Mg2Si Particles Research Articles

Numerical Simulation of Density Segregation of Al Alloy During Centrifugal Casting

The centrifugal casting process of 6082 Al alloy was simulated by ANSYS Fluent software. The effect of rotation speed on the flow field and the degree of density segregation of Mg2Si particles was analysed. The linear velocity of the molten metal increased as the rotational speed increased. The Discrete Phase Model was used to track the movement of the particles. In centrifugal casting, the Mg2Si with low density is segregated toward the inner wall of the casting. As the rotation speed increased, the thickness of the enriched layer decreased, but the mass fraction in enriched layer increased, and the degree of segregation intensified.

Effect of Cooling Rate on Microstructural and Microhardness Properties of Al-(Mg2Si + Al3Ni) Matrix Composite

Among the high-tech industries like automotive, aerospace, electronics, etc., aluminum matrix cast composites (AMCCs) are widely applied for the fabrication of accountable and especially acute pieces. During the present study, hybrid aluminum base composites containing Mg2Si and Al3Ni particles were fabricated successfully in casting moods and their structural characteristics were evaluated under different solidification conditions.

Tribological behavior of as-cast and wrought Al–Mg2Si hybrid composites reinforced by Ti-based intermetallics

In this study, the tribological properties of Al–15Mg2Si (AC), Al–15Mg2Si–3TiB2–TiAl3 (C31), and Al–15Mg2Si–5TiB2–4TiAl3 (C54) in-situ composites were evaluated. In the as-cast state, the optimal results were obtained for the C31 sample, where the wear rate and the average coefficient of friction (ACOF) under the load of 60 N decreased by ∼54% and ∼27% compared to those obtained for the AC sample, respectively. Morphological modification of primary and eutectic Mg2Si particles and increasing the volume fractions of TiB2 particles were characterized as key factors for improving wear resistance of C31 sample. On the other hand, the presence of needle-like TiAl3 particles resulted in severe delamination and separation of tribolayer and increased mass loss of C54 sample. Alternatively, the fragmentation and redistribution of eutectic/primary Mg2Si and TiB2/TiAl3 particles during elevated-temperature deofrmation, the reduction of casting defect by thermomechanical processing effects, as well as intense grain refinement by dynamic recrystallization (DRX) improved the mechanical properties of hot-extruded samples and led to a notable enhancement in the load bearing behavior and stability of the formed tribolayer even under high loads. Therefore, the wear mechanism changed from the combination of severe delamination, adhesive, and three-body abrasive wear in the as-cast composites to mild abrasive wear in the hybrid composites subjected to hot deformation by the extrusion process. Consequently, in the optimal condition and under load of 60 N, the wear rate decreased from 29.6 to less than 10 mg/km and ACOF decreased by about 24% in hot-extruded C54 sample compared to the AC sample.

Good combination of strength and mechanical isotropy in AA6082 alloy processed by high temperature intermediate annealing

The microstructure, textures and mechanical property anisotropy of AA6082 alloy sheets after intermediate annealing were investigated. The result shows that the anisotropy of final cold-rolled and T6 alloy sheets decrease and the strengths increase as the intermediate annealing temperatures rise from 400 °C to 550 °C. Higher intermediate annealing temperature promotes the coarsening of soluble Mg2Si particles, which influences subsequent recrystallization and precipitation. The final cold-rolled sheet intermediately annealed at 550 °C presents weak rolling textures, thereby decreasing in-plane anisotropy (IPA) of yield strength from 4.4% to 2.5%. The T6 sheet intermediately annealed at 550 °C exhibits high yield strength (326 MPa), which is ascribed to the synergistic effects of precipitation strengthening, texture strengthening and grain refinement. Meanwhile, it presents high volume fractions of CubeND and random textures. This causes that r̅ value increases by 9.2% and ∆r value decreases by 80%.

The Effect of Small Additions of Fe and Heavy Deformation on the Precipitation in an Al–1.1Mg–0.5Cu–0.3Si At. Pct Alloy

The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al–1.1Mg–0.5Cu–0.3Si at. pct alloy was investigated. Following solution heat treatment and natural aging, the alloys were analyzed in an undeformed, artificially aged condition and in a two-step deformed condition consisting of 80 pct deformation, artificial aging, 50 pct deformation and a final, short artificial aging. Using electron microscopy, it was found that both alloys contained similar amounts of primary Mg2Si particles, while the higher Fe level alloy produced roughly twice the number density and volume fraction of primary bcc α-AlFeSi particles. Lower volume fractions of hardening precipitates were measured in the high Fe level alloy, as attributed to the lower amount of Si available for precipitation. Using atomic resolution scanning transmission electron microscopy, a mix of L phases and structural elements of GPB zones was found in the undeformed conditions. In the deformed conditions, scanning precession electron diffraction revealed that the precipitates were nucleated both on and between deformation induced defects. The addition of Fe affected the relative ratio of these precipitates. Hardness measurements of conditions combining deformation and artificial aging were performed to investigate the hardening mechanisms at each processing step.Graphical

Indentation creep behaviour of the magnesium AZ61–0.7Si–xBi cast alloys

Creep behaviour of the AZ61–0.7Si–xBi cast magnesium alloys were studied by Vickers indentation testing under constant load of 5 N in the temperature range of 423–523 K. The results indicate that increasing Bi content improved the creep resistance at all test temperatures. This was caused by the higher volume fraction of the thermally stable Mg3Bi2 intermetallic particles, as the principal strengthening cause, which compensated the possible effects of the lower amount of the Mg2Si particles. According to the obtained stress exponents of about 6.7 and activation energies in the range of 84.6–88.1 kJ mol−1, dislocation pipe diffusion was suggested as the dominant creep mechanism.

Enhanced tensile properties in a high-pressure synthesized Al–Si–Cu-Ge-Mg alloy with nano-sized Al particles in eutectic Si

The microstructure and tensile properties of Al–7Si–3Cu-0.5Ge-(0.4Mg) alloys solidified under high pressure were investigated. Dense nano-sized particles formed in the Al matrix owing to the high solid solubility of alloying elements in both alloys. Adding Mg could provide beneficial strengthening effects through forming Mg2Si(Ge) particles and assisting the precipitation of nano-sized Al particles in eutectic Si. The Al particles could not only accommodate lattice strain but also inhibit crack propagation in eutectic Si. Accordingly, the Al–7Si–3Cu-0.5Ge-0.4Mg alloy solidified under high pressure exhibited higher strength and better ductility. The strain distribution and the corresponding strengthening effect of nanoscale particles were discussed by the GPA analysis.

Microstructure and age hardening behavior of Al/Fe bimetal prepared by one-step compound casting

Al-7Si-0.6Mg/Fe bimetal was prepared by compound casting; it was heat-treated to investigate the age-hardening behavior of the aluminum matrix near the interface. Metallurgical bonding of the interface is accompanied by the formation of an oxide layer in the aluminum matrix near the interface. The intermetallic layer grows at the expense of the Si and Mg2Si particles within the diffusion reach during the solution heat treatment. The fraction of both AlFeSi and Si is low near the interface, the fraction of the AlFeSi phase is the highest just outside the oxide layer and decreases with increasing distance from the interface, which is accompanied by the increase in the fraction of the Si phase. The presence of the continuous oxide layer decreases the age-hardening ability and bonding strength of the aluminum matrix near the bimetal interface; such a negative effect is mitigated by the broken oxide layer. The lower age-hardening ability is resulted from the segregation of the Mg element to the oxide layer.

In-situ 3D observation of hydrogen-assisted particle damage behavior in 7075 Al alloy by synchrotron X-ray tomography

We directly captured, classified, and evaluated 3D particle debonding and fracture behavior in a H-charged 7075 Al alloy throughout the entire tensile deformation using synchrotron X-ray tomography and microstructural feature tracking techniques. The effects of particle size, shape, spatial clustering and stress state on strain-dependent particle damage were identified and isolated from each other. Moreover, state-of-the-art imaging and tracking techniques enabled the establishment of spatially and time-resolved hydrogen distributions during deformation. Based on realistic hydrogen partitioning among various nanoscopic trap sites, the contributions of particles to hydrogen trapping and the hydrogen effect at individual damaged particles were assessed quantitatively. Fracturing of coarse and irregular Al7Cu2Fe particles was found to be the predominant particle damage mode due to the spatial clustering and brittleness of these particles, but a hydrogen effect was not observed. The debonding of Mg2Si particles seemed to be the result of competition between hydrogen and clustering-induced stress localization, but detrimental effects of hydrogen on ductile fracture induced by accelerating interfacial debonding were found to be limited. The quantitative evaluation of particle damage in the present model material clarified a viable strategy for mitigating hydrogen embrittlement, which involves introducing and modifying intermetallic particles with strong hydrogen trapping capacities.

Microstructural characterization and mechanical behavior of Al-4 wt% Mg2Si in-situ metal matrix composite synthesis via cooling slope casting technique

In the present steady, A319-4 wt%Mg2Si metal matrix composite is cast by cooling slope casting technique with an objective to develop globalized fine microstructure and compare the results with conventional gravity cast specimen of same composition. The casting was subjected to microstructural characterization by optical microscopy and scanning electron microscopy. The in-situ generated Mg2Si particles are observed to be remarkably refined and uniformly dispersed in the matrix. Mechanical properties like hardness and tensile strength of the cooling slope cast in-situ composite are enhanced because of globalization of matrix structure and refined and uniform distribution of Mg2Si particles as compare to gravity cast sample.

Microstructure Examination and Sliding Wear Behavior of Al-15%Mg2Si-xGd In Situ Composites before and after Hot Extrusion

In current study; the effect of various Gadolinium (Gd) additions on the microstructure and sliding wear behaviour of Al-15%Mg2Si composite before and after the hot extrusion process was examined. Optical microscopy (OM), scanning electron microscopy (SEM) equipped with EDX facility and X-ray diffraction (XRD) were used to characterize the microstructure. The results showed that with addition of 1.0 wt.% Gd to Al-15%Mg2Si composite, the primary Mg2Si particles size reduced from 44 µm to 23 µm and its morphology altered from dendritic to polygonal shape. Further refinement of primary Mg2Si particles was achieved after conducting hot extrusion which resulted in a decrease in its size to 19 µm with a transfer to near-spherical morphology. The Vickers hardness value increased from 55.6 HV in the as-cast and unmodified composite to 72.9 HV in the extruded 1.0% Gd modified composite. The wear test results revealed that composites treated with Gd possess higher wear resistance in comparison with those of without Gd. The highest wear resistance obtained with the lowest wear rates of 0.19 mm3/km and 0.14 mm3/km in the Al-15%Mg2Si-1.0% Gd before and after the hot extrusion, respectively. The high wear resistance of extruded Gd-modified Al-15%Mg2Si composite is due to the refinement of primary Mg2Si particles with uniform distribution in the composite matrix along with fragmentation of Gd intermetallic compounds.

Application of Nanosilicon to the Sintering of Mg-Mg2Si Interpenetrating Phases Composite.

The new in situ fabrication process for Mg-Mg2Si composites composed of interpenetrating metal/intermetallic phases via powder metallurgy was characterized. To obtain the designed composite microstructure, variable nanosilicon ((n)Si) (i.e., 2, 4, and 6 vol.% (n)Si) concentrations were mixed with magnesium powders. The mixture was ordered using a sonic method. The powder mixture morphologies were characterized using scanning electron microscopy (SEM), and heating and cooling-induced thermal effects were characterized using differential scanning calorimetry (DSC). Composite sinters were fabricated by hot-pressing the powders under a vacuum of 2.8 Pa. Shifts in the sintering temperature resulted in two observable microstructures: (1) the presence of Mg2Si and MgO intermetallic phases in α-Mg (580 °C); and (2) Mg2Si intermetallic phases in the α-Mg matrix enriched with bands of refined MgO (640 °C). Materials were characterized by light microscopy (LM) with quantitative metallography, X-ray diffraction (XRD), open porosity measurements, hardness testing, microhardness testing, and nanoindentation. The results revealed that (n)Si in applied sintering conditions ensured the formation of globular and very fine Mg2Si particles. The particles bonded with each other to form an intermetallic network. The volume fraction of this network increased with (n)Si concentration but was dependent on sintering temperature. Increasing sintering temperature intensified magnesium vaporization, affecting the composite formation mechanism and increasing the volume fraction of silicide.

Microstructure Evolution of AS41 Magnesium Alloy in ECAP

ECAP is a continuous multi-pass extrusion process that enables the specimen to obtain considerable cumulative deformation to refine the grain. In this paper, ECAP was used to deform AS41 magnesium alloy at 350°C, and the microstructure was observed and analyzed. The results show that the ECAP process has excellent effect on grain refinement and uniform microstructure. The grain size of AS41 decreases from 200μm to 20μm, and the microstructure is more uniform than that of as-cast sample. The reason is that the original grain is broken and refined under the action of shear force, and dynamic recrystallization occurs at the same time, resulting in small recrystallized grains. The Mg2Si particles were redistributed during ECAP and uniformly distributed in the crystal in rod shape.

Microstructure and Corrosion Resistance of AA4047/AA7075 Transition Zone Formed Using Electron Beam Wire-Feed Additive Manufacturing.

A gradient transition zone was obtained using electron beam deposition from AA4047 wire on AA7075 substrate and characterized for microstructures, tensile strength and corrosion resistance. The microstructure of the transition zone was composed of aluminum alloy grains, Al/Si eutectics and Fe-rich and Si-rich particles. Such a microstructure provided strength comparable to that of AA7075-T42 substrate but more intense corrosion due to the higher amount of anodic Mg2Si particles. The as-deposited AA4047 zone formed above the transition zone was composed of aluminum alloy dendrites and interdendritic Al/Si eutectics with low mechanical strength and high corrosion potential.

Microstructure, mechanical properties and wear behaviour of the AZ91–Mg2Si–SiC hybrid composites

The present study investigates the effect of different amounts of SiC particles on the microstructure, mechanical properties and wear behaviour of the cast and extruded AZ91–Mg2Si composite. The microstructural analysis of the cast samples showed the primary α-Mg, semicontinuous networks of the Mg17Al12 intermetallics and scattered Mg2Si and SiC particles. The hot extrusion resulted in a refined grain structure and homogenously distributed particles. More SiC particles had a positive influence on the microstructural refinement and decrement of the grain size. Increasing the SiC particles improved the hardness and compressive strength and decreased compressive elongation. Furthermore, the wear tests exhibited that more SiC particles enhanced the wear properties. However, at the highest loads, the extruded composite with large SiC particles displayed weak wear resistance.

Influence of Solution Heat Treatment on Microstructure and Tensile Properties of Gd-Treated Al-15% Mg2Si In-Situ Composites

ABSTRACT Microstructural alteration and tensile properties of Al-15% Mg2Si composite specimens was examined after addition of gadolinium (Gd) and conducting solution heat treatment. Various percentages of gadolinium (0.5, 1.0, 2.0 and 5.0 wt. % Gd) were added to the composite Al-15% Mg2Si composite. The specimens then solutionized at 500 °C for 4h followed by quenching. The results showed that regular morphology and small size of primary Mg2Si particles is achieved after addition of 1.0 wt.% Gd compared to untreated composite. Due to solutionizing effect, Mg2Si dissolution occurred which led to alter the morphology of primary Mg2Si particles to round shape. Tensile testing results revealed that enhancement in UTS and El% values owns to influence of both Gd addition and solution heat treatment on the Al-15% Mg2Si composite. The fracture surface of untreated composite depicted a cellular fracture, while the fracture surface of Gd treated and heat treated composite showed a ductile surface containing fine dimples, in which alteration of fracture mode is due to the role of Gd and heat treatment on microstructural modification, which results in reduction of potential sites for stress concentration and crack initiation areas.

Effects of Eu modification and heat treatment on microstructure and mechanical properties of hypereutectic Al–Mg2Si composites

To modify the coarse primary Mg2Si phase and improve mechanical properties of Mg2Si reinforced aluminum matrix composites, hypereutectic Al–18Mg2Si composites with different Eu contents were fabricated by permanent mold casting and extrusion followed by heat treatment. Results show that the as-cast Al–18Mg2Si composites consisted of primary Mg2Si and eutectic structure (Al + Mg2Si). Eu addition can obviously modify the primary Mg2Si morphology from dendrite to flat truncated octahedron shape, and the average size also decreased from ∼90 μm to ∼16 μm with increasing Eu content from 0 to 0.1%. But further increasing Eu content would cause over-modification. After T6 treatment, sharp corners of primary Mg2Si were spheroidized and the average size of primary Mg2Si were further decreased. DTA result shows the nucleation temperature of primary Mg2Si increased by Eu addition. Al2Si2Eu phase can act as the heterogeneous nucleation substrate for the primary Mg2Si phase and thus refine the size of primary Mg2Si particle. TEM results show the segregation and/or selective adsorption of Eu on the {100} facets of primary Mg2Si suppress the growth of primary Mg2Si, and thus refine and modify the composites, which proposed to the dominant reason for the refinement and modification of the primary Mg2Si phase. Tensile tests show that the mechanical properties enhanced with increasing Eu content. The elongation and ultimate tensile strength of the T6-treated Al–18Mg2Si-0.1Eu composite improved to 5.2% and 241 MPa, which enhanced 225% and 91% compared to the unmodified as-cast Al–18%Mg2Si composite. It is concluded that the morphology transition of primary Mg2Si from dendrite to tetrakaidecahedron and the refinement of primary Mg2Si size with Eu modification, the passivation of the sharp corners in primary Mg2Si particles as well as the appearance of β" precipitates all contribute to the improvement of the mechanical properties of the T6-treated Al–18Mg2Si composites.

Study on the modification effect of copper on Al–15Mg2Si composite

The effect of different concentrations of Cu (0, 1, 3, and 5 wt %) on the microstructure and mechanical properties of in-situ Al–15Mg2Si composites was studied. The thermal analysis approach was employed to better understand the effect of Cu on the solidification behavior and microstructure evolution. The results showed that adding Cu, narrows the time interval between liquidus and eutectic lines within which the melt is being solidified that can reduce the average size of the primary Mg2Si (Mg2SiP) particles. Adding Cu also modifies the hopper-like morphology of Mg2SiP particles and leads to the formation of hard Cu-rich compounds (θ-Al2Cu and Q-Al5Mg8Si6Cu2) in the microstructure. According to the tensile tests results, the maximum tensile strength and fracture strain belong to the composites containing 3.0 and 1.0 wt % Cu, respectively. However, the maximum quality index (290 MPa) was obtained in the composite containing 3.0 wt % Cu which was about 25% higher than that of the unmodified composite. Increasing the Cu content over 3 wt % increases the volume fraction of brittle Cu-rich compounds and microporosities in the microstructure that adversely affects the composite quality.

Tailoring microstructure and tensile properties of Mg-Si alloys varying solidification cooling rate and Si content

Mg-Si alloys were investigated in terms of their microstructural characteristics and tensile properties, by varying solidification cooling rate and Si content. This type of investigation becomes essential since these alloys are considered potentially base alloys for new biocompatible and biodegradable materials that might be used to produce a variety of temporary implants. This because Silicon (Si) has been recognized as a vital mineral in the human body, aiding both the healing process and the development of the immune system. Despite these characteristics provided by Si, Mg-Si alloys typically have low ductility and tensile strength due to the presence of coarse Mg2Si particles. Therefore, efforts to understand and improve these properties are most welcome. In order to deepen the knowledge of these alloys, the present research analyzed three Mg-Si alloys: Mg-0.6 wt% Si, Mg-1.3 wt% Si and Mg-1.7 wt% Si regarding their microstructures and phase's morphologies produced in a broad range of solidification rates' samples and their corresponding tensile properties. The predominance of dendritic arrangement with the interdendritic region composed of the (Mg + Mg2Si) eutectic was noted for the Mg-0.6 wt% Si and Mg-1.7 wt% Si alloys. Eutectic cells prevailed for the Mg-1.3 wt% Si alloy, with cells varying from squarer and hexagonal to a more rounded shape with the decrease in cooling rate. Experimental influences of the microstructural parameters on the tensile properties have been verified. Except for the Mg-1.3 wt% Si alloy, the tensile properties of the other alloys were found to be roughly independent of the dendritic length scales in the verified ranges. In general, increased Si content led to a reduction in strength and ductility, probably due to the increase in the fraction of Mg2Si particles, which is an effective phase in the stress concentration during loading, shortening the break.

Synergetic modification effects on primary Mg2Si in Al-20Mg2Si alloy induced by the co-addition of beryllium and antimony

Modifying the primary Mg2Si phase in hypereutectic Al-Mg2Si system with controllable sizes and morphologies is difficult to realize by the single addition of elements, which can only enhance nucleation or control its growth process via adsorption-poisoning. This research provides insights into modification mechanisms of the co-addition of Sb and Be in an Al-20Mg2Si alloy to refine the primary Mg2Si phase by controlling the nucleation and growth process simutaneouly. With 0.5 wt% Be-Sb, truncated octahedrons with rounded corners are obtained, along with the size refinement from ~150 µm to ~10 µm. The formation of Mg3Sb2 particles significantly refines the primary phase by acting as heterogeneous nucleation sites during solidification. Meanwhile, Be could adsorb on the Mg2Si surfaces and restrain the advanced growth of Mg2Si<100> direction, which contributes to the final morphology of the primary phase. The formation of truncated octahedrons with rounded corners contributes to an improvement in elongation to failure (from ~0.7% to ~1.9%) and ultimate tensile strength (from ~142 MPa to ~198 MPa) comparing to the unmodified alloy, which relieves the stress concentration and restrains the crack source. This study offers a simple methodology to prepare Al-Mg2Si alloys reinforced with close to spherical Mg2Si particles, which is critical to design lightweight Al-Mg2Si alloys with improved performance.