated yielding behavior that is not fully explained here. The refinement by Li and enhanced cooling rate is explained in terms of an analogy with the effect of Sr and cooling rate in Al-Si alloys, and is ultimately attributed to the effect of the alkali and alkaline earth metals deactivating oxide double films (bifilms) suspended in Al melts as favored substrates for intermetallics.

Microstructure and mechanical properties of in situ Al–Mg2Si composites

In situ metal matrix composites (MMCs) with Mg2Si particulate reinforcement have been developed recently as ultralight materials. In this paper, a brief overview of the physical and mechanical properties of Mg2Si and the current status of research on Mg2Si reinforced MMCs is presented, followed by more detailed information on recent progress in the research group of the present authors. The effects of element additions and processing parameters on the microstructure of the composites obtained by gravity casting are discussed, together with some mechanical property data.

Wear behaviour of nitrided steel: B. Ralph et al (Brunel University, Uxbridge, UK), Materials World, Vol 2, No 7, 1994, 365–368.

The influence of Nd on the microstructures, tensile properties and fracture behavior of cast Al-18 wt.%Mg2Si in situ metal matrix composite was investigated. Experimental results showed that, after introducing a proper amount of Nd, both primary and eutectic Mg2Si in the Al-18 wt.%Mg2Si composite were well modified. The morphology of primary Mg2Si was changed from irregular or dendritic to polyhedral shape, and its average particle size was significantly decreased from 47.5 to 13.0 μm. Moreover, the morphology of the eutectic Mg2Si phase was altered from flake-like to a thin laminar, short fibrous or dot-like structure. Tensile tests revealed that Nd addition improved the tensile strength and ductility of the material. Compared with those of unmodified composite, the ultimate tensile strength and percentage elongation with 0.5% Nd were increased by 32.4% and 200%, respectively. At the same time, Nd addition changed the fracture behavior from brittle to ductile.