Relationship Between Microstructures and Microhardness in High-Speed Friction Stir Welding of AA6005A-T6 Aluminum Hollow Extrusions

AA6005 A-T6 aluminum hollow extrusions were friction stir welded at a fixed high welding speed of 2000 mm/min and various rotation speeds.The results showed that the heat-aff ected zone(HAZ)retained the similar grain structure as the base material except some grain coarsening,and the density of dislocations andβ′precipitates were almost unchanged,indicating that the high welding speed inhibited the coarsening and dissolution ofβ″precipitates via fast cooling rate.The thermo-mechanically aff ected zone(TMAZ)was characterized by elongated and rotated grains,in which a low density ofβ′precipitates and the highest density of dislocations were observed.The highest heat input and severest plastic deformation occurring in the nugget zone(NZ)resulted in the occurrence of dynamic recrystallization and a high density of dislocations.Hence,all theβ″precipitates and most of theβ′precipitates dissolved into the matrix,and a fewβ′precipitates were transformed intoβprecipitates.The microhardness was controlled by the precipitation and solution strengthening in the HAZ,by the dislocation and precipitation strengthening in the TMAZ,and by the fine-grain and dislocation strengthening in the NZ.With the increase in rotation speed,the peak and the lowest microhardness value increased monotonously.

Correlation between microstructures and mechanical properties of high-speed friction stir welded aluminum hollow extrusions subjected to axial forces

The AA6005A-T6 aluminum hollow extrusions were friction stir welded at a high welding speed of 2000mm/min and various axial forces. The results show that the nugget zone （NZ） is characterized by fine equiaxed grains, in which a low density of equilibrium phase β is observed. The grains in the thermo-mechanically affected zone （TMAZ） are elongated, and the highest density of dislocations and a low density of β precipitates can be found in grains. The heat affected zone （HAZ） only experiences a low thermal cycle, and a high density of β precipitates and a low density of β precipitates remain in the coarsened grains. The microhardness evolutions in the NZ, TMAZ and HAZ are governed by the grain refinement and dislocation strengthening, the dislocation and precipitation strengthening, and the precipitation and solid solution strengthening, respectively. When increasing the axial force, the changing trend of one strengthening mechanism is contrary to the other in each zone, and the microhardness increases in different zones. As a result, the tensile strength roughly increases with raising the axial force, and all joints show good tensile properties as the high welding speed inhibits the coarsening and dissolution of strengthening precipitates significantly.

Effects of the extrusion parameters on microstructure,texture and room temperature mechanical properties of extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy

Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.

Influence of undissolved second-phase particles on dynamic recrystallization behavior of Mg–7Sn–1Al–1Zn alloy during low-and high-temperature extrusions

This study investigates the effects of fine and coarse undissolved particles in a billet of the Mg–7 Sn–1 Al–1 Zn(TAZ711)alloy on the dynamic recrystallization(DRX)behavior during hot extrusion at low and high temperatures and the resultant microstructure and mechanical properties of the alloy.To this end,partially homogenized(PH)and fully homogenized(FH)billets are extruded at temperatures of250 and 450°C.The PH billet contains fine and coarse undissolved Mg_(2) Sn particles in the interdendritic region and along the grain boundaries,respectively.The fine particles(<1μm in size)retard DRX during extrusion at 250°C via the Zener pinning effect,and this retardation causes a decrease in the area fraction of dynamically recrystallized(DRXed)grains of the extruded alloy.In addition,the inhomogeneous distribution of fine particles in the PH billet leads to the formation of a bimodal DRXed grain structure with excessively grown grains in particle-scarce regions.In contrast,in the FH billet,numerous nanosized Mg_(2) Sn precipitates are formed throughout the material during extrusion at 250°C,which,in turn,leads to the formation of small,uniform DRXed grains by the grain-boundary pinning effect of the precipitates.When the PH billet is extruded at the high temperature of 450°C,the retardation effect of the fine particles on DRX is weakened by their dissolution in theα-Mg matrix and the increased extent of thermally activated grain-boundary migration.In contrast,the coarse Mg_(2) Sn particles in the billet promote DRX during extrusion through the particle-stimulated nucleation phenomenon,which results in an increase in the area fraction of DRXed grains.At both low and high extrusion temperatures,the extruded material fabricated using the PH billet,which contains both fine and coarse undissolved particles,has a lower tensile strength than that fabricated using the FH billet,which is virtually devoid of second-phase particles.This lower strength of the former is attributed mainly to the larger grains and/or absence of nanosized M2 Sn precipitates in it.

Effect of characteristics and distribution of Mg_(17)Al_(12)precipitates on tensile and bending properties of high-Al-containing Mg alloys

This study investigates the effect of characteristics and distribution of Mg_(17)Al_(12)precipitates on the uniaxial tensile and three-point bending properties of extruded Mg alloys containing high Al contents.The extruded Mg–9Al–1Zn–0.3Mn(AZ91)alloy contains lamellar-structured Mg_(17)Al_(12)discontinuous precipitates along the grain boundaries,which are formed via static precipitation during natural air cooling.The extruded Mg–11Al–1Zn–0.3Mn(AZ111)alloy contains spherical Mg_(17)Al_(12)precipitates at the grain boundaries and inside the grains,which are formed via dynamic precipitation during extrusion.Due to inhomogeneous distribution of precipitates,the AZ111 alloy consists of two different precipitate regions:precipitate-rich region with numerous precipitates and finer grains and precipitate-scarce region with a few precipitates and coarser grains.The AZ111 alloy exhibits a higher tensile strength than the AZ91 alloy because its smaller grain size and more abundant precipitates result in stronger grain-boundary hardening and precipitation hardening effects,respectively.However,the tensile elongation of the AZ111 alloy is lower than that of the AZ91 alloy because the weak cohesion between the dynamic precipitates and the matrix facilitates the crack initiation and propagation.During bending,a macrocrack initiates on the outer surface of bending specimen in both alloys.The AZ111 alloy exhibits higher bending yield strength and lower failure bending strain than the AZ91 alloy.The bending specimens of the AZ91 alloy have similar bending formability,whereas those of the AZ111 alloy exhibit considerable differences in bending formability and crack propagation behavior,depending on the distribution and number density of precipitates in the specimen.In bending specimens of the AZ111 alloy,it is found that the failure bending strain(ε_(f,bending))is inversely proportional to the area fraction of precipitates in the outer zone of bending specimen(A_(ppt)),with a relationship ofε_(f,bending)=–0.1A_(ppt)+5.86.

An oxygenating colloidal bioink for the engineering of biomimetic tissue constructs

Ensuring a sufficient oxygen supply is pivotal for the success of bioprinting applications since it fosters tissue integration and natural regeneration.Variation in oxygen concentration among diverse tissues necessitates the precise recreation of tissue-specific oxygen levels in imprinted constructs to support the survival of targeted cells.Although oxygen-releasing biomaterials,such as oxygen-generating microparticles(OMPs),have shown promise for enhancing the oxygen supply of microenvironments in injured tissues,whether this approach is scalable for large tissues and whether tissue-specific bioinks with varying OMP concentrations remain printable remain unknown.This study addresses this critical gap by introducing an innovative class of engineered oxygenated bioinks that combine colloidal-based microgels with OMPs.We report that incorporating nanosized calcium peroxide(nCaO_(2))and manganese oxide nanosheets(nMnO_(2))into hydrophobic polymeric microparticles enables precise modulation of oxygen release while controlling hydrogen peroxide release.Moreover,the fabrication of oxygenating and cytocompatible colloidal gels is achieved using an aqueous two-phase system.This study thoroughly evaluates the fundamental characteristics of the resulting bioink,including its rheological behaviors,printability,shape fidelity,mechanical properties,and oxygen release properties.Moreover,this study demonstrates the macroscopic scalability and cytocompatibility of printed constructs produced via cell-laden oxygenating colloidal bioinks.By showcasing the effectiveness of extrusion-based bioprinting,this study underscores how it can be used to fabricate biomimetic tissues,indicating its potential for new applications.The findings presented here advance the bioprinting field by achieving scalability with both high cell viability and the possibility of mimicking specifically oxygenated tissues.This work thereby offers a promising avenue for the development of functional tissues with enhanced physiological relevance.

Predictive factors for coronal and sagittal graft extrusion length after using tendon autograft for medial meniscus reconstruction

BACKGROUND Meniscus extrusion occurs in most elderly individuals and most patients after meniscus allograft transplantation.The risk factors and correlative factors of meniscus extrusion have been extensively studied.However,for using tendon autograft for meniscus reconstruction,both graft type and surgical method are different from those in previous studies on meniscus extrusion.AIM To identify predictive factors for coronal and sagittal graft extrusion length after using tendon autograft for medial meniscus reconstruction.METHODS Ten patients who underwent medial meniscus reconstruction with tendon autograft were selected for this retrospective observational study.The graft extrusions and potential factors were measured and correlation and regression analyses were performed to analyze their relationships.RESULTS The medial graft extrusion correlated with the preoperative bilateral hip-kneeankle angle difference,preoperative Kellgren-Lawrence grade,preoperative relative joint space width,and preoperative bilateral medial edge incline angle difference.The anterior graft correlated with the anterior tunnel edge distance at 1 week after operation.The posterior graft extrusion correlated with the preoperative bilateral hip-knee-ankle angle difference,preoperative relative joint space width,and posterior tunnel edge distance at 1 week after operation.The mean graft extrusion correlated with the preoperative bilateral hip-knee-ankle angle difference and preoperative relative joint space width.The preoperative joint space width and anterior and posterior tunnel edge distance at 1 week can be used to predict the medial,anterior,posterior,and mean graft extrusion length.CONCLUSION The preoperative joint space width and tunnel position can be used to predict the coronal and sagittal graft extrusion length after using tendon autograft for medial meniscus reconstruction.

Advantages of rapid solidification over casting of Mg-0.4Zn-1Y alloy

The Mg-Y-Zn magnesium alloy system is commonly recognized for its remarkable combination of high strength and ductility,achieved even with minimal amounts of alloying elements.This exceptional performance is attributed to its unique microstructure,which includes Long-Period Stacking Ordered(LPSO)phases or the distinctive microstructure derived from the LPSO phase,referred to as the Mille-Feuille structure(MFS).This study systematically compares the traditional ingot metallurgy method with the rapid solidification technique,coupled with diverse heat treatments and extrusion processes.Microscopic analyses reveal variations in the presence of LPSO phases,Mille-Feuille structure,and grain size,leading to divergent mechanical and corrosion properties.The rapid solidification approach stands out,ensuring superior mechanical properties alongside a reasonable corrosion rate.

Influence of Sr on microstructure evolution,mechanical and corrosion properties of extruded Mg-2Zn-0.5Ca alloy

Degradable Mg-Zn-Ca alloys with Sr addition were prepared by vacuum melting and hot extrusion.Effect of Sr on microstructure,mechanical and corrosion properties of hot extruded Mg-2Zn-0.5Ca-xSr(x=0,0.5,1.0)alloys was investigated.The results show that Sr addition into Mg-2Zn-0.5Ca alloys produced significant grain refinement in ingots and obvious texture weakening effects in extruded bars.The ultimate compressive strength increased as the Sr content increased,while the ultimate tensile strength increased firstly and then declined with the increasing of Sr content.Electrochemical tests indicated the corrosion current density of the surface parallel to extrusion direction(ED)was much lower than that of the surface perpendicular to ED.In-vitro immersion tests demonstrated the increase in the pH of solution and weight loss of Mg-2Zn-0.5Ca-0.5Sr alloy remain the lowest during immersion tests.The best comprehensive property was obtained in Mg-2Zn-0.5Ca-0.5Sr alloy,which has the largest strength and the best corrosion resistance.

Microstructure evolution and enhanced fatigue behavior in the Mg-10Li-5Zn-0.5Er alloys micro-alloyed with Yb

In this paper,(0.2-1 wt%)Yb was added to improve the tensile properties and high-cycle fatigue behavior of the as-cast and as-extruded Mg-10Li-5Zn-0.5Er alloys.It is found that Yb mainly affects the mechanical properties of the alloy by changing the grain size,type and morphology of the second phases.Yb mainly exists in the formation of Mg_(2)Yb and Mg-Zn-Yb phases in the metallographic structure.With the addition of Yb,the grains are refined and these Yb-containing phases replace the large-sized MgLiZn phase to be enriched at the grain boundaries.While the addition of excess Yb reduces the number of small-sized MgLiZn phases in the grain,thus reducing the alloys’mechanical performance.After extrusion,the small-sized MgLiZn phase is refined and the number increases,which effectively improves the tensile and fatigue strength of the alloy.The fatigue strength is mainly affected by the number and morphology of the second phase,positively correlated with the strength.Balanced in grain size and number and size of second phases,the extruded alloy with 0.2Yb added exhibits excellent mechanical properties with the yield strength,ultimate tensile strength and elongation of 292 MPa,303 MPa and 11.7%,and an fatigue strength of 130 MPa.

Promoting dynamic recrystallization and improving strength and ductility of Mg-7Bi alloy through Al addition

This study investigated the influence of the addition of Al to a Mg-7Bi(B7,wt%)alloy,particularly its recrystallization behavior during extrusion and its resulting mechanical properties.The addition of 2 wt%Al to the B7 alloy resulted in a lower grain size,a reduction in the number density of fine Mg3Bi2 particles,and a higher area fraction of relatively coarse Mg3Bi2 particles in the extrusion billet.These microstructural changes increased the nucleation sites for recrystallization,reduced the Zener pinning effect,and enhanced particle-stimulated nucleation,all of which promoted dynamic recrystallization behavior during extrusion.As a result,the area fraction of recrystallized grains in the extruded alloy increased from 77%to 94%.The extruded B7 alloy exhibited a strong<10-10>fiber texture,whereas the extruded Mg-7Bi-2Al(BA72)alloy had a weak<10-10>-<2-1-10>texture,which was attributed to the minimal presence of unrecrystallized grains and the dispersed orientation of the recrystallized grains.The tensile yield strength(TYS)of the extruded BA72 alloy was higher than that of the extruded B7 alloy(170 and 124 MPa,respectively),which resulted from the enhanced grain-boundary and solid-solution strengthening effects.The tensile elongation(EL)of the BA72 alloy also exceeded that of the B7 alloy(20.3%and 6.1%,respectively),the result of the uniform formation of fine twins under tension in the former and the formation of a few coarse twins among the unrecrystallized grains in the latter.Consequently,the addition of a small amount of Al to the B7 alloy significantly improved both the strength and ductility of the extruded alloy,resulting in a remarkable increase in the product of the TYS and EL from 756 to 3451 MPa%and expanding its potential range of applications as a lightweight extruded structural component.

Investigation of high rate mechanical flow followed by ignition for high-energy propellant under dynamic extrusion loading

Investigating the ignition response of nitrate ester plasticized polyether(NEPE) propellant under dynamic extrusion loading is of great significant at least for two cases. Firstly, it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident stimulus.Secondly, evaluates the risk of a shell crevice in a solid rocket motor(SRM) under a falling or overturning scene. In the present study, an innovative visual crevice extrusion experiment is designed using a dropweight apparatus. The dynamic responses of NEPE propellant during extrusion loading, including compaction and compression, rapid shear flow into the crevice, stress concentration, and ignition reaction, have been firstly observed using a high-performance high-speed camera. The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s. Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA, a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions. The stress concentration occurs in the crevice location of the propellant sample, the shear stress is relatively large, the effective plastic work is relatively large, and the ignition reaction is easy to occur. When the sample thickness decreases from 5 mm to 2.5 mm, the shear stress increases from 22.3 MPa to 28.6 MPa, the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 μs, and the triangular area is easily triggering an ignition reaction. The propellant sample with a small thickness is more likely to stress concentration, resulting in large shear stress and effective work, triggering an ignition reaction.

Microstructure and mechanical behavior of AXM Mg alloy systems—A review

Automobiles are the inevitable mode of transportation.However,increasing fuel prices and carbon dioxide emissions are posing a serious threat to automobile users and the environment.Thus,the development of new lightweight materials has been a key area of research.Magnesium-based commercial alloys(AZ and ZK series alloys)are the lightest among all structural metals.However,there is still a question about the replacement of Aluminum-based alloys due to HCP crystal structure.In this connection,Mg-Al-Ca-Mn(AXM)Mg alloy can be a choice as an alternative to the existing Mg-based commercial alloys for structural applications.It contains(Al,Mg)_(2)Ca,Al_(2)Ca,Mg_(2)Ca,and Al_(8)Mn_(5)as the secondary phases,contributing to the microstructural refinement and property enhancement.However,the formation of those precipitates depends on the amount of Al,Ca,and Mn,especially,the Ca/Al ratio.In addition,the secondary processes influence the grain refinement and property enhancement of texture modifications.Hence,this review article focuses on elaborating on the significance of the Ca/Al ratio for the precipitate formation,secondary process,and texture modifications.The co-segregation behavior of other micro-alloying elements like Cerium,Lanthanum,and Zinc in AXM Mg alloy systems has also been discussed for property enhancement.

Deformation mechanisms and microstructural characteristics of AZ61 magnesium alloys processed by a continuous expansion extrusion approach

The unique continuous extrusion-based severe plastic deformation approaches were proposed recently to process high-performance magnesium (Mg) alloys,while the in-depth deformation mechanisms under such complicated thermomechanical conditions were not well understood In the present work,the fundamental deformation behaviors of AZ61 Mg alloy from 25 to 400°C were firstly examined under uniaxial compression deformation.Then the deformation mechanisms and microstructural characteristics of AZ61 Mg alloy during continuous expansion extrusion forming (CEEF) were systematically investigated by microstructural observations,finite element and cellular automata simulations The results showed that the continuous evolutions of temperature,larger strain level and complex stress state with strain rate range of 0~5.98 s-1during CEEF brought the distinctive dynamic recrystallization behaviors and texture development in AZ61 Mg alloy,which were different to that of uniaxial compression deformation.In details,a remarkable grain refinement was achieved via CEEF processing due to the simultaneous actions of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX).Gradually enhanced CDRX were observed from center to edge region,which had significant effects on the texture distribution and texture strength.The c-axis of most grains rotated under distinctive shear strain following parabolic metal flow,resulting in stable fiber texture.In addition,the evolution of the internal texture of the alloy led to an obvious increase in the Schmid factor for the activation of basal(c+a)slip system.©2022 Chongqing University.Publishing services provided by Elsevier B.V.on behalf of Ke Ai Communications Co.Ltd.

Extrusion 3D printing of carbon nanotube-assembled carbon aerogel nanocomposites with high electrical conductivity

Carbon nanotubes(CNTs)with high aspect ratio and excellent electrical conduction offer huge functional improvements for current carbon aerogels.However,there remains a major challenge for achieving the on-demand shaping of carbon aerogels with tailored micro-nano structural textures and geometric features.Herein,a facile extrusion 3D printing strategy has been proposed for fabricating CNT-assembled carbon(CNT/C)aerogel nanocomposites through the extrusion printing of pseudoplastic carbomer-based inks,in which the stable dispersion of CNT nanofibers has been achieved relying on the high viscosity of carbomer microgels.After extrusion printing,the chemical solidification through polymerizing RF sols enables 3D-printed aerogel nanocomposites to display high shape fidelity in macroscopic geometries.Benefiting from the micro-nano scale assembly of CNT nanofiber networks and carbon nanoparticle networks in composite phases,3D-printed CNT/C aerogels exhibit enhanced mechanical strength(fracture strength,0.79 MPa)and typical porous structure characteristics,including low density(0.220 g cm^(-3)),high surface area(298.4 m^(2)g^(-1)),and concentrated pore diameter distribution(~32.8nm).More importantly,CNT nanofibers provide an efficient electron transport pathway,imparting 3D-printed CNT/C aerogel composites with a high electrical conductivity of 1.49 S cm^(-1).Our work would offer feasible guidelines for the design and fabrication of shape-dominated functional materials by additive manufacturing.

Method of fabricating artificial rock specimens based on extrusion free forming(EFF)3D printing

Three-dimensional(3D)printing technology has been widely used to create artificial rock samples in rock mechanics.While 3D printing can create complex fractures,the material still lacks sufficient similarity to natural rock.Extrusion free forming(EFF)is a 3D printing technique that uses clay as the printing material and cures the specimens through high-temperature sintering.In this study,we attempted to use the EFF technology to fabricate artificial rock specimens.The results show the physico-mechanical properties of the specimens are significantly affected by the sintering temperature,while the nozzle diameter and layer thickness also have a certain impact.The specimens are primarily composed of SiO_(2),with mineral compositions similar to that of natural rocks.The density,uniaxial compressive strength(UCS),elastic modulus,and tensile strength of the printed specimens fall in the range of 1.65–2.54 g/cm3,16.46–50.49 MPa,2.17–13.35 GPa,and 0.82–17.18 MPa,respectively.It is capable of simulating different types of rocks,especially mudstone,sandstone,limestone,and gneiss.However,the simulation of hard rocks with UCS exceeding 50 MPa still requires validation.

Multifunctional HDPE/Cu biocidal nanocomposites for MEX additive manufactured parts: Perspectives for the defense industry

In this study, we investigated the performance improvement caused by the addition of copper(Cu)nanoparticles to high-density polyethylene(HDPE) matrix material. Composite materials, with filler percentages of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 wt% were synthesized through the material extrusion(MEX)3D printing technique. The synthesized nanocomposite filaments were utilized for the manufacturing of specimens suitable for the experimental procedure that followed. Hence, we were able to systematically investigate their tensile, flexural, impact, and microhardness properties through various mechanical tests that were conducted according to the corresponding standards. Broadband Dielectric Spectroscopy was used to investigate the electrical/dielectric properties of the composites. Moreover, by employing means of Raman spectroscopy and thermogravimetric analysis(TGA) we were also able to further investigate their vibrational, structural, and thermal properties. Concomitantly, means of scanning electron microscopy(SEM), as well as atomic force microscopy(AFM), were used for the examination of the morphological and structural characteristics of the synthesized specimens, while energy-dispersive Xray spectroscopy(EDS) was also performed in order to receive a more detailed picture on the structural characteristics of the various synthesized composites. The corresponding nanomaterials were also assessed for their antibacterial properties regarding Staphylococcus aureus(S. aureus) and Escherichia coli(E. coli) with the assistance of a method named screening agar well diffusion. The results showed that the mechanical properties of HDPE benefited from the utilization of Cu as a filler, as they showed a notable improvement. The specimen of HDPE/Cu 4.0 wt% was the one that presented the highest levels of reinforcement in four out of the seven tested mechanical properties(for example, it exhibited a 36.7%improvement in the flexural strength, compared to the pure matrix). At the same time, the nanocomposites were efficient against the S. aureus bacterium and less efficient against the E. coli bacterium.The use of such multi-functional, robust nanocomposites in MEX 3D printing is positively impacting applications in various fields, most notably in the defense and security sectors. The latter becomes increasingly important if one takes into account that most firearms encompass various polymeric parts that require robustness and improved mechanical properties, while at the same time keeping the risk of spreading various infectious microorganisms at a bare minimum.

Improving the ductility and toughness of nano-TiC/AZ61 composite by optimizing bimodal grain microstructure via extrusion speed

In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical properties of the composites is investigated.The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed.When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s,the microstructure transforms from uniform to HBG structure.Compared with Uniform-0.75 mm/s composite,Heterogeneous-3.5 mm/s composite achieves a 116.7%increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength.This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced(HDI)hardening.Moreover,Heterogeneous-3.5 mm/s composite achieves a 108.3%increase in toughness compared with the Uniform-0.75 mm/s composite.It is mainly because coarse grain(CG)bands can capture and blunt cracks,thereby increasing the energy dissipation for crack propagation and improving toughness.In addition,the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability.Thus,the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite.

Effect of thermo-mechanical conditions during constrained friction processing on the particle refinement of AM50 Mg-alloy phases

Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In this study,the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material,in particular the eutecticβ-Mg_(17)Al_(12)and Al-Mn phases.For that purpose,as-cast and solution heat-treated base material and processed samples were analyzed.The Al_(8)Mn_(5) intermetallic phase was identified as the main secondary phase present in all samples before and after the processing.A notorious refinement of these particles was observed,starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing.The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution,where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces.As for the eutectic phase,the results indicate the presence of the partially divorcedβ-Mg_(17)Al_(12)particles exclusively in the as-cast base material,indicating that no further phase transformations regarding the eutectic phase,such as dynamic precipitation,occurred after the CFP.In the case of the processed as-cast material analyzed after the CFP,the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase,which associated with the mechanical breakage of the particles,enabled the complete dissolution of this phase.Therefore,CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects,in terms of grain sizes of theα-Mg phase and presence and morphology of the Al-Mn and eutecticβ-Mg_(17)Al_(12).

Insights and implications from the study on meniscus reconstruction using tendon autograft

This letter addresses the recent study by Zhu et al on the predictive factors for coronal and sagittal graft extrusion length following medial meniscus reconstruction using tendon autografts.The study provides valuable insights into the importance of preoperative joint space width and tunnel positioning as predictors of graft extrusion.Specifically,it found strong correlations between preoperative joint space width and medial,posterior,and mean graft extrusion at both 1 week and 8 months post-operation.Additionally,tunnel edge distance at 1 week postoperation correlated with anterior and posterior graft extrusion.These findings offer critical guidance for improving surgical outcomes.However,the letter highlights the need for further research with larger sample sizes and comparative studies involving different graft types to strengthen these findings and broaden their applicability in clinical settings.The study's contributions to understanding meniscus reconstruction using tendon autografts are acknowledged,along with suggestions for future research directions.