High Dislocation Density Research Articles

Hot deformation and processing map of in-situ graphene reinforced magnesium matrix nanocomposites

It is necessary to have a deep understanding of the deformation behavior of magnesium matrix nanocomposites to achieve precise control of components. In this work, the as-cast graphene reinforced magnesium matrix nanocomposites were produced by in-situ vapor-liquid reaction. The flow stress features of the nanocomposites were studied by isothermal compression. The constitutive equation and the processing map of nanocomposites were established under the given load conditions based on the stress-strain curve. The sample is in a stable processing state at a compression temperature of 350 ℃∼450 ℃ with a compression rate of 0.001 s−1 and a compression temperature of 350 ℃ with a compression rate of 0.01 s−1. Furthermore, graphene distributed within the grains facilitated the retention of high dislocation density, which increased the driving force of recrystallization. Recrystallized grains can be generated by the progressive rotation of subgrain due to grain boundary migration being inhibited by graphene. This work provides an important guideline for the optimization of deformation techniques of in-situ nanocomposites.

Magnetooptical Faraday and Kerr effects in nanosized BiYIG/GGG structures

AnnotationMagnetooptical Faraday and Kerr effects are studied in the nanosized BiY2Fe5O12 films within the spectral region of 1.3 eV<E<4.5 eV and magnetic fields of up to 10 kOe. It is shown that the thin-films BiY2Fe5O12 with the thicknesses ranging from 5 to 51 nm obtained by magnetron sputtering on the single-crystalline Gd3Ga5O12 substrates have high magneto-optical quality. The specific Faraday rotation for the nanosized Bi0.5Y1.5Fe5O12-δ films reaches about 140000 deg/cm close to that for bulk BiY2Fe5O12. Meanwhile, the polar Kerr effect reaches about 30 min within the range of 1.6 eV–4.1 eV at the magnetic fields above 2 kOe.It is shown that the strong paramagnetic contribution of Gd3Ga5O12 substrates significantly affects the Faraday and Kerr effect for the films. The defining of magnetooptical parameters and Verdet constant for the Gd3Ga5O12 substrate permitted to separate the substrate contribution and reveal peculiarities of spectral dependences of both Faraday and Kerr effects for magnetic films of various thicknesses. The estimated critical thickness of the film-substrate interface region is as large as 35 lattice constants of BiY2Fe5O12. It is shown that the magnetooptical effects for the thin films with the thickness above the critical one correspond to those for bulk BiY2Fe5O12. For samples with the smallest thicknesses of the film (5 nm) the contributions from magnetically dead and magnetically passive layers lead to a drastic reduction in the observable Faraday and Kerr effects with a dominating contribution from the substrate. The high density of displacement dislocations at the film-substrate interface leads to the decrease the magnetooptical quality of the nanosized films.

Influence of hydrogen ingress and capture on the mechanical properties of spray formed 2195 aluminum alloy

The current research has focused on the hydrogen capturing and its impact on the mechanical properties of spray-formed 2195 (SF2195) aluminum alloy. Microstructure characterization, thermal desorption spectra (TDS) and hydrogen trapping of characteristic microstructure, are used to investigate the generation, migration and trapping of hydrogen. The retention of moisture in the carrier gas is believed to induce high concentration of hydrogen and the amorphous Al2O3 layer within the SF2195 billet, and the local retention of carrier gas brings about pores with the Al2O3 layer on the inner wall. High concentration of hydrogen is captured in the hot-rolled alloy while around 60 % of the hydrogen can be eliminated during the solution-quenching. Particles of T1 phase trap large quantity of hydrogen and the high-density dislocations developed from the pre-stretch promote the migration of hydrogen towards dispersoids and precipitates. The presence of hydrogen and Al2O3 layer contributes to the reduced plasticity of SF2195 alloy. The spreading of flattened pores can induce intensified hydrogen damage effect in local regions and thus contribute to the unusually decreased ductility along the thickness direction in the T8 aged alloy.

Study on microstructure evolution and deformation behavior of Mg– Zn base alloy pipes during hot bending

The strong basal fiber texture of magnesium (Mg) alloy pipes usually leads to poor secondary forming performance. In this study, Mg–2Zn-0.4Ce-0.4Mn (ZME) and Mg–2Zn-0.4Ce-0.4Mn-0.2Ca (ZMEX) pipes were prepared. Compared with the ZME pipe, the ZMEX pipe with a weaker initial texture exhibits excellent bending performance, with a peak load displacement (PLD) of 14.5 ± 0.5 mm and a total energy absorption (TEA) of 142.9 ± 1.7 J. The difference in bending performance between the two pipes is related to the deformation mechanism during hot bending. In the hardening stage, the deformation of the compression zone (CZ) of the two pipes is mainly ETW nucleation, and the overall proportion of twin grains is similar. However, in the tensile zone (TZ), the deformation of the ZME pipe is mainly prismatic slip, while the weak initial texture of the ZMEX pipe leads to the deformation dominated by both prismatic and multiple pyramidal slips, resulting in a higher hardening rate. In the softening stage, the deformation behavior in the CZ and TZ of both pipes tends to be similar. In addition, it is revealed that the softening phenomenon of both pipes after the bending displacement reaches PLD is caused by discontinuous dynamic recrystallization (DDRX) driven by high-density dislocations accumulated in the later CZ and TZ. The research on the microstructure evolution and deformation mechanism of Mg alloy pipe during bending deformation carried out in this study is of great significance for optimizing its secondary forming controllability and further expanding its application.

Quantitative Study of Dislocation Density Effects on (100)-Orientated Cu in CO2RR

For the electrochemical CO2 reduction reaction, (CO2RR) structural defects have been reported to create key active sites. Previous reports have demonstrated the relationship between structural defects and CO2RR activities. However, an in-depth understanding of the connection between defect structure and selectivity study has proved challenging. In this presentation, we elucidate the relationship between dislocation density, activity, and selectivity on Cu in CO2RR. To accomplish this, we successfully synthesized (100)-oriented Cu samples with dislocation densities varying by a factor of 9, and we quantitatively studied the relationship between dislocation density and CO2RR performance.In this work, we employ (100)-oriented Cu prepared by physical vapor deposition. This approach creates an atomically smooth surface that eliminates the differences in the relative influence based on differences in surface reconstruction and roughness factor. A suite of X-ray-based methods are applied to characterize the defect structure. Here, X-ray diffraction pole figures confirm the good epitaxial growth of Cu (100). X-ray diffraction (XRD) θ/2θ symmetrical scan are applied to facilitate calculation of the dislocation density. Unlike TEM and metallographic etching, this method provides precise structure information over large areas of the Cu catalyst.It is demonstrated that under the potential of -1.04 V vs. RHE, the sample with the largest dislocation density favors HER more. With high dislocation density, HER and C1 products are dominant. The situation changes with the dropping dislocation density, and the best CO2RR performance is achieved at a medium dislocation density changing from 1.668 x 1015 m-2 to 1.106 x 1015 m-2, indicating a favorable catalyst surface for C-C coupled products. Here, a combination of mechanistic study via electrochemical methods and X-ray absorption spectroscopy suggests that a combination of low- and full-coordinated Cu sites is more beneficial for C-C coupling. Figure 1

Wear and neutron shielding resilience of titanium-hexagonal boron nitride coatings against extreme lunar radiation and thermal cycles

Ti6Al4V and Al6061 are aerospace alloys used in lunar structural components and rovers owing to their high specific strength. However, they deteriorate rapidly when subjected to demanding conditions of the lunar environment, such as extreme thermal cycles, solar particle radiation, and abrasive regolith. Cryo-milled powders were employed to deposit hBN-reinforced protective titanium coatings through plasma spray (atmospheric-APS and vacuum-VPS) with 2 and 10 vol% of hBN on Ti6Al4V and Al6061 substrates. These coatings were evaluated for durability under extreme lunar-like conditions, including thermal cycling, electron radiation, and synergistic (electron radiation-thermal cycle) exposure. The coatings exhibited radiation-induced hardening, resulting in a substantial increase in their microhardness ~20–40 % compared to virgin condition. Bright-field transmission electron microscopy (TEM) analysis reveals the presence of high dislocation densities, black dot defects, and dislocation clusters, providing evidence of the severe impact of synergistic environmental stresses. Ball-on-disk tribological tests were conducted in the presence of JSC-1 A lunar regolith simulant to evaluate the wear performance of coatings. Compared to conventional Ti6Al4V substrate, 50 %, 90 %, and 70 % reductions in wear volume were observed in the Ti/2 vol% hBN coatings in thermal-only, radiation-only, and synergistic environments. Neutron shielding tests indicate that the synergistic coatings offer higher neutron shielding performance by up to 28 % compared to virgin coatings, attributed to improved neutron capture by 10B isotopes. Upon a comprehensive assessment and ranking of multiple coatings under varying conditions, the VPS Ti/2 vol% hBN coating emerges as the top choice for protection against extreme radiation and thermal cycles for future lunar explorations.

The phase and morphology evolution of Y-Zr-O complex oxide dispersion-strengthened (ODS) Mo powders during mechanical alloying and annealing

Nanostructural Y-Zr-O complex oxide dispersion-strengthened (ODS) Mo alloys are designed for accident-tolerant fuel cladding. The phase and morphology evolution of ODS Mo powders during mechanical alloying (MA) and annealing were studied. The dissolution and reprecipitation mechanisms were revealed by quantitative calculation of dissolved Y and Zr amounts, thermodynamics and dynamics analysis, and phase analysis. The results reveal MA induces Mo grain refinement and a high density of dislocations in powders, facilitating the dissolution of Y2O3 and Mo2Zr and the formation of Mo supersaturated solid solution, rather than the negative mixing heat. By subtracting vacancies and oxygen effects, the dissolved amount is estimated as 2.2 at.% Y and 1.8 at.% Zr after 96 h-milling. During annealing, the Y-Zr-O complex oxide is precipitated in Mo-10 wt%Y2O3 powders above 900 °C since the introduced ZrO2 contamination during MA, and then cubic-Y2O3 beyond 1100 °C. The findings provide a scientific basis for controlling Y-Zr-O complex oxide nanoprecipitates and optimizing the service performance of Mo alloys.

The origin of good mechanical and soft magnetic properties in a CoFeNi-based high-entropy alloy with hierarchical structure

With the industry development, materials that combine good mechanical properties with new functional applications are in high demand. Here, a solution was provided to overcome low mechanical properties of soft magnetic materials through heterostructure design in CoFeNi high-entropy alloys (HEA). A CoFeNi-based HEA with a hierarchical structure with heterogeneous microstructure, consisting of body-centered cubic (BCC) bands, ultra-fine grained dual-phase and non-recrystallized lamellae (NRL) zones containing a high-density of nanoprecipitates, was fabricated and finely tuned by cold rolling (CR) and annealing. The HEA annealed at 850 °C (HEA-850) exhibits a noteworthy strength-ductility synergy than the counterparts with homogeneous dual-phase microstructures. The yield strength and elongation of the HEA-850 sample are nearly up to 1 GPa and 24%, respectively. Furthermore, because of the elimination of high-density dislocations, this alloy possesses good soft magnetic characteristics, and the saturation magnetization (Ms) and coercivity are 120 emu/g and 455 A/m, respectively. Detailed microstructure observations reveal that the high yield strength is mainly attributed to the interphase boundary strengthening from the dual-phase ultra-fine regions and nanoprecipitate strengthening as well as dislocation strengthening from NRL regions. Due to the mechanical and microstructural heterogeneity, multiple hetero-deformation induced hardening sustains persistent work hardening during tensile deformation, resulting in the reasonable ductility in the HEA-850 sample. The novel provides an important insight into developing high-performance materials with a superior combination of mechanical and functional properties using heterogeneous microstructure.

Effect of different extrusion parameters on the microstructure and mechanical properties of Mg-4Sm-3Gd-2Yb-0.5Zr alloy

The effect of different extrusion parameters on the microstructure and mechanical properties of Mg-4Sm-3Gd-2Yb-0.5Zr (SGY2) alloy was investigated. It was observed that under different extrusion parameters, unDRXed grains of SGY2 alloy exhibited a pronounced basal plane texture, specifically <011¯0>//ED, while the texture of DRXed grains was relatively dispersed. Under the condition of 420 °C and an extrusion ratio of 9.4 (420 °C-ER9.4), the basal plane texture strength of unDRXed grains in SGY2 alloy was the highest. Furthermore, SGY2 alloy at different extrusion parameters exhibited recrystallization mechanisms mainly characterized by continuous dynamic recrystallization (CDRX), with some DRXed grains and deformed grains experiencing discontinuous dynamic recrystallization (DDRX). Additionally, at the 420 °C-ER9.4, the second phase particles in the as-extruded SGY2 alloy were smaller in size and exhibited a dispersed distribution. Under this condition, a significant amount of dislocation accumulation, dislocation bypassing, and dislocation tangling phenomena were observed in the SGY2 alloy. The primary deformation mechanism of unDRXed grains in the SGY2 alloy at the 420 °C-ER9.4 may involve prismatic plane 〈a〉, pyramidal plane 〈a〉, and pyramidal plane 〈c + a〉 slip, thereby activating a significant amount of dislocations. Compared to other extrusion conditions, this condition is more prone to activate non-basal plane slip. The as-extruded SGY2 alloy exhibited superior mechanical properties, with ultimate tensile strength (UTS) and yield strength (YS) of 332 MPa and 278 MPa, respectively. This is mainly attributed to the extremely fine grains, with many DRXed grains having grain sizes smaller than 1 µm, and higher density grain boundaries produced under this condition. Additionally, the unDRXed grains contain a high density of dislocations with small Schmid factor (SF), thus effectively inhibiting basal plane slip and strengthening the alloy to some extent. Similarly, the increased presence of second phase particles will also contribute to strengthening the alloy matrix through precipitation hardening.

Effect of welding current on the organization and properties of welded joints of Q690D high-strength steel

In this study, the effects of various welding currents used in the CO2 gas shielded welding process on the microstructure, EBSD, texture and mechanical properties of Q690D steel were investigated. The results show that the number of ferrite in the welded joints increases with the increase of welding current; the EBSD analysis results show that the welded core area shows a coarse columnar organization with a long stripe distribution, a high average value of KAM, a high density of dislocations, and a large number of dynamic recrystallisation of GOS in the tempering area; the welded joints have both a rolled weave and a recrystallized weave; The XRD diffraction peaks show a sharp shape, with the main peaks pointing to the α-Fe phase, and the grains are orientated in the (110) direction. The ideal mechanical properties were obtained at a welding current of 170 A. The tensile residual stress was a compressive stress of 117 MPa, and the tensile strength and elongation were 680.7 MPa and 10.13 %, respectively, which showed ductile fracture; the microhardness of the welded joints was the lowest in the incompletely recrystallized zone, which was about 250 HV.

Microstructure evolution of diboride and carbide phases in platelets-toughened (Zr, Ti)C-(Ti, Zr)B2 ceramics via reaction pressureless sintering

Fully dense (Zr, Ti)C-(Ti, Zr)B2 composites were sintered via reactive pressureless sintering of ZrB2 and TiC based on the in-situ reaction and solid solution coupling effects. The effects of TiC content and sintering temperature on microstructure evolution and mechanical properties were explored. Elongated (Ti, Zr)B2 platelets were observed, stemming from the in-situ reaction between ZrB2 and TiC, and exhibited a high aspect ratio with the increase of TiC content. Besides, phase decomposition structures featuring semi-coherent interfaces were identified in the ZrB2-70mol.% TiC system sintered at 2200 °C, attributed to the chemical miscibility gap. High values of hardness (27.0 GPa), flexural strength (533 MPa), and fracture toughness (4.6 MPa m1/2) are found in ZrB2-70 mol.% TiC composite sintered at 2200 °C. The low porosity, solid solution strengthening, grain refinement caused by carbide phase decomposition, and high dislocation densities and strain concentration at the semi-coherent interfaces of carbide phase decomposed structures play an important role on hardening and strengthening. Furthermore, the presence of in-situ synthesized (Ti, Zr)B2 platelets with a high aspect ratio significantly contributes to toughening.

Challenges in characterizing additively manufactured AlSi10Mg using X-ray Laue micro-beam diffraction

Abstract Additive manufacturing of metals using for example laser powder bed fusion systems generally results in grains of complex shapes with cellular structure of submicron sizes, accompanied by a high dislocation density. This paper presents preliminary results from characterizing an AlSi10Mg alloy manufactured by L-PBF using non-destructive three-dimensional X-ray Laue micro-beam diffraction. Both synchrotron and laboratory X-ray methods are used. The aim is to identify challenges in characterizing these microstructural features and to propose future research directions to address them.

High-performance Al/Ti laminated composite via asymmetric cryorolling and its interface enhancement mechanism

The interface is crucial in determining the properties of laminated metal composites (LMCs). In this study, AA6061/TA1/AA6061 LMCs were produced via hot rolling and subsequent asymmetric cryorolling, followed by aging at 160 °C for 1.5 h. The mechanical properties of the materials were systematically investigated with regard to the impact of the interface during this process. The results demonstrated that the combination of asymmetric cryorolling and aging achieved superior mechanical properties of the composites, yielding a tensile strength of 397 MPa and a uniform elongation of 5.2 %, attributed to the introduced jagged interface and the reduction of interface voids, this procedure notably enhanced the bonding quality of the composites. The bonding strength was improved to 9.06 N/mm, 4.45 N/mm higher than the room temperature rolling + aged sample. Additionally, a more pronounced interface affected zone, approximately 64.7 µm, was noted in the subsequent deformation of the asymmetric cryorolling + aged sample, resulting in higher strain hardening capability. Furthermore, asymmetric cryorolling resulted in higher dislocation density, which maintained a high level even after aging. This phenomenon, along with the precipitated phase formed in the AA6061 layer, contributed to the enhanced strength.

Effect of cold rolling deformation on microstructure evolution and mechanical properties of spray formed Al−Zn−Mg−Cu−Cr alloys

The impact of cold rolling deformation, which was introduced after solid solution and before aging treatment, on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu− 0.13Cr (wt.%) alloy, was investigated. SEM, TEM, and EBSD were used to analyze the microstructures, and tensile tests were conducted to assess mechanical properties. The results indicate that the D1-T6 sample, subjected to 25% cold rolling deformation, exhibits finer grains (3.35 μm) compared to the D0-T6 sample (grain size of 4.23 μm) without cold rolling. Cold rolling refines the grains that grow in solution treatment. Due to the combined effects of finer and more dispersed precipitates, higher dislocation density and smaller grains, the yield strength and ultimate tensile strength of the D1-T6 sample can reach 663 and 737 MPa, respectively. In comparison to the as-extruded and D0-T6 samples, the yield strength of the D1-T6 sample increases by 415 and 92 MPa, respectively.

Significant improvement in hot corrosion resistance of Inconel 690 by laser shock peening

The effects of laser shock peening (LSP) with different peening times on the hot corrosion behavior (molten salt of 75 wt% Na2SO4 + 25 wt% NaCl) of Inconel 690 at three different temperatures (700 °C, 800 °C, 900 °C) were investigated. The corrosion conditions of the three specimens were also compared in the extreme case, i.e. after 900 °C, 300 h of hot corrosion. The results showed that LSP effectively prevented the surface oxides from shedding. As times of LSP increased, the strengthening effect improved and the rate of weight loss gradually slowed down. The dense oxide film generated by the high Cr content of the material itself, LSP-induced high-density dislocation structure, mechanical twinning and grain refinement is one of the key factors in improving the hot corrosion resistance of Inconel 690. The CRS layer and microhardness layer are another key factor in preventing the cracking of the oxide film to enhance the hot corrosion resistance. Under extreme conditions, the hot corrosion resistance of LSPed specimens is still better than that of unLSPed specimen.

Investigation of the Dislocation Behavior of 6- and 8-Inch AlGaN/GaN HEMT Structures with a Thin AlGaN Buffer Layer Grown on Si Substrates

Developing cost-effective methods to synthesize large-size GaN films remains a challenge owing to the high dislocation density during heteroepitaxy. Herein, AlGaN/GaN HEMTs were grown on 6- and 8-inch Si(111) substrates using metal–organic chemical vapor deposition, and their basic properties and dislocation evolution characteristics were investigated thoroughly. With the insertion of a 100 nm thin AlGaN buffer layer, bow–warp analysis of the epitaxial wafers revealed excellent stress control for both the 6- and 8-inch wafers. HR-XRD and AFM analyses validated the high crystal quality and step-flow growth mode of GaN. Further, Hall measurements demonstrated the superior transport performance of AlGaN/GaN heterostructures. It is worth noting that dislocations tended to annihilate in the AlN nucleation layer, the thin AlGaN buffer layer, and the GaN buffer layer in the initial thickness range of 200–300 nm, which was indicated by ADF-STEM. To be specific, the heterointerfaces exhibited a significant effect on the annihilation of c-type (b = &lt;0001&gt;) dislocations, which led to the formation of dislocation loops. The thin inserted layers within the AlGaN buffer layer played a key role in promoting the annihilation of c-type dislocations, while they exerted less influence on a-type (b = 1/3&lt;112¯0&gt;) and (a+c)-type (b = 1/3&lt;112¯3&gt;) dislocations. Within an initial thickness of 200–300 nm in the GaN buffer layer, a-type and (a+c)-type dislocations underwent strong interactions, leading to considerable dislocation annihilation. In addition, the EELS results suggested that the V-shaped pits in the AlN nucleation layer were filled with the AlGaN thin layer with a low Al content.

Multiphase-field analysis of the intermetallic compounds formation & evolution in friction stir welding of dissimilar Al/Mg alloys

It is essential to understand the formation and evolution mechanism of intermetallic compounds (IMCs) in friction stir welding (FSW) of dissimilar Al/Mg alloys to mitigate the deleterious effect of hard and brittle IMCs on the performance of dissimilar joints. To this end, a multiphase-field model with input variables of both temperature and strain rate is developed to study the whole IMCs formation and growth process at the Al/Mg bonding interface in weld nugget zone. The effects of diffusion, elastic deformation, and large plastic deformation on the generation and growth of IMCs are considered. The numerical simulation results indicate that due to the influence of high dislocation density, the higher diffusion coefficient of the Mg matrix leads to the nucleation of Al12Mg17 first. When IMCs grow into layers, the higher diffusion coefficient of Al3Mg2 leads to a faster growth rate of Al3Mg2 than that of Al12Mg17. The elastic energy caused by lattice mismatch between IMCs and matrix plays an inhibitory role in the growth of IMCs. Large plastic deformation in FSW causes an increase in both the stored energy which promotes the IMCs growth and the dislocation density which intensifies the diffusion process, causing IMCs to form at the interface in a short time. With the model, the IMCs evolution from generation to growth is quantitatively analyzed. The predicted thickness of IMCs matches well with the experimental measurements.

The synergistic effect of gradient nanostructure and residual stress induced by expansion deformation on the tension-tension fatigue performance of Ti6Al4V holes

A large number of titanium alloy structural components in aircraft are joined and assembled through holes. The complex service conditions pose high requirements for the fatigue performance of the holes. The study aims to use expansion deformation to induced gradient nanostructures and residual stress enhance the fatigue performance of Ti6Al4V holes. By studying the evolution process of the microstructure in titanium alloys, the formation mechanism of gradient nanostructures has been obtained, and their impact on various stages of fatigue fracture is analyzed. The results showed that the split sleeve cold expansion (CE) process caused severe plastic deformation on the surface of the hole, resulting in a large amount of LAB production and a transformation of the main texture components. Meanwhile, the gradient nanostructures are formed on the hole surface, which include nanocrystalline layer, superfine lath grain layer, lath grain layer and severe deformation layer. During the expansion deformation process, the slip of dislocations leads to the formation of high-density dislocation structures, which evolve into subgrain boundaries and then undergo dynamic recrystallization through subgrain rotation to achieve grain refinement. What's more, the degree of grain refinement, depth of gradient nanostructure, and residual stress increase as the expansion deformation intensifies. The depth of gradient nanostructure is 300 μm, and the maximum residual stress is −419 MPa, when the deformation is 5 %. The combined effect of gradient nanostructures and high residual compressive stress induced by expansion deformation has increased the total fatigue life and crack propagation life of CE-5 specimen by 2.9 and 3.4 times compared to NCE specimen. This work provides an effective method and theoretical analysis for improving the fatigue life of titanium alloy holes.

Gradient microstructures and mechanical properties of WAAMed and aged Al–Cu alloy after laser shock peening

The integration of wire-arc additive manufacture (WAAM) and laser shock peening (LSP) facilitated the study of the gradient microstructure in T6-treated WAAM Al–Cu alloy and the synergistic strengthening mechanisms involving the precipitation phase and LSP parameters. The results indicate that pore closures, increases in kernel average misorientation (KAM), and low angle grain boundary (LAGB) are positively associated with LSP energy density. Residual stress positively correlates with LSP energy density and inversely with spot diameter, where larger spots exacerbate non-uniformity. The values of dislocation density, microhardness and residual stress of the post-LSP specimen gradually increase with the increase of depth, and reach the maximum value at ~100 μm. As the depth continues to increase, the value begins to decrease gradually. Dislocation accumulation near grain boundaries, interacting with θ’-Al2Cu, contributes to strength enhancement. The main strengthening mechanisms enhanced by LSP involve creating a gradient microstructure through significant plastic deformation, pore closure, and the presence of high-density dislocations. Post-T6 treatment, θ’-Al2Cu significantly restricts dislocation slip, pins dislocations, and encourages the emergence of new dislocation sources, thereby enhancing the strengthening effect and stability induced by LSP.

Effect of intermediate processing treatment on the structure and mechanical properties of Al–4 wt%Cu–3 wt%Mn alloy manufactured by electromagnetic casting followed by high-pressure torsion (HPT)

In this work, a thermally stable model Al–4Cu–3Mn (wt%) alloy has been manufactured by electromagnetic casting (EMC), followed by compression, intermediate heat treatment and high-pressure torsion (HPT). Structural changes of the alloy during subsequent processing stages have been analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the X-ray diffraction (XRD). The results indicate that variations in the intermediate heat treatment temperature of the compressed samples lead to a significant difference in strain hardening and thermal stability after HPT. According to microstructure investigations the hardening of samples processed by HPT resulted from formation of mixture of grains and subgrains with high dislocation density as well as mechanical fragmentation of eutectic Al2Cu particles and precipitation of nanoscale Mn-rich dispersoids which are identified as Al6Mn. The intermediate heat treatment of the EMC rod at 350 ºC for 3 hours and heat treatment of HPT sample at 250 ºC for 5 hours exhibited the best mechanical properties in terms of ultimate tensile strength (UTS), yield strength (YS) and elongation (El), reaching 610 MPa, 560 MPa and 10 % respectively. At the same time intermediate annealing at 450 °C makes the HPT processing ineffective.