查看更多>>摘要：Low-density δ-quenching and partitioning(δ-QP)steels with excellent strength and ductility have been recently developed.However,there are still rare reports on the formability of δ-QP steels,which are critical for satisfying the manufacture of structural parts during the application in automotive industry.In the present work,an 1180 MPa Fe-Mn-Al-C-Nb δ-QP steel with a high ductility was adopted for the stretch-flangeability study.The δ-QP steel was developed by separated quenching and partitioning processes.A good hole expansion ratio(HER)of 34.9±0.9％ was obtained in the quenched steel,but it has been further increased to 52.2％ by the tempering treatment.The improved stretch-flangeability was attributed to the enhanced austenite stability and deformation uniformity.On the one hand,the stability of austenite was increased by carbon partitioning during tempering,which reduced crack possibility via the suppression of the fresh martensite formation.On the other hand,the tempering treatment released the internal stress caused by martensitic transformation and reduced the difference in strength among different phases,resulting in an increase in the resistance to crack initiation and propagation.
查看更多>>摘要：Magnesium alloys have a significant advantage,lower density over the other structure materials;hence,they have been widely used in various fields such as transportation and aerospace.With the development of research and the enlargement of the research scope,more advantages have been revealed:excellent shielding efficiency,extraordinarily high damping capacity,as well as impressive thermal conductivity.Therefore,Mg alloys have the potential to be various functional materials,such as electromagnetic shielding material,damping material,and thermal conductive material.This review comprehensively summarizes the research progress and the up-to-date summary of Mg alloys as structure-function integrated materials in recent years.Solute atoms,heat treatment,deformation,secondary phase,and temperature,which have a significant influ-ence on the properties of magnesium alloys,are highlighted.We expect this review to be helpful for those who are working on developing structure-function integrated materials with superior comprehensive performance.
查看更多>>摘要：Exfoliation corrosion(EFC)has rarely been reported for wrought magnesium alloys.Enhanced EFC of the as-extruded Mg-1Li-1Ca alloy was observed after the removal of outermost fine-grained skins.The microstructure and corrosion products were investigated using optical microscopy,scanning electron microscopy,electron backscattered diffraction,X-ray diffraction,and Fourier transform infrared spectrometry.The corrosion behavior was analyzed using electrochemical polarization,electrochemical impedance spectroscopy,and scanning Kelvin probe techniques.The results indicated that the surface of Mg-1Li-1Ca,with the superficial layer removed,was more susceptible to EFC.A linear correlation between grain boundary density and corrosion resistance was established.Additionally,the influence of factors such as grain size,intermetallic compounds,different alloy surfaces,and corrosion products on EFC were discussed,and the corresponding EFC mechanism was clarified.
查看更多>>摘要：Zirconium(Zr)emerges as the most effective grain refiner for magnesium(Mg)alloys incorporating Zr.Typically,Zr is introduced in the form of an Mg-Zr master alloy.However,within Mg-Zr master alloys,Zr predominantly exists in a par-ticle form,which tends to aggregate due to attractive van der Waals forces.The clustered Zr is prone to settling,thereby reducing its refining impact on Mg alloys.In this work,a combined pretreatment process for Mg-Zr master alloys was proposed,encompassing the introduction of a physical field to intervene the agglomeration of particle Zr and the employ of high-temperature dissolution and peritectic reactions to promote the solid solution of Zr.The results demonstrate that the particle Zr within the pretreated Mg-Zr master alloy is effectively dispersed and refined,and greater solute Zr levels can be achieved.The subsequent grain refinement ability was studied on a typical Mg-6Zn-0.6Zr(wt％ )alloy.The outcome highlights that an improvement in the grain refinement efficacy(32.4％ )of Mg-Zr master alloys was obtained with a holding time of 60 min.The pretreated Mg-Zr master alloy significantly augments the efficiency of grain refinement for Mg alloys through a synergistic strategy involving heterogeneous nucleation and solute-driven growth restriction.The crucial factor in achieving effective grain refinement of Zr in Mg alloys lies in regulating the presence and morphology of Zr in the Mg-Zr master alloy,distinguishing between particle Zr and solute Zr.This study introduces a novel method for developing more efficient Mg-Zr refiners.
查看更多>>摘要：In this work,a good combination of strength and ductility is achieved in a Mg-13Gd-0.2Ni alloy by conventional extru-sion and following aging treatment.The aged Mg-13Gd-0.2Ni alloy exhibits a yield strength(YS)of 363 MPa,an ultimate tensile strength(UTS)of 433 MPa,and an elongation of 11.9％ .The aged Mg-13Gd-0.2Ni alloy contains a microstructure with a 95％ proportion of dynamically recrystallized(DRXed)grains with a micron size,weak texture,and a high number density of prismatic β'precipitates within grains.The bulk compounds enriched with Ni element which are mainly formed during casting and stable in the extruded and aged samples.Few dynamic compounds are formed during extrusion,and a high density of prismatic β'precipitates are formed during aging.The high density of prismatic β'precipitates results in a significant increase in the strength of the Mg-13Gd-0.2Ni alloy,and the YS and UTS are increased by 153 and 136 MPa,respectively.The high proportion of DRXed grains with a weak texture contributes mainly to the high ductility and the fine compounds with a low density at grain boundaries formed during aging have no significant adverse effect on ductility of the aged Mg-13Gd-0.2Ni alloy.These findings for the novel Mg-Gd-Ni alloy can provide guidance for the design of wrought Mg alloys with superior mechanical properties.
查看更多>>摘要：There are nanotwins in the shear band formed in a moment(about 10-5 s)in some NiCrFe-based medium-entropy alloys(MEAs),and these shear bands can be recognized as a special kind of materials due to their high strength and good plastic-ity.In this study,the single shear band of the NiCrFe MEA was prepared at 77 K.A series of characterizations were carried out to analyze the microstructures in the shear band.The strength of the shear band was investigated by the split Hopkinson pressure bar and in-situ compression.The micropillar in the shear band containing nanotwins exhibits excellent strength-plasticity synergy.The compressive yield strength of the shear band measured by in-situ compression is 175％ higher than that of the matrix,reaching 1405 MPa,with the fracture strain exceeding 0.5.The strengthening mechanism of the shear band was revealed by the combination of the experimental results and molecular dynamics simulation.The synergistic effect of multiple strengthening mechanisms enhances the strength of the NiCrFe MEA containing nanotwins,in which the grain boundary strengthening of the ultrafine equiaxed grains and the dynamic Hall-Petch effect of the nanotwins dominate.In addition,the good plasticity of the shear band is ascribed to the stress concentration reduction of the twin boundaries of nanotwins and the activation of multiple slip systems due to the randomly oriented nanotwins.These findings provide theo-retical guidance for the design of nanotwinned MEAs to realize excellent strength-plasticity synergy for structural materials.
查看更多>>摘要：A refractory high entropy alloy Ti62Nb12Mo12Ta12W2 was prepared by mechanical alloying and spark plasma sintering.The microstructure and mechanical properties of the Ti62Nb12Mo12Ta12W2 alloy were analyzed.The experimental results show that the microstructure of the alloy is composed of two BCC phases,an FCC precipitated phase,and the precipitated phase which is a mixture of TiC,TiN and TiO.The alloy exhibits good room temperature compressive properties.The plasticity of the sample sintered at 1550 ℃ can reach 10.8％ ,and for the sample sintered at 1600 ℃,the yield strength can be up to 2032 MPa,in the meantime the plasticity is 9.4％ .The alloy also shows high strength at elevated temperature.The yield strength of the alloy exceeds 420 MPa at 900 ℃,and value of which is still above 200 MPa when the test temperature reaches 1000 ℃.Finally,the compressive yield strength model at room temperature is constructed.The prediction error of the model ranges from-7.9％ to-12.4％ ,expressing fair performance.
查看更多>>摘要：La-Mg-Ni-based hydrogen storage alloys have excellent hydrogen storage properties.This work reports the hydrogen storage performance of a series of A2B7-type La0.96Mg0.04Ni3.34Al0.13 alloy and La0.96-xYxMg0.04Ni3.47-0.6xAl0.6x(x=0,0.22,0.33,0.44)alloys,and explores the effect of Y and Al element combined substitution on the microstructure and hydrogen stor-age performance of A2B7-type La-Mg-Ni-based alloys.The alloys are composed of Ce2Ni7 phase and LaNi5 phase.With the increase of x,the cell volume of Ce2Ni7 phase decreases,while that of LaNi5 phase increases,indicating that Y atom mainly enters Ce2Ni7 phase and Al atom mainly enters LaNi5 phase.An appropriate amount of co-substitution increases the hydrogen storage capacity and reduces the hydrogen absorption/desorption plateau pressure hysteresis of the alloy.When x=0.44,the hydrogen storage capacity of the alloy is 1.449 wt％ ,and the hysteresis coefficient is 0.302.The cell volume of Ce2Ni7 phase and LaNi5 phase expands to different degrees after 20 absorption/desorption cycles.With the increase of x,the volume expansion rate decreases,and the cycle capacity retention rate also gradually decreases.This is related to the amorphization of Ce2Ni7 phase.When x=0.22,the capacity retention rate of the alloy is 91.4％ .
查看更多>>摘要：B4C/Al composites are widely utilized as neutron absorbing materials for the storage and transportation of spent nuclear fuel.In order to improve the high-temperature mechanical properties of B4C/Al composites,in-situ nano-Al2O3 was introduced utilizing oxide on Al powder surface.In this study,the Al2O3 content was adjusted by utilizing spheroid Al powder with varying diameters,thereby investigating the impact of Al2O3 content on the tensile properties of(B4C+Al2O3)/Al compos-ites.It was found that the pinning effect of Al2O3 on the grain boundaries could hinder the recovery of dislocations and lead to dislocation accumulation at high temperature.As the result,with the increase in Al2O3 content and the decrease in grain size,the high-temperature strength of the composites increased significantly.The finest Al powder used in this investigation had a diameter of 1.4 μm,whereas the resultant composite exhibited a maximum strength of 251 MPa at room temperature and 133 MPa at 350 ℃,surpassing that of traditional B4C/Al composites.
查看更多>>摘要：Obtaining an appropriate grain size is crucial for Al alloys or Al matrix composites prior to processing,as it significantly influences the mechanical properties of components and workability during the manufacturing process.TiB2 particles are exceptional grain refiners in Al and serve as excellent reinforcement particles for particulate-reinforced aluminum matrix composites.However,the optimal particle content for achieving excellent refinement and strengthening effects depends on the matrix composition and requires further investigation.Additionally,homogenization is essential for mitigating the ele-ment segregation in the ingot.Although it is anticipated that adding suitable particles can effectively inhibit undesired grain growth during homogenization,comprehensive investigations on this aspect are currently lacking.Therefore,TiB2/2219Al matrix composites with varying reinforcement contents(0,1,3,5 wt％ )were fabricated through traditional casting followed by homogenization treatment to address these research gaps.The effects of reinforcement content and homogenization treatment on the microstructure and mechanical properties of in-situ TiB2/2219A1 composites were investigated.The results demonstrate a gradual strengthening of the refining effect with increasing particle concentration.Moreover,composites containing 3 wt％ TiB2 particles exhibit superior comprehensive mechanical properties in both as-cast and homogenized state.Additionally,potential orientation relationships are observed and calculated between undissolved Al2Cu eutectic phase and submicron or nanometer-sized TiB2 particles,resulting in a mixture structure with enhanced bonding strength.This mixture structure is continuously distributed along grain boundaries during solidification,forming a three-dimensional cellular network that acts as primary retarding forces for grain growth during homogenization.Furthermore,the established homogenization kinetic equations were further utilized to analyze the correlation between homogenization time and grain size,as well as the influence of homogenization temperature.
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