Al Matrix Research Articles

Laser Surface Melting to Mitigate Intergranular Corrosion of Sensitized AA5083

AA5083 is a solution-strengthened, supersaturated Al-Mg alloy. It has become widely used in corrosive and harsh environments, such as marine settings, due to its exceptional corrosion resistance and impressive strength-to-weight ratio. However, when exposed to moderately elevated temperatures, the alloy undergoes a process called sensitization, resulting in the precipitation of the β phase. This intermetallic precipitate is rich in magnesium and has anodic properties, creating a microgalvanic couple with the more noble aluminum (Al) matrix. Consequently, the sensitized alloy experiences intergranular corrosion due to the anodic dissolution of the grain boundary in a corrosive environment. Various techniques for dissolving intermetallic particles into the matrix have been reported in the literature, but they are often impractical for service components, and traditional solutionizing treatments tend to decrease mechanical properties. This study aimed to investigate the impact of pulsed excimer laser irradiation, as a novel approach, on the surface morphology, chemical composition, and electrochemical behavior of highly sensitized AA5083 samples. To achieve this, various analytical techniques were used, including profilometry, optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and localized potentiostat scans. The results of this investigation showed that laser surface melting (LSM) led to a reduction in the open-circuit potential and exchange current density in a 0.6 M NaCl aqueous solution, mainly due to increased surface homogenization. Furthermore, multiple grazing incident x-ray diffraction scans were performed to identify the changes in the metallurgical and crystallographic parameters in the near-surface region. Anodic polarization scans of the LSM surface galvanically coupled with a more cathodic base metal exhibited a lower corrosion current density than the theoretical value suggested by mixed potential theory. The improved performance could potentially be attributed to the surface homogenization and formation of a robust passive layer on the LSM surface.

Effect of tool–pin offset on microstructure, mechanical properties, and corrosion behavior of friction stir welded AA2024-T3 and SS304 dissimilar joints

The combination of aluminum and steel materials in hybrid structures shows promising applications in the automotive, marine, and aerospace sectors. The present study investigates how the tool–pin offset impacts the microstructural, mechanical, and electrochemical characteristics of friction stir-welded joints between dissimilar AA2024-T3 and SS304 materials. The optimum conditions were achieved at a tool rotation of 560 r/min, a traverse speed of 25 mm/min, and a tool–pin offset of 1 mm towards the Al side. Upon increasing the tool–pin offset to 1.5 mm, insufficient heat input resulted in inadequate plastic deformation and material flow, leading to the creation of flaws like voids, tunnels, and interfacial gaps. However, under optimal conditions, the joint exhibited a well-defined and serrated interface, with fine steel fragments securely embedded in the Al matrix. Additionally, thin intermetallic compounds were observed around the steel fragments within the Al matrix. This favorable combination resulted in enhanced tensile strength and increased ductility in the joint. The Vickers hardness test revealed that the stir zone exhibited the highest hardness values, primarily attributed to the ultra-refinement of grains. Furthermore, the potentiodynamic test revealed that the welded samples show improved corrosion resistance against the base material AA2024-T3, although BM-SS304 exhibited the highest corrosion resistance among all the samples, likely due to its higher chromium content.

Effect of pressure on the microstructure refinement, solidification mechanism and fracture behavior of wrought Al-Zn-Mg-Cu alloys prepared by squeeze casting

Squeeze casting process can effectively resolve the casting difficulties for wrought aluminum alloys by pressurized solidification. The effects of applied pressure (0.1–125 MPa) on the microstructure refinement, non-equilibrium eutectic phase aggregation and fracture behavior of Al-Zn-Mg-Cu alloys prepared by squeeze casting were investigated through metallography, scanning electron microscopy and energy dispersive spectroscopy. The results showed that the primary α-Al grains transformed from coarse dendrites to refined equiaxed grains with increasing pressure. Considerable primary refinement was achieved at 100 MPa, with a significant decrease by 63% in the average grain size from 273 µm to 101 µm; the non-equilibrium eutectic phases were homogenized and refined, and almost dissolved into the Al matrix after T6 heat treatment. The mechanism of solidification behaviors in pressurized solidification was elucidated. Firstly, the applied pressure increased the thermodynamic driving force to promote primary grain nucleation. Secondly, the solute diffusion and constitutional undercooling at the front of the solid/liquid interface front were inhibited by pressure, and grain growth in a dendritic structure was thus restrained. Thirdly, interdependence theory and thermodynamic calculations were conducted to quantitatively describe the primary grain size changes under pressurized solidification. Lastly, the ternary eutectic reaction L → α-Al + T-Mg (Al, Zn, Cu)2 + Al2Cu and binary eutectic reaction L→ α-Al + Al7Cu2Fe were suppressed by the reduced solute segregation. Furthermore, when the pressure increased from 0.1 MPa to 125 MPa, the ultimate tensile strength was raised from 428 MPa to 538 MPa, almost approaching that of samples by forging process. The refined eutectic phases decreased stress concentration and improved fracture behaviors.

Mechanical and conductivity properties of 6061Al matrix composites reinforced with different pH Cu-coated graphene

ABSTRACT The lightweight designs of automobiles and space shuttles have raised the bar for aluminum (Al) and its alloys. Graphene (GP) has found widespread application in aluminum matrix composites due to its exceptional mechanical, electrical, and thermal properties. In this study, a successful preparation of 6061Al reinforced with GP was achieved through a powder metallurgy method. This involved mixing GP with 6061Al alloy powders via ball milling, followed by hot-pressing sintering to produce the final GP-reinforced Al alloy nanocomposite. The effect of the pH value of the plating solution on the electroless plating of GP has been studied for the first time. The results show that the strength of the aluminum-matrix composites with copper plating has been significantly improved compared with that of the composites without copper plating. When the pH value of the plating solution is 12, the tensile strength of the composites obtained has been increased by 60.41%. Compared with the matrix material, the conductivity of the composite material has also increased. This work shows that the mechanical behavior of graphene-reinforced metal matrix composites (MMCs) can be improved by adjusting the distribution of graphene coatings, which is of great benefit for the preparation of high strength and lightweight composites with good electrical conductivity.

Microstructure and mechanical properties of selective laser melted Al-Zn-Mg-Si-Sc-Zr alloy with high hot-cracking resistance

A novel additive manufacturing dedicated Al-Zn-Mg-Si-Sc-Zr alloy is designed in this work, and its formability during selective laser melting (SLM) is investigated. Adding 3 % Si to the Al-Zn-Mg alloy leads to a refined microstructure and significant enhancement of hot-cracking resistance. By means of SEM, TEM and EBSD analysis some aspects of the alloy microstructure in as-built and thermal-treated states are discussed. Unlike traditional Al-Zn-Mg alloys, the main strengthening phase in the Al-Zn-Mg-Si-Sc-Zr alloy is Mg2Si, which forms a cellular structure and contributes to the favorable mechanical properties of the as-printed alloy. The as-built alloy exhibits a hardness of 138 HV, ultimate tensile strength (UTS) of 383 MPa, and elongation of 9.5 %. After solution and aging treatment, the UTS decreases to approximately 341–349 MPa, while the elongation increases to 17.6 %. However, with direct multistage aging treatment, the UTS can be increased to 409 MPa, albeit with a reduced elongation of 0.6–1.6 %. The variations in mechanical properties are attributed to the morphology of the Mg2Si phase and its coherent relationship with the Al matrix under different heat treatment processes.

Microstructure evolution and mechanical behavior of magnetron sputtering AlN–Al nanostructured composite film

In this paper, a series of AlN–Al nanocomposite films are prepared by reactive magnetron sputtering. The effects of N2 flow rate on the microstructure and mechanical properties of the films are studied. The formation and evolution mechanism of the nanocomposite structure are revealed. The results show that with the decrease of N2 flow rate, the microstructure goes through three stages: pure AlN, amorphous Al surrounded nanocrystalline AlN and AlN nanoparticle reinforced Al matrix composite. Benefiting from the good wettability of Al on AlN ceramics, the film deposited at 6 sccm N2 flow rate forms a nanocomposite structure of about 8 nm AlN grains wrapped by 1–2 nm amorphous Al. The hardness of the films increases first and then decreases with the decrease of N2 flow rate, ranging from 4 GPa to 25 GPa. The toughness of the films is analyzed by the ratio of H/E, H3/E2, the normalized plastic depth (δH) and the morphology of large load indentation. The results show that the toughness of the nanocomposite film obtained at 6 sccm N2 flow rate is significantly improved while maintaining the hardness equivalent to that of pure AlN film. The improvement in toughness comes from the microcracks initiated in AlN hindered by the surrounding Al phase.

Revisiting a Cu-rich layer on the aluminum surface after twin-jet electropolishing

Twin-jet electropolishing (TJE) is a well-known method to prepare Cu-containing Al alloys for transmission electron microscopy (TEM) observation. Previous studies have reported a Cu-rich layer usually formed between Al matrix and outermost alumina layer at the electropolished Al surface. However, characteristics and formation mechanisms of the Cu-rich layer remain largely unexplored. Herein, configurations, formation process and property of the Cu-rich layer formed during TJE of Al alloys are revealed detailly employing aberration-corrected scanning TEM (STEM), STEM image simulations and first-principles calculations. The results reveal a new orientation relationship between the Cu-rich layer (θ’-Al2Cu) and Al matrix, which produces a low interfacial Al strain field. Formations of ∼2-nm-thick θ’ layer and its beneath ∼6-nm-thick Cu diffusion zone at the electropolished Cu-containing Al surface are mainly associated with traces of Cu in the electrolyte and anodization. Selective oxidation of elements, Cu-emitting alumina layer and spontaneous solute Cu segregation at the Al surface are also responsible for formations of the θ’ layer and Cu diffusion zone. Further study reveals that the θ’ layer behaves a strong self-healing ability after damaged by high-energy electron beam. The obtained results provide a potential insight into the surface modification of metals and alloys using electrochemical method.

Plasticity of solid solution Al-Mn and Al-Mn-Si alloys

The influence of Mn and Si on the mechanical properties of solid solution Al-Mn and Al-Mn-Si alloys have been studied at 4 K, 78 K, and 298 K. The solute strengthening potency of the yield strength increases with decreasing temperature. The addition of Si stimulates the precipitation of Mn-containing dispersoids and decreases the solubility of Mn in the Al matrix, reducing the strengthening effect. The alloys exhibit Stage III of declining work hardening rate with the flow stress during the plastic flow at three temperatures. The mean slip length Λ in the work hardening model of Nabarro, Basinski, and Holt (NBH) evaluated from σΘ curves correlates with the scale of the microstructure. The strain rate sensitivity (SRS) measurements conducted at 78 K show positive SRS of Al and the alloys. At 298 K, one observes a change in SRS due to the change of the mechanism from solute-dislocation to dislocation-dislocation dominated interactions. Mn and Si decrease SRS at 298 K. Al-Mn-Si alloys exhibit negative SRS and jerk flow at a sufficiently low strain rate at 298 K. Analysis of the apparent activation volume, distance, and work has been conducted at 78 K and 298 K to understand the rate-controlling mechanisms. The results indicate that dislocation intersections are rate-limiting processes, but the atomistic mechanism of dislocation cutting varies vastly depending on the temperature and alloy composition. It is suggested that at 78 K, forest obstacles are passed by the formation of jogs and sequential activation of individual partials without making constriction to the perfect defect. At 298 K, the cutting involves constriction, the creation of jogs, and the creation of point defects at each intersection site. The calculated activation work and distance provide signatures of these processes.

Phase transition and damping behavior of Al matrix composites reinforced by a NiTi particle layer

Phase transition and damping behavior of Al matrix composites reinforced by a NiTi particle layer

Improved heat and corrosion resistance of high electrical conductivity Al-Mg-Si alloys by multi-alloying of Ce, Sc and Y

In order to improve the corrosion and heat resistance of Al-Mg-Si alloy conductor materials, Ce, Sc, Y and Zr were added in Al-Mg-Si alloy to regulate the microstructure. The Al-Mg-Si-Ce-Sc-Y alloy was designed with excellent pitting and intergranular corrosion resistance by obtaining the micron-sized Fe-containing second phase with a lower potential difference to Al matrix, more dispersed grain boundary precipitates with a higher proportion of Si particles, narrower width of PFZ and ideal distribution of intergranular precipitates. The Al-Mg-Si-Ce-Sc-Y alloy also maintained higher hardness, strength and electrical conductivity after overaging and annealing and the corrosion/heat resistance mechanisms were proposed.

Synchronous improvement of strength and corrosion resistance by an improved variable-rate non-isothermal aging process in Al-Zn-Mg-Cu alloy

Overcoming the trade-off between high strength and excellent corrosion resistance of Al-Zn-Mg-Cu alloys is a challenging problem. In this study, a variable-rate non-isothermal retrogression and re-aging (VNRRA) process has been proposed to solve this problem in AA7085 aluminum alloy and is compared with conventional isothermal aging treatments (T6, T77, and T73 tempers) in detail. This improved aging process consists of a slowly heating stage at low temperature, a rapidly heating stage at elevated temperature and an isothermal aging stage at 120 °C, and can synchronously improve the strength and corrosion resistance of Al-Zn-Mg-Cu alloy. Precipitation behaviors, mechanical properties and corrosion resistance have been systematically investgated. Compared with T6 temper, the VNRRA sample exhibits higher hardness and yield strength, which can be attrubuted to the high-density η’ precipitates that fully grow up but are not severely coarsened in Al matrix. Meanwhile, the corrosion resistance of the optimal VNRRA specimen is comparable with that of T77-treated specimen, which is closely linked with the discontinuous distribution of Cu-rich GBPs.

Investigation On Tensile Properties Of Aluminum 7075 - Silica Particles -Boron Fiber- Reinforced Hybrid Metal Matrix Composites

Hybrid metal matrix composites (MMCs), particularly those using an Aluminum 7075 (Al7075) base combined with silica particles and boron fibers, have emerged as a focal point in engineering for their superior strength-to-weight ratio. This study examines a composite of Al7075 reinforced with varying amounts of silica particles (0%, 2%, 4%, 6%) and boron fibers (1%, 3%, 5%, 7%). The research aims to discern the impact of these reinforcements on the composite's tensile properties. Employing the stir casting technique, these reinforcements were melted into the Al7075 matrix. The composites underwent tensile testing to gauge their mechanical performance, with a tensometer measuring tensile strength. The findings indicate that the inclusion of silica and boron fibers enhances tensile strength, with the greatest increase of 43.5% rise in tensile stress observed in the sample with 6% silica and 7% boron fiber. Variance analysis reveals that silica contributes 85.51% to the strength, boron fiber contributes 12.70%, and there is an error margin of 1.49%. Furthermore, a comparison of experimental, regression, and Artificial Neural Network (ANN) predicted values confirms consistency within an error margin of 5.86%.

Effect of TiB2 and GNP reinforcements on machinability in drilling of Al7075/TiB2/GNP hybrid composites produced by powder metallurgy

In this study, it has been aimed to investigate the machinability performances by drilling by producing Al7075 matrix hybrid composite samples with graphenenanoplate (GNP) and titaniumdiboride (TiB2) reinforced at different rates by powder metallurgy. The impacts of GNP and TiB2 reinforcing materials on the cutting parameters and wear behavior of the cutting tool have been examined and discussed. As a result of the drilling tests which are carried out by applying different cutting parameters, it was observed that GNP additive has positive impact on the cutting forces, surface roughness, and hole quality in general. As a result of the machining experiments, the lowest cutting force was obtained as 150 N at a feed rate of 0.100 mm/rev and a cutting speed of 60 m/min in the 1% GNP reinforced sample. The minimum roughness value was obtained as 0.886 micron at 60 m/min cutting speed in the 1% GNP reinforced sample. The minimum deviations from cylindricality and circularity were also measured as 0.03 and 8.005 mm from the 1% GNP reinforced sample. While the lubricating effect was low with a GNP ratio of 0.5%, the abrasive effect was observed more with a GNP ratio of 1.5%. While GNP supplementation decreased the diameter deviation and cylindrical deviation values, it increased the perpendicularity deviation values. In general, swarf chip formation occurred with a small amount of flank wear on the cutting tools. While hard TiB2 reinforcement particles in the composite structure were effective in flank wear, the most important cause of chip formation was the presence of ductile aluminum matrix and relatively low cutting speeds. When the entire experimental study was evaluated, it was evaluated that the solid lubricant property of the GNP reinforcement material was effective at the most 1% GNP reinforcement rate.

Effects of solution temperatures on microstructures and mechanical properties of B4C/7A04Al composites: A comparison study with 7A04Al alloys

To prepare particle-reinforced aluminum matrix composites with ultra-high strength, high-strength 7xxx Al alloys are commonly employed as matrices. Heat treatment plays a crucial role in enhancing the mechanical properties of the alloys and their composites, but the influence of solution temperatures on composites based on 7xxxAl alloys remains unexplored. In this study, the effects of solution temperatures on the microstructures and mechanical properties of B4C/7A04Al composites fabricated via powder metallurgy (PM) technology were investigated, as well as those of 7A04Al alloys for comparison. Before solution treatments, the prominent second phases in the composite were MgZn2 phases, while those in the 7A04Al alloy consisted of MgZn2 and Al2CuMg phases. At lower solution temperature (420 °C), MgZn2 phases dissolved completely, whereas Al2CuMg phases persisted. Al2CuMg phases dissolved at 450 °C, and thus the 7A04Al alloy obtained the optimum strength and elongation. Further elevating the solution temperature caused abnormal grain growth (AGG) in the 7A04Al alloy, leading to a deterioration of strength and plasticity. In contrast, at various solution temperatures, the composite exhibited stability in grain size, which could be attributed to the pinning effects of B4C particles and Mg(Al)B2 phases, the reaction products between the boron impurity and the Al matrix. However, at higher solution temperatures (510 °C and 600 °C), the segregation of Mg and O around B4C particles was aggravated, and thus the elongation of the composite deteriorated. Interestingly, the strength remained relatively unaffected due to the strengthening effects of Mg(Al)B2 phases. The results indicate that the composite exhibited a broad range of solution temperature with comparable strength and elongation across a temperature range of 420 °C–470 °C. But for the 7A04Al alloy, the optimal solution temperature is 450 °C.

The coating of ex–situ AlN particles with in–situ AlN nanolayers in an (AlN + AlB2)/Al composite

In this paper, an (AlN + AlB2)/Al composite was produced via liquid–solid reaction. Except for in–situ formed AlN and AlB2 phases, a nanolayer with the thickness of roughly 10 nm was found coating the ex–situ AlN. The nanolayer has the same crystal structure with ex–situ AlN, which is supposed beneficial for the combination between ex–situ AlN and Al matrix. The composite exhibits attractive ultimate tensile strength at 25 °C and 350 °C, which is 416 MPa and 242 MPa, respectively.

Effects of cold deformation modes on microstructure uniformity and mechanical properties of large 2219 Al–Cu alloy rings

Abstract The mechanical properties of large 2219 Al–Cu alloy rings need to be further improved with the diameter of the launch vehicle being more than 10 m. In this study, the effects of cold rolling (CR) and cold compression on microstructure evolution and the comprehensive mechanical properties of such rings were compared. The evolution of dislocation characteristics, grain structure, second phase, and the mechanical properties of the T8-aged samples were examined. Results show that compared with CR, because of deformation characteristics, cold compression deformation induces less increase in dislocation densities; however, the increase in dislocation densities on the core was higher than at other positions, resulting in a more uniform grain structure and elongation in the axial and radial direction. The cold compression deformation contributes to the uniform dissolution of the secondary phase, resulting in denser precipitates, and thus improved strength. Brittle fractures occur in fewer CR samples because of the longer moving distance of the Al matrix. In summary, both CR and cold compression can improve the mechanical properties. However, the cold-compressed sample exhibits more uniform microstructure and higher comprehensive mechanical properties (the radial elongation increased from 7.1 to 11.2%; the in-plane anisotropy decreased from 36.6 to 8.9%), without any brittle fractures, because of more uniform metal flow.

Structural analysis of η14 phase and its forming mechanism in Al-Zn-Mg-Cu alloy

The structural characteristic and formation mechanism of a latest reported η14 phase formed in Al-Zn-Mg-Cu alloy were systematically studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). By detail structural analysis, the orientation relationship (OR) of the η14 and Al matrix is modified as: (112¯0)η14//(11¯2¯)Al, [1¯103]η14//[1¯11¯]Al and [1¯100]η14//[3¯1¯1¯]Al. Structural analysis demonstrated that the η14 phase displays the C14 Laves stacking structure, however, the Zn1 and Zn2 columns composed the R'-units are only half filled by Zn. This phenomenon is mainly due to the Zn1–2 columns composed the R'-units and Zn3 column composed the R-units formed with different processes, leading to uneven intensity among these columns for the η14 phase. The formation mechanism of the η14 phase does not shows any relevance with the faulted layers reported in previous work. In contrast, The η14 phase is suggested to evolved from a metastable η14’ phase with OR of (0001)η14’//(021¯)Al and [112¯0]η14’//[11¯2¯]Al, formed by regularly replacements of Zn and Mg at the (021¯)Al habit planes The special habit plane of η14’ phase contributes to the unusual OR of η14 phase with Al matrix. Our findings extend the understanding of the precipitates formation and evolution appearing in Al-Zn-Mg-Cu alloys.

Fabrication of Al matrix composite reinforced with Fe-Cu particles using friction stir processing

Friction stir processing (FSP), as an advanced technique, was employed to fabricate in situ aluminum composites with the aim to elucidate the correlation between microstructure and mechanical properties of the obtained composites. The novelty of the work is to utilize simultaneous incorporation of Fe and Cu powders into the friction stir zone in order to fabricate in situ aluminum composites. To achieve the goal, the loading content of Cu and Fe powders and the process pass number (1 pass to 5 passes) were altered. While the total loading content of Fe and Cu powders was kept constant, the weight percentages of these reinforcements were varied (25%, 50%, and 75%). Microstructural characteristics were examined using scanning electron microscopy and optical microscopy. Five passes FSP resulted in smaller grain sizes of the Al matrix, smaller and less agglomeration of the reinforcements as well as homogeneous dispersion of the reinforcement features and thus, enhancement of the mechanical properties of the composites. X-ray analysis and energy dispersive spectroscopy confirmed in situ formation of Fe-Al and Al-Cu intermetallic compounds in the composites. The tensile testing outcomes proposed the 50wt% Fe-50wt% Cu/Al composite fabricated in 5 passes as the optimum formulation achieved in this research. This can be attributed to the smaller grain size of the matrix in the friction stirred zone and more homogeneous dispersion of the reinforcements in the matrix. Furthermore, this strengthening was affected from the presence of more amounts of well dispersed intermetallic compounds in situ formed during 5 passes. The average tensile strength (207 MPa) and hardness (73 Vickers) of the composite were approximately 175% and 160% greater than that of the unreinforced aluminum (75 MPa, 28 Vickers), respectively. Increasing the process pass number from 3 to 5 passes not only had strengthening and hardening effects but also improved the composite elongation at break.

Realizing reversible phase transformation of shape memory ceramics constrained in aluminum

Small-scale shape memory ceramics exhibit superior shape memory or superelasticity properties, while their integration into a matrix material and the subsequent attainment of their reversible tetragonal-monoclinic phase transformations remains a challenge. Here, cerium-doped zirconia (CZ) reinforced aluminum (Al) matrix composite is fabricated, and both macroscopic and microscopic mechanical tests reveal more than doubled compressive strength and energy absorbance of the composites as compared with pure Al. Full austenitization in the CZ single-crystal clusters is achieved when they are constrained by the Al matrix, and reversible martensitic transformation triggered by thermal or stress stimuli is observed in the composite micro-pillars without causing fracture in the composite. These results are interpreted by the strong geometric confinement offered by the Al matrix, the robust CZ/Al interface and the local three-dimensional particle network/force-chain configuration that effectively transfer mechanical loads, and the decent flowability of the matrix that accommodates the volume change during phase transformation.

Crystal plasticity finite element modelling and mechanical deformation mechanism of nanolaminated graphene reinforced metal matrix composites

Metal matrix composites with certain hierarchical structures are potential to break out the conflicts between strength and toughness. Nano-carbon like graphene (Gn) reinforced metal matrix composites with nanolaminated structures have been largely developed to overcome this issue. However, the plastic deformation mechanism hiding behind the nanolaminated structures is still lacking. In this study, crystal plasticity finite element simulations and composite structure modeling are combined in order to uncover the mechanical deformation behavior of nanolaminated Gn/Al composites. Different lateral Gn sizes of 180, 360 and 720 nm are considered, while the hybrid lateral Gn sizes of 180 and 720 nm are applied as well. Good consistency between experimental and numerical results indicates the reliability of performed simulations. It is found that the strengthening and hardening behaviors of Gn/Al composites are dominated by Gn rather than Al matrix. The edges of Gn serving as a major dislocation nucleation source produce localization of plastic deformation, while the interiors of Gn activate more slip systems but reduce total shear strains. The edges and interiors of Gn determine the stability of plastic deformation of Gn/Al composites; large edge vs. interior area of Gn will lead to early necking. The rule of mixture fails in predicting the peak tensile strength and tensile strain of Gn/Al composites with hybrid lateral Gn sizes, because the microscopic plastic deformation can largely localize around 180 nm Gn in these hybrid Gn/Al composites. This work is enlightening to design and develop novel smart metal matrix composites.