The microstructural evolution characteristics of the thermomechanically affected zone （TMAZ） alloy during friction stir processing （FSP） of thixoformed （TF） AZ91D alloy were investigated. Simultaneously, a surfa...The microstructural evolution characteristics of the thermomechanically affected zone （TMAZ） alloy during friction stir processing （FSP） of thixoformed （TF） AZ91D alloy were investigated. Simultaneously, a surface composite layer reinforced by SiC particles （SiCps） was prepared on the alloy by FSP and the corresponding tribological properties were examined. The experimental results indicate that dynamic recrystallization and mechanical separation （including splitting and fracture of the primary grains） are the main mechanisms of grain refinement for the TMAZ. A composite surface reinforced by uniformly distributed SiCps was prepared on the alloy. Compared with the corresponding permanent mould casting alloy and the TF alloy without composite surface, the TF alloy with composite surface has the highest wear resistance and lowest friction coefficient.展开更多
The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investig...The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investigated at temperature ranging from 673 to 723 K under loads of 95-108 MPa. For a comparative purpose,the creep behavior of the monolithic matrix alloy AZ91D was also conducted under loads of 15-55 MPa at 548-598 K. The creep mechanisms were theoretically analyzed based on the power-law relation. The results showed that the creep rates of both TiC/AZ91D composites and AZ91D alloy increase with increasing the temperature and load. The TiC/AZ91D composites possess superior creep resistance as compared with the AZ91D alloy. At deformation temperature below 573 K, the stress exponent n of AZ91D alloy approaches theoretical value of 5, which suggests that the creep process is controlled by dislocation climb. At 598 K, the stress exponentof AZ91D is close to 3, in which viscous non-basal slip deformation plays a key role in the process of creep deformation. However, the case differs from that of AZ91D alloy when the stress exponent n of TiC/AZ91D composites exceeds 9, which shows that there exists threshold stress in the creep process of the composites, similar to other types of composites. The average activation energies for the creep of the AZ91D alloy and TiC/AZ91D composites were calculated to be 144 and 152 k J/mol, respectively. The existence of threshold stress in the creep process of the composites leads to an increase in activation energy for creep.展开更多
In this experimental study,magnesium(AZ91D)based boron carbide(B4C)and graphite(Gr)particle reinforced hybrid composite materials were manufactured by stir casting.The tribological and mechanical properties of these c...In this experimental study,magnesium(AZ91D)based boron carbide(B4C)and graphite(Gr)particle reinforced hybrid composite materials were manufactured by stir casting.The tribological and mechanical properties of these composite materials were investigated.The results of the tests revealed that the graphite reinforced hybrid composites exhibited a lower wear loss compared to the unreinforced AZ91D alloy and AZ91D–B4C composites.It was found that with an increase in the B4C content,the wear resistance increased monotonically with hardness and ultimate tensile strength decreased.This study revealed that the addition of both a hard reinforcement(e.g.,B4C)and soft reinforcement(e.g.,graphite)significantly improves the wear resistance of magnesium composites.These entire results designate that the hybrid magnesium composites can be considered as an excellent material where high strength,ultimate tensile strength and wear-resistant components are of major importance,primarily in the aerospace and automotive engineering sectors.展开更多
To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by las...To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.展开更多
AZ91 D and 8.5 vol.%SiC_(p)/AZ91 D magnesium matrix composites were fabricated by a semi-solid extruded processing method,and treated with solution and aging heat treatment.The effects of SiC_(p)on the microstructures...AZ91 D and 8.5 vol.%SiC_(p)/AZ91 D magnesium matrix composites were fabricated by a semi-solid extruded processing method,and treated with solution and aging heat treatment.The effects of SiC_(p)on the microstructures of the semi-solid extruded AZ91 D magnesium alloy during recrystallization were studied by observing and analyzing the microstructure evolution during extrusions and heat treatments.The results show that the addition of SiC_(p)inhibits the dynamic recrystallization of AZ91 D during the semi-solid extrusion with only 26% of the volume fraction of recrystallization.Furthermore,the addition of SiC_(p)refines the sizes of grains and second phases,and upgrades the volume fraction of second phase.After solution and aging treatment,the recrystallization continues,and the addition of SiC_(p)promotes the recrystallization and the recrystallized microstructure is much more stable.Meanwhile,the sizes of grains and second phases continue to be refined,and the volume fraction of second phases continues to increase.展开更多
The influence of chemical composition on corrosion resistance of AZ91D magnesium alloys ingots has been investigated. Mass loss method was applied to evaluate the corrosion resistance of AZ91D alloys and the data were...The influence of chemical composition on corrosion resistance of AZ91D magnesium alloys ingots has been investigated. Mass loss method was applied to evaluate the corrosion resistance of AZ91D alloys and the data were analyzed by multiple regression. The results show that the corrosion resistance of this alloy can be improved by increasing Al, Zn and Mn in a certain degree, and will drop with increasing Si and heavy metals (Fe, Cu, Ni). It is found that ingots received from company F should be listed into unusable materials in terms of the corrosion resistance, while among the five suppliers, the only local company E supplied excellent AZ91D magnesium alloy ingots with the best corrosion resistance.展开更多
In-situ ZrB2/AZ91D magnesium matrix composite was successfully synthesized with Al/K2ZrF6+NH4BF4 by means of Direct Melt Reaction.The fabricated ZrB2/AZ91D magnesium matrix composite through direct melt mixing method ...In-situ ZrB2/AZ91D magnesium matrix composite was successfully synthesized with Al/K2ZrF6+NH4BF4 by means of Direct Melt Reaction.The fabricated ZrB2/AZ91D magnesium matrix composite through direct melt mixing method was investigated.Results from X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) confirmed the existence of ZrB2 particles in the AZ91D alloy,and most ZrB2 particles were in the size range of just several microns,some even to 100 nm.The cast specimens were studied through corrosion testing and heat treatment.The average grain size of AZ91D decreased markedly from about 250μm to 50μm.In addition,the shape and size of the β-Mg17Al12 phase as well as the morphologies of primary α-Mg in the magnesium matrix composite were greatly changed.The network structure of the β-Mg17Al12 phase was broken into small blocks and the size of α-Mg decreased significantly.展开更多
The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MC...The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MCC)coatings on AZ91D magnesium alloys were prepared by Micro-arc Oxidation(MAO)and electrophoresis technologies.The microstructure,corrosion resistance,abrasion resistance,stone impact resistance and adhesion of MCC coatings were studied respectively.The cross section morphologies showed that the outer organic coating was filled into the hole on surface of MAO coating,and it acted as a shelter against corrosive products.The copper-accelerated acetic acid salt spray Test,abrasion resistance test,stone impact resistance test,thermal shock resistance test and adhesion test were used to evaluate the protective characterization by the third testing organization which approved by GM.The test results showed the composite coatings meet all the requirements.The MCC coating on Mg presents excellent properties,and it is a promising surface treatment technology on magnesium alloys for production vehicles.展开更多
In the present investigation, composites with silicon carbide particle （SiCp） as reinforcement and AZ91 magnesium alloy as matrix have been synthesized using liquid metal stir-casting technique with optimized proces...In the present investigation, composites with silicon carbide particle （SiCp） as reinforcement and AZ91 magnesium alloy as matrix have been synthesized using liquid metal stir-casting technique with optimized processing conditions. The composites with good particle distribution in the matrix, and better grain refinement and good interfacial bonding between the matrix and reinforcement have been obtained. The effect of SiCp content on the physical, mechanical, and tribological properties of Mg-based metal matrix composite （MMC） is studied with respect to particle distribution, grain refinement, and particle/matrix interfacial reactions. The electrical conductivity, coefficient of thermal expansion, microas well as macro-hardness, tensile and compressive properties, and the fracture behavior of the composites along with dry sliding wear of the composites have been evaluated and compared with the base alloy.展开更多
基金Funded by the State Key Development Program for Basic Research of China (2007CB613706)the Natural Science Foundation of Gansu Province(3ZS042-B25-003)the Development Program for Outstanding Young Teachers in Lanzhou university of Technology (SKL03004)
文摘The microstructural evolution characteristics of the thermomechanically affected zone （TMAZ） alloy during friction stir processing （FSP） of thixoformed （TF） AZ91D alloy were investigated. Simultaneously, a surface composite layer reinforced by SiC particles （SiCps） was prepared on the alloy by FSP and the corresponding tribological properties were examined. The experimental results indicate that dynamic recrystallization and mechanical separation （including splitting and fracture of the primary grains） are the main mechanisms of grain refinement for the TMAZ. A composite surface reinforced by uniformly distributed SiCps was prepared on the alloy. Compared with the corresponding permanent mould casting alloy and the TF alloy without composite surface, the TF alloy with composite surface has the highest wear resistance and lowest friction coefficient.
基金Financial supports from Natural Science Foundation （Grant No. 20032012）；Liaoning Province, China； the Scientific Research Foundation for the Returned 0verseas Chinese Scholars；State Education Ministry, China and from the Starting for New Scientific Researchers of Institute of Metal Research （IMR）；Chinese Academy of Sciences （CAS）, are gratefully acknowledged.
文摘The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investigated at temperature ranging from 673 to 723 K under loads of 95-108 MPa. For a comparative purpose,the creep behavior of the monolithic matrix alloy AZ91D was also conducted under loads of 15-55 MPa at 548-598 K. The creep mechanisms were theoretically analyzed based on the power-law relation. The results showed that the creep rates of both TiC/AZ91D composites and AZ91D alloy increase with increasing the temperature and load. The TiC/AZ91D composites possess superior creep resistance as compared with the AZ91D alloy. At deformation temperature below 573 K, the stress exponent n of AZ91D alloy approaches theoretical value of 5, which suggests that the creep process is controlled by dislocation climb. At 598 K, the stress exponentof AZ91D is close to 3, in which viscous non-basal slip deformation plays a key role in the process of creep deformation. However, the case differs from that of AZ91D alloy when the stress exponent n of TiC/AZ91D composites exceeds 9, which shows that there exists threshold stress in the creep process of the composites, similar to other types of composites. The average activation energies for the creep of the AZ91D alloy and TiC/AZ91D composites were calculated to be 144 and 152 k J/mol, respectively. The existence of threshold stress in the creep process of the composites leads to an increase in activation energy for creep.
文摘In this experimental study,magnesium(AZ91D)based boron carbide(B4C)and graphite(Gr)particle reinforced hybrid composite materials were manufactured by stir casting.The tribological and mechanical properties of these composite materials were investigated.The results of the tests revealed that the graphite reinforced hybrid composites exhibited a lower wear loss compared to the unreinforced AZ91D alloy and AZ91D–B4C composites.It was found that with an increase in the B4C content,the wear resistance increased monotonically with hardness and ultimate tensile strength decreased.This study revealed that the addition of both a hard reinforcement(e.g.,B4C)and soft reinforcement(e.g.,graphite)significantly improves the wear resistance of magnesium composites.These entire results designate that the hybrid magnesium composites can be considered as an excellent material where high strength,ultimate tensile strength and wear-resistant components are of major importance,primarily in the aerospace and automotive engineering sectors.
基金supported by the Open Fund of the State Key Laboratory of Advanced Welding Production Technology in Harbin Institute of Technology,Chinathe Open Fund of the State Key Laboratory of Materials Processing and Die&Mould Technology in Huazhong University of Science and Technology,China
文摘To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.
基金financially supported by the National Natural Science Foundation of China(51474153).
文摘AZ91 D and 8.5 vol.%SiC_(p)/AZ91 D magnesium matrix composites were fabricated by a semi-solid extruded processing method,and treated with solution and aging heat treatment.The effects of SiC_(p)on the microstructures of the semi-solid extruded AZ91 D magnesium alloy during recrystallization were studied by observing and analyzing the microstructure evolution during extrusions and heat treatments.The results show that the addition of SiC_(p)inhibits the dynamic recrystallization of AZ91 D during the semi-solid extrusion with only 26% of the volume fraction of recrystallization.Furthermore,the addition of SiC_(p)refines the sizes of grains and second phases,and upgrades the volume fraction of second phase.After solution and aging treatment,the recrystallization continues,and the addition of SiC_(p)promotes the recrystallization and the recrystallized microstructure is much more stable.Meanwhile,the sizes of grains and second phases continue to be refined,and the volume fraction of second phases continues to increase.
文摘The influence of chemical composition on corrosion resistance of AZ91D magnesium alloys ingots has been investigated. Mass loss method was applied to evaluate the corrosion resistance of AZ91D alloys and the data were analyzed by multiple regression. The results show that the corrosion resistance of this alloy can be improved by increasing Al, Zn and Mn in a certain degree, and will drop with increasing Si and heavy metals (Fe, Cu, Ni). It is found that ingots received from company F should be listed into unusable materials in terms of the corrosion resistance, while among the five suppliers, the only local company E supplied excellent AZ91D magnesium alloy ingots with the best corrosion resistance.
基金financially supported by the Specialized Research Fund Project for the Doctoral Program of Higher Education of China (No.20070299004)the Jiangsu Higher Education Institutions Natural Science Foundation Research Program (No.10KJD430003)+2 种基金the Jiangsu University Outstanding Talents Building Project (No.1213000004)the Jiangsu University Undergraduate Practice-Innovation Training Project (No.1201220038)Doctoral Foundation of Jiangsu University (No.1281220014)
文摘In-situ ZrB2/AZ91D magnesium matrix composite was successfully synthesized with Al/K2ZrF6+NH4BF4 by means of Direct Melt Reaction.The fabricated ZrB2/AZ91D magnesium matrix composite through direct melt mixing method was investigated.Results from X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) confirmed the existence of ZrB2 particles in the AZ91D alloy,and most ZrB2 particles were in the size range of just several microns,some even to 100 nm.The cast specimens were studied through corrosion testing and heat treatment.The average grain size of AZ91D decreased markedly from about 250μm to 50μm.In addition,the shape and size of the β-Mg17Al12 phase as well as the morphologies of primary α-Mg in the magnesium matrix composite were greatly changed.The network structure of the β-Mg17Al12 phase was broken into small blocks and the size of α-Mg decreased significantly.
基金Support from National Natural Science Foundation of China(Grant NO.51271144)as well as from the National Key Technologies Research and Development Program of China(Grant No.2011BAE22B05)is gratefully acknowledged.And thanks to General Motors research and development center for provided test equipment.
文摘The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MCC)coatings on AZ91D magnesium alloys were prepared by Micro-arc Oxidation(MAO)and electrophoresis technologies.The microstructure,corrosion resistance,abrasion resistance,stone impact resistance and adhesion of MCC coatings were studied respectively.The cross section morphologies showed that the outer organic coating was filled into the hole on surface of MAO coating,and it acted as a shelter against corrosive products.The copper-accelerated acetic acid salt spray Test,abrasion resistance test,stone impact resistance test,thermal shock resistance test and adhesion test were used to evaluate the protective characterization by the third testing organization which approved by GM.The test results showed the composite coatings meet all the requirements.The MCC coating on Mg presents excellent properties,and it is a promising surface treatment technology on magnesium alloys for production vehicles.
文摘In the present investigation, composites with silicon carbide particle （SiCp） as reinforcement and AZ91 magnesium alloy as matrix have been synthesized using liquid metal stir-casting technique with optimized processing conditions. The composites with good particle distribution in the matrix, and better grain refinement and good interfacial bonding between the matrix and reinforcement have been obtained. The effect of SiCp content on the physical, mechanical, and tribological properties of Mg-based metal matrix composite （MMC） is studied with respect to particle distribution, grain refinement, and particle/matrix interfacial reactions. The electrical conductivity, coefficient of thermal expansion, microas well as macro-hardness, tensile and compressive properties, and the fracture behavior of the composites along with dry sliding wear of the composites have been evaluated and compared with the base alloy.
