AlSi7Mg is an age hardening aluminium alloy that is growing in popularity in additive manufacturing as its good processability makes it well suited to the powder bed fusion process,allowing for its use in the aerospac...AlSi7Mg is an age hardening aluminium alloy that is growing in popularity in additive manufacturing as its good processability makes it well suited to the powder bed fusion process,allowing for its use in the aerospace and automotive industries.The alloy relies on heat treatment to reach its peak strength,with precipitates in the Mg_(2) Si precipitation sequence providing the majority of this strengthening.Powder bed fusion,however,produces components with unique microstructures that differ to those of traditional manufacturing methods such as casting,meaning heat treatments must be carefully tailored for additively manufactured parts.This study therefore investigated the effects of solution treatment temperatures on the final properties and microstructures of T6 treated,additively manufactured AlSi7Mg.Due to the use of a heated build plate,samples aged from the as built and stress relieved conditions exhibited over ageing behaviour,necessitating a solution treatment step to induce useful strength properties.Solution treatments below 500℃were found to provide minimal strengthening upon ageing due to the pres-ence of theπ-Al_(18) Fe_(2)Mg_(7) Si_(10) phase,which reduced the amount of magnesium in solid solution and so reduced the age hardening response of the alloy by restricting the growth of strengthening precipitates.Solution treatments over 500℃,however,demonstrated excellent age hardening due to the replacement of theπ-Al_(18) Fe_(2)Mg_(7) Si_(10) phase with theβ-Al_(9)Fe_(2)Si_(2) phase,increasing the concentration of magnesium in solid solution and therefore improving its age hardening response.A T6 treatment then demonstrated an improvement in yield strength and ductility when compared to the as built state,but a decrease in tensile strength and impact toughness.The variability in the age hardening response of AlSi7Mg suggests that the careful selection of a solution treatment temperature is crucial to property optimisation.展开更多
Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions during isothermal ageing were investigated by microhardness measurements,transmission electron microscopy,atom p...Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions during isothermal ageing were investigated by microhardness measurements,transmission electron microscopy,atom probe tomography and density functional theory-based simulations.The results demonstrate that the Er additions significantly improve the hardness during elevated temperature ageing,especially at 400℃.This is mainly because Er additions increase the nucleation rate of the Al_(3)(Er,Sc,Zr)precipitates,resulting in a higher density of fine and uniform dispersion of L1_(2)structured nanoparticles.First-principles calculations demonstrate that the second nearest neighboring solute-solute interactions for the species Sc,Zr and Er are energetically favored–a key feature to rationalize the observed precipitate structure and the underlying formation mechanism.The sequential formation of the core/shell precipitates in the Er-free alloy and core/double-shell precipitates in the Er-containing alloy arises due to the different solute-solute and solute-vacancy interaction energies,and the relative diffusivities of the Er,Sc and Zr species in Al.These results shed light on the beneficial effects of Er additions on the agehardening behavior of Al-Sc-Zr alloy and provide guidance for designing the ageing treatments for the Al-Sc-Zr(-Er)alloys.展开更多
The effect of small addition of Sc on the microstructural evolution in Al-15Ag alloy was investigated by Monte Carlo simulation and transmission electron microscopy （TEM）. Monte Carlo simulation results indicate tha...The effect of small addition of Sc on the microstructural evolution in Al-15Ag alloy was investigated by Monte Carlo simulation and transmission electron microscopy （TEM）. Monte Carlo simulation results indicate that Ag clustering is suppressed by the addition of Sc during the initial ageing stage, and there is a little chemical repulsion between Ag atoms and Sc atoms. TEM observations show that the morphology of γ′ precipitation can be modified by the small addition of Sc, which does result in a refinement of γ′ precipitates in Al-15Ag-0.2Sc. The mechanism by which trace Sc affect the microstructure is to reduce the ledge density of γ′precipitates.展开更多
All-inorganic lead-free CsSnBr_(3)is attractive for applications in solar cells due to its nontoxicity and stability,but the device performance to date has been poor.Besides the intrinsic properties,impurities induced...All-inorganic lead-free CsSnBr_(3)is attractive for applications in solar cells due to its nontoxicity and stability,but the device performance to date has been poor.Besides the intrinsic properties,impurities induced from electrodes may significantly influence the device performance.Here,we systematically studied the stability,transition energy levels,and diffusion of impurities from the most commonly used electrodes(Au,Ag,Cu,graphite,and graphene)in CsSnBr_(3)based on density functional theory calculations.Our results reveal that,whereas graphite and graphene electrodes exhibit negligible influence on CsSnBr_(3)due to the relatively high formation energies for carbon impurities in CsSnBr_(3),atoms from the metal electrodes can effectively diffuse into CsSnBr_(3)along interstice and form electrically active impurities in CsSnBr_(3).In this case,a significant amount of donor interstitial impurities,such as Agti,Cuti,and Auti,will be formed under p-type conditions,whereas the Sn-site substitutional acceptor impurities,namely Au_(Sn)^(2-),Ag_(Sn)^(2-),and Cu_(Sn)^(2-),are the dominant impurities,especially under n-type conditions.In particular,except for Auti,all these major impurities from the metal electrodes act as nonradiative recombination centers in CsSnBr_(3)and significantly degrade the device performance.Our work highlights the distinct behaviors of the electrode impurities in CsSnBr_(3)and their influence on the related devices and provides valuable information for identifying suitable electrodes for optoelectronic applications.展开更多
文摘AlSi7Mg is an age hardening aluminium alloy that is growing in popularity in additive manufacturing as its good processability makes it well suited to the powder bed fusion process,allowing for its use in the aerospace and automotive industries.The alloy relies on heat treatment to reach its peak strength,with precipitates in the Mg_(2) Si precipitation sequence providing the majority of this strengthening.Powder bed fusion,however,produces components with unique microstructures that differ to those of traditional manufacturing methods such as casting,meaning heat treatments must be carefully tailored for additively manufactured parts.This study therefore investigated the effects of solution treatment temperatures on the final properties and microstructures of T6 treated,additively manufactured AlSi7Mg.Due to the use of a heated build plate,samples aged from the as built and stress relieved conditions exhibited over ageing behaviour,necessitating a solution treatment step to induce useful strength properties.Solution treatments below 500℃were found to provide minimal strengthening upon ageing due to the pres-ence of theπ-Al_(18) Fe_(2)Mg_(7) Si_(10) phase,which reduced the amount of magnesium in solid solution and so reduced the age hardening response of the alloy by restricting the growth of strengthening precipitates.Solution treatments over 500℃,however,demonstrated excellent age hardening due to the replacement of theπ-Al_(18) Fe_(2)Mg_(7) Si_(10) phase with theβ-Al_(9)Fe_(2)Si_(2) phase,increasing the concentration of magnesium in solid solution and therefore improving its age hardening response.A T6 treatment then demonstrated an improvement in yield strength and ductility when compared to the as built state,but a decrease in tensile strength and impact toughness.The variability in the age hardening response of AlSi7Mg suggests that the careful selection of a solution treatment temperature is crucial to property optimisation.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1737206 and 51971077)the AUSMURI program(Grant No.AUSMURI000005)funded under the auspices of the Commonwealth Department of Industry,Innovation and Sciencesupported by the Science and Technology Plan Project of Guangzhou City(Grant No.201807010063)
文摘Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions during isothermal ageing were investigated by microhardness measurements,transmission electron microscopy,atom probe tomography and density functional theory-based simulations.The results demonstrate that the Er additions significantly improve the hardness during elevated temperature ageing,especially at 400℃.This is mainly because Er additions increase the nucleation rate of the Al_(3)(Er,Sc,Zr)precipitates,resulting in a higher density of fine and uniform dispersion of L1_(2)structured nanoparticles.First-principles calculations demonstrate that the second nearest neighboring solute-solute interactions for the species Sc,Zr and Er are energetically favored–a key feature to rationalize the observed precipitate structure and the underlying formation mechanism.The sequential formation of the core/shell precipitates in the Er-free alloy and core/double-shell precipitates in the Er-containing alloy arises due to the different solute-solute and solute-vacancy interaction energies,and the relative diffusivities of the Er,Sc and Zr species in Al.These results shed light on the beneficial effects of Er additions on the agehardening behavior of Al-Sc-Zr alloy and provide guidance for designing the ageing treatments for the Al-Sc-Zr(-Er)alloys.
基金the Doctorate Foundationof National Education Ministry of China under grant.No.20040533022.
文摘The effect of small addition of Sc on the microstructural evolution in Al-15Ag alloy was investigated by Monte Carlo simulation and transmission electron microscopy （TEM）. Monte Carlo simulation results indicate that Ag clustering is suppressed by the addition of Sc during the initial ageing stage, and there is a little chemical repulsion between Ag atoms and Sc atoms. TEM observations show that the morphology of γ′ precipitation can be modified by the small addition of Sc, which does result in a refinement of γ′ precipitates in Al-15Ag-0.2Sc. The mechanism by which trace Sc affect the microstructure is to reduce the ledge density of γ′precipitates.
基金This research was undertaken with the assistance and resources from the National Computational Infrastructure(NCI Australia),an NCRIS enabled capability supported by the Australian Government.We acknowledge the support provided by the Sydney Informatics Hub at the University of Sydney in accessing these resources.This work is partially supported by the Australian Research Council(DE180100167).
文摘All-inorganic lead-free CsSnBr_(3)is attractive for applications in solar cells due to its nontoxicity and stability,but the device performance to date has been poor.Besides the intrinsic properties,impurities induced from electrodes may significantly influence the device performance.Here,we systematically studied the stability,transition energy levels,and diffusion of impurities from the most commonly used electrodes(Au,Ag,Cu,graphite,and graphene)in CsSnBr_(3)based on density functional theory calculations.Our results reveal that,whereas graphite and graphene electrodes exhibit negligible influence on CsSnBr_(3)due to the relatively high formation energies for carbon impurities in CsSnBr_(3),atoms from the metal electrodes can effectively diffuse into CsSnBr_(3)along interstice and form electrically active impurities in CsSnBr_(3).In this case,a significant amount of donor interstitial impurities,such as Agti,Cuti,and Auti,will be formed under p-type conditions,whereas the Sn-site substitutional acceptor impurities,namely Au_(Sn)^(2-),Ag_(Sn)^(2-),and Cu_(Sn)^(2-),are the dominant impurities,especially under n-type conditions.In particular,except for Auti,all these major impurities from the metal electrodes act as nonradiative recombination centers in CsSnBr_(3)and significantly degrade the device performance.Our work highlights the distinct behaviors of the electrode impurities in CsSnBr_(3)and their influence on the related devices and provides valuable information for identifying suitable electrodes for optoelectronic applications.
