Microstructure and mechanical properties of aged Mg-10Gd-2Y-0.4Zr-0.4Ag alloy sheets prepared by different rolling routes were investigated.The results showed that the cross rolling aged(CRA)sheet possesses larger gra...Microstructure and mechanical properties of aged Mg-10Gd-2Y-0.4Zr-0.4Ag alloy sheets prepared by different rolling routes were investigated.The results showed that the cross rolling aged(CRA)sheet possesses larger grain size than unidirectional rolling aged(URA)sheet due to the occurrence of dynamic recovery during rolling which reduces the dislocation density and delays dynamic recrystallization(DRX).The URA sheet has basal texture and RD favored texture while CRA sheet has multiple-peak texture.Both sheets precipitate β'phase and CRA sheet exhibits a stronger aging response.The CRA sheet has higher yield strength and tensile strength than URA sheet,with reduced yield strength anisotropy but increased tensile strength anisotropy.Taking into account different strengthening mechanisms,although the finer grain size of URA sheet enhances grain boundary strengthening,CRA sheet is more responsive to aging,leading to superior aging-precipitated phase strengthening and consequently higher yield strength.展开更多
The microstructures,mechanical properties,and fracture behaviors of an Al-5.9Zn-1.9Mg alloy subjected to thermomechanical treatment across different pre-rolling temperatures have been exhaustively investigated in pres...The microstructures,mechanical properties,and fracture behaviors of an Al-5.9Zn-1.9Mg alloy subjected to thermomechanical treatment across different pre-rolling temperatures have been exhaustively investigated in present work.The pre-deformation temperature exerts a modest influence on grain morphology,while it profoundly impacts the dislocation configurations and precipitation behaviors.Elevating the rolling temperature from ambient to 170℃results in a reduction in dislocation density within grains accompanied by a notable enhancement in their distributional uniformity.While advancing the temperature to 320℃prompts the premature formation of precipitates during deformation,which diminishes the precipitation during the subsequent ageing.Tensile results reveal that the thermomechanical treatment incorporating pre-rolling at 170℃confers a substantial strengthening effect on the alloy on the basis of both grain boundary strengthening and dislocation strengthening stemmed from pre-deformation along with the precipitation strengthening generated by ageing.Furthermore,the microstructure exhibits a relatively scarce presence of inhomogeneous features such as dislocation pile-ups and micro shear bands,contributing favorably to enhance the ductility of the alloy that presents the mixture of cleavage fracture and dimple-induced failure.展开更多
Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematicall...Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematically investigated using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS),combined with Tafel polarization and electrochemical impedance spectroscopy(EIS)analyses.The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al_(3)Er with Al.The Er and Mg in the matrix co-oxidize to form a dense MgO/Er_(2)O_(3)composite oxide,preventing the formation of loose magnesium hydroxide/basic magnesium carbonate.The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase,reducing micro-galvanic corrosion driving force.Electrochemical testing in a 3.5%NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a(AZ 31 Mn alloy)to 0.44 mm/a(AZ31Mn-1.2Er alloy).This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.展开更多
This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode ...This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode positive(DCEP)polarities yielded crack-free partial penetration welds for6 mm thick AZ31B alloy sheet.Welding under direct current electrode negative(DCEN)polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks.Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1.The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld.Welds produced with pulse duration ratios of 1:2and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input.The arc constriction by the high frequency pulsing in the Activ Arc■-High frequency(AA-HF)mode welding was responsible for deeper penetration.Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN,DCEP and AC GTA welds,attributed to the finer microstructure.AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/mechanical properties and also gave an advantage of 50%enhanced productivity when welded at1500 Hz.展开更多
It is of great significance to study the corrosion process of aluminum(Al)alloys fasteners in order to mitigate corrosion for their widespread applications.In this paper,a method for enhancing the corrosion resistance...It is of great significance to study the corrosion process of aluminum(Al)alloys fasteners in order to mitigate corrosion for their widespread applications.In this paper,a method for enhancing the corrosion resistance of Al alloy fasteners is proposed.7075 Al alloy parts with a fine-grained microstructure were prepared by pre-heat treatment(PHT),combined subsequent equal channel angular pressing(ECAP)and cold upsetting(CU).The corrosion behavior of the specimens was investigated by intergranular corrosion and electrochemical test.Microstructure investigations were carried out by field emission scanning electron microscopy,energy dispersive spectrometer and transmission electron microscopy.The relationship between microstructural evolution and corrosion resistance changes was also explored.The results show that both PHT and ECAP-CU significantly improved the corrosion resistance of the samples and modified the corrosion process.The open circuit potential,corrosion current density and corrosion rate of the alloy on electrochemical test were(-0.812±8.854)×10^(-5) V(vs.SCE),(6.379±0.025)×10^(-6) A/cm^(2) and 0.066 mm/year,respectively,and the intergranular corrosion depth was(557±8)μm.The main factor controlling the corrosion behavior was the microstructure evolution.After PHT,the disappearance of the dendritic structure and the dissolution of the nonequilibrium second phase eliminated the potential difference between the phases,reducing the free energy in the as cast state.When ECAP-CU was used after PHT,the grain refinement was accompanied by a high density of grain boundaries and dislocations,which led to the formation of a denser passivation film on the alloy surface,improving the corrosion resistance in an aggressive environment.展开更多
Mg–8Li–3Al–0.7Si alloy was prepared by casting and deformed by hot extrusion in this study.And the microstructure of as-cast and extruded specimens was analyzed with OM,XRD,SEM and EDS.Results show that the specime...Mg–8Li–3Al–0.7Si alloy was prepared by casting and deformed by hot extrusion in this study.And the microstructure of as-cast and extruded specimens was analyzed with OM,XRD,SEM and EDS.Results show that the specimens are composed ofα-Mg,β-Li,AlLi,MgLiAl2 and Mg2Si phases.In as-extruded specimen,the microstructure is refined and theβ-Li phase has the effect of coordination during deformation.After hot extrusion,Chinese script Mg2Si phase is crushed into block-like and distributes uniformly in the matrix.Mechanical properties results show that the strength and elongation are both improved after hot extrusion.展开更多
The effects of rare earth ytterbium(Yb)addition and hot extrusion on the microstructure and corrosion behavior of as-cast ADC12 were studied by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersiv...The effects of rare earth ytterbium(Yb)addition and hot extrusion on the microstructure and corrosion behavior of as-cast ADC12 were studied by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The experimental results demonstrate that both the Si phase andβ-Al_(5)FeSi phase in the alloy with 0.9 wt%Yb have been remarkably refined,and the Al3Yb intermetallic compound has also been obtained.The Si,β-Al5FeSi,and rare earth phases are further refined in the alloy at 0.9 wt%Yb and hot extrusion.The results of the immersion corrosion tests and electrochemical experiments show that the corrosion current density(8.56μA/cm^(2))of the alloy with 0.9 wt%Yb addition and hot extrusion is 50.6%lower than the untreated alloy(17.33μA/cm^(2)),and the polarization resistance(9252Ω·cm^(2))was 71.3%higher than the untreated alloy(2654Ω·cm^(2)).The corrosion in the cathode phase in the micro-battery was refined to varying degrees attributable to the addition of Yb and hot extrusion,where the cathode reaction in the corrosion process caused a decrease of the corrosion rate.展开更多
The microstructures, tensile properties and compressive creep behaviors of Mg-5%Sn-（0-1.0）%Pb （mass fraction） alloys were studied. The microstructures of the Mg-Sn-Pb alloys consist of dendritic a-Mg and Mg2Sn pha...The microstructures, tensile properties and compressive creep behaviors of Mg-5%Sn-（0-1.0）%Pb （mass fraction） alloys were studied. The microstructures of the Mg-Sn-Pb alloys consist of dendritic a-Mg and Mg2Sn phase. The addition of Pb can refine the size of Mg2Sn phase and grain size, reduce the amount of Mg2Sn phase at grain or inter-dendrite boundaries and change the distribution of Mg2Sn phase. Pb exists in the Mg2Sn phase or dissolves in a-Mg matrix. The mechanical properties of the tested alloys at room temperature are improved with the addition of Pb. When the Pb content is over 0.5%, the mechanical properties are decreased gradually. The Mg-5%Sn-0.5%Pb shows the best ultimate tensile strength and elongation, 174 MPa and 14.3%, respectively. However, the compressive creep resistance of the Mg-Sn-Pb alloys is much lower than that of the Mg-Sn binary alloy at 175℃ with applied load of 55 MPa, which means that Pb has negative effects on the compressive creep resistance of the as-cast Mg-Sn alloys.展开更多
Mg-6Al-2Sr alloys with different Sm contents(0%, 0.5%, 1%, 1.5%, 2%, mass fraction) were prepared by melting and casting method. The effects of Sm on the microstructure and mechanical properties of as-cast Mg-6Al-2Sr ...Mg-6Al-2Sr alloys with different Sm contents(0%, 0.5%, 1%, 1.5%, 2%, mass fraction) were prepared by melting and casting method. The effects of Sm on the microstructure and mechanical properties of as-cast Mg-6Al-2Sr alloys were studied by optical microscope, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope, X-ray diffraction and tensile test. The results show that the microstructure of as-cast Mg-6Al-2Sr alloy is composed of α-Mg, Mg_(17)Al_(12), Mg_(13)Al_(3)Sr and lamellar acicular Al_(4)Sr phase. After adding Sm element, granular block Al2Sm phase appears in the grain. With the increase of Sm content, the discontinuous long strip reticular Mg_(17)Al_(12)phase and the lamellar acicular Al4Sr phase gradually decrease, and the Al_(2)Sm phase increases and distributes more dispersedly, so the alloy microstructure is continuously refined. The average grain size of the alloys decreases at first and then increases with the increase of Sm content. When the Sm content is 1.5 wt%, the average grain size reaches the minimum value of 94.6 μm. With the increase of Sm content, the mechanical properties of the alloy at room temperature first increase and then decrease. When the Sm content is 1.5 wt%, the alloy has the best comprehensive mechanical properties at room temperature.展开更多
Mg-8Sn-1Al-1Zn-xNi(x=0.5%, 1.0%, 1.5%, 2.0%, mass fraction) alloys were designed and prepared. The microstructures and the mechanical properties were studied by using optical microscope, scanning electronic microscope...Mg-8Sn-1Al-1Zn-xNi(x=0.5%, 1.0%, 1.5%, 2.0%, mass fraction) alloys were designed and prepared. The microstructures and the mechanical properties were studied by using optical microscope, scanning electronic microscope, energy dispersive X-ray spectroscope, X-ray diffraction and a standard universal testing machine. The results show that the microstructure of Ni-containing alloys consist of α-Mg, Mg2 Sn, β-Mg-Ni-Al and γ-AlNi phases. No β-Mg-Ni-Al phase was observed in TAZ811-2.0Ni alloy due to its 1:1 atomic ratio of Ni/Al. The addition of Ni refines the α-Mg dendrites and suppresses the formation of coarse Mg2 Sn phase. The tensile properties results show that the TAZ811-0.5Ni alloy presented the best mechanical properties, which is due to the rod-like β-Mg-Ni-Al phase, refined α-Mg dendrites and Mg2 Sn phase, as well as γ-AlNi phase. The tensile fracture mechanism transits from cleavage to quasi-cleavage fracture with the increasing Ni addition.展开更多
The modification behavior of different Er contents on the microstructures and properties of as-cast 8030 aluminum alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction(XR...The modification behavior of different Er contents on the microstructures and properties of as-cast 8030 aluminum alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),hardness test,electrical conductivity test and tensile property test.The results show that the addition of Er can refine the grains of as-cast alloy,which mainly promotes the nucleation ofα-Al by causing constitutional supercooling and forming the Al 3 Er nanoparticles as a heterogeneous nucleation core.Er can change the morphology of Al-Al_(6) Fe eutectic structure of the alloy,furthermore,Er can adsorb on the surface of the Al_(6) Fe phase to refine the Al_(6) Fe phase in eutectic structure.Er can improve the tensile properties,especially the elongation of as-cast 8030 aluminum alloy,which is attributed to the modification of Al-Al_(6) Fe eutectic and Al_(6) Fe phase.展开更多
Laser cladding experiment of Ti+Al+SiO2+C was carried out on Ti6Al4V alloy substrate, then the microstructure of the clad layer was analyzed with SEM and its Anti-oxidation function was discussed. Analyses microstruct...Laser cladding experiment of Ti+Al+SiO2+C was carried out on Ti6Al4V alloy substrate, then the microstructure of the clad layer was analyzed with SEM and its Anti-oxidation function was discussed. Analyses microstructure show that the clad coating can be divided into three zones along the depth direction: clad, binding and heat-affected zones. Ti5Si3 in the clad zone exists in the form of fine dendrites, TiAl matrix filling among Ti5Si3 dendrites plays a role of connecting the Ti5Si3 with the TiAl3 and transferring load, so the clad coating has been strengthened obviously.展开更多
Blended elemental Ti 34%Al powders (mass fraction), containing 1.5%TiC, were hot isostatic pressed to prepare TiAl alloys. The effects of HIPing pressure on the sintered density, microstructure, constitutions phase we...Blended elemental Ti 34%Al powders (mass fraction), containing 1.5%TiC, were hot isostatic pressed to prepare TiAl alloys. The effects of HIPing pressure on the sintered density, microstructure, constitutions phase were studied in details. The results show that the density of TiAl alloy increases repaidly with the increase of the HIPing pressure. At the same time, with the increase of pressure, the Ti 3Al phase in matrix disappears. TiC reacts with other substance, forming Ti 2AlC phase, which precipitates at grain boundaries. With the increase of hot isostatic pressing(HIPing) pressure, the shrinkage of the alloys increases, the fine spherical Ti 2AlC phase can meet together and forms a needle shape Ti 2AlC, and the amount of needle shaped Ti 2AlC phase increases. The composite material of TiAl containing C can be made easily by HIPing technology.展开更多
The microstructural evolution and mechanical properties of high speed indirect-extruded Mg-5%Sn-(1, 2, 4) Zn(mass fraction, %) alloys were investigated by optical microscopy(OM), X-ray diffraction(XRD), scanning elect...The microstructural evolution and mechanical properties of high speed indirect-extruded Mg-5%Sn-(1, 2, 4) Zn(mass fraction, %) alloys were investigated by optical microscopy(OM), X-ray diffraction(XRD), scanning electron microscopy(SEM), differential thermal analysis(DTA) and a static tension tester. All the studied alloys can be extruded successfully at a high speed of 10 m/min. The grain size, area fraction of particles and tensile properties are found to be greatly affected by the extrusion speed and Zn content, resulting in tensile properties showing lower strength and ductility as the extrusion speed increases and Zn content decreases. The dependence of grain size and tensile properties on the second phase particles is also discussed.展开更多
Effect of element cerium （Ce） on microstructure and mechanical properties of A1-Zn-Mg-Cu alloys has been investigated by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, differential s...Effect of element cerium （Ce） on microstructure and mechanical properties of A1-Zn-Mg-Cu alloys has been investigated by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC） and hardness test. The results show that addition of Ce can remarkably refine the as-cast grains and eutectic microstructure. A transformation from Mg（Zn,Cu,A1）2 phase to A12CuMg phase is observed during homogenization. Furthermore, the Ce addition introduces changes in the precipitation process and consequently in the age-hardening behavior of the alloy. Microstructural measurements reveal that the addition of Ce promotes the precipitation of η＇ phase, but it also partly retards the precipitation of GP zones. The density of precipitates decreases in a certain degree and rod-like η＇ precipitates increase when Ce content is from 0.2% to 0.4% （mass fraction）.展开更多
(CrFeCoNi)high-entropy alloy(HEA)was reinforced with various contents of WC particles from 5 wt%to 20 wt%,and prepared by powder metallurgy.The mixed powders were compacted under 700 MPa and then sintered at 1200℃in ...(CrFeCoNi)high-entropy alloy(HEA)was reinforced with various contents of WC particles from 5 wt%to 20 wt%,and prepared by powder metallurgy.The mixed powders were compacted under 700 MPa and then sintered at 1200℃in a vacuum furnace for 90 min.Density,phase composition,and microstructure of sintered samples were investigated.Hardness,compressive strength,wear resistance and coefficient of thermal expansion(CTE)were estimated.The results revealed the improvement of the density with the addition of WC.XRD results revealed the formation of new FCC chromium carbide phases.Scanning electron microscopy(SEM)results show a good distribution of the carbide phases over the alloy matrix.The CTE was decreased gradually by increasing the WC content.Compressive strength was improved by WC addition.A mathematical model was established to predict the behavior of the strength of the HEA samples.The hardness of the investigated HEAs was increased gradually with the increasing of WC content about 20.35%.Also,the wear rate of HEA without WC is 1.70×10^(−4)mm^(3)/(N·m),which is approximately 4.5 times the wear rate of 20 wt%WC HEA(3.81×10^(−5)mm^(3)/(N·m)),which means that wear resistance was significantly improved with the increase of WC content.展开更多
Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried ou...Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.展开更多
The Al-Cu wheel adopting the new Al alloy was prepared by the liquid-die forging,and the mechanical properties,composition distribution,microstructure and fracture behavior were investigated.The results showed that se...The Al-Cu wheel adopting the new Al alloy was prepared by the liquid-die forging,and the mechanical properties,composition distribution,microstructure and fracture behavior were investigated.The results showed that serious Cu segregation was found in the wheel specimen;the microstructure of the Al-Cu wheel was comprised of the casting microstructure and a small amount of the deformed microstructure;the best heat treatment and water quenching system were found to solution treated at(530±5)℃ for 4 h followed by(535±5)℃ for 24 h and aging treated at(155±5)℃ for 4 h;the fracture morphologies of the samples heated under T 6 and T 5-1 heat treatment showed flat,tough nest,and poor plastic characteristics;the fracture morphologies of the samples heated under T 4 heat treatment exhibited complete resilience,but no residual metallographic characteristic;the sample treated under T 4 protocol had the best elongation;the fracture failure was mainly due to the formation of the CuAl_(2)(θ)phases;and the fracture mechanism of the Al-Cu wheel was intergranular fracture.展开更多
The mechanical properties and stress corrosion cracking （SCC） resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstrueture and mechanical properties o...The mechanical properties and stress corrosion cracking （SCC） resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstrueture and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment （RRA）, the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy （TEM） results show that the precipitates η（MgZn2） at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η＇（MgZn2）and η（MgZn2） phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120℃, 24h ＋ 180 ℃, 30 min ＋ 120 ℃, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition.展开更多
基金Project(2023GK2020)supported by the Key Research and Development Program of Hunan Province,China。
文摘Microstructure and mechanical properties of aged Mg-10Gd-2Y-0.4Zr-0.4Ag alloy sheets prepared by different rolling routes were investigated.The results showed that the cross rolling aged(CRA)sheet possesses larger grain size than unidirectional rolling aged(URA)sheet due to the occurrence of dynamic recovery during rolling which reduces the dislocation density and delays dynamic recrystallization(DRX).The URA sheet has basal texture and RD favored texture while CRA sheet has multiple-peak texture.Both sheets precipitate β'phase and CRA sheet exhibits a stronger aging response.The CRA sheet has higher yield strength and tensile strength than URA sheet,with reduced yield strength anisotropy but increased tensile strength anisotropy.Taking into account different strengthening mechanisms,although the finer grain size of URA sheet enhances grain boundary strengthening,CRA sheet is more responsive to aging,leading to superior aging-precipitated phase strengthening and consequently higher yield strength.
基金Project(ZZYJKT2025-03) supported by the Project of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,ChinaProject(2024YFB3411200) supported by the National Key Research and Development Program of China。
文摘The microstructures,mechanical properties,and fracture behaviors of an Al-5.9Zn-1.9Mg alloy subjected to thermomechanical treatment across different pre-rolling temperatures have been exhaustively investigated in present work.The pre-deformation temperature exerts a modest influence on grain morphology,while it profoundly impacts the dislocation configurations and precipitation behaviors.Elevating the rolling temperature from ambient to 170℃results in a reduction in dislocation density within grains accompanied by a notable enhancement in their distributional uniformity.While advancing the temperature to 320℃prompts the premature formation of precipitates during deformation,which diminishes the precipitation during the subsequent ageing.Tensile results reveal that the thermomechanical treatment incorporating pre-rolling at 170℃confers a substantial strengthening effect on the alloy on the basis of both grain boundary strengthening and dislocation strengthening stemmed from pre-deformation along with the precipitation strengthening generated by ageing.Furthermore,the microstructure exhibits a relatively scarce presence of inhomogeneous features such as dislocation pile-ups and micro shear bands,contributing favorably to enhance the ductility of the alloy that presents the mixture of cleavage fracture and dimple-induced failure.
基金Projects(82171030,81870678)supported by the National Natural Science Foundation of China。
文摘Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematically investigated using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS),combined with Tafel polarization and electrochemical impedance spectroscopy(EIS)analyses.The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al_(3)Er with Al.The Er and Mg in the matrix co-oxidize to form a dense MgO/Er_(2)O_(3)composite oxide,preventing the formation of loose magnesium hydroxide/basic magnesium carbonate.The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase,reducing micro-galvanic corrosion driving force.Electrochemical testing in a 3.5%NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a(AZ 31 Mn alloy)to 0.44 mm/a(AZ31Mn-1.2Er alloy).This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.
文摘This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode positive(DCEP)polarities yielded crack-free partial penetration welds for6 mm thick AZ31B alloy sheet.Welding under direct current electrode negative(DCEN)polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks.Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1.The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld.Welds produced with pulse duration ratios of 1:2and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input.The arc constriction by the high frequency pulsing in the Activ Arc■-High frequency(AA-HF)mode welding was responsible for deeper penetration.Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN,DCEP and AC GTA welds,attributed to the finer microstructure.AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/mechanical properties and also gave an advantage of 50%enhanced productivity when welded at1500 Hz.
基金Project(52275350)supported by the National Natural Science Foundation of ChinaProject(0301006)supported by International Cooperative Scientific Research Platform of SUES,China。
文摘It is of great significance to study the corrosion process of aluminum(Al)alloys fasteners in order to mitigate corrosion for their widespread applications.In this paper,a method for enhancing the corrosion resistance of Al alloy fasteners is proposed.7075 Al alloy parts with a fine-grained microstructure were prepared by pre-heat treatment(PHT),combined subsequent equal channel angular pressing(ECAP)and cold upsetting(CU).The corrosion behavior of the specimens was investigated by intergranular corrosion and electrochemical test.Microstructure investigations were carried out by field emission scanning electron microscopy,energy dispersive spectrometer and transmission electron microscopy.The relationship between microstructural evolution and corrosion resistance changes was also explored.The results show that both PHT and ECAP-CU significantly improved the corrosion resistance of the samples and modified the corrosion process.The open circuit potential,corrosion current density and corrosion rate of the alloy on electrochemical test were(-0.812±8.854)×10^(-5) V(vs.SCE),(6.379±0.025)×10^(-6) A/cm^(2) and 0.066 mm/year,respectively,and the intergranular corrosion depth was(557±8)μm.The main factor controlling the corrosion behavior was the microstructure evolution.After PHT,the disappearance of the dendritic structure and the dissolution of the nonequilibrium second phase eliminated the potential difference between the phases,reducing the free energy in the as cast state.When ECAP-CU was used after PHT,the grain refinement was accompanied by a high density of grain boundaries and dislocations,which led to the formation of a denser passivation film on the alloy surface,improving the corrosion resistance in an aggressive environment.
基金Project(51601024)supported by the National Natural Science Foundation,ChinaProjects(2016YFB0700403,2016YFB0301100)supported by the National Key Research and Development Program of China+1 种基金Project(cstc2016jcyj A0418)supported by the Chongqing Research Program of Basic Research and Frontier Technology,ChinaProject(106112016CDJXZ138811)supported by the Fundamental Research Funds for the Central Universities,China
文摘Mg–8Li–3Al–0.7Si alloy was prepared by casting and deformed by hot extrusion in this study.And the microstructure of as-cast and extruded specimens was analyzed with OM,XRD,SEM and EDS.Results show that the specimens are composed ofα-Mg,β-Li,AlLi,MgLiAl2 and Mg2Si phases.In as-extruded specimen,the microstructure is refined and theβ-Li phase has the effect of coordination during deformation.After hot extrusion,Chinese script Mg2Si phase is crushed into block-like and distributes uniformly in the matrix.Mechanical properties results show that the strength and elongation are both improved after hot extrusion.
基金Project(51965040)supported by the National Natural Science Foundation of ChinaProject(20181BAB206026)supported by the Natural Science Foundation of Jiangxi Province,China。
文摘The effects of rare earth ytterbium(Yb)addition and hot extrusion on the microstructure and corrosion behavior of as-cast ADC12 were studied by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The experimental results demonstrate that both the Si phase andβ-Al_(5)FeSi phase in the alloy with 0.9 wt%Yb have been remarkably refined,and the Al3Yb intermetallic compound has also been obtained.The Si,β-Al5FeSi,and rare earth phases are further refined in the alloy at 0.9 wt%Yb and hot extrusion.The results of the immersion corrosion tests and electrochemical experiments show that the corrosion current density(8.56μA/cm^(2))of the alloy with 0.9 wt%Yb addition and hot extrusion is 50.6%lower than the untreated alloy(17.33μA/cm^(2)),and the polarization resistance(9252Ω·cm^(2))was 71.3%higher than the untreated alloy(2654Ω·cm^(2)).The corrosion in the cathode phase in the micro-battery was refined to varying degrees attributable to the addition of Yb and hot extrusion,where the cathode reaction in the corrosion process caused a decrease of the corrosion rate.
基金Project(03GG009-007-4) supported by the Key Program of Science and Technology Bureau of Sichuan Province, China
文摘The microstructures, tensile properties and compressive creep behaviors of Mg-5%Sn-（0-1.0）%Pb （mass fraction） alloys were studied. The microstructures of the Mg-Sn-Pb alloys consist of dendritic a-Mg and Mg2Sn phase. The addition of Pb can refine the size of Mg2Sn phase and grain size, reduce the amount of Mg2Sn phase at grain or inter-dendrite boundaries and change the distribution of Mg2Sn phase. Pb exists in the Mg2Sn phase or dissolves in a-Mg matrix. The mechanical properties of the tested alloys at room temperature are improved with the addition of Pb. When the Pb content is over 0.5%, the mechanical properties are decreased gradually. The Mg-5%Sn-0.5%Pb shows the best ultimate tensile strength and elongation, 174 MPa and 14.3%, respectively. However, the compressive creep resistance of the Mg-Sn-Pb alloys is much lower than that of the Mg-Sn binary alloy at 175℃ with applied load of 55 MPa, which means that Pb has negative effects on the compressive creep resistance of the as-cast Mg-Sn alloys.
基金Project(51975167) supported by the National Natural Science Foundation,China。
文摘Mg-6Al-2Sr alloys with different Sm contents(0%, 0.5%, 1%, 1.5%, 2%, mass fraction) were prepared by melting and casting method. The effects of Sm on the microstructure and mechanical properties of as-cast Mg-6Al-2Sr alloys were studied by optical microscope, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope, X-ray diffraction and tensile test. The results show that the microstructure of as-cast Mg-6Al-2Sr alloy is composed of α-Mg, Mg_(17)Al_(12), Mg_(13)Al_(3)Sr and lamellar acicular Al_(4)Sr phase. After adding Sm element, granular block Al2Sm phase appears in the grain. With the increase of Sm content, the discontinuous long strip reticular Mg_(17)Al_(12)phase and the lamellar acicular Al4Sr phase gradually decrease, and the Al_(2)Sm phase increases and distributes more dispersedly, so the alloy microstructure is continuously refined. The average grain size of the alloys decreases at first and then increases with the increase of Sm content. When the Sm content is 1.5 wt%, the average grain size reaches the minimum value of 94.6 μm. With the increase of Sm content, the mechanical properties of the alloy at room temperature first increase and then decrease. When the Sm content is 1.5 wt%, the alloy has the best comprehensive mechanical properties at room temperature.
基金Projects supported by the Shanxi Selective Funds for Returned Scholars,ChinaProject(2013021013-4)supported by the Shanxi Province Science Foundation for Youths China+1 种基金Projects(2012L053,2012L003)supported by the Taiyuan University of Technology Funds for Young Scientists,ChinaProject(2014021017-2)supported by the Natural Science Foundation for Young Scientists for Shanxi Province,China
文摘Mg-8Sn-1Al-1Zn-xNi(x=0.5%, 1.0%, 1.5%, 2.0%, mass fraction) alloys were designed and prepared. The microstructures and the mechanical properties were studied by using optical microscope, scanning electronic microscope, energy dispersive X-ray spectroscope, X-ray diffraction and a standard universal testing machine. The results show that the microstructure of Ni-containing alloys consist of α-Mg, Mg2 Sn, β-Mg-Ni-Al and γ-AlNi phases. No β-Mg-Ni-Al phase was observed in TAZ811-2.0Ni alloy due to its 1:1 atomic ratio of Ni/Al. The addition of Ni refines the α-Mg dendrites and suppresses the formation of coarse Mg2 Sn phase. The tensile properties results show that the TAZ811-0.5Ni alloy presented the best mechanical properties, which is due to the rod-like β-Mg-Ni-Al phase, refined α-Mg dendrites and Mg2 Sn phase, as well as γ-AlNi phase. The tensile fracture mechanism transits from cleavage to quasi-cleavage fracture with the increasing Ni addition.
基金Project(5500-202128250A-0-0-00)supported by the State Grid Corporation of China。
文摘The modification behavior of different Er contents on the microstructures and properties of as-cast 8030 aluminum alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),hardness test,electrical conductivity test and tensile property test.The results show that the addition of Er can refine the grains of as-cast alloy,which mainly promotes the nucleation ofα-Al by causing constitutional supercooling and forming the Al 3 Er nanoparticles as a heterogeneous nucleation core.Er can change the morphology of Al-Al_(6) Fe eutectic structure of the alloy,furthermore,Er can adsorb on the surface of the Al_(6) Fe phase to refine the Al_(6) Fe phase in eutectic structure.Er can improve the tensile properties,especially the elongation of as-cast 8030 aluminum alloy,which is attributed to the modification of Al-Al_(6) Fe eutectic and Al_(6) Fe phase.
文摘Laser cladding experiment of Ti+Al+SiO2+C was carried out on Ti6Al4V alloy substrate, then the microstructure of the clad layer was analyzed with SEM and its Anti-oxidation function was discussed. Analyses microstructure show that the clad coating can be divided into three zones along the depth direction: clad, binding and heat-affected zones. Ti5Si3 in the clad zone exists in the form of fine dendrites, TiAl matrix filling among Ti5Si3 dendrites plays a role of connecting the Ti5Si3 with the TiAl3 and transferring load, so the clad coating has been strengthened obviously.
文摘Blended elemental Ti 34%Al powders (mass fraction), containing 1.5%TiC, were hot isostatic pressed to prepare TiAl alloys. The effects of HIPing pressure on the sintered density, microstructure, constitutions phase were studied in details. The results show that the density of TiAl alloy increases repaidly with the increase of the HIPing pressure. At the same time, with the increase of pressure, the Ti 3Al phase in matrix disappears. TiC reacts with other substance, forming Ti 2AlC phase, which precipitates at grain boundaries. With the increase of hot isostatic pressing(HIPing) pressure, the shrinkage of the alloys increases, the fine spherical Ti 2AlC phase can meet together and forms a needle shape Ti 2AlC, and the amount of needle shaped Ti 2AlC phase increases. The composite material of TiAl containing C can be made easily by HIPing technology.
基金Project(2012R1A1A1012802) supported by Basic Science Research Program through the National Research Foundation(NRF)of Korea funded by the Ministry of Education,Science and TechnologyProject(2013021013-4) supported by Shanxi Province Science Foundation for Youths,China+1 种基金Project supported by Advanced Programs of Department of Human Resources and Social Security of Shanxi Province for Returned ScholarsProject(2012L003) supported by Foundation for Young Scholars of Taiyuan University of Technology,China
文摘The microstructural evolution and mechanical properties of high speed indirect-extruded Mg-5%Sn-(1, 2, 4) Zn(mass fraction, %) alloys were investigated by optical microscopy(OM), X-ray diffraction(XRD), scanning electron microscopy(SEM), differential thermal analysis(DTA) and a static tension tester. All the studied alloys can be extruded successfully at a high speed of 10 m/min. The grain size, area fraction of particles and tensile properties are found to be greatly affected by the extrusion speed and Zn content, resulting in tensile properties showing lower strength and ductility as the extrusion speed increases and Zn content decreases. The dependence of grain size and tensile properties on the second phase particles is also discussed.
基金Project(2010CB731706) supported by the National Basic Research Program of China
文摘Effect of element cerium （Ce） on microstructure and mechanical properties of A1-Zn-Mg-Cu alloys has been investigated by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC） and hardness test. The results show that addition of Ce can remarkably refine the as-cast grains and eutectic microstructure. A transformation from Mg（Zn,Cu,A1）2 phase to A12CuMg phase is observed during homogenization. Furthermore, the Ce addition introduces changes in the precipitation process and consequently in the age-hardening behavior of the alloy. Microstructural measurements reveal that the addition of Ce promotes the precipitation of η＇ phase, but it also partly retards the precipitation of GP zones. The density of precipitates decreases in a certain degree and rod-like η＇ precipitates increase when Ce content is from 0.2% to 0.4% （mass fraction）.
文摘(CrFeCoNi)high-entropy alloy(HEA)was reinforced with various contents of WC particles from 5 wt%to 20 wt%,and prepared by powder metallurgy.The mixed powders were compacted under 700 MPa and then sintered at 1200℃in a vacuum furnace for 90 min.Density,phase composition,and microstructure of sintered samples were investigated.Hardness,compressive strength,wear resistance and coefficient of thermal expansion(CTE)were estimated.The results revealed the improvement of the density with the addition of WC.XRD results revealed the formation of new FCC chromium carbide phases.Scanning electron microscopy(SEM)results show a good distribution of the carbide phases over the alloy matrix.The CTE was decreased gradually by increasing the WC content.Compressive strength was improved by WC addition.A mathematical model was established to predict the behavior of the strength of the HEA samples.The hardness of the investigated HEAs was increased gradually with the increasing of WC content about 20.35%.Also,the wear rate of HEA without WC is 1.70×10^(−4)mm^(3)/(N·m),which is approximately 4.5 times the wear rate of 20 wt%WC HEA(3.81×10^(−5)mm^(3)/(N·m)),which means that wear resistance was significantly improved with the increase of WC content.
基金Projects(51375269,51675307) supported by the National Natural Science Foundation of China
文摘Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.
基金Project(2019 YFC 1511400)supported by the National Key Technologies R&D Program of China。
文摘The Al-Cu wheel adopting the new Al alloy was prepared by the liquid-die forging,and the mechanical properties,composition distribution,microstructure and fracture behavior were investigated.The results showed that serious Cu segregation was found in the wheel specimen;the microstructure of the Al-Cu wheel was comprised of the casting microstructure and a small amount of the deformed microstructure;the best heat treatment and water quenching system were found to solution treated at(530±5)℃ for 4 h followed by(535±5)℃ for 24 h and aging treated at(155±5)℃ for 4 h;the fracture morphologies of the samples heated under T 6 and T 5-1 heat treatment showed flat,tough nest,and poor plastic characteristics;the fracture morphologies of the samples heated under T 4 heat treatment exhibited complete resilience,but no residual metallographic characteristic;the sample treated under T 4 protocol had the best elongation;the fracture failure was mainly due to the formation of the CuAl_(2)(θ)phases;and the fracture mechanism of the Al-Cu wheel was intergranular fracture.
基金Project(2006AA03Z523) supported by the National High-tech Research and Development Program of China
文摘The mechanical properties and stress corrosion cracking （SCC） resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstrueture and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment （RRA）, the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy （TEM） results show that the precipitates η（MgZn2） at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η＇（MgZn2）and η（MgZn2） phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120℃, 24h ＋ 180 ℃, 30 min ＋ 120 ℃, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition.
