Eutectic Si Research Articles

A Comparative Study on Microstructure, Segregation, and Mechanical Properties of Al-Si-Mg Alloy Parts Processed by GISS-HPDC and SEED-HPDC.

There are multiple routes to prepare semi-solid slurries with a globular microstructure for semi-solid forming. The variations in the microstructure of semi-solid slurries prepared using different routes may lead to significant differences in the flow behavior and mechanical properties of rheo-diecasting parts. Therefore, it is crucial to have a comprehensive understanding of the microstructure evolution associated with different slurry preparation routes and their resulting effects. In this study, the gas-induced semi-solid process (GISS) and the swirl enthalpy equilibrium device (SEED) routes were employed to prepare semi-solid Al-Si-Mg slurries for their simplicity and productivity in potential industrial applications. The prepared slurries were then injected into the shoot sleeves of a high-pressure die casting (HPDC) machine to produce tensile test bars. Subsequently, the bars underwent T6 treatment to enhance their mechanical properties. The microstructure, segregation, and mechanical properties of the samples were investigated and compared with those of conventional HPDC. The results indicated that the GISS and SEED can produce semi-solid slurries containing a spherical α-Al primary phase, as opposed to the dendritic structure commonly found in conventional castings. The liquid fraction had a significant effect on the flow behavior, resulting in variations in liquid segregation and mechanical properties. It was observed that a higher solid fraction (>75%) had a suppressing effect on surface liquid segregation. In addition, the tendency for liquid segregation gradually increased along the filling direction due to the special flow behavior of the semi-solid slurry with a low solid fraction. Furthermore, under the same die-casting process parameters, the conventional HPDC samples exhibit higher yield stress (139 ± 3 MPa) compared to SEED-HPDC and GISS-HPDC samples, which may be attributed to the small grain size and the distribution of eutectic phases. After undergoing the T6 treatment, both SEED-HPDC and GISS-HPDC samples showed a significant improvement in yield and tensile strength. These improvements are a result of solution and precipitation strengthening effects as well as the spheroidization of the eutectic Si phase. Moreover, the heat-treated SEED-HPDC samples demonstrate higher ultimate strength (336 ± 5 MPa) and elongation (13.7 ± 0.3%) in comparison to the GISS-HPDC samples (307 ± 4 MPa, 8.8 ± 0.2%) after heat treatment, mainly due to their low porosity density. These findings suggest that both GISS-HPDC and SEED-HPDC processes can be utilized to produce parts with favorable mechanical properties by implementing appropriate heat treatments. However, further investigation is required to control the porosities of GISS-HPDC samples during heat treatment.

Microstructure features and mechanical properties of non-heat treated HPDC Al9Si0.6Mn–TiB2 alloys

This study aimed to enhance the mechanical properties of high pressure die casting (HPDC) Al9Si0.6Mn alloys by incorporating in-situ TiB2 particles. The effects of TiB2 addition on the microstructure and mechanical properties of as-HPDC Al9Si0.6Mn alloys were investigated. The results showed that TiB2 addition refined the bimodal grain structure and eutectic Si morphology in the central region of the as-HPDC alloys, which was the primary contributor to the mechanical properties. The thickness of the skin region and band zone increased with increasing TiB2 addition, while the central region exhibited a reduced thickness but remained dominant on the entire cross-section. The optimal TiB2 content was found to be 1 wt%, resulting in the 23.4 % reduction in grain size and 10.7 % enhancement in yield strength. The modified strengthening model based on the microstructure features of the central region accurately predicted the yield strengths of as-HPDC alloys. Finally, the morphological strengthening factors induced by TiB2 particles were analytically illustrated in the HPDC Al9Si0.6Mn–TiB2 alloys.

Effect of various Er/Al-Ti-C ratios on microstructure and tensile properties of the As-cast Al-10Si-0.8Fe alloy

This paper investigates the improvement of the microstructure and tensile properties of Al-Si-Fe alloys by adding small amounts of Er and Al-Ti-C. The refinement and strengthening mechanisms of this modified alloy are also investigated. The experimental results show that the addition of Al-Ti-C in the Al-Si-Fe alloy can induce multiple refining effects, including the refinement of α-Al grains, SDAS, and eutectic Si particles. When the compound addition ratio is close to 1:2, with the addition of 0.20 % Al-Ti-C and 0.40 % Er, the grain size, SDAS, and eutectic silicon particle area decrease, resulting in the best refinement of the alloy structure. Due to the microstructure refinement, the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL %) are improved, leading to the best strengthening of the mechanical properties. In the eutectic Si phase, small Al3Er particles formed by Er and Al play an important role in refining eutectic silicon and increasing the strength of the alloy. The rare earth element Er can form small Al3Er particles in the matrix and generate Al3Er and AlSiEr phases, which can play an anchoring role in the alloy and improve the Al-Si-Fe alloy strength.

Effect of rare earth Ce on the microstructure and mechanical properties of cast Al–7Si alloys

Casting experiments were carried out on Al–7Si using different additions of rare earth Ce at a reaction temperature of 1200 K. Based on the ternary phase diagram of Al–Si–Ce, the effects of rare earth Ce on the α-Al grain refinement, the mechanism of the eutectic Si phase modification, as well as on the mechanical properties and fracture morphology of the alloy were investigated. The results show that the addition of rare earth Ce generates a Ce-containing phase inside the alloy, which becomes a heterogeneous core of eutectic Si and changes the nucleation conditions of eutectic Si. The mechanical properties of the alloy were optimal when the Ce addition was 0.2 wt.%, and the defect porosity and average pore area were minimized. Ce-containing phases were found at fracture cracks, and these Ce-containing phases were deviated and aggregated at grain boundaries, which induced defects to be generated, and microcracks were easily produced during plastic deformation, which ultimately led to the fracture of the alloy. According to the growth kinetic relationship, due to the difference of different atomic radii, the inter-atomic forces lead to different nucleation densities of grains. With the generation of Ce-containing phases at the interfaces, the eutectic Si changes its growth direction and grows towards a 70° angle to the original direction with a tighter atomic ordering sequence of the stacking, and more twinned Si is generated and gradually stacked up at the interfaces, which directly alters the morphology of the eutectic Si.

Revealing nucleation kinetics of entrained eutectic Si droplets in high purity melt spun Al-5Si based alloys with additions of Ta, TiB2, Eu and P

High purity (HP) Al-5 wt% Si with additions of Ta, TiB2, Eu and P were produced by arc melting and melt-spinning. Nucleation kinetics of entrained eutectic Si droplets in HP melt spun Al-5Si based alloys was investigated using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). No significant effect of Ta and/or TiB2 on nucleation kinetics and microstructure of entrained eutectic Si droplets was observed, although Al3Ta was observed at hyperperitectic concentrations. In contrast, a significant effect of Eu and/or P on nucleation kinetics and microstructure of entrained eutectic Si droplets was observed. Increasing P concentration increases the onset temperature and exhibits a lower undercooling required for the nucleation of entrained eutectic Si droplets. Large Al2Si2Eu phase was observed both within the Al matrix and along the boundaries of entrained eutectic Si droplets, while small Al2Si2Eu phase was also observed within entrained eutectic Si droplets. With increasing P, EBSD reveals the transition from fine randomly multiply-oriented fibrous eutectic Si to coarse single-oriented plate eutectic Si within the entrained eutectic Si droplets. With further increasing P, fewer coarse Si crystals were observed within the entrained eutectic Si droplets. EBSD indicates that the entrained eutectic Si droplet can be nucleated from AlP nucleation site.

Mechanistic understanding of strengthening in a novel MXene/AlSi10Mg matrix composite processed by laser powder bed fusion

The fabrication of high-performance two-dimensional nanosheets strengthened Al matrix composites (AMCs) is challenging due to the agglomeration issue of traditional nanosheets (graphene) and their high reactivity with Al powder. To address these concerns, Ti3C2 MXene nanosheets with superior chemical stability were employed as a substitute for graphene in this study. Furthermore, a novel MXene/AlSi10Mg composite powder for the laser powder bed fusion (LPBF) was synthesized using a powder coating strategy. The approach involves three steps, including intercalation treatment of MXene flakes, uniform dispersion of the delaminated MXene nanosheets in aqueous solution, followed by the powder coating treatment using a solid-liquid fluidized bed. Differing from conventional methods for making powder mixtures, such as mechanical blending and ball milling, our powder coating approach achieved uniform distribution and high purity of MXene on the surface of AlSi10Mg powder, while maintaining the original sphericity and flowability of powder. The MXene-coating exhibited exceptional stability under intense conditions of high-energy laser exposure and high-temperature Al melt, enabling the successful retention of MXene nanosheets after LPBF processing. Experimental results show that the retained MXene effectively strengthened the Al matrix through load transfer from Al matrix, pinning effect on the movement of grain boundaries, and inhibiting effect on the deformation and fracture of eutectic Si. Consequently, compared to the bare AlSi10Mg sample processed by LPBF, a small addition of MXene (0.25 wt%) yielded a significant improvement in tensile strength (over 60%), while maintaining an acceptable ductility.

Microstructure, segregation and mechanical properties of A356 alloy components fabricated by rheo-HPDC combined with the swirled enthalpy equilibration device (SEED) process

The challenges commonly associated with conventional high pressure die casting (HPDC) have led to increased interest in semi-solid metal (SSM) forming processes. In the present study, semi-solid slurries of A356 alloy prepared by the Swirled Enthalpy Equilibration Device (SEED) process were used for manufacturing components with complex shape by using a high pressure die casting machine. The segregation phenomenon and the effect of heat treatment on the microstructure evolution and mechanical properties were investigated. The results showed that the alloy consists of primary spherical α-Al grains, secondary solidified α-Al grains, eutectic Si, iron-rich intermetallic phases and low porosities. The microstructural investigations revealed that the eutectic Si particles underwent fragmentation, spheroidization and coarsening with increasing solution temperature. Furthermore, the solution treatment results in the dissolution of the π-Al8FeMg3Si6 phase and the growth of the β-Al5FeSi phase. The hardening peaks at 170 °C could be obtained with ageing for 5 h. Due to both solution and precipitation strengthenings, the yield strength, ultimate tensile strength and hardness of A356 alloy after heat treatment increase significantly compared to those in the as-rheocast state: they reach 266 MPa, 343 MPa and 110 HV0.2, respectively. The analysis of fracture surfaces of rheo-HPDC samples in both the as-rheocast and the heat-treated states revealed a mixed mechanism of dimples and quasi-cleavage. The microstructure inside the part was found to be quasi-homogeneous while the segregation phenomenon in different zones of the part is affected by die geometry during the filling process. The results imply that the SEED-HPDC process has the potential to be industrialized by implementing appropriate heat treatments for producing complex components with good mechanical properties.

Effect of chemical composition and T6 heat treatment on microstructure and mechanical properties of a hyper eutectic Al–Si alloy

The automotive and aircraft industries’ requirements have led to increasing application of Al–Si alloys thanks to their great potential as a replacement to cast iron and steel. The current work is an investigation of the effect of chemical composition and T6 heat treatment on the microstructure and mechanical properties of a hyper eutectic Al–Si alloy. Secondary Al–Si alloy ingot was cast using the sand casting technique. Samples were prepared for microstructural examination and mechanical properties tests. One set of the samples was subjected to solution heat treatment at 530°C, quenched in water at room temperature and aged at 175°C for five hours. Microstructural examination of cast samples using scanning electron microscopy (SEM) revealed three main phases in the alloy. Primary α–Al dendritic phase, eutectic Si phase and intermetallic phases of Fe and Mg. After heat treatment, the eutectic Si phase was spheroidized and uniformly distributed, the bonding strength of the α–Al dendritic phase and Si eutectic phase were well distributed, and the Fe and Mg phases precipitated. The ultimate tensile strength and hardness improved by 37.17% and 40.38% respectively. T6 heat treatment is therefore a necessary step in the production of parts made of Al–Si alloy by sand casting.

Effect of Ti and Sr on the microstructure and mechanical properties of Al-12Si-4.5Cu-2Ni alloy

The effect of Ti and Sr on the microstructure and mechanical properties of Al-Si-Cu-Ni alloy was studied. Research showd that the addition of 0.1% Ti and 0.02% Sr significantly reduced grain size and changed the morphology of eutectic Si. Sr promoted the formation of stacking faults and nano-Al2Cu. The strength and plasticity were significantly increased with ultimate tensile strength, yield strength and elongation being 239.6 MPa, 140.6 MPa, and 2.11%, respectively.

Effect of scandium on grain refinement mechanism and mechanical properties of Al–7Si–0.6 Mg alloy at different cooling rates

The effects of scandium (Sc) additions on the solidification microstructure and mechanical properties of Al–7Si–0.6Mg-0.25Ti alloy at different cooling rates have been systematically studied by thermal analysis and detailed SEM and TEM microstructure characterization of the castings. It is found that the addition of Sc has significant effects of refining the grain structure and modifying the Al–Si eutectics into fibrous structure. As a result, substantially improved strength and ductility in the as-cast state have been achieved in the Sc-added alloy. More importantly, the addition of Sc reduces the sensitivity of the alloy's strength and ductility to local cooling rates in the castings. The underlying mechanisms on the grain refinement, modification of Al–Si eutectics and strengthening by Sc addition have been studied. A new phase, DO22 structured (Al, Si)3(Ti, Sc), has been found to form in the liquid aluminium, acting as high potency nucleation sites of Al grains, which overcomes the Si poisoning effect on grain refinement for Al–Ti–B grain refiners.

A Comparative Study on Microstructure, Mechanical Property, and Electrical Conductivity of Al-7Si-0.6Mg Alloy Produced by High Pressure Die Casting and Semisolid Die Casting

Two casting technologies were introduced to fabricate the Al-7Si-0.6Mg alloy, including high pressure die casting (HPDC) and semi-solid die casting (SSM). The microstructure and mechanical property were studied by optical microscopy (OM), scanning electron microscopy (SEM), X-Ray diffraction (XRD), microhardness and tensile test. The electrical conductivity was also introduced to evaluate the thermal conductivity of the alloys. Results show that the as-cast microstructure of the HPDC alloy and SSM alloy both consists of primary α-Al, eutectic Si and Mg2Si phase. The primary α-Al phase in HPDC alloy possesses fine equiaxed dendrite structure with an average grain size of 29.4 μm. While the SSM alloy forms abundant coarse and globular structure α-Al phase, and the average grain size reaches 98.9 μm. This is because of the lower cooling rate during slurry preparation promotes the formation of a relative coarse microstructure in the SSM alloy. Furthermore, the increased content of eutectic Mg2Si phase was also detected in the SSM alloy. Therefore, the average yield strength and ultimate tensile strength decreases from 148 MPa and 275 MPa of the HPDC alloy to 140 MPa and 254 MPa of the SSM alloy, respectively. However, the elongation and electrical conductivity of the SSM alloy both increases from 5.8±1.3% and 20.0±0.1 MS/m of the HPDC alloy to 7.5±1.2% and 20.6±0.1 MS/m, respectively.

Combination of hot plastic deformation and T6 heat treatment for enhancing mechanical properties of an A356 alloy

ABSTRACT This study evaluates the relationship between solution heat treatment and hot plastic deformation before aging treatment and its effect on A356 alloys’ mechanical properties and microstructural features. The study employed tensile tests, Vickers microhardness tests, and electron microscopy analysis. The results show that hot plastic deformation before the solution treatment leads to higher elongation, ultimate tensile stress, and yield strength values, which can be attributed to modifications in eutectic Si particles (spheroidisation, aspect ratio and roundness). On the other hand, hot plastic deformation after the solution treatment mainly affects the elongation of the alloy. This effect is due to the fracture of eutectic Si particles and the formation of cracks and voids between these particles, which facilitate crack nucleation. Thus, the combination of hot plastic deformation and subsequent solution treatment significantly improves the mechanical properties of the A356 alloy. The observed changes in microstructure and mechanical behaviour provide valuable insights for optimising the material's properties and refining an established process in the automotive wheel industry.

Microscopic mechanism of mechanical property improvement of the casted Al-7Si-0.4Mg-0.3Y alloy

This paper investigates the effect of different casting conditions on the microstructure of Al-7Si-0.4 Mg alloys with 0.3 wt.% rare earth Y addition and the effect of T6 heat treatment on their mechanical properties. The experimental studies showed that the addition of 0.3 wt.% rare earth Y at 30 min or 1200 k resulted in the optimum microstructure and mechanical properties of the alloys, and the addition of Y led to the formation of Y-containing nanoparticles on eutectic Si, which were re-solidified by T6 heat treatment and precipitated a more stable orthorhombic cubic structure of Al2Si2Y compounds at the grain boundaries. According to the growth kinetic relationship, the addition of Y replaces the nucleation center of the original eutectic Si, and the preferential precipitation of the Y-containing phase destroys the heterogeneous nucleation conditions of the original eutectic Si, which leads to the growth of eutectic Si towards the original growth direction close to 60°, and generates more heterogeneous twins at the interface and gradually builds up, which has an inhibitory effect on the growth of eutectic Si. The fracture morphology and energy spectra show that the precipitated Y-containing coexist in these precipitates will lead to local stress concentration resulting in microcracks and ultimately fracture, which will change the mechanical properties of the alloy significantly.

Strengthening mechanisms and work hardening in a heterostructured cast aluminum alloy under compressive loading: Correlation with nanomechanical properties

The compressive deformation behavior of a high-pressure die-cast Silafont®-36 aluminum alloy was evaluated in relation to the microstructural changes during deformation. No strain rate sensitivity was observed for the alloy compressed at room temperature. The as-cast microstructure consisted of softer primary α-Al dendrites and harder Al-Si eutectic structure, which was well depicted by the difference in the nanohardness values using high-speed nanoindentation mapping. The load-bearing capacity of eutectic Si particles and thermal mismatch enhanced dislocation density strengthening were identified to be the predominant strengthening mechanisms in the alloy, plus a certain degree of Orowan strengthening mechanism. The work hardening capacity of the cast alloy was mainly attributed to the increase in the dislocation density in the softer α-Al matrix, which was further assisted by the presence of eutectic Si particles. The relative increase in the flow stresses also corresponded well to that in the nanohardness values of the α-Al grains with increasing strain levels.

Development of a novel high strength Al-Si-Cu-Ni alloy by combining micro-alloying and squeeze casting

In this paper, a new type of Al-8Si-1.5Cu-1Ni-0.5Mg-0.5Mn-0.2Ti-0.2Zr-0.2V-0.06Sr alloy (Al-Si-Cu-Ni alloy for short) was prepared by combining micro-alloying and squeeze casting (SC) forming technology, and its microstructure and mechanical properties were investigated. The results show that the average diameter and secondary dendritic arm spacing of α-Al grains in Al-Si-Cu-Ni alloy prepared by SC are 63 µm and 12.8 µm respectively, and the internal pores of the alloy are basically eliminated. Moreover, the eutectic Si and complex second phases (i.e., AlSiMnFe, Al3CuNi and (Al,Si)3(Zr,Ti,V)) are greatly refined and more uniformly distributed in the SC alloy. In particular, the eutectic Si can even be refined to sub-micron or nanoscale, and its average F value (i.e., average shape factor) for eutectic Si in the SC alloy is 0.57, which is 29.5 % higher than that of GC alloy. The as-cast ultimate tensile strength (UTS), yield strength (YS) and elongation of the SC Al-Si-Cu-Ni alloy are 310 MPa, 169 MPa and 3.8 %, respectively. Interestingly, its UTS and ductility are much higher than those of most other Al-Si alloys formed by same method, especially its UTS can even be comparable to that of some T6 heat-treated alloys. The increase in strength and elongation is mainly attributed to a reduction in porosity, grain refinement and improvement in the morphology of the second phases.

Thermochemical modelling and mechanical property of the Al-7.6Si-xZr alloy

This study utilised the gravity casting method to modify hypoeutectic Al-7.6Si alloys with Zr at varying weight percentages (0.1%, 0.2%, and 0.3%). The unmodified alloy typically consists of a needle or platelike eutectic silicon within the dendritic α-Al phase. The addition of Zr increases the liquidus temperature of the alloy and results in the formation of ZrSi and ZrSi2 compounds, which act as nucleation sites for both the eutectic Si and α-Al grains. As a result, the needle or platelike eutectic silicon transforms into a fibrous structure with a more uniform distribution, and the α-Al phase becomes finer and globular. These microstructural changes lead to improved bulk hardness, ductility, and mechanical properties of the alloy.

Effect of pulsed electric field on the microstructure and mechanical properties of a recycled ADC12 aluminum alloy

The effect of current density on the microstructure and mechanical properties of cast ADC12 recycled aluminum has here been investigated by using a pulsed electric field and a self-developed high-power pulsed device. The results showed that the pulsed electric field could refine the microstructure of cast ADC12 recycled aluminum alloy and enhance its frictional properties. As a result of the pulsed electric field treatment, the eutectic Si phase changed from long rod-like (or platelet-like) to short rod-like (or fiber-like) and was aggregated and distributed around the α-Al phase. Also, the long needle-like β-Fe phase changed to short needle-like, and the number of round spherical β-Fe phases decreased and changed to small-sized spherical. For a current density of 13.636 A/mm2, the average area of the α-Al phase decreased by 10% (as compared with the original sample). Also, the average area of the eutectic Si phase and β-Fe phase decreased by 8% and 86%, respectively. In addition, the average length decreased by 36%, and the refinement effect was the best. Furthermore, the deep etching analysis showed that the three-dimensional morphology of each phase was significantly refined. The current density was 13.636 A/mm2 and the friction coefficient decreased by 17.8%, as compared with the original sample. Also, the Rockwell hardness and yield strength became significantly increased. In addition, there was an obvious wear surface refinement, the alloy wear surface became smoother, the area of spalling pits was smaller, and the furrow parallel to the friction direction was both shallower and smaller. The size of the plastic shear lip, as accumulated on both sides of the furrow, was smaller, and the wear degree of the alloy surface was greatly reduced.

Solidification of Al12Si Melt Pool in Laser Powder Bed Fusion

An understanding of the solidification characteristics of the melt pool during laser powder bed fusion, L-PBF, metal printing is essential to ensure the manufacture of sound parts. This is the main theme of this article where it is attempted to unlock the solidification black box through calculation/measurement of the main solidification parameters of cooling rate, growth rate, temperature gradient, and undercooling. The very small melt pool size and its rapid cooling hinder the application of conventional tools to extract such information. A knowledge of these parameters and their effect on the microstructure and morphology of constituent phases could help to better control the L-PBF process and indeed all the fusion-based additive manufacturing routes, to fabricate high-quality parts. Al12Si alloy solidification during the L-PBF fabrication route is examined to highlight the extreme changes in solidification parameters and their effect on the morphology and size of eutectic Si. This is because the morphology of Si controls the mechanical properties of the finished part. The Al–Si eutectic has a divorced architecture attributed to the difficulty associated with Si growth resulted from rapid solidification. The generation of a temperature gradient of about 7700 °C/mm resulted in cooling rates in the range of 1.1 × 106 °C/s and a growth rate of 140 mm/s. Such values were then used to predict the morphology of eutectic Si based on the traditional approach.

A novel Al-Si-Ni-Fe near-eutectic alloy for elevated temperature applications

A novel near-eutectic Al-15.0Si-4.1Ni-1.9Fe (wt%) alloy with a ternary eutectic reaction of Liquid→α-Al+Si+(Al,Si)5(Fe,Ni) was investigated. Eutectic Si and (Al,Si)5(Fe,Ni) phases exhibit short nanoscale fibrous morphologies with volume fractions of 14.3 ± 1.6% and 15.1 ± 1.9%, respectively. The (Al,Si)5(Fe,Ni) phase has a tetragonal Al2.7FeSi2.3-type crystal structure with excellent thermal stability, which contributes to high mechanical properties at room and elevated temperatures. First-principles density-functional theory (DFT) calculations reveal its chemical composition of tetragonal (Al4.75Si0.25)(Fe0.5Ni0.5) having Si solution at the Al sites with two Fe neighbours contributes to the lowest solution energy. The newly developed alloy has superior mechanical properties at room and elevated temperatures compared with other typical heat-resistant aluminium alloys, which has great potential for industrial applications.

Fabrication of hypereutectic Al–Si alloy with improved mechanical and thermal properties by hot extrusion

Silicon phase in hypereutectic AlSi powders appears as primary Si and eutectic Si. Due to the poor thermal stability of eutectic Si, the material suffers from pores, stress concentration and dislocation packing during hot extrusion process, resulting in low density and poor thermal properties. In order to eliminate the eutectic Si, a heat treatment is conducted on Al20Si powders before hot extrusion. Because of the Ostwald ripening effect, the eutectic Si and dislocations in the powders are replaced by isolated Si lumps and a clear Al matrix. As a result, the formability and thermal properties of the material are greatly improved. The extruded samples made from the treated powder present high relative densities 99.7–100%, ultimate tensile strength (UTS) 167–170 MPa, elongations 8.8–10.8% and thermal conductivities (TCs) 191–195 Wm−1 K−1 and low coefficient of thermal expansions (CTEs) 13.8–14.5 × 10−6/K. The excellent mechanical and thermal properties are attributed to the elimination of eutectic Si from the treated powders and as-extruded alloys. In addition, hot extrusion introduces in-situ Al2O3 in the Si surface, Al grain boundary and Al grains, which is beneficial to reducing and stabilizing the CTE of the material. Moreover, it hinders Ostwald ripening and thus growth of the Si particles during the service of the material.