Mg2Si Composite Research Articles

Effect of Sc Addition and Heat Treatment on the Fracture Behavior of Al-20%Mg2Si Composites: Experiments and Finite Element Simulations

Effect of Sc Addition and Heat Treatment on the Fracture Behavior of Al-20%Mg2Si Composites: Experiments and Finite Element Simulations

The effect of Cu–8%P master alloy, SIMA process, thixoforming, and heat treatment on the microstructure and mechanical properties of Al–20%Mg2Si composite

In the present research, the effect of thixoforming and age-hardening heat treatment on the microstructure and mechanical properties of un-modified and modified Al–20%Mg2Si composites produced through the strain-induced melt activation (SIMA) process has been investigated. This method showed promising potential for manufacturing the ideal microstructure, achieving globular grains, and enhancing mechanical properties. Quantitative analysis has revealed that adjusting the semi-solid heat treatment parameters to a temperature of 570 °C and a holding time of 25 min optimizes the globular α-Al grains and Mg2Si particles, achieving the size of 20.62 μm and 66.71 μm and the shape factor of 0.81 and 0.83 for Mg2Si particles and α-Al grains, respectively. The yield strength of the modified Al–20%Mg2Si composite increased by 23.67% and the ultimate tensile strength increased by 21.20%, compared to the un-modified specimen. Both composites underwent the thixoforming process, illustrating the ultimate tensile strength and elongation of 93.68 MPa and 4.32% for the original composite and 138.86 MPa and 7.29% for the modified composite. The modified Al–20%Mg2Si composite was subjected to the effective combination of thixoforming and age-hardening. According to the tensile test results, the yield strength, ultimate tensile strength, elongation, and toughness raised by 138.72%, 140.92%, 267.70%, and 471.12%, respectively, compared to the as-cast specimen. Moreover, its impressive hardness of 125.1HB contributes to its overall performance.

Effect of strontium addition, cooling rate and T6 heat treatment on the corrosion behaviour of Al-20%Mg2Si composite

Mg2Si reinforced AMCs are considered a promising structural material as the in-situ formation of Mg2Si particle offers excellent matrix/reinforcement stability that allow effective load transfer. Addition of Strontium (Sr) could minimize sharp edges shape of Mg2Si particles in as-cast condition improving the mechanical properties. Incorporating Strontium (Sr) can reduce the sharp-edged morphology of Mg2Si particles in their initial cast state, leading to enhanced mechanical properties. However, existing research on Mg2Si reinforced AMCs does not show sufficient data on corrosion behavior. This research aims to investigate the microstructural changes and corrosion performance of as-cast Al-20 %Mg2Si under various influencing factors including varying solidification rate, addition of Sr and post- fabrication metalwork such as T6 heat treatment. The composite materials were prepared using in-situ casting procedure with high purity of the elements. Microstructure characterization was carried out by optical microscopy, in which the primary Mg2Si particle sizes were measured by image analyser. Corrosion behaviour of the fabricated composite was analysed using electrochemical test. Optical microscopic images reveals that the primary Mg2Si was refined and transform to polyhedron upon addition of 0.01w.t. % Sr into Al-20 %Mg2Si and resulted in improved corrosion resistance upon immersion testing and potentiodynamic polarization testing in 3.5 % NaCl with decreasing the Icorr from 0.80 to 0.41 μA/cm2.The Al-20 %Mg2Si which solidified under lower cooling rate have coarser dendritic primary Mg2Si which results in higher corrosion rate (Icorr = 4.98 μA/cm2). T6 heat treatment transformed the primary Mg2Si to fine dendrites with spherical secondary Mg2Si phase and consequently enhancing the corrosion resistance by decreasing the Icorr to 2.93 μA/cm2.

Role of YSZ Particles on Microstructural, Wear, and Corrosion Behavior of Al-15%Mg2Si Hybrid Composite for Marine Applications

This study aims to investigate the microstructural alterations, mechanical properties, sliding wear behavior, and corrosion properties of Al-15%Mg2Si composites with different contents of yttria-stabilized zirconia (YSZ). Al-15%Mg2Si composites with the different contents of YSZ (0, 3, 6, and 9 wt.%) were fabricated using the stir-casting technique. The fabricated composites were characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), Vickers hardness tester, linear reciprocating tribometer (LRT), and electrochemical test. The results showed that with the introduction of YSZ particles, the average size of the primary Mg2Si particles in the base composite was 137.78 µm, which was reduced to 88.36 µm after adding 9 wt.% YSZ. The aspect ratio of Mg2Si particles also decreased from 3, for the base composite, to 1.27 in the composite containing 9 wt.% YSZ. Moreover, the hardness value displays an incremental trend from 102.72 HV, as recorded for the base in situ composite, to 126.44 HV in the composite with 9 wt.% YSZ. On top of that, the Al-15%Mg2Si-9%YSZ demonstrates exceptional wear resistance, with the lowest wear rate of 0.46 mm3/km under a 25 N applied load. Its average coefficient of friction (COF) was recorded at 0.42, which is lower than both the 3 and 6 wt.% of YSZ-containing composites. The smoother worn surface in Al-15%Mg2Si-9%YSZ hybrid composite implies the abrasion phenomenon, as dominant wear behavior is milder than the other fabricated composites. On top of that, the Al-15%Mg2Si-9%YSZ also possesses optimum corrosion resistance. The corrosion rate is 0.080 mmpy, comparable to the 0.164 mmpy rate obtained in the in situ composite.

Morphological modification of Mg2Si phase and strengthening mechanism in Mg2Si/Al composites by Eu addition and T6 heat treatment

In order to improve mechanical properties of Mg2Si/Al composites, Eu element was added to modify Mg2Si morphology, and T6 heat treatment was used to control Mg2Si morphology and precipitate strengthening phase. Microstructure and morphology of Mg2Si were observed by synchrotron X-ray tomography and TEM, and first-principles calculations were also performed to testify the effect of Eu modification. Results show that the size of primary Mg2Si particles decreases and eutectic Mg2Si phase transforms from lamellar to fibrous by Eu addition. After heat treatment, sharp angles of primary Mg2Si particles passivate, and eutectic Mg2Si dissolves and appears to be short dot-like. Meanwhile, nano-sized β" phase precipitates in the matrix. For morphology of Mg2Si with Eu modification, TEM results show that Eu impedes the growing of Mg2Si, which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg2Si {100} facet. The adsorption and suppression growing of Mg2Si transform the morphology of Mg2Si and thus improve the elongation. UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%, which improved 81% and 200% compared to the as-cast Al-15%Mg2Si composite. The strengthening mechanism mainly results from precipitation strengthening of nano-sized β" precipitates in the heat-treated composite.

Microstructure based numerical simulation of the micromechanics and fracture in hypereutectic Al–Mg2Si composites

In the present study, both experimental and numerical examinations were performed to understand the hypereutectic Al–Mg2Si composite's microstructural morphology, mechanical properties and fracture correlation. The innovation of this research includes the micromechanics studies and failure initiation in hypereutectic Al–Mg2Si composite through the compiled induce stress, deformation plasticity and energy dissipation theory subjected to tension. Ultimate tensile strength (UTS), toughness and elongation have decreased, but the yield strength has increased up to 25% Mg2Si addition and then decreased at the composites with 30 wt% Mg2Si because the brittle fracture increases due to the presence of comparatively coarser and dendritic primary Mg2Si particles. Additionally, an increase in the microporosity with the increase in Mg2Si concentration also affects the same. Finite element analysis (FEA) was performed using the Ramberg-Osgood constitutive model and actual microstructure 2D representative volume elements model. The FEA and experimental results have a satisfactory agreement. The fractography unveils the presence of a mix-mode of fracture, i.e. the ductile and the brittle fracture of the composites. Mises and Tresca failure criteria reveal that the distribution of stress is non-homogeneous and stress is localized in the narrow eutectic and irregular Mg2Si phase region, which acts as a crack initiation site. Analysis of the stress triaxiality and equivalent plastic strain distribution shows that void initiation and growth take place during the deformation of the Al–Mg2Si composites. The plastic dissipated energy distribution in deformed RVEs interestingly consents to the von mises stress, plastic strain and stress triaxiality analysis findings.

X-ray computed tomography of cast metal matrix composites

The development of new cast metal matrix composites and technological processes for their production are inextricably linked with the need to improve the methods of quantitative non-destructive testing. In this work, the features of the spatial structure of cast in-situ metal matrix composites (on example of the Al – Mg2Si system) were studied using X-ray computed microtomography. The parameters of tomographic scanning were optimized to identify structural components with close ranges of radioparency. The rational selection of the scanning parameters of the samples made it possible, during the subsequent computer processing of the slice sets, to clearly identify the structural constituents of the metal matrix composites depending on the gray levels in their comparison with the characteristic morphology of the observed constituents (primary Mg2Si crystals, pseudobinary eutectic, compounds of impurity elements). The total volume of porosity in the studied samples of Al + 15 wt.% Mg2Si composites after melt thermal-rate treatment at 900 °C did not exceed 0.05 mm3, which corresponds to a porosity content in the sample of 0.13 vol.%. The presented results show the significant potential of tomography in the study of the structural and morphological characteristics of composite materials and internal defects in cast products made from them. This research was funded by the Russian Science Foundation (Project № 20-19-00687).

Enhanced dry sliding friction and wear behaviors of Mg–Mg2Si composites

Dry sliding tribological behaviors of the as-cast (AC) and multi-pass friction stir processed (FSPed) Mg–2Si alloys (Mg–Mg2Si composites) were evaluated using pin on disk method under different loads of 15, 30 and 45 N. In general, FSP implementation and pass number increase reduced the average grain size, fragmented the Mg2Si particles and rearranged them more uniformly in the structure. Hence, the intensive microstructural modification (particularly after 2nd pass) improved the hardness and ductility of the substrate and led to enhanced O-rich tribolayer steadiness and reduced the wear rate and friction coefficient (FC). In the optimum condition (4-pass FSPed sample), the mass loss and FC reduced by about 71% and 46% compared to AC composite. Wear mechanisms of AC and FSPed composites were also studied.

Enhancing the elevated temperatures tribological properties of Al–Mg2Si composites by in-situ addition of Ti-based intermetallics and hot working

Dry-sliding wear and friction behaviors of Al–15Mg2Si–5TiB2–4TiAl3 in-situ hybrid composites were evaluated at different temperatures (100–300 °C) and loads (10–60 N). The addition of TiB2 and TiAl3 particles enhanced the wear resistance. Moreover, the severe wear transition condition was changed from 300 °C to 10 N for the as-received Al–15Mg2Si composite to 300 °C - 60 N for the as-cast Al–15Mg2Si–5TiB2–4TiAl3 hybrid composite. This change was ascribed to the presence of thermostable particles and refined/modified Mg2Si particles via nucleation mechanism. Applying thermomechanical processing and hot deformation by the extrusion process necessitated higher loads and temperatures for this transition. Indeed, fragmentation and more homogeneous dispersion of reinforcements, higher hardness and toughness of composite due to grain refinement by dynamic recrystallization (DRX), reduction and closure of casting defects, and stability of tribolayer were recognized as leading reasons for replacing severe adhesive/plastic deformation wear with the abrasive mechanism. Accordingly, this study introduced an Al matrix hybrid composite with excellent performance at elevated temperatures.

Tailoring the mechanical properties of hypereutectic in situ Al–Mg2Si composites via hybrid TiB2 reinforcement and hot extrusion

Tailoring the mechanical properties of hypereutectic in situ Al–Mg2Si composites via hybrid TiB2 reinforcement and hot extrusion

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.

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.

Effect of microalloying by Ca on the microstructure and mechanical properties of as-cast and wrought Mg–Mg2Si composites

The effects of calcium addition at microalloying levels and hot extrusion process on the modification of the microstructure and enhancement of the mechanical properties of the Mg–3Si metal matrix composite (MMC) were studied. Electron backscatter diffraction (EBSD), X-ray diffraction (XRD), cooling curve thermal analysis, simulation based on the finite element method (FEM), thermodynamics predictions, tensile testing, and optical microscopy were used for characterization. The Ca addition modified the primary and eutectic Mg2Si phase, resulted in grain refinement of the matrix, led to better tensile properties in the as-cast condition, and gradually changed the isothermal eutectic reaction to a non-isothermal route. Moreover, hot extrusion led to the extreme grain refinement induced by dynamic recrystallization (DRX) and the break up of the eutectic structure into fine and well-distributed particles. For the Ca-containing composites, the modified primary Mg2Si particles enhanced the particle stimulated nucleation (PSN) mechanism, leading to the formation of a higher volume fraction of DRX grains with more random orientations (crystallographic texture). Accordingly, remarkable improvements in tensile properties (such as tensile toughness) were observed via extrusion of the modified in situ composites.

Role B4C Addition on Microstructure, Mechanical, and Wear Characteristics of Al-20%Mg2Si Hybrid Metal Matrix Composite

In the current study, the effect of different B4C additions (0, 2.5, 5, and 10 wt%) on the microstructural, solidification behavior, mechanical, and tribological properties of Al-20%Mg2Si composite were studied by means of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness, tensile, and dry sliding wear tests. The cooling curve thermal analysis (CCTA) approach was utilized to monitor the influence of B4C particles on the solidification behavior of Al-20%Mg2Si composite. The results revealed that the addition of B4C particles up to 10 wt% reduced the nucleation temperature (TN) and growth temperature (TG) of the primary Mg2Si phase. Moreover, the proper amount of B4C added to Al-20%Mg2Si composite has a significant effect on the microstructural alteration, mechanical, and tribological properties of the composite. The mean size of primary Mg2Si in Al-Mg2Si composite was 47 μm, in which with the addition of 5 wt% B4C, the particle size decreased to 33 μm. The highest UTS (217 MPa) and El% (7%) was achieved in Al-20%Mg2Si-5%B4C hybrid composite. The cast Al-20%Mg2Si composite revealed the brittle mode of fracture with some cleavage characterization, in which with the addition of 5%B4C, the fracture mode altered to a more ductile fracture. The wear results revealed that the Al-20%Mg2Si-5%B4C hybrid composite has the highest wear resistance with the lowest wear rate (0.46 mm3/Km) and friction coefficient (µ = 0.52) under 20 N applied load compared to other fabricated composites with mild abrasion as the governed wear mechanism.

Biodegradable Zn−3Mg−0.7Mg2Si composite fabricated by high-pressure solidification for bone implant applications

Zinc (Zn)-based alloys have been considered potential biodegradable materials for medical applications due to their good biodegradability and biocompatibility. However, the insufficient mechanical properties of pure Zn do not meet the requirements of biodegradable implants. In this study, we have developed a biodegradable Zn−3Mg−0.7Mg2Si composite fabricated by high-pressure solidification. Microstructural characterization revealed that the high-pressure solidified (HPS) composite exhibited uniformly distributed fine MgZn2 granules in an α-Zn matrix. Comprehensive tests indicated that the HPS composite exhibited exceptionally high compression properties including a compressive yield strength of 406.2 MPa, an ultimate compressive strength of 1181.2 MPa, and plastic deformation up to 60% strain without cracking or fracturing. Potentiodynamic polarization tests revealed that the HPS composite showed a corrosion potential of −0.930 V, a corrosion current density of 3.5 μA/cm2, and a corrosion rate of 46.2 μm/y. Immersion tests revealed that the degradation rate of the HPS composite after immersion in Hanks’ solution for 1 month and 3 months was 42.8 μm/y and 37.8 μm/y, respectively. Furthermore, an extract of the HPS composite exhibited good cytocompatibility compared with as-cast (AC) pure Zn and an AC composite at a concentration of ≤25%. These results suggest that the HPS Zn−3Mg−0.7Mg2Si composite can be anticipated as a promising biodegradable material for orthopedic applications.

Role of Gd addition on machinability of Al-15%Mg2Si in-situ composite during dry turning

Recently, Al-Mg2Si in-situ composites have achieved considerable attention due to their excellent physical and mechanical properties. In fact, there are some limitations of knowledge regarding the machinability characteristics of these composites - particularly when being inoculated with rare earth additions. This study in turn aimed to investigate the influence of machining parameters as well as Gd addition on the machinability of Al-15%Mg2Si composite. To examine the effect of modifier (1.0 wt. % Gd) and machining parameters (feed rate, cutting speed), microstructural evolution, surface roughness (Ra) and cutting force (Fc) were evaluated during dry turning. The results revealed that Gd addition as modifier element led to better surface roughness and higher cutting force owning to the modification of Mg2Si particle structure as well as the formation of Gd intermetallic compounds.

Effect of equal channel angular pressing on microstructure and mechanical properties of thermally-homogenized Al–Mg2Si composites

The effect of equal-channel angular pressing (ECAP) on the microstructure, hardness, shear, and tensile properties of thermally-homogenized Al-xMg2Si (x = 10, 15, and 20 wt %) composites was studied. According to the microstructural characterization results, increasing ECAP passes progressively reduced the size of primary Mg2Si (Mg2SiP) and eutectic Mg2Si (Mg2SiE) particles, and improved their distribution within the matrix. These microstructural changes significantly improved the mechanical properties of the composites. For instance, after the final pass of ECAP, the shear yield strength (SYS) of composites containing 10, 15 and 20 Mg2Si increased by 89, 86 and 64%, while their tensile yield strength (TYS) increased by 174, 149 and 182%, respectively. A linear correlation between the tensile and shear strengths was also observed which is in agreement with the previous studies as well as Tresca and von Mises criteria.

Corrosion behaviour of friction stir processed Al–Mg2Si composites

This study aimed to apply the multi-pass friction stir processing (FSP) to Al–25Mg2Si as-cast composite in some optimised conditions. Also, microstructural modification effects were assessed on the corrosion behaviour of composite in a 3.5-wt-% NaCl solution. The corrosion resistance of the FSPed composites enhanced as the number of passes increased from 1 to 3. The grain refinement of the Al matrix, uniform distribution of Mg2Si particles, reduction in solidification-induced porosities, and deeper penetration of surface Mg2Si particles improved stability and adhesion of the passive oxide layer, which prohibited the galvanic/pitting corrosion and diminished the corrosion rate.