Al Matrix Composites Research Articles

Effect of volume fraction ratio of Ti to Al3Ti on mechanical and tribological performances of the in situ Ti–Al3Ti core–shell structured particle reinforced Al matrix composite

Effect of volume fraction ratio of Ti to Al3Ti on mechanical and tribological performances of the in situ Ti–Al3Ti core–shell structured particle reinforced Al matrix composite

Regulating microstructure of Al matrix composites with nanocarbon architecture design towards prominent strength-ductility combination

Evading the strength-ductility trade-off is essential for engineering application of metal matrix composites. Herein, we propose a novel strategy to achieve the prominent strength-ductility combination of nanocarbon-Al composites. The strategy makes use of the nanocarbon architecture design via longitudinally unfolding the multi-walled carbon nanotubes (CNTs) into graphene nanoribbons (GNRs). It was found that the nano-sized intragranular and interfacial Al4C3 (length: 64±23 nm) easily formed in GNR/Al via the “heterogeneous nucleation-growth” pattern, which is contrary to the submicron-sized epitaxial Al4C3 (length: 133±39 nm) in CNT/Al. Detailed characterizations reveal the specific orientation relationships between Al4C3 and Al in GNR/Al, which benefits the robust interfacial bonding. The intragranular Al4C3 and intergranular GNR with large aspect ratio effectively increase the dislocation storage and hence working hardening ability, which leads to the strength-ductility synergy of GNR/Al. Meanwhile, the GNR anchored by dense interfacial Al4C3 introduces extra toughening effect by crack bridging, blunting and deflection.

Synergistic reinforcement effect of Fe and in-situ synthesized MgAlB4 whiskers in Al matrix composites

Interfacial bonding is an important factor affecting the mechanical properties of composites. The interface between the in-situ synthesized ceramic phase and the metal matrix is considered ideal, so little attention is paid to the interfacial modification. In this work, we found that interfacial segregation affects the growth of the MgAlB4 whisker and the interface of reinforcement and matrix in the composites. Systematic experiments and theoretical calculations indicate Fe solute prefer to segregate at the MgAlB4-{101‾0}/Al interfaces in in-situ synthesized MgAlB4/Al composites, which is helpful to reduce system free energy. On the one hand, Fe segregation induces the whisker coarsening and the formation of planar defects with a sandwich structure formed by a layer of Fe atoms and two layers of Al atoms in coarse-whiskers, on the other hand, it improves the interfacial strength. Although extra Fe aggravates the whisker coarsening, the synergistic reinforcing effect of the whiskers and the extra Fe is greater than the sum of their individual reinforcing effects. This work demonstrates that interfacial segregation can be used to modulate the size of reinforcements and improve interfacial strength.

Microstructure characterization and enhanced mechanical properties of quasi-continuous network structured Ti3AlC2-Al3Ti/2024Al composite

Al matrix composites (AMCs) with high specific strength are highly desirable for a wide range of critical applications due to their unique mechanical and electrical characteristics. On the target of the effective production of high-performance AMCs, a novel quasi-continuous network structure based on Ti3AlC2 was devised rationally and developed a heterogeneous Ti3AlC2-Al3Ti synergistically reinforced 2024 Al composites by the technique of reactive hot press. Herein, the produced Ti3AlC2-Al3Ti/2024Al composite exhibited superior mechanical strength, importantly, it exhibits a minimal ductility reduction in comparison with pure 2024Al. Compressive yield strength, tensile ultimate and yield strength along with bending strength increased with the increasing Ti3AlC2 content; the optimal values for 5vol%Ti3AlC2/2024Al composite were increased by 16.9% in compressive yield strength, 11.5% in UTS and 30.0% in YTS compared with 2024Al. The mechanical properties increment was attributed to the synergistic effect of the quasi- network structure, dispersion strengthening, load transfer strengthening and thermal mismatch strengthening mechanism. The approach reported in this study is expected to open new avenues for advanced AMCs synthesis with tunable morphology and mechanical strength for their widespread applications.

Microstructure Evolution and Mechanical Properties of 20%SiCp/Al Joint Prepared via Laser Welding.

SiC particles-reinforced Al matrix composites (SiCp/AMCs) have been widely used in the aerospace structural components. In this work, 20 vol% SiCp/2A14 joint was fabricated by laser welding technology. The effects of different laser power/welding velocity on the 20 vol% SiCp/2A14 joint forming, microstructure evolution and mechanical properties were studied in detail. The results showed that, under the same heat input, the high power/high welding velocity was beneficial to reduce the porosity of SiCp/2A14 joint and inhibited the formation of brittle phase of Al4C3. At 8 kW-133 mm/s welding parameters, the maximum tensile strength of the SiCp/2A14 joint reached 199 MPa, which is ~64% higher than that of the SiCp/2A14 joint prepared at 4 kW-66 mm/s welding parameters. By analyzing the fracture morphology and SEM image of SiCp/2A14 joint section, it is was found that the porosity of weld and Al4C3 brittle phase were the important factors limiting the strength of SiCp/2A14 joint. This work provides a reference for the process window design of laser welding SiCp/2A14 composites.

Fatigue behavior and tribological properties of laser additive manufactured aluminum alloy/boron nitride nanosheet nanocomposites

Laser additive manufacturing is a promising approach to prepare near-neat shape parts from Al nanocomposites with high mechanical and tribological properties. Owing to its lubricious nature, boron nitride nanosheets (BNNSs) were added into AlSi10Mg alloy via high-speed ball milling and laser metal deposition (LMD) to manufacture self-lubricating Al alloy nanocomposites with outstanding wear resistance and fatigue performance. The study shows that number of cycles-to-failure due to tensile fatigue increased from 103 for pure AlSi10Mg to 106 upon adding only 0.1 wt% of BNNSs. At 0.2 wt% BNNSs, the friction coefficient and wear-out volume of AlSi10Mg alloy decrease by 58% and 57%, respectively. Scanning electron microscopy micrographs show that pure AlSi10Mg has a worn surface of grooves, wide ridges, debris and large protrusions of worn material along the groove edges. The wear mechanism is mainly plastic deformation, delamination and adhesion in pure AlSi10Mg. On the other hand, the LMD-built AlSi10Mg/BNNS composites exhibit less rough surface with clear wear trails due to the thin lubricant layer formed from the extruded BNNSs during the test. An extended finite element model for the crack propagation during fatigue testing is developed, where the obtained results are in accord with the experimental measurements. The present study shows that additive manufacturing technology is capable to fabricate Al matrix composites with tailored properties for various design applications.

Impact of multiple FSP passes on structure, mechanical, tribological and corrosion behaviors of AA6061/316 stainless-steel reinforced Al matrix composites

Stainless steel particulates were chosen as alternatives to ceramic particles to improve particle-matrix bonding, toughness, and performance of aluminum metal matrix composites. A multi-pass friction stir processing route was utilized for the development of AA6061/316 stainless steel reinforced composites by varying the number of tool passes (1–4). Detailed microstructure analysis, corrosion, hardness, wear, tensile, and impact toughness behaviors of the developed composites were studied. An increment in the number of tool passes (1–4) did not cause a particle-matrix reaction or alter the presence of inherent Mg2Si, Al, and ferrous phases in the composites. The progressive increment in the tool passes significantly enhanced the dislocation density, grain refinement, particle refinement (36.4–22.4 μm), and dispersion within the composite's structure due to the successive rotating tool-induced high straining and plastic deformation, dynamic recrystallization, and Zener pinning phenomena. The successive tool pass-induced microstructure improved the microhardness value (129–146 HV), tensile strength (163–241 MPa), impact toughness (5.7 ± 0.1–11.35 ± 0.1 J/cm3), and corrosion resistance of the composite while the wear rate (0.37–0.11 mm3/Nm) and the mean friction coefficient (0.37 ± 0.1–0.21 ± 0.1) of the composite were significantly reduced as the number of the tool passes was increased. The 4-pass friction stir processing technique is thus recommended for the development of AA6061/316 stainless steel reinforced composites.

In-situ TEM study on the effect of stacking faults on micro-plasticity and proportional limit in SiC/Al composites

Enhancing the proportional limit of Al matrix composites (AMCs) is critical to the reliability of precision electronic instruments. In this paper, SiC/Al composites containing stacking faults (SFs) were successfully fabricated using pressure infiltration method. The proportional limit (σp5 and σp100) of SiC/Al composites with SFs reached 65 MPa and 124 MPa, respectively, which was 8%–22% higher than theoretical prediction of the Brown-Lukens empirical formula. In-situ TEM tensile test was conducted to reveal the strengthening behavior of SFs during micro-plasticity. The results showed that the extra strengthening effect in SiC/Al composites with SFs includes elastic interactions of SF extension, sessile stair-rod partial dislocations and interactions of SF networks and dislocation arrays. This work reveals the influence of SFs on the micro-plasticity and strengthening behavior of AMCs and proposes a new strategy to endow AMCs with higher proportional limit for precision instrumentation applications.

Effects of artificial aging on precipitation behavior, mechanical properties and corrosion resistance of Si3N4/6061Al composite fabricated by sintering and hot extrusion processes

Artificial aging plays important roles on the final performances of the manufactured components of Al matrix composites, and it is of great importance to find the appropriate aging parameters to obtain a good combination of mechanical properties and corrosion resistance. In this study, the Si3N4 particle reinforced 6061Al (Si3N4/6061Al) composite was produced by sintering and hot extrusion, and both single and two-step aging were carried out to examine the precipitation behavior. It was found that the grain structure of Si3N4/6061Al and 6061Al did not show a notable change after solution treatment, while Mg element inclined to concentrate at the Si3N4/6061Al interface. The compounds containing Mg and Cu formed at Si3N4/6061Al interface during aging process, and β″ and β′ phases precipitated after peak and two-step aging, respectively. β″ phase contributed to improving the hardness, strength and wear resistance, while β′ phase caused an opposite trend. The Si3N4 particles could also enhance the mechanical properties due to the load transfer and dislocation strengthening. The samples treated by solution exhibited the best corrosion resistance, while the peak-aged ones were sensitive to intergranular corrosion owing to the continuously distributed precipitates and the precipitate free zones at grain boundaries, and two-step aging could alleviate the intergranular corrosion susceptibility. Due to the preferential dissolutions of Mg element in Mg-containing layers and Mg/Cu-containing phases, the Al matrix around Si3N4 particles was seriously corroded.

Microstructure regulation and strengthening mechanism of Al/Ag composites prepared by Plasma Activated Sintered

The objective of this study is to modulate the size of intermetallic compounds to increase the strength of Al–Ag composites. In this study, we prepared Al–Ag composites using plasma-activated sintering (PAS). The effect of the applied current on the nucleation barrier of the Al/Ag alloy phase was investigated. The strengthening mechanism of Ag-reinforced Al matrix composites was explored. We found that two alloy phases, Ag2Al and Ag3Al, were generated in the Al–Ag composites. The alloy phases distributed at the grain boundaries strengthened the Al–Ag composites by enhancing the dislocation density in the matrix and by impeding dislocation motion. The ultimate tensile strength and yield strength of the Al–7Ag composite increased by 60.1% and 166%, respectively, compared with those of pure Al. Moreover, we calculated the contribution of each strengthening mechanism to the overall yield strength. The applied current lowered the nucleation barrier of the alloy phase and facilitated the nucleation process.

Effects of size and oxidation treatment for SiC particles on the microstructures and mechanical properties of SiCp/Al composites prepared by powder metallurgy

SiC particles (SiCp) reinforced Al matrix composites as the one of the most representative ones in the field of metal matrix composites, and many researches about the enhancement effect of SiCp size on mechanical properties of SiCp/Al composites have mainly focused on the comparison of micron-sized and nano-sized SiCp. In this paper, low-cost submicron-sized SiCp with rare attention was used as novel reinforcements, and the enhancement effect was compared with that of nano-sized SiCp. At the same time, a strategy of oxidation treatment for SiCp is developed in the field of powder metallurgy, and related work has been carried out. Raw submicron-sized SiCp (hereafter named SiCsmp) and raw nano-sized SiCp (hereafter named SiCnp) were calcined at 1100 °C. Then, SiCsmp (raw and oxidized) and SiCnp (raw and oxidized) were used as reinforcements to prepare Al matrix composites with different reinforcement content by powder metallurgy. The enhancement effect of raw SiCnp is slightly better than that of raw SiCsmp when the content is below 7 vol%. Although the agglomerations of oxidized SiCp were found owing to increased agglomeration tendency after oxidation treatment for SiCp, the tensile strength of composites were enhanced significantly, especially for SiCnp/Al composites. Furthermore, the ductility of SiCsmp/Al composites was also improved after calcining for SiCsmp and thus excellent comprehensive mechanical properties were obtained.

Mechanical behavior and interfacial micro-zones of SiCp(CNT) hybrid reinforced aluminum matrix composites

Micro-sized silicon carbide particles (SiCp) reinforced aluminum (Al) matrix composites have been widely used in the aerospace, electronics and transportation applications. However, due to the easily formed stress concentration in the SiCp/Al interfacial micro-zones, the large-sized SiCp may cause serious plastic loss of SiCp/Al composites that have limited their applications. In this study, the 14.5 μm SiCp was selected to prepare the SiCp(CNT) hybrid reinforcement, and then the 15 wt. % SiCp/Al and SiCp(CNT)/Al composites were fabricated by the vacuum hot-pressing sintering, respectively. Compared to the SiCp/Al composite, the SiCp(CNT)/Al composites own the larger mechanical properties such as the Young's modulus, the yield strength and the tensile strength. Among these composites, the SiCp(0.5CNT)/Al composite presents the best matching of strength and plasticity as a result of the existence of CNTs in the SiCp/Al interfacial micro-zones. Strengthening and toughening effects of CNTs in the SiCp/Al interfacial micro-zones can contribute to: 1) increasing the punched zone size around the SiCp; 2) increasing the dislocation density in the SiCp/Al interfacial micro-zones; 3) changing the dislocation distributions in the SiCp/Al interfacial micro-zones; 4) pinning the dislocation movements by CNTs in the SiCp/Al interfacial micro-zones. From the analysis above, the strengthening and toughening mechanism of the CNTs introduced in the SiCp/Al interfacial micro-zones of SiCp(CNT)/Al composites can be revealed, which can be further developed to guide and prepare the hybrid particles reinforced metal matrix composites. • The strength-plasticity matching relationship of SiCp/Al composites can be improved by the presence of CNTs at the interface micro-zones. • Compared with SiCp/Al composites, the introduction of CNTs can increase the dislocation density at the interface micro-zones and pin the dislocation movement. • The existence of CNTs can change the dislocation distribution of SiCp/Al interface micro-zones.

Fe-based metallic glass particles carry carbon nanotubes to reinforce Al matrix composites

Aluminum matrix composites (AMCs) reinforced with novel carbon nanotube (CNT)-Fe-based metallic glass (FMG) synergistic reinforcements were successfully prepared by powder metallurgy. The CNT-FMG reinforcements were obtained by growing CNTs on the surface of FMG particles using chemical vapor deposition (CVD). By controlling the catalytic temperature, the grown CNTs exhibited good morphology, a high degree of graphitization, and thermal oxidation stability. CNTs were homogeneously dispersed in the Al matrix through the carrying action of FMG particles. The CNT-FMG synergistic reinforcements significantly improved the mechanical properties of the composite, and formed a tight interfacial bonding with the Al matrix. The CNT-FMG reinforcements had a remarkable synergistic strengthening effect on the composite.

Microstructure evolution, mechanical properties and strengthening mechanisms in the hot extruded Si3N4 particle reinforced Al–Cu–Mg composite

Si3N4 particles, with high modulus, hardness and thermal stability, are important reinforced phase candidates in Al matrix composite. In this work, Si3N4 particles were introduced into the 2026 Al alloy by a novel Al–Si–N master alloy and the Si3N4/2026 Al composite was successfully prepared via gravity casting and hot extrusion process. According to the SEM results, the Si3N4 particles tend to distribute at the grain boundary and coexist with the eutectic phases after solidification; however, a Si3N4 particles chain structure appears in the matrix after subsequent hot extrusion. The TEM results indicate that a nano-AlN particles transition layer is present on the surface of the Si3N4 particles, which has a good interfacial bonding with the Al matrix. The EBSD results show that the grains are refined significantly and the <111>Al fiber texture is improved in the Si3N4/2026 Al composite. At room temperature, the yield strength, ultimate tensile strength and Brinell hardness of composite are 454 MPa, 586 MPa and 143.5 HBW, respectively, which are increased by 15%, 12% and 11% than those of matrix alloy. The enhanced mechanical properties of the composite can be attributed to the load-bearing effect of the Si3N4 particles, grain boundary strengthening, dislocation strengthening and Orowan strengthening. This work will provide a new idea for the development of low cost and high strength Al matrix composites.

Effect of tool offsetting on friction stir welding of dissimilar aluminium matrix composite and aluminium alloy

Commercial 6061 Al alloy and SiCp reinforced 6092 Al matrix composite (AMC) were joined by friction-stir welding (FSW) with different tool offsets. Results show offsetting the pin to Al alloy side could significantly reduce tool wear, while maintaining ultimate tensile strength of the joint around 180 MPa. As tool offset increased from zero to 3 mm, pin and shoulder wear length reduced from 0.17 mm to almost zero and from 0.28 to 0.02 mm, respectively. The corresponding estimated maximum safe welding length increased from 568 to 3125 mm. Fe debris were generated from the steel pin by the sharp SiC particles, then transferred into the nugget zone, eventually formed Al8Fe2Si particles during the FSW process.

Investigations on Mechanical and Wear Properties of Al Matrix Composites Reinforced with Hybrid SiC and Al2O3 Micro-Particles

Investigations on Mechanical and Wear Properties of Al Matrix Composites Reinforced with Hybrid SiC and Al2O3 Micro-Particles

Lightweight and near-zero thermal expansion ZrW2O8-SiCnw/Al hybrid composites

• We reported a novel hybrid design strategy to achieve near-zero thermal expansion and high strength Al matrix composites. • NTE ZrW 2 O 8 and lowCTE SiC successfully control the high CTE of Al. • The addition of SiC (particle and nanowire) significantly reduces the thermal mismatch stress of ZrW 2 O 8 /Al composites. • Yield stress rises by increasing the SiCnw content, resulting in reduction of the unfavorable high pressure γ-ZrW 2 O 8 and microcracks. Negative thermal expansion particles can compensate metal matrix composites to achieve near-zero thermal expansion materials. However, there are huge thermal residual mismatch stresses in the particles due to the thermal expansion mismatch between matrix and reinforcement. The use of hybrid reinforcement is required to solve the stress concentration problem. In this study, the hybrid Al matrix composites reinforced with ZrW 2 O 8 and SiC reinforcements (SiCp, SiCnw) were fabricated by the pressure infiltration process. The effect of SiC content on microstructure, phase composition, thermal expansion and mechanical properties were examined by a combination of XRD, SEM, thermal dilatometer and bending tests. The results showed that the high-pressure phase (γ-ZrW2O8) content of hybrid metal matrix composites decreased with increasing SiC fraction. Among them, the composites containing 61.7 vol%ZrW 2 O 8 and 3.3vol%SiCnw achieved the best performance with a bending strength of 100–150 MPa and a near-zero thermal expansion (2.0–3.0 ×10 –6 K −1 ) in a wide range of − 50–120 °C, which was attributed to the synergetic hybrid effects of SiCnw and ZrW 2 O 8 . This work opens up a new frontier for the design and preparation of lightweight zero-thermal expansion materials.

Modification of cold-sprayed high-entropy alloy particles reinforced aluminum matrix composites via friction stir processing

In this study, a kind of novel Al matrix composite reinforced by CoCrFeNi HEA particles was fabricated by cold spray (CS) and subsequent friction stir processing (FSP) for the first time. The microstructure and mechanical properties of cold-sprayed (CSed) and friction stir processed (FSPed) CoCrFeNip/6061Al composites were examined using scanning electron microscopy, energy dispersive spectroscopy, electron backscattering diffraction, X-ray diffraction, and hardness and tensile tests. The results demonstrated that CSed samples exhibited a number of micro-pores in the Al matrix with homogeneous distribution of HEA particles, but heterogeneously distributed grain size. Continuous dynamic recrystallization and geometric dynamic recrystallization occurred at the interface between the HEA particles and Al matrix. Following FSP, the micro-pores were eliminated, and a small amount of HEA particles was fragmented and uniformly dispersed in the Al matrix. Moreover, the average size of HEA particles was refined from ~21–14 µm. The Al matrix exhibited dynamic recrystallization and particle-stimulated nucleation recrystallization, thus resulting in an average grain size of ~1.9 µm. Obvious diffusion layers of 0.5 µm and 1 µm in thickness occurred at the interface between the HEA particles and Al matrix in CSed and FSPed samples, respectively. A new phase with a body-centered cubic structure was confirmed to be an HEA in diffusion layers. Compared with CSed samples, the microhardness, ultimate tensile strength, and elongation of the FSPed samples increased by 91%, 60%, and 130%, respectively. The improved mechanical properties are attributed to the high density and enhanced interfacial bonding. Thus, this study provided a novel method for preparing high-performance Al matrix composites reinforced by HEA particles.

Enhancing the Strengthening Effect of Graphene-Nanoplates in Al Matrix Composites by Heterogeneous Matrix Design.

In the present work, the properties of graphene-nanoplates/aluminum (GNPs/Al) composites with a heterogeneous matrix design were investigated. The advantage of the heterogeneous matrix was investigated by the finite element method. Then, 0.6 wt.% (GNPs/6061Al)/2024Al (heterogeneous matrix) and 0.6 wt.% GNPs/6061Al composites were prepared by ball milling, pressure infiltration technology, and hot extrusion. The aggregation of GNPs was eliminated and the interlayer slide of GNPs was observed. Mechanical property test results show that the mechanical properties of the heterogeneous matrix composite are better than that of a homogeneous matrix composite, including strength, elastic modulus, and plasticity. It is assumed that the heterogeneous matrix design enhances the non-uniform stress field during the deformation treatment. This improves the dispersion of GNPs, grain refinement, and produces the few-layer graphene (FLG), thus enhancing the strengthening effect of GNPs. Meanwhile, heterogeneous matrix design is thought to introduce more hardening mechanisms to increase the plasticity of materials and improve the intrinsic trade-off of strength and toughness.

Higher proportional limit of SiC/Al composites with nano-scaled stacking faults

Enhancing the proportional limit of Al matrix composites (AMCs) is critical to the reliability of precision electronic instruments. In this paper, SiC/Al composites containing stacking faults (SFs) were successfully fabricated using pressure infiltration method. The proportional limit (σp5 and σp100) of SiC/Al composites with SFs reached 65 MPa and 124 MPa, respectively, which is 8%∼22% higher than theoretical prediction of the Brown-Lukens empirical formula. The nucleation of SFs may be related to the lattice distortion fluctuation in Al matrix. The origin and stress conditions of SF nucleation in SiC/Al composites were deduced from the perspective of effective stacking fault energy (SFE). This paper provides theoretical support for preparing SF-containing AMCs with higher proportional limit.