Ductility Enhancement Research Articles

High strength and high ductility nano-Ni-Al2O3/A356 composites fabricated with nickel-plating and equal channel angle semi-solid extrusion (ECASE)

Abstract The nano-Ni-Al2O3/A356 nanocomposites prepared with nickel-plating, stir casting, and equal channel angle semi-solid extrusion (ECASE). The microstructure, tensile property, and fracture morphology of the fabricated nanocomposites have been investigated. The microstructure observation showed the nickel-plating could stimulate nucleation and break nanoparticle aggregation, resulting the matrix grains in a smaller size (63 μm) and the nanoparticles more uniform located on the grain boundary. The ECASE could further refine the grains size (23 μm) and improve the nanoparticle dispersion. Although 5 passes refine the grains to 16 μm, it would cause the particles to re-agglomerate, due to the nanoparticles exist in the semi-solid liquid phase for a long time. The fabricated nanocomposites exhibited an enhancement in both strength and ductility, about 1.2–2.5 times higher than those of the corresponding aluminum matrix composites. Due to the Orowan strengthening and fine grain strengthening, i.e., increased the number of grain boundaries and improved the resistance of particles to cooperative grain deformation. Meanwhile, the ECASE eliminated the intergranular defects and improved the grain boundary bonding. The enhanced mechanical properties of the nanocomposites were attributed to the grain boundary control increased by the nickel-plating and ECASE. The grain boundary control, such as increasing the grain boundary number, improving the particle-matrix adhesion and particle dispersion, can be applied to the development of high mechanical properties aluminum matrix composites.

Experimental and extended finite element simulations for tensile fracture phenomenon of cryorolled aluminium alloy 5754

In present work, cryorolling is performed to obtain the higher mechanical strength of the received material. Close to 50% and 30% increments in tensile and yield strengths of the material are observed for 40% thickness reduction. However, limited ductility has been obtained for cryorolled samples. Post annealing heat treatment is performed on cryorolled samples to obtain combined enhancement in strength and ductility of the alloy. Difference in the ductile fracture along with crack initiation and its advancement with plastic straining is also compared for cryorolled and annealed cryorolled samples. Fracture angle and crack propagation behavior at vicinity of gauge section is evaluated by using extended finite element method (XFEM) and compared with experimental tested work piece. XFEM has been adopted to simulate the crack growth behavior from nucleation till fracture of the investigated alloy. Triaxial stress contour plots are also captured by XFEM near to the crack initiation zone.

Microstructure evolution and mechanical properties in an ultralight Mg-2.76Li–3Al-2.6Zn-0.39Y alloy

A novel Mg-2.76Li–3Al-2.6Zn-0.39Y alloy was prepared by multidirectional forging (MDF) and rolling (R) to improve strength and ductility, and its microstructural evolution and mechanical properties were investigated by an optical microscope, X-ray diffraction (XRD), transmission electron microscope (TEM), and tensile tester. After MDFR, the ultimate tensile strength was 275 ± 8 MPa, the yield strength was 207 ± 7 MPa, and the elongation was 29% at a grain size of 6.8 ± 1.1 μm. The specific modulus of this alloy was 30.04 MN m kg−1, and the specific strength was 183.58 kN m kg−1. Microstructural examination of decreased-temperature MDF revealed the presence of a bimodal microstructure, which is favorable for the enhancement of both strength and ductility. The deformation mechanisms of MDF are intense mechanically shearing fragmentation and incomplete dynamic recrystallization. XRD analysis revealed that the present alloy consists of α(Mg) phase, and Al2Y, Mg17(Al,Zn)12, Mg2Y, and AlLi intermetallic compounds. TEM analysis confirmed the existence of Mg17(Al,Zn)12 compound and dislocation wall and pile-up. Portevin–Le Chatelier (PLC) effect or serrated flow was discovered in this alloy. The relationship between the break-away stress and the experimental stress was proposed as a criterion for judging the occurrence of the PLC effect. The estimated stress is consistent with the experimental stress. The contributions of different strengthening mechanisms to tensile yield strength were estimated. The estimated tensile yield strength is in good agreement with the experimental tensile yield strength.

Strength–ductility enhancement in multi-layered sheet with high-entropy alloy and high-Mn twinning-induced plasticity steel

In this study, a high-entropy-alloy-cored multi-layered sheet (MLS) clad with an austenitic high-Mn twinning-induced-plasticity steel (HEA/high-Mn MLS) is proposed and its room- and cryogenic-temperature tensile behaviors were investigated. The MLS was fabricated using a commercial roll-bonding procedure. Its interface was well bonded without critical defects such as pores or voids. During the MLS fabrication and subsequent annealing, the interdiffusion of alloying elements and interfacial friction resulted in the formation of ε-martensite and V-rich carbides in the high-Mn and HEA layers, respectively, as well as grain refinement. Nevertheless, the interface remained strongly bonded after the tensile deformation at room and cryogenic temperatures, thereby providing larger strength and elongation than the values calculated based on the rule of mixtures. The improvement in tensile properties beyond the calculated values was interpreted by the activation of deformation twins, transformation-induced plasticity, and generation of geometrically necessary dislocations in the HEA/high-Mn interfacial region. Deformation twins were populated at both high-Mn and HEA layers at room temperature. However, at cryogenic temperatures, ε-martensite and body-centered cubic martensite were additionally formed in the high-Mn and HEA layers. Thus, both strength and ductility were considerably improved. In addition, the consequent good strength–ductility balance was comparable to or better than those of other HEAs or medium-entropy alloys. This indicates that our MLS can be an attractive design strategy to tailor various properties by controlling the thickness fraction of each layer and develop strong alloys for cryogenic applications.

Shear and Flexural Strengthening of Steel Beams with Thick Carbon Fiber Reinforced Polymer Laminate

In this paper, shear and flexural behavior of structural steel beams strengthened by high modulus carbon fiber reinforced polymer (CFRP) laminates are presented. Totally, 18 steel specimens including 6 un-strengthened beams as control specimens and 12 strengthened steel beams with simple supports were tested under 3-point bending test set-up. All specimens were strengthened using the bonded system. Influence of different parameters including length of steel beams, section size of specimens, number of CFRP laminates, and location of CFRP laminates were studied. Based on anticipated failure modes, the bonded laminates were implemented on the surface of tension flange, compression flange, and web of beams. Three failure modes of flexural, shear, and lateral-torsional buckling failures were observed in the tested beams. The main goal of these experiments was to evaluate the enhancement in load capacity, beam ductility, and initial stiffness. The results showed that the yield load, ultimate load capacity, and energy absorption of strengthened steel beams improved up to 15, 29 and 28 percent, respectively. Finally, in order to predict test results and compare the actual and predicted valves, analytical and numerical studies were carried out.

Precipitation of Al3Zr by two-step homogenization and its effect on the recrystallization and mechanical property in 2195 Al–Cu–Li alloys

To improve the recrystallization resistance of 2195 Al–Cu–Li alloys, we proposed a two-step homogenization (TS) to facilitate the homogeneous nucleation of Al3Zr, and the effect of Al3Zr precipitate on the recrystallization behavior and on the strength and ductility of 2195 alloys were investigated. It is shown that the first low-temperature homogenization in TS promotes the nucleation of Al3Zr due to large driving force, and second high-temperature homogenization helps to accelerate diffusion process of Zr, resulting in fine and dense Al3Zr distribution (radius of 22.6 ± 4.1 nm and number density of 1.94 × 1020/m3). As a result, the recrystallization resistance of 2195 alloys is significantly improved comparing with those treated by the traditional one-step homogenization (OS). The TS alloys exhibits best yield strength (566.7 MPa), tensile strength (598.8 MPa) and elongation of 11.9% comparing with OS alloys. The strength improvement of TS 2195 alloys mainly originates from Orowan mechanism and grain refinement induced by Al3Zr precipitate. The remained deformed lamellar structure in TS alloys effectively deflectes and zigzags the propagation of cracks, which is beneficial to the energy dissipation, leading to the enhancement of ductility.

A unified mechanistic model for Hall–Petch and inverse Hall–Petch relations of nanocrystalline metals based on intragranular dislocation storage

Nanocrystalline (NC) metals often show transition from Hall–Petch (HP) strengthening to inverse HP softening as the average grain size decreases below a critical value. Compared to the HP behavior whose mechanism is well understood as the dislocation pile-up at grain boundaries (GBs), several hypotheses have been proposed to explain the veiled inverse HP behavior and no consensus has been reached yet. In this work, we propose a size-dependent model considering the influence of grain size on the intragranular dislocation storage ability and unify the HP and inverse HP relations for NC metals. The reduction of the intragranular dislocation storage ability with decreasing grain size is revealed as the underlying mechanism of the breakdown of the HP behavior in NC. Prediction of the critical grain size of 26.9nm for the HP-inverse HP transition of NC copper agrees well with experimental results. Numerical results suggest that the harmonized deformation of GB and grain interior (GI) dominates the remarkable ductility enhancement of NC metals in the inverse HP region. Moreover, our results suggest that the formation of dimple structures spanning several grains at fracture surfaces of NC metals is attributed to the coalescence of inter- and intra-granular microcracks and microvoids in clustered grains with Goss texture in local shear bands. As the GB strength increases, NC metals show enhancement in yield strength and delay in occurrence of the inverse HP behavior. Our studies give new insight into the contribution of GB sliding to the plastic behaviors of NC metals, and provide valuable guidance for the rational design of NC metals with high ductility and high strength.

Immunity of Al0.25CoCrFeNi high-entropy alloy to hydrogen embrittlement

The influence of hydrogen via electrochemical charging on the mechanical behavior of the cryo-rolled and annealed Al0·25CoCrFeNi high entropy alloy (HEA) through tensile experiments was investigated. The results indicated that the Al0·25CoCrFeNi alloy mainly composed of FCC phase has immunity to electrochemical hydrogen embrittlement. Analysis on the fracture surfaces revealed that hydrogen permeates into a shallow depth and transforms the deformation mechanism. The deformation twins and stress-induced phase transformation (FCC-to-HCP) are introduced in the surface near fracture of tensile sample when the Al0·25CoCrFeNi alloy is not charged by hydrogen. After hydrogen charging, the dissolved hydrogen decreases the stacking fault energy and promotes the planar dislocation slip, resulting in the enhancement of strength and ductility in Al0·25CoCrFeNi HEA.

Mechanical Properties Enhancement of the Au-Cu-Al Alloys via Phase Constitution Manipulation

To enhance the mechanical properties (e.g., strength and elongation) of the face-centered cubic (fcc) α-phase in the Au-Cu-Al system, this study focused on the introduction of the martensite phase (doubled B19 (DB19) crystal structure of Au2CuAl) via the manipulation of alloy compositions. Fundamental evaluations, such as microstructure observations, phase identifications, thermal analysis, tensile behavior examinations, and reflectance analysis, have been conducted. The presence of fcc annealing twins was observed in both the optical microscope (OM) and the scanning electron microscope (SEM) images. Both strength and elongation of the alloys were greatly promoted while the DB19 martensite phase was introduced into the alloys. Amongst all the prepared specimens, the 47Au41Cu12Al and the 44Au44Cu12Al alloys performed the optimized mechanical properties. The enhancement of strength and ductility in these two alloys was achieved while the stress plateau was observed during the tensile deformation. A plot of the ultimate tensile strength (UTS) against fracture strain was constructed to illustrate the effects of the introduction of the DB19 martensite phase on the mechanical properties of the alloys. Regardless of the manipulation of the alloy compositions and the introduction of the DB19 martensite phase, the reflectance stayed almost identical to pure Au.

Optimal ductility enhancement of RC framed buildings considering different non-invasive retrofitting techniques

Existing RC framed buildings lack significant ductility, especially when they have been built with pre-code criteria. Improving their ductile capacity can help to prevent them from the brittle collapse mechanism and to reduce the seismic damage expected. This paper aims to investigate the enhancement of the ductile response behaviour of RC framed buildings considering different non-invasive retrofitting techniques. To do so, a pre-code RC framed school located in the Spanish province of Huelva has been selected as a case study. Five non-invasive retrofitting techniques have been tested: FRP wraps and steel jackets in columns, steel beams and plates under RC beams and single steel braces. They have been selected so that they can be easily implemented in the building. Some of them have been studied in detail in previous works and others have been included for further research in this paper. In order to compare the results obtained, the most typical technique in the seismic retrofitting of RC framed buildings, the addition of X-bracings in bays, has also been tested. Most previous studies on the seismic retrofitting of RC buildings are focused on validating a method based on artificial models. This paper compares the different techniques in terms of the capacity improvement and the damage reduction, performing analyses in detail and adding them in an existing RC building. A sensitivity analysis has been carried out to determine the influence of each technique in the building’s ductile capacity considering the finite element method. Nonlinear static analyses have been performed to obtain the capacity, the displacement ductility factor (μ) and the behaviour factor (q) of each model defined. The damage expected has been determined considering the ductile and fragile failure of the elements according to the Eurocode-8 (EC8) requirements. To analyse the suitability and the efficiency of each solution, a benefit/cost ratio has been obtained taking into account the ductility improvement and the damage reduction with regards to the retrofitting costs. The results have shown that the best benefit has been obtained with the addition of steel braces. However, the optimal solutions have been single braces and steel jackets due to their combination between benefit and cost. It has been observed that the solutions that increase the stiffness of the joints have had a higher improvement due to the key role that joints have in the resistant capacity of RC structurers. Also, it has been obtained that the values of the fundamental periods have been reduced, when adding the retrofitting elements and materials, up to 30% owing to the increase of the stiffness of the system. Finally, it must be highlighted that a detailed analysis of the behaviour of the whole building must be conducted in order to avoid additional rotation effects and shear forces that could worsen the building’s seismic behaviour.

The effect of initial densification on the spallation damage of silica glass induced by planar impact

Densification, one of the main properties of silica glass, is very important in understanding the dynamics of materials. In this work, we investigate the effect of initial densification on the spallation damage of silica glass induced by planar impact with classical molecular dynamics simulations. At the same impact velocity, the higher the initial densification, the higher the shock pressure and shock wave velocity, but the lower shock temperature. As a result, the higher densified silica glass has higher spall stress. The spall strength from bulk decreases approximately linearly with the impact velocity, but it increases with initial densification to a certain extent and especially at higher impact velocity. The spall strength from the surface is underestimated at lower impact velocity and overestimated at higher impact velocity. Of course, that can be improved distinctly by the modified acoustic method. The microstructure analysis reveals that the higher densified silica glass causes a higher nucleation rate and wider spallation damage region. Except for shear transformation, tension transformation zones coalescence also happens in higher densified silica glass that has more porosity during spallation, reflecting the enhancement of spall ductility. In addition, spall damage of higher initial densified silica glass develops more rapidly and tends to form locally larger voids. After spallation, parts of 4-fold Si are converted to 3-fold Si and 5-fold Si, and initial densification can weaken the conversion.

Incorporation of Natural Fibres in Rendering Mortars for the Durability of Walls

One of the main functions of renders, together with the overall aesthetic appearance of the building, is the protection of the walls against external aggressive actions, such as water, salts solutions, erosion, and mechanical impacts. However, some anomalies of renders may drastically hinder their protection ability. In fact, cracking, high water permeability, and loss of adherence to the substrate of renders limit their barrier effect and favour the exposure of the substrate to external actions. The incorporation of fibres in mortars is commonly pointed out to reduce their cracking susceptibility, due to the probable enhancement in tensile strength and ductility of the composite. The use of lime in substitution of the part of the cement binder is seen as a method to reduce the modulus of elasticity and therefore enhance the resistance to cracking due to drying shrinkage. Therefore, this study investigates the wall protection-related properties of natural fibre-reinforced renders with cement-lime as a binary binder at 1:1:6 volumetric ratio. With this purpose, wool, coir, and flax fibres are used at 20% by total mortar volume and the water behaviour, cracking susceptibility, and adherence to the substrate of the mortars are assessed. Specifically, the water absorption by capillarity, drying rates, permeability to water under pressure, adherence strength, and shrinkage are evaluated. In order to evaluate the renders’ durability and therefore the durability of the protection to the walls, an artificial accelerated ageing test is performed based on heating-freezing and humidification-freezing cycles. The results indicate that the fibres’ addition reduced the shrinkage and modulus of elasticity of the mortars, which suggests lower susceptibility to cracking. The addition of fibres in mortars seemed to slightly affect their water performance and only at early ages. From the results, it was concluded that the adherence strength is not affected by the fibres’ incorporation. The fibres seem also to reduce the impacts of the ageing cycles on the mortar and the improvements provided by the fibres’ addition to the mortars’ performance remained after ageing when compared to the mortars without fibres, thus being a potential alternative to increase their durability. These aspects are particularly important for buildings, since they can extend their service life and promote their sustainability.

Behavior of GFRP bar reinforced geopolymer concrete filled GFRP tube columns under different loading conditions

This paper proposes a new type of column. The glass fiber reinforced polymer (GFRP) bar reinforced geopolymer concrete (GPC) filled GFRP tube column is presented as a potential substitute of steel reinforced ordinary Portland cement concrete (OPC) column. Type of concrete (OPC and GPC), type of longitudinal reinforcement bars (steel and GFRP) and type of transverse reinforcement (steel helix and GFRP tube) were the test parameters investigated in this study. The specimens of 200 mm diameter and 800 mm height were tested under different loading conditions. Experimental load-axial deformation, load-lateral deformation and flexural load-midspan deflection of the tested specimens are presented and discussed. An equation was also proposed for the prediction of the concentric load capacity of the column. It was found that GFRP reinforcement and GFRP tube confinement resulted in a higher ductility enhancement for GPC based specimens as compared to the OPC based specimens. Also, the ductility of GFRP bar reinforced GPC or OPC filled GFRP tube columns increased with the load eccentricity. Whereas, the ductility of the steel reinforced specimens decreased with the increase of load eccentricity.

Tensile fracture behavior and texture evolution of a hot-rolled W–Y2(Zr)O3 alloy

• A W–0.4wt% Y 2 (Zr)O 3 alloy with high recrystallization temperature and superior tensile strength have been prepared. • The strength and elongation of the RD and TD orientation samples of the WYZ alloy depend on the length of the free dislocation slip path and the capacity of grains to dislocations. • With the increase of tensile temperature, the α- and γ-fiber texture on the fracture side surface were significantly enhanced. • Larger tensile strain rates overestimate DBTT but exhibit high tensile strength at temperatures above DBTT. A W–0.4wt% Y 2 (Zr)O 3 (WYZ) alloy plate with superior mechanical properties and improved high-temperature stability was prepared by hot rolling. The tensile properties of WYZ alloys with different orientations and recrystallization states were investigated at a temperature range from room temperature (RT) to 500°C. The texture intensity of the original WYZ alloy was weak, but it was significantly enhanced after annealing. The initial recrystallization temperature of the WYZ alloy was approximately 1400°C. After recrystallization annealing, the strength of the WYZ alloy decreased significantly, but it showed an increased ductility. The ultimate tensile strength and fracture elongation of the samples along the rolling direction (RD) were always significantly higher than those of the samples along the transverse direction (TD). Orientation and annealing had no evident effect on ductile-to-brittle transition temperature (DBTT) from tensile data, but increasing strain rate would overestimate DBTT. The DBTT of the WYZ alloy from tensile data was approximately between 200°C and 300°C. With the increase in tensile test temperature, the strengths of α- and γ-fiber textures on the side of fracture surface increased significantly. The increase in α- and γ-fiber texture contents was beneficial to ductility enhancement in the WYZ plate.

Simultaneous enhancement of strength and ductility by aging treatment in fine-grained Mg-13Gd alloy

Ideal structural materials should have both high strength and good ductility. Aging treatment is an effective way to increase the strength of Mg alloys, but usually sacrifices their ductility. Here we have successfully achieved the synergetic enhancement of strength and ductility of the extruded Mg-13Gd alloy via aging treatment, and obtained a Mg alloy with a tensile yield strength of 400 MPa and an elongation of 15%. The synergetic improvement of strength and ductility is mainly attributed to the formation of high-density nanoscale β′ precipitates and a certain proportion of precipitation free zone in the microstructure dominated by dynamically recrystallized fine grains. The yield drop phenomenon in the tensile curves is sensitive to the existence of movable pinned-dislocations within grains. It is expected that the discussion in this study will be helpful to developing Mg alloys with high strength and ductility via aging treatment.

Understanding the enhanced ductility of Mg-Gd with Ca and Zn microalloying by slip trace analysis

This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis. The ductility and microstructure of extruded Mg-0.6Gd and Mg-0.6Gd-0.3Ca-0.2Zn (wt%) sheets were investigated. Basal slip was the main deformation mode under investigation. Ca and Zn microalloying increased the frequency of grain boundaries (GBs) with misorientation angles (θs) < 35°, promoted slip transfer across GBs and restricted the basal slip localization. In addition, there were a higher number of GB cracks homogeneously distributed in the Mg-0.6Gd sheet than in the Mg-0.6Gd-0.3Ca-0.2Zn sheet, attributed to the increased cohesion of GBs. The enhancement of basal slip, the suppression of slip localization and the suppression of GB cracking were contributed to the increased ductility for Mg-0.6Gd-0.3Ca-0.2Zn sheet.

Multifunctionality of Reduced Graphene Oxide in Bioderived Polylactide/Poly(Dodecylene Furanoate) Nanocomposite Films.

This work reports on the first attempt to prepare bioderived polymer films by blending polylactic acid (PLA) and poly(dodecylene furanoate) (PDoF). This blend, containing 10 wt% PDoF, was filled with reduced graphene oxide (rGO) in variable weight fractions (from 0.25 to 2 phr), and the resulting nanocomposites were characterized to assess their microstructural, thermal, mechanical, optical, electrical, and gas barrier properties. The PLA/PDoF blend resulted as immiscible, and the addition of rGO, which preferentially segregated in the PDoF phase, resulted in smaller (from 2.6 to 1.6 µm) and more irregularly shaped PDoF domains and in a higher PLA/PDoF interfacial interaction, which suggests the role of rGO as a blend compatibilizer. rGO also increased PLA crystallinity, and this phenomenon was more pronounced when PDoF was also present, thus evidencing a synergism between PDoF and rGO in accelerating the crystallization kinetics of PLA. Dynamic mechanical thermal analysis (DMTA) showed that the glass transition of PDoF, observed at approx. 5 °C, shifted to a higher temperature upon rGO addition. The addition of 10 wt% PDoF in PLA increased the strain at break from 5.3% to 13.0% (+145%), and the addition of 0.25 phr of rGO increased the tensile strength from 35.6 MPa to 40.2 MPa (+13%), without significantly modifying the strain at break. Moreover, rGO decreased the electrical resistivity of the films, and the relatively high percolation threshold (between 1 and 2 phr) was probably linked to the low aspect ratio of rGO nanosheets and their preferential distribution inside PDoF domains. PDoF and rGO also modified the optical transparency of PLA, resulting in a continuous decrease in transmittance in the visible/NIR range. Finally, rGO strongly modified the gas barrier properties, with a remarkable decrease in diffusivity and permeability to gases such as O2, N2, and CO2. Overall, the presented results highlighted the positive and sometimes synergistic role of PDoF and rGO in tuning the thermomechanical and functional properties of PLA, with simultaneous enhancement of ductility, crystallization kinetics, and gas barrier performance, and these novel polymer nanocomposites could thus be promising for packaging applications.

Enhanced mechanical properties of boron nitride nanosheets/copper composites with a bioinspired laminated structure

ABSTRACT Poor mechanical properties of copper (Cu) hinder its applications as structural materials. Developing bioinspired-laminated structure is among the most promising strategies for obtaining modern structural materials with excellent combination mechanical properties. To explore the possibility of enhancing mechanical properties of Cu, herein, we fabricated boron nitride nanosheets/copper (BNNSs/Cu) composites with a bioinspired laminated structure, achieved by ball milling and spark plasma sintering (SPS). Their mechanical properties were investigated. The results indicate that their tensile strength and toughness are both larger than those of pure Cu: the addition of 0.3 vol% of BNNSs improves the tensile strength from 187 MPa to 216 MPa and the elongation from 41% to 56%, respectively. The enhancement of ductility is due to the unique lamellar distribution of BNNSs in composites, which resulted in retarding cracks propagation; the strengthening effect of BNNSs is determined by the moderate interfacial bonding strength and possible agglomeration of BNNSs.

Improvement of ductility and work hardening ability in a high strength Zn-Mg-Y alloy via micron-sized and submicron-sized YZn12 particles

In this study, the effects of Y addition on microstructure and mechanical properties of Zn-Mg alloy during multi-pass equal channel angular pressing (ECAP) were systematically investigated. The results show that apart from α-Zn matrix and network-shaped eutectic Zn+Mg2Zn11 structure, micron-sized and submicron-sized YZn12 particles were formed in as-cast alloy. During multi-pass ECAP, the α-Zn matrix was refined via dynamic recrystallization (DRX), and the eutectic structure was fragmented into fine particles gradually, while the YZn12 particles became further refined (~100 nm) only from 8p to 12p ECAP. Tensile tests at room temperature indicated that the 12p-ECAP alloy exhibits the optimal mechanical properties with ultimate tensile strength of 465 MPa and fracture elongation of 11%. The fine and uniform microstructure contributes to the enhancement of ductility. Furthermore, the improved work hardening ability of 12p alloy was mainly ascribed from the generation of submicron-sized YZn12 particles with the size of ~100 nm, which could induce twinning with them and increase the density of geometrically necessary dislocations. The results suggest that the introduction of second phase particles with twinning ability may be effective to improve the work hardening ability of Zn alloys.

Effect of microwave heating on fracture behavior of granite: An experimental investigation

Hard rock breaking is a great challenge for deep drilling and mining engineering, and the microwave-assisted rock breaking technique offers a promising solution. However, the lack of knowledge of the effects of microwave irradiation on hard rocks limits the further development of this technology. Laboratory tests have been conducted to investigate the variations of fracture properties of granite subjected to microwave heating. The semi-circular bend (SCB) specimens were prepared, and mode I fracture tests were conducted on the microwave treated granite specimens. The acoustic emission (AE) events was recorded and the strain field was calculated by the digital image correlation (DIC) technique. The test results demonstrated that the temperature of the sample surface increased linearly as the increasing heating time, and increasing microwave power contributes to enhancing the heating rate. According to the results of scanning electron microscope (SEM), intergranular cracks were the main form of cracks, and the transgranular cracks usually appeared in samples with high microwave power or longer heating time. The generation of micro-cracks can be attributed to the high temperature and the thermal shock. With the increasing heating time, the fracture toughness decreased exponentially, the AE active period prolonged, and the fractal dimension of the fracture surfaces (FSD) continuous increased. Compared to an untreated sample, the maximum principal strain and fracture process zone (FPZ) size of the microwave heated sample were larger at the same loading level, which indicated the enhancement of ductility. According to the experimental results, the relationships between FPZ size, fracture toughness and FSD were empirically regressed. Understanding the effects of microwave heating on the fracture properties is of significant to improve hard rock breaking efficiency.