Eutectic Si Phase Research Articles

Microstructure evolution and mechanical properties of Al-12Si-xCu-yNi-1Mg alloy with different Ni/Cu ratios

High-temperature properties are the key factor affecting the industrial application of cast Al-Si alloy. In this paper, four kinds of Al-12Si-xCu-yNi-1Mg (y = 7.5-x, x:4.84, 5.17, 5.55, 6.00.) alloys were prepared by changing the Ni/Cu ratio and regulating the type and proportion of the heat-resistant phase, and then systematically analyzed the changing of microstructure and mechanical properties and clarified the heat resistance mechanism of the alloy. The experimental results show that with the increase of the Ni/Cu ratio, the eutectic Si phase of the as-cast alloys was refined, the blocky Al2Cu phase and the strip Al7Cu4Ni phase disappeared, and the reticular Al3CuNi heat-resistant phase increased, and the size of Al3CuNi phase decreases first and then increases. After T6 heat treatment, the eutectic silicon spheroidized, and the nickel-rich phase did not change significantly. As the Ni/Cu ratio increases, the tensile strength of the alloy at room temperature increases first and then decreases, and its tensile strength at high temperature increases continuously. When the Ni/Cu ratio is 0.45, and the maximum value of tensile strength at room temperature is 355 MPa. When the Ni/Cu ratio is 0.55, the content of the Al3CuNi phase with high thermal stability is most, and the Al2Cu phase with poor stability is less, so the high-temperature tensile strength is the highest, and the value of tensile strength at 275 °C, 325 °C and 375 °C is 192 MPa, 172 MPa, and 89 MPa, respectively.

Significantly enhanced fatigue resistance and mechanisms of hypoeutectic Al-Si composite calibrated using trace in-situ nanocrystals

Fatigue resistance under extreme stress conditions is an important indicator to evaluate industrial application potential of Al-Si-Mg alloys, but their fatigue resistance is inherently weakened by large grain size, long-needle Si phases and coarse precipitates. This work reports significantly optimized microstructure configuration and fatigue resistance of hypoeutectic Al-Si composite optimized by the nanocrystallization products of a NiNbTi metallic glass. It was proved the in-situ NiTi (B2) nanocrystals can serve as the heterogeneous nucleation sites of α-Al and β-Mg2Si and the growth retarder of eutectic Si. Particularly, the optimized composite exhibited nearly 5 times and 6 times longer fatigue life than the unoptimized alloy at 120 MPa (60 Hz) and 240 MPa (20 Hz), respectively. The fatigue strength (N = 107) was increased by 21.7 % and 25.9 % at 60 Hz and 20 Hz, respectively. The α-Al refinement enhanced the resistance to fatigue crack initiation. The refinement and spheroidization of eutectic Si phases reduced stress concentration. Also, the austenite-martensite phase transformation of NiTi afforded more energy for precipitation. Refined β-Mg2Si and β'' phases were facilitated to interact with dislocations, improving the resistance to dislocation slip during cyclic strain through the dislocation shearing effect. This work provides a theoretical basis for the future development of Al-Si alloys and composites with excellent fatigue resistance for expanding their industrial application scope.

Effect of Si Content on Microstructures and Electrochemical Properties of Al-xSi-3.5Fe Coating Alloy

Hot-dip aluminum alloy is widely used in the engineering fields. However, during the aluminum plating process, Fe inevitably enters and reaches a saturation state, which has a significant impact on the corrosion resistance and microstructure of the coating. Currently, adding Si during the hot-dip aluminum process can effectively improve the quality of the coating and inhibit the Fe-Al reaction. To understand the effect of Si content on the microstructure and electrochemical performance of Al-xSi-3.5Fe coating alloys, the microstructure and post-corrosion morphology of the alloys were analyzed using SEM (Scanning Electron Microscope) and XRD (X-ray Diffraction). Through electrochemical tests and complete immersion corrosion experiments, the corrosion resistance of the coating alloys in 3.5 wt.% NaCl was tested and analyzed. The results show that the Al-3.5Fe coating alloy mainly comprises α-Al, Al3Fe, and Al6Fe. With the increase in Si addition, the iron-rich phase changes from Al3Fe and Al6Fe to Al8Fe2Si. When the Si content reaches 4 wt.%, the iron-rich phase is Al9Fe2Si2, and the excess Si forms the eutectic Si phase with the aluminum matrix. Through SKPFM (Scanning Kelvin Probe Force Microscopy) testing, it was determined that the electrode potentials of the alloy phases Al3Fe, Al6Fe, Al8Fe2Si, Al9Fe2Si2, and eutectic Si phase were higher than that of α-Al, acting as cathode phases to the micro-galvanic cell with the aluminum matrix, and the corrosion form of alloys was mainly galvanic corrosion. With the addition of silicon, the electrode potential of the alloy increased first and then decreased, and the corrosion resistance results were synchronous with it. When the Si content is 10 wt.%, the alloy has the lowest electrode potential and the highest electrochemical activity.

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.

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.

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.

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.

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.

Effect of Intensification Pressure on Eutectic Si Segregation of Al-12Si-1Cu Alloy in Squeeze Casting

Squeeze casting is an advanced technology to produce aluminum alloy components with excellent mechanical property. Due to good fluidity and castability, the Al-Si alloy is the most common aluminum material in squeeze casting. However, the segregation in solid α-Al phase and liquid eutectic Si phase happens during solidification, which leads to microstructural inhomogeneous in the final microstructure. In this study, the eutectic Si segregation of Al-12Si-1Cu alloy under different intensification pressure in squeeze casting was investigated by Optical Microscopy (OM). The results show that increasing intensification pressure promotes the eutectic Si segregation at center zone, while the eutectic Si phase at skin zone is not much influenced. Increasing the intensification pressure from 65 MPa to 140 MPa, the segregation degree of eutectic Si at center zone increases from 0.05 to 0.29, while the segregation degree at skin zone levels at 0.2. Under high intensification pressure, the feeding effect of liquid phase at center zone is prominent, which results to high tendency of eutectic Si segregation in the final microstructure.

Enhanced comprehensive performance via alloying and rheo-diecasting in a semi-solid Al–Si–Fe–Mg–Cu–Sr alloy

A semi-solid Al alloy with superior comprehensive performance was obtained via alloying design concept and rheo-diecasting (RDC). The semi-solid alloy slurry was obtained via the vibrating contraction sloping plate. As the contents of Cu and Mg elements increased, the secondary dendrite arm spacing (SDAS) decreased and solubility of Cu and Mg elements increased, which improved the mechanical property and decreased the thermal conductivity of as-cast alloys. The effect of microstructure evolution induced by pouring temperature on mechanical properties at room and elevated temperatures, thermal conductivity, and corrosion behavior of the RDC alloy was investigated. The results demonstrated that the low porosity and refined primary α1-Al grains, secondary α2-Al grains, β-Al5FeSi phases, eutectic Si phases played a significant role in enhancing mechanical properties of the alloy at room temperature. Meanwhile, some submicron β-Al5FeSi phases effectively hindered grain boundary sliding, resulting in the increased mechanical properties of the alloy at elevated temperatures. The improvement in thermal conductivity was related to the decreased electron scattering due to the reduced porosity and small-sized secondary phases. The decrease in the potential difference between the β-Al5FeSi phase and matrix helped improve the corrosion resistance of the alloy.

Effect of high pressure on solidification microstructure evolution of near-eutectic Al-11.5Si-0.5Fe-0.2 Mg alloy

The microstructures evolution of near-eutectic Al-11.5Si-0.5Fe-0.2 Mg alloy solidified under different pressures (1 GPa and 3 GPa) were investigated. The results show that the increase in solidification pressure leads to a transition from the typical eutectic structure to the hypoeutectic structure of the alloy by increasing the melting point, and a change in the morphology of the eutectic Si phase from a needle-like structure to a short sheet-like structure and contact with each other. The increase of solid solubility drives the disappearance of the π-Al8FeMg3Si6 phase at 1 GPa, the disappearance of the α-Al8Fe2Si phase, and the occurrence of the δ-Al4FeSi2 phase at 3 GPa. The α-Al8Fe2Si phase and β-Al5FeSi phases are separated from each other in the matrix, indicating that these two phases are formed by independent reactions. In contrast, the β-Al5FeSi and δ-Al4FeSi2 phases can remain stable during solidification at higher pressures.

Mechanism of AlP modifying the morphology of Si in Al-20Si alloys based on experimental studies and first-principles calculations

ABSTRACT The modifying influence of aluminium phosphide to the morphology of primary Si and eutectic Si was investigated in hypereutectic Al-20Si alloys via adding Al-Cu-P master alloy (0.5, 1, 20 wt.%). Microstructural results showed when Al-Cu-P addition from 0 to 0.5%, primary Si phase decreases and eutectic Si phase size remains invariable; when addition higher than 0.5%, primary Si phase keeps invariable, eutectic Si phase size increases. To prove the nucleation effect of AlP on Si phase, interfacial properties of Si/AlP interface were investigated using first-principles calculations. Results showed the AlP(100)/Si(100) interface energy is between −1.45 J/m2 and −1.38 J/m2 for Al-terminated and P-terminated AlP model, both is much smaller than liquid Si/crystalline Si interface (0.34 J/m2), consolidates that AlP particles possess strong nucleation potency for Si phases. Therefore, the modifying influence of AlP to the morphology Si phase is well clarified as a function of AlP content in Al-20Si alloys.

Evaluating comparative wear behaviour of Al-15%Si based alloy/composites reinforced with zinc and zirconium oxide

ABSTRACT The tribological characteristics of stir cast Al-15%Si-10%Zn matrix with 15%ZrO2 reinforced composite were investigated. The microstructure of the Al-15Si alloy consisted of coarse primary Si and acicular eutectic Si phases randomly distributed in the Al dendrites. The Al-15%Si-10%Zn/ZrO2 composite showed spherical Si with a size between 25 and 75 µm; fragmented eutectic Si phase and uniform dispersion of ZrO2 particles in the matrix. The wear test was conducted using in a pin-on-disc method at different loads and sliding velocities. It was found reduced coefficient of friction, significant increase in the hardness and wear resistance of the composite compared to the matrix alloy. High wear resistance in the composite due to the effect of solid lubrication provided by Zn, and good fracture toughness and wear resistance by the reinforced ZrO2 particles. The predominant oxidative and abrasive wear were identified as the mechanisms leading to material failure through plastic deformation and delamination.

INFLUENCES OF P AND Sr ON MICROSTRUCTURE AND ITS EFFECTS ON MACHINABILITY AND MECHANICAL PROPERTIES OF HYPEREUTECTIC Al-20%Si

Hypereutectic Al-Si alloys are widely utilized in the automotive industry due to their high strength-to-weight ratio, minimal thermal expansion, and superior castability. The downside of hypereutectic Al-Si alloys is the formation of coarse primary silicon particles. The primary Si phases were controlled by the growth-hindering agents, phosphorus (refiner), and strontium (modifier) by using a conventional stir casting technique at room temperature. The microstructural changes were observed through an optical microscope and SEM analysis. The additions of 0.08% P have ensured the formation of the uniformly distributed fine-grained particles in the alloy. The primary silicon particle size was reduced from 220[Formula: see text][Formula: see text]m to 150[Formula: see text][Formula: see text]m as compared to the untreated alloy. The tensile and yield properties of the treated alloy were increased by 12.7% when compared to the untreated alloy with a hardness of 131 BHN. The treated alloy imparted better impact toughness, ensuring a ductile mode of failure through the fractography studies. The influence of the microstructure on the machinability of the alloy was investigated in a dry environment with uncoated and coated inserts (code: CCGT 09T304 FL K10) by varying the process parameters, i.e. speed, feed rate, and depth of cut (DoC). Modification of the primary and eutectic Si phases of an Al-20Si hypereutectic alloy increases machinability with coated inserts as well as its mechanical properties.

The Effect of Process Parameters on the Properties and Microstructure of A380 Aluminum Alloy Casting with Different Wall Thicknesses

In the present work, the effects of different die-casting process parameters on the mechanical properties and microstructure of A380 aluminum alloy casting with different wall thicknesses during the solidification process have been experimentally investigated. The experimental results show that both boost pressure and injection speed have a significant effect on the mechanical properties of the casting. As the injection speed increases, the changes in mechanical properties are more significant in the thin-walled area, while increasing the boosting pressure has a greater effect on the mechanical properties of the thick-walled area. In addition, the evolution of microstructure composition, including the α-Al phase, eutectic Si phase and Al-Si-Fe-Mn phase, has been analyzed and compared by energy-dispersive spectroscopy (EDS), optical microscopy (OM) and scanning electron microscopy (SEM). It was found that the α-Al phase in the thin-walled area is significantly refined with the increase of injection speed. Meanwhile, with the increase of boost pressure, the α-Al phase in the thick-walled area gradually becomes finer, and the distribution of the eutectic Si phase and the Al-Si-Fe-Mn phase in the alloy becomes more uniform. Thus, the injection speed and boost pressure have an important impact on the overall forming quality of the casting.

Effects of thermal ageing on the wear behavior of the cerium modified Al-18si-3.6cu alloy

ABSTRACT In the present investigation, an Al-18Si-3.6Cu alloy was modified by cerium (Ce), heat treated (T6), and aged for 1, 3, 5, and 7 h at 210°C. The resulting microstructures revealed that the addition of Ce as a modifier changed the morphology of the primary Si from coarse with a sharp edge to spherical, large-acicular/needle-like eutectic Si into a fibrous state, and dendrites of the Al phase into round branches with less interface separation. After thermal ageing, the microstructure of the modified alloy revealed no change in the morphology of the primary Si phase. However, a considerable change in the eutectic Si phase and the formation of fine precipitates of Al2Cu and Al2CeSi intermetallics in the matrix. Hardness was found to be significantly higher in the modified and age-hardened alloys. A Pin-on-disc wear tester was used to investigate the dry sliding wear behavior of alloys at different loads (10, 20, 30, and 40 N) and 1.0 m/s sliding velocity. The results indicated that the wear rate in the modified alloy was lower than the base alloy. Furthermore, the modified alloy after 5 h age hardening demonstrated high wear resistance and improved wear bearing capacity compared to the 1, 3, and 7 h age hardened alloys.

Effect of Zn Addition on the Microstructural Heterogeneity and Mechanical Properties of Vacuum‐Assisted High‐Pressure Die Casting Al–Si–Mg–Cu alloys

Herein, Al–8Si–0.5Mn–0.5 Mg–0.2Cu–xZn alloys (x = 0, 1, 2, and 3 wt%) are produced by a vacuum‐assisted high‐pressure die casting process. The effects of Zn addition on the surface layer thickness and segregation band, the number density of externally solidified crystals (ESCs), and mechanical properties of the alloys are systemically investigated. As the Zn content increases, the size and number density of the ESCs increase. The morphology and size of the eutectic Si phase could be modified by the addition of Zn. In addition, the microstructural heterogeneity indicates that the thickness of the surface layer and segregation band zone increase with increasing Zn content. Proper Zn addition can effectively promote the improvement of strength and elongation in the as‐cast state. When the Zn content is 2 wt%, the yield strength, ultimate tensile strength, and elongation of the alloy are 167, 311 MPa, and 10.8%, respectively.

Microstructure and mechanical properties of graphene and nano-zirconia reinforced AlSi10Mg composite fabricated by laser powder bed fusion

In this work, the graphene nano-platelets (GNPs) and ZrO2 nanoparticles single- and hybrid-reinforced AlSi10Mg composites were fabricated by laser powder bed fusion (LPBF). The influences of the introduction of single and hybrid reinforcements on the microstructure and tensile properties were investigated. Furthermore, the strengthening and toughening mechanisms of the LPBF-ed composites were systematically discussed. The results shows that the addition of the hybrid reinforcement (GNPs + ZrO2) reduces grain size of composites more effectively than the addition of either reinforcement alone. The GNPs and ZrO2 nanoparticles promote the columnar-to-equiaxed transition of α-Al grains at the bottom of the melt pool during LPBF processing of single- and hybrid-reinforced composites, resulting in a bimodal microstructure. The hybrid-reinforced composites had the greatest volume of fine equiaxed grains. There are several reinforcing phases in the (GNPs + ZrO2)/AlSi10Mg composite: eutectic Si phase distributed along cell boundaries, large numbers of un-melted GNPs and ZrO2 nanoparticles uniformly distributed along cell and grain boundaries, Si precipitate and some un-melted ZrO2 nanoparticles inside the cells, as well as rod-like Al4C3 nanoparticles distributed along cell boundaries. Compared to the single modified composites, the (GNPs + ZrO2)/AlSi10Mg composite had a highest tensile strength of 520 ± 12 MPa however the lowest elongation of 8 ± 1.8%. The grain refinement strengthening and the Orowan strengthening contribute to the most increment in strength of the hybrid modified composites, while the Si precipitation and some un-melted ZrO2 nanoparticles inside the cells and the bimodal microstructure play a dominant role in increasing ductility.

Wettability, Self-Cleaning Property, and Mechanical Durability of A390 Aluminum Alloy with the Major Effect of Si Phases.

Si phases with specific shapes, including primary and eutectic Si phases, were etched on the surface of A390 Al alloy by chemical etching. Meanwhile, their effects on the wettability, self-cleaning properties, and mechanical durability of etched A390 aluminum alloy surfaces were investigated. The results showed that the surface etched for 5 min and modified by 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS-17) demonstrated a contact angle of 153.2 ± 1.4° and a sliding angle of 11.2 ± 1.6°. The theoretical contact angle calculated by constructing a wetting model of Si phases approximates the actual contact angle. Further experiments indicated that the etched surface acquired excellent self-cleaning properties. In addition, the exposed Si phases formed a strong support skeleton, which greatly improved the wear resistance of the hydrophobic surface.