Size Gradient Research Articles

Predation affects body shape in the knife livebearer Alfaro cultratus (Cyprinodontiformes: Poeciliidae).

Livebearing fishes are a common model for studying the effects of predation on prey biology. Numerous studies have found differences in life history, sexual selection, behavior, and morphology between populations of the same species that co-occur with predators and those that do not. Alfaro cultratus is a livebearing fish with populations in different predation environments, but unlike other livebearers, this species also has an extreme body shape that is laterally compressed. Given this unusual morphology, we asked if predation environment would still predict overall body shape, as has been documented in other species. We collected specimens from both predator and no predator sites in Costa Rica and used a geometric morphometrics analysis to determine if body shape is affected by predation environment, while controlling for size and river gradient. Body shape does indeed differ between predation environments; however, the observed differences contrast with the patterns found in other livebearer systems. Alfaro cultratus in predation environments had deeper and shorter bodies and deeper caudal peduncles than those found in environments without dominant fish predators.

The combined effects of habitat fragmentation and life history traits on specialisation in lichen symbioses

Abstract Interactions between organisms are determined by life‐history traits. Ecological strategies regarding species specialisation range from generalist to highly specialised relationships. Although it is expected that habitat fragmentation's effect on species abundance and survival depends on their degree of specialisation and life‐history traits, few studies have delved into the interplay between interaction specialisation, life‐history traits and habitat fragmentation. Here, we investigate the combined effect of habitat fragmentation, forest structure and life‐history traits (growth form and reproductive mode) on the specialisation of lichen‐forming fungi (mycobionts) toward their photosynthetic partners (photobionts) in lichen symbioses. We studied mycobiont specialisation in epiphytic lichen communities present in 10 fragments of Quercus rotundifolia forest embedded in an agricultural matrix. Both mycobionts and photobionts were identified DNA barcoding and mycobiont specialisation was measured through interaction parameters calculating the relative number of interactions (normalised degree; ND) and the specialisation of each species based on its discrimination from a random selection of partners (d'). Phylogenetic generalised linear mixed models were used to analyse the effect of patch size as well as the life history traits growth form (crustose, foliose, fruticose) and reproduction mode (sexual vs. asexual) on mycobiont specialisation. Both mycobiont and photobiont richness along the patch size gradient followed a hump‐back pattern, which was more pronounced in photobionts. Mycobionts forming crustose thalli established the largest number of interactions. Mycobiont specialisation (d') was larger for fruticose and foliose forms and species with vegetative reproduction. Along the gradient of fragment size, the relative number of interactions decreased and the specialisation of mycobionts with vegetative reproduction increased. Synthesis. The study of mycobiont specialisation towards their photobionts in epiphytic lichen communities in a fragmented Mediterranean forest revealed a complex interaction between species' life history traits and habitat fragmentation. In particular, this interplay had a significant impact on the specialisation of mycobionts. The results show the ability of some species to modulate their specialisation according to habitat conditions, suggesting that some species may be more resilient to abiotic changes than expected.

Competing mechanisms govern the thermal rectification behavior in semi-stochastic polycrystalline graphene with graded grain-size distribution

Thermal rectifiers are devices that have different thermal conductivities in opposing directions of heat flow. The realization of practical thermal rectifiers relies significantly on a sound understanding of the underlying mechanisms of asymmetric heat transport, and two-dimensional materials offer a promising opportunity in this regard owing to their simplistic structures together with a vast possibility of tunable imperfections. However, the in-plane thermal rectification mechanisms in 2D materials like graphene having directional gradients of grain sizes have remained elusive. In fact, understanding the heat transport mechanisms in polycrystalline graphene, which are more practical to synthesize than large-scale single-crystal graphene, could potentially allow a unique opportunity, in principle, to combine with other defects and designs for effective optimization of thermal rectification. In this work, we investigate the thermal rectification behavior in periodic atomistic models of polycrystalline graphene whose grain arrangements were generated semi-stochastically to have different gradient grain-density distributions along the in-plane heat flow direction. We employ the centroidal Voronoi tessellation technique to generate realistic grain boundary structures for graphene, and the non-equilibrium molecular dynamics simulations method is used to calculate the thermal conductivities and rectification values. Additionally, detailed phonon characteristics and propagating phonon spatial energy densities are analyzed based on the fluctuation-dissipation theory to elucidate the competitive interplay between two underlying mechanisms, namely, (1) propagating phonon coupling and (2) temperature-dependence of thermal conductivity that determine the degree of asymmetric heat flow in graded polycrystalline graphene.

Silicon Poisoning and Effects of Tantalum on AlSi Alloys

Grain refinement in Al-Si alloys is crucial for enhancing material castability and mechanical properties. Industrial practice involves adding inoculants, composed of TiB2 particles coated with metastable Al3Ti via adsorption, to the melt. This introduces essential free titanium for metastable phase formation and subsequent growth restriction. The superstoichiometric grain refiner Al-5Ti-1B, with 2.2 wt.% free titanium, is applied for this purpose. A peritectic reaction forms α-aluminium from this layer. However, when silicon content exceeds 3.5 wt.%, grain coarsening occurs due to silicon’s detrimental effect. This study quantified silicon poisoning in an Al-10Si alloy using stoichiometric and superstoichiometric grain refiners through ASTM-standardized TP1 tests. Adding 0.02 wt.% tantalum acted as an antidote to the τ1 phase, resulting in a finer microstructure. This was attributed to the formation of a Ta-rich layer on TiB2 particles, which causes α-aluminium formation via a peritectic reaction without generating ternary phases with Ti or Si. Correlating to the increasing particle size curves from the TP1 tests, phases were collected in the filter cake with the help of a PoDFA apparatus. These could be examined more closely on the SEM and identified as needle- or plate-shaped. By using an EDS unit, the phases found were assigned to the poisoning phase and further investigated. After the addition of tantalum, a solubility of tantalum could be detected in former poisoning phases. In combination with the gradients of the grain size, it can thus be assumed that tantalum is both an antidote for silicon poisoning in the Al-Si-Ti system and can itself have a grain-refining effect in this system.

Achieving superior strength-ductility synergy in a unique multi-scale heterostructured titanium laminate fabricated by temperature-controlled rolling and subsequent annealing

Here we proposed a low-cost and high-efficiency strategy for fabricating novel multi-scale gradient-structured/heterogeneous lamella structured (GS/HLS) pure titanium laminates with superior strength-ductility synergy, by temperature-controlled rolling and subsequent annealing of as-sintered multilayered pure titanium foils with preset grain size gradient. A preliminary gradient structure with the average grain size decreasing from the center layer (alternating stacking of equiaxed fine grain bands and elongated grain bands) to the surface layer (equiaxed fine grains) is formed by optimizing the rolling process. Generalized Schmidt factor analysis based on electron backscatter diffraction indicated that there were slip-dominated and twin-dominated grain refinement mechanisms during the rolling process. In addition to the prismatic slip, two kinds of contraction twinning could be activated to achieve the grain refinement in hard domains where slip systems were hard to be activated. After subsequent annealing, equiaxed fine grains in the laminates did not significantly coarsen, while the elongated grains in the center layer had partially merged and grew up into the elongated coarse grains. Thus, the microstructure of the center layer displayed a typical heterogeneous lamella structure composed of alternately stacking of elongated coarse grains and fine grain bands, together with the grain size gradient, a unique multi-scale heterostructured titanium laminate was formed. Tensile test indicated that the as-rolled Ti laminates exhibited extremely high ultimate tensile strength (UTS) of 930 MPa with an acceptable total elongation to fracture (ETF) of 12.3 %, while GS/HLS Ti laminates after annealing at 425 °C possessed a superior combination of high UTS (823 MPa) and high ETF (22.4 %). The main reason was that the annealing treatment significantly reduced the dislocation density in the elongated coarse grains of GS/HLS Ti laminates. This meant that more geometrically necessary dislocations (GNDs) could accumulate in the plastic deformation process, resulting in the hetero-deformation induced (HDI) strengthening and an extra HDI hardening caused by the unique GS/HLS structure, therefore, an excellent strength-ductility synergy of final GS/HLS Ti laminates was achieved.

Modeling of a catalytic fluidized bed reactor via coupled CFD-DEM with MGM: From intra-particle scale to reactor scale

The Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) method is extended by coupling with the multi-grain model (MGM) to include particle growth due to a gas-solid reaction, as well as intra- and inter-particle phenomena such as heat and mass transfer, and reaction, next to the inter-particle and fluid-particle interactions in the reactor. This comprehensive model treats each particle individually and accounts for changes in particle properties due to both the particle growth and temporal and spatial variations of the process conditions. It also captures the impact of the change in the particles' properties on the fluidized bed reactor characteristics, such as the hydrodynamic regime. The results of the model revealed that the fluidization characteristics and solids mixing can be altered by particle growth. Particle growth also led to the formation of a particle size gradient along the height of the reactor. The coupling allows for monitoring of both external and internal mass transfer limitations. For the adopted reaction kinetics, growth rate and properties the external mass transfer limitations remained negligible, however the internal mass transfer limitation plays a significant role in the process performance.

Synergetic effect of initial shear texture and grain size gradient on plastic deformation of gradient interstitial free (IF) steel

Synergetic effect of initial shear texture and grain size gradient on plastic deformation of gradient interstitial free (IF) steel

Rib remodelling changes with body size in fossil hippopotamuses from Cyprus and Greece

Large species that are isolated for thousands of years on islands often evolve extreme degrees of dwarfism. Very little is known about physiological processes that accompany such extreme transitions in extinct dwarf species. We tested whether physiological cycles of bone maintenance (remodelling) in dwarf adult hippopotamuses correlate with insularity-driven body mass shifts that may occur due to variables such as ecological release from predation pressure and change in access to resources. We hypothesised that hippopotamuses with the smallest body size should show higher values of osteocyte lacunae, proxies for osteoblast proliferation during cycles of remodelling, when compared to relatively larger dwarf forms, as well as much larger mainland common hippopotamuses. We examined 20 ribs from three extinct Pleistocene Hippopotamus species spanning a gradient in body size: H. minor (~132 kg, Cyprus), H. creutzburgi (~398 kg, Crete), and H. antiquus (~3200 kg, mainland Greece). Ribs were selected because they reflect bone metabolic rates that are not completely clouded by factors such as biomechanics. Densities of osteocyte lacunae (Ot.Dn) were examined in 864 individual secondary osteons observed in histology sections. We found the highest average Ot.Dn in the H. minor ribs, intermediate Ot.Dn in the H. creutzburgi ribs, and the lowest Ot.Dn in the H. antiquus ribs. It appears that Ot.Dn distinctly separated these three species, possibly signifying a gradient in bone remodelling such that bone tissue optimises maintenance in the face of insularity-driven reduction of body size. We discuss hippopotamus rib bone microstructure and the utility of Ot.Dn in palaeontological analyses for elucidating intricate biological processes occurring in bone of insular fossil mammals.

What is environmental DNA?

AbstractDNA collected from the environment (eDNA) can provide valuable understanding of ecological patterns and processes. eDNA is highly physically heterogeneous, but this has not been well‐characterized, so most eDNA sampling strategies do not target any particular physical fraction. Consequently, we have limited evidence to understand and interpret the physical behavior of eDNA, to improve the efficiency of sampling, nor to target components of the eDNA spectrum for taxonomic and molecular attributes. We perform the first detailed characterization of the components of a marine eDNA sample using serial filtering from an 80 to <0.22 μm particle size gradient, a tree of life metabarcoding approach using taxon‐specific and universal assays, coupled with scanning electron microscopy and fluorescent confocal microscopy. We confirm that eDNA is manifest in a broad spectrum of physical states, ranging from extracellular DNA fragments to whole cells, tissue fragments, and whole organisms. The largest of these fractions of eDNA were embedded in microbial biofilms, rather than particulate. We show that the choice of filter size and types can target components of this spectrum, can affect the detectable species richness, and notably, also enrich samples for specific taxonomic groups. Our results imply that there is considerable scope to improve the efficiency of eDNA collection from aquatic environments, and its informativeness.

Analysis of Nonlinear Flow and Heat Transfer Issues in Nanofluid by Using RK-4th Order Method

Nanofluids, composed of a base fluid with dispersed nanoparticles, have gained significant attention due to their unique thermal and flow characteristics. Understanding the nonlinear flow and heat transfer phenomena in nanofluids is crucial for optimizing their performance in engineering applications. In this study, we propose using the Runge-Kutta 4th order (RK-4) numerical method to analyze these issues. The RK-4 method is known for its accuracy and efficiency in solving ordinary differential equations. By applying this method to the governing equations of fluid flow and heat transfer, we can accurately capture the nonlinear behavior of nanofluids. We investigate various nonlinear phenomena, such as boundary layer separation, flow instability, and heat transfer enhancement, considering factors like nanoparticle concentration, size, shape, fluid properties, Reynolds number, and temperature gradient. The RK-4 method provides accurate solutions, revealing critical parameters that affect flow and heat transfer behavior. Comparisons with experimental data and other numerical methods validate the approach, demonstrating its reliability. Parametric studies are conducted to optimize nanofluid characteristics for improved heat transfer and fluid flow. This research enhances our understanding of nonlinear flow and heat transfer in nanofluids and enables efficient numerical analysis, opening new avenues for improving nanofluid-based systems.

Tensile behaviors and hetero-deformation-induced hardening mechanisms in medium entropy alloys with dual gradients of grain size and coherent nanoprecipitate

Heterogeneous structures with dual gradients of grain size and coherent L12 nanoprecipitation have been designed and fabricated in a Co34.46Cr32.12Ni27.42Al3Ti3 medium entropy alloy. These heterogeneous structures with dual gradients show improved tensile properties over both the single grain-size gradient structure and the coarse grained structures with homogeneously distributed L12 nanoprecipitates. Hetero-deformation-induced hardening rate was observed to be higher and the strain hardening capacities at each depth were also found to be higher in the structures with dual gradients, as compared to the single grain-size gradient structure. Deformation twins and stacking faults were observed at both the topmost and center layers, while deformation bands at two directions were only found at the topmost layer after tensile deformation in the single grain-size gradient structure. Strong interactions between defects and coherent L12 nanoprecipitates can be observed at all depths after tensile deformation in the structures with dual gradients, resulting in strong precipitation hardening. While, stronger precipitation hardening was achieved at the topmost layer due to the higher volume fraction and smaller spacing of coherent L12 nanoprecipitates, which could delay the early necking trend at the topmost layer for better tensile ductility in the structures with dual gradients.

Prey selection along a predators' body size gradient evidences the role of different trait-based mechanisms in food web organization.

An increase in prey richness, prey size and predator trophic position with predator body size has been consistently reported as prime features of food web organization. These trends have been explained by non-exclusive mechanisms. First, the increase in energy demand with body size determines that larger predators must reduce prey selectivity for achieving the required number of resources, being consumption relationships independent of prey traits. Second, when consumption is restricted by gape limitation, small predators are constrained to select among small prey. However, this selection weakens over large predators, which progressively consume more and larger prey. Finally, the optimal foraging mechanism predicts that larger predators optimize their diet by selecting only large prey with high energy reward. Each one of these mechanisms can individually explain the increase in prey richness, prey size and predator trophic position with predator body size but their relative importance or the direct evidence for their combined role was seldom considered. Here we use the community assembly by trait selection (CATS) theory for evaluating the support for each one of these mechanisms based on the prey selection patterns that they predict. We analyzed how prey body size and trophic guild determine prey selection by predators of increasing body size in a killifish guild from a temporary pond system. Results support the combination of the three mechanisms to explain the structural trends in our food web, although their strength is contingent on prey trophic group. Overall, high energy prey are preferred by larger predators, and small predators select small prey of all trophic status. However, large predators prefer large primary producers and avoid large carnivorous prey, probably because of the inherent risk of consuming other carnivorous. Our study provides a mechanistic understanding of how predator traits determine the selection of prey traits affecting food web assembly.

A robust and accurate centerline extraction method of multiple laser stripe for complex 3D measurement

Multiple laser stripe measurement (MLSM) is a vital technique in optical three-dimensional (3D) measurement. The accurate extraction of the laser stripe centerlines plays a decisive role in achieving high measurement accuracy. However, complex 3D measurement scenarios pose challenges due to various interferences, such as optical interference caused by dense stripes and no-ideal distribution caused by non-uniform reflectivity. To address these challenges, we propose an adaptive step size gradient centerline extraction method based on an 2D linear filter. This method incorporates local adaptive variable parameters for fine-tuning while utilizing global parameters. We validate its performance by conducting comprehensive comparative experiments with two commonly used methods. The results demonstrate that our proposed method enables more precise centerline extraction, exhibits enhanced stability, and yields lower measurement errors in complex 3D measurement conditions and highlight the effectiveness and superior performance of our method.

Optimizing strength and ductility synergy achieved by multistage strain hardening in gradient recrystallized pure titanium

Metallic materials with gradient nanostructure (GNS) have attracted much attention for their enhanced strength and ductility synergy. However, GNS materials still suffer from poor strain hardening, especially in extremely refined grains. In this work, we performed an ultrasonic surface rolling process (USRP) and post-deformed annealing for fabricating a gradient recrystallized (GRS) pure titanium. A gradient of grain size and recrystallization is presented, resulting in a new hardness gradient with a maximum value at the subsurface layer. The sequential activation of hetero-deformation-induced (HDI) hardening and mechanical-induced grain growth synergistically contributed to the multistage strain hardening behavior, leading to a considerable strength and ductility synergy. This work may expand the possibilities for optimizing the mechanical properties in the GNS materials by tailoring the recrystallized structure.

Functionally graded IWP reinforced cementitious composites: Design, fabrication, and the enhanced ductility

The Schoen I-graph-wrapped package (IWP) structures have many promising applications for their high specific mechanical properties. In this work, functionally graded IWP (FG-IWP) architectures were developed and constructed to enhance the ductility of the produced cementitious composites. The FG-IWP architectures were designed using two grading strategies: relative-density-based and cell-size-based. The flexural test was used to investigate the mechanical behavior of the proposed composites, including flexural strength and deflections. The failure patterns and strain distributions of the specimens were measured using the Digital image correlation (DIC) approach. The results reveal that the designed IWP architectures noticeably improve the flexural strength and ductility of the composites. Comparing the FG-IWP to the uniformly configured IWP architectures, the grading strategies exhibit an increased ductility. Furthermore, the two grading strategies have different effects on ductility improvement. Cell size gradient strategy yields greater enhancement in flexural strength, whereas relative density strategy leads to better enhancement in ductility. The variations of cell size and relative density parameter ranges also result in distinct improvement on mechanical properties. Overall, the outcomes of this study present an FG-IWP-based novel approach for improving the ductility of cementitious materials.

An improved vapor chamber with enhanced two-phase transport by using structured surfaces

The novel type of vapor chamber (VC) with combined superhydrophilic/superhydrophobic surface holds great potential in hot spot cooling. In this study, an improved VC was developed by implementing structured surfaces on both condenser and evaporator. The thermal resistance, condenser temperature uniformity, and gravity independence were discussed. It was found that sintering an appropriate copper mesh on condenser could reduce the thermal resistance but would cause a slight deterioration in the temperature uniformity of the condenser. On the evaporator, the thermal performance of VC was further improved by introducing micro grooves on the wick in order to enhance bubble discharge of the boiling working fluid. Moreover, to strengthen the liquid recirculation on the evaporator, pore size gradient was adopted in the evaporator wick. Compared to the axial gradient of pore size, the radial gradient of pore size was more efficient in accelerating the working fluid recirculation. Among all the results reported in this study, the combination of sintering copper mesh on the condenser and implementing micro-grooves and pore size gradient on the evaporator wick yields optimal results, with the minimum thermal resistance of the VC reaching 0.041 K/W and the critical heat flux exceeding 213.3 W/cm2, which shows excellent thermal performance.

Body size and trophic level increase with latitude, and decrease in the deep-sea and Antarctica, for marine fish species.

The functional traits of species depend both on species' evolutionary characteristics and their local environmental conditions and opportunities. The temperature-size rule (TSR), gill-oxygen limitation theory (GOLT), and temperature constraint hypothesis (TCH) have been proposed to explain the gradients of body size and trophic level of marine species. However, how functional traits vary both with latitude and depth have not been quantified at a global scale for any marine taxon. We compared the latitudinal gradients of trophic level and maximum body size of 5,619 marine fish from modelled species ranges, based on (1) three body size ranges, <30, 30-100, and >100 cm, and (2) four trophic levels, <2.20, 2.20-2.80, 2.81-3.70, >3.70. These were parsed into 5° latitudinal intervals in four depth zones: whole water column, 0-200, 201-1,000, and 1,001-6,000 m. We described the relationship between latitudinal gradients of functional traits and salinity, sea surface and near seabed temperatures, and dissolved oxygen. We found mean body sizes and mean trophic levels of marine fish were smaller and lower in the warmer latitudes, and larger and higher respectively in the high latitudes except for the Southern Ocean (Antarctica). Fish species with trophic levels ≤2.80 were dominant in warmer and absent in colder environments. We attribute these differences in body size and trophic level between polar regions to the greater environmental heterogeneity of the Arctic compared to Antarctica. We suggest that fish species' mean maximum body size declined with depth because of decreased dissolved oxygen. These results support the TSR, GOLT and TCH hypotheses respectively. Thus, at the global scale, temperature and oxygen are primary factors affecting marine fishes' biogeography and biological traits.

Synaptic activity is not required for establishing heterogeneity of inner hair cell ribbon synapses.

Neural sound encoding in the mammalian cochlea faces the challenge of representing audible sound pressures that vary over six orders of magnitude. The cochlea meets this demand through the use of active micromechanics as well as the diversity and adaptation of afferent neurons and their synapses. Mechanisms underlying neural diversity likely include heterogeneous presynaptic input from inner hair cells (IHCs) to spiral ganglion neurons (SGNs) as well as differences in the molecular profile of SGNs and in their efferent control. Here, we tested whether glutamate release from IHCs, previously found to be critical for maintaining different molecular SGN profiles, is required for establishing heterogeneity of active zones (AZs) in IHCs. We analyzed structural and functional heterogeneity of IHC AZs in mouse mutants with disrupted glutamate release from IHCs due to lack of a vesicular glutamate transporter (Vglut3) or impaired exocytosis due to defective otoferlin. We found the variance of the voltage-dependence of presynaptic Ca2+ influx to be reduced in exocytosis-deficient IHCs of otoferlin mutants. Yet, the spatial gradients of maximal amplitude and voltage-dependence of Ca2+ influx along the pillar-modiolar IHC axis were maintained in both mutants. Further immunohistochemical analysis showed an intact spatial gradient of ribbon size in Vglut3-/- mice. These results indicate that IHC exocytosis and glutamate release are not strictly required for establishing the heterogeneity of IHC AZs.

Upgrading mechanical property and corrosion resistance of a low cost 45 steel by remelting a Cr film of ∼1μm in thickness

It is well-known that the overall mechanical or chemical properties of the metallic material could be tailored by introducing either grain size gradient or chemical gradient. In this work, we, taking one of the widely used low cost 45 steel as a model material, demonstrated that both mechanical properties and corrosion resistance can be greatly upgraded by laser remelting a Cr film of ∼1 μm in thickness. The yield strength was increased by ∼110 MPa and the elongation was almost unchanged in contrast to the Cr-free substrate. The corrosion resistance was also enhanced with a higher self-corrosion voltage (increased by 0.1 V) and a lower self-corrosion current (decreased by 80 nA/cm2). The upgraded strength-ductility synergy derives from the laser induced rapid melting and solidification, where the top surface layer incorporates both grain size gradient and chemical gradient. Greatly refined grain size and micro-alloying of Cr in the form of both solid solution and nanoprecipitates contribute to the enhanced strength, while higher concentration of Cr resulting in the formation of passivation film, accounts for the superior corrosion resistance. The findings in this work provide a strategy for optimizing the mechanical and chemical properties through surface medications, making metallic materials multi-functional.

Study on Microstructure Evolution Mechanism of Gradient Structure Surface of AA7075 Aluminum Alloy by Ultrasonic Surface Rolling Treatment.

The materials with grain size gradient variation on the surface, which were prepared with mechanical-induced severe plastic deformation, always show high resistance to high and low cycle fatigue and frictional wear because of their good strength-ductility synergy. The ultrasonic surface rolling treatment (USRT) has the advantages of high processing efficiency, good surface quality, and large residual compressive stress introduced to the surface after treatment. The USRT was used to prepare aluminum alloy (AA7075) samples with a surface gradient structure; meanwhile, the microstructural evolution mechanism of the deformation layers on the gradient structure was studied with XRD, SEM, and TEM. The microstructure with gradient distribution of grain size and dislocation density formed on the surface of AA7075 aluminum alloy after USRT. The surface layer consists of nanocrystals with random orientation distribution, and high-density dislocation cells and subgrains formed in some grains in the subsurface layer, while the center of the material is an undeformed coarse-grained matrix. The results show that the dislocation slip dominates the grain refinement process, following the continuous cutting and refinement of dislocation cells, subgrains, and fragmentation of the second precipitates. This study systematically clarified the mechanism of grain refinement and nanocrystallization on the surface of high-strength aluminum alloys and laid a theoretical foundation for further research on mechanical behavior and surface friction and wear properties of high-strength non-ferrous materials with gradient structure.