The AlSi7Mg alloy was fabricated by selective laser melting(SLM),and its microstructure and properties at different building directions after heat treatment were analyzed.Results show that the microstructure of SLM Al...The AlSi7Mg alloy was fabricated by selective laser melting(SLM),and its microstructure and properties at different building directions after heat treatment were analyzed.Results show that the microstructure of SLM AlSi7Mg samples containes three zones:fine grain zone,coarse grain zone,and heat affected zone.The fine-grain regions locate inside the molten pool,and the grains are equiaxed.The coarse-grain regions locate in the overlap of molten pools.After T6 treatment,the microstructure at the molten pool boundary is still the network eutectic Si,but the network structure becomes discrete,and is composed of intermittent,chain-like eutectic Si particles.The yield strength at three directions(xy,45°,z direction)of the AlSi7Mg alloy samples fabricated by SLM is improved after T6 heat treatment.The fracture mechanism of the samples is a mixed ductile and brittle fracture before heat treatment and ductile fracture after heat treatment.展开更多
The effect of different pouring heights and evenly soaking process in the liquidus and solidus range on the solidified microstructure of AlSi7Mg alloy has been studied. The results show that if the pouring temperature...The effect of different pouring heights and evenly soaking process in the liquidus and solidus range on the solidified microstructure of AlSi7Mg alloy has been studied. The results show that if the pouring temperature is 630 or 650℃ and the pouring height is 40 mm, the microstructure of the solidified melt is not homogeneous and there are many rosette-like primary α-Al grains. But if the pouring height is increased to 400 mm, the solidified microstructure becomes more homogeneous and favorable to obtain spherical primary α-Al grains in the solidified melt. With further being evenly soaked in the liquidus and solidus range for some time, the temperature difference between the melt center and the melt periphery can be controlled within ±2℃ and the primary α-Al grains will evolve into more spherical grains. The theoretical analysis indicates that the higher pouring height promotes the melt flow motion and makes the temperature field in the melt more homogeneous and restrains the large rosette primary α-Al grains. This flow motion can also promote the ripening effect and the primary α-Al grains in the melt are gradually changed into spherical grains. It can be concluded from the experiments that pouring at an appropriate superheat and from a proper height is a good new method for preparing the semisolid slurry of AlSi7Mg alloy, its process control is easy and the preparation cost is lower.展开更多
Semi-solid ingots of an A1SiTMg alloy were obtained using the method of near liquidus casting. Their microstructures exhibit the characteristics of free, equiaxed, and non-dendrite, which are required for semi-solid f...Semi-solid ingots of an A1SiTMg alloy were obtained using the method of near liquidus casting. Their microstructures exhibit the characteristics of free, equiaxed, and non-dendrite, which are required for semi-solid forming. The influences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is freer than that with graphite mould.展开更多
The effect of different pouring temperatures and different pouring heights, the distance between the mouth of the pouring ladle and the top of the mold, on the microstructure of AlSi7Mg alloy have been researched in t...The effect of different pouring temperatures and different pouring heights, the distance between the mouth of the pouring ladle and the top of the mold, on the microstructure of AlSi7Mg alloy have been researched in the paper. When the pouring temperature is close to the liquidus temperature, the primary alpha -Al in 'the billets of AlSi7Mg alloy solidified into spherical and nodular fine grains distributed homogeneously. The optimum pouring temperature for semi-solid AlSi7Mg billet with spherical or nodular primary alpha -Al is 615 degreesC. At the same pouring temperature, the higher the pouring ladle, the more easily the spherical and nodular primary alpha -Al obtained in the semi-solid AlSi7Mg billet. When the pouring temperature is close to the liquidus temperature and the pouring ladle is relatively high, it is the great cooling rate, the flow of the molten allay caused by pouring and the large simultaneous solidification region induced by the near liquidus temperature, that promote the formation of spherical or nodular primary cr-Al.展开更多
Many studies have investigated the selective laser melting(SLM)of AlSi10Mg and AlSi7Mg alloys,but there are still lack of researches focused on Al-Si-Mg alloys specifically tailored for SLM.In this work,a novel high M...Many studies have investigated the selective laser melting(SLM)of AlSi10Mg and AlSi7Mg alloys,but there are still lack of researches focused on Al-Si-Mg alloys specifically tailored for SLM.In this work,a novel high Mg-content AlSi8Mg3 alloy was specifically designed for SLM.The results showed that this new alloy exhibited excellent SLM processability with a lowest porosity of 0.07%.Massive lattice distortion led to a high Vickers hardness in samples fabricated at a high laser power due to the precipitation of Mg_(2)Si nanoparticles from theα-Al matrix induced by high-intensity intrinsic heat treatment during SLM.The maximum microhardness and compressive yield strength of the alloy reached HV(211±4)and(526±12)MPa,respectively.After aging treatment at 150℃,the maximum microhardness and compressive yield strength of the samples were further improved to HV(221±4)and(577±5)MPa,respectively.These values are higher than those of most known aluminum alloys fabricated by SLM.This paper provides a new idea for optimizing the mechanical properties of Al-Si-Mg alloys fabricated using SLM.展开更多
The semisolid AlSi7Mg alloy slurry with large capacity was prepared by low superheat pouring and week traveling-wave electromagnetic stirring. The effects of electromagnetic stirring power and frequency on the shape a...The semisolid AlSi7Mg alloy slurry with large capacity was prepared by low superheat pouring and week traveling-wave electromagnetic stirring. The effects of electromagnetic stirring power and frequency on the shape and distribution of primary α-A1 grains in the AlSi7Mg alloy slurry were discussed. The experimental results show that the AlSi7Mg alloy slurry with fine and spherical primary α-A1 grains distributed homogeneously can be obtained. Under the condition of low superheat pouring and week traveling-wave electromagnetic stirring, when the pouring temperature is 630℃, raising the stirring power or frequency appropriately can gain a better shape of primary α-Al grains; but if the stirring power or frequency is increased to a certain value (1.72 kW or10 Hz), the shape of primary α-A1 grains cannot be obviously improved and spherical primary α-Al grains distributed homogeneously can be still obtained.展开更多
The effects of pouring temperature and short electromagnetic stirring with low strength on the microstructures of AlSi7Mg alloy were investigated. The results show that if liquid AlSi7Mg alloy is poured at 630 or 650...The effects of pouring temperature and short electromagnetic stirring with low strength on the microstructures of AlSi7Mg alloy were investigated. The results show that if liquid AlSi7Mg alloy is poured at 630 or 650℃, many primary α-Al grains in the solidified melt are rosette-like, and only a small number of them are spherical. However, if liquid AlSi7Mg alloy is poured at a lower superheat and meanwhile is stirred by an electromagnetic field at a low power for a short time, then most primary α-Al grains in the solidified melt become spherical, and only a few are rosette-like. The theoretical analysis indicates that the strengthened melt flow motion induced by the short electromagnetic stirring makes the temperature field more homogeneous in the melt, which is poured at a lower superheat, and makes the primary α-Al grains deposit in a larger region at the same time, so this new solidification kinetic condition leads to the microstructure of spherical primary α-Al grains. The experiments also demonstrate that pouring at an appropriate superheat and stirring by an electromagnetic field at a low power for a short time is a good new method for preparing the semi-solid slurry or billet of AlSi7Mg alloy.展开更多
To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi- solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill (DC...To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi- solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill (DC) casting is simpler and more effective. In this study, the billets of AISi7Mg alloy were prepared by low- superheat DC casting at various withdrawal rates. The effect of withdrawal rate on the surface quality of the billets was investigated, and the evolution mechanism of the microstructural morphology in the billets was analyzed. The results show that the periodic corrugations and a large quantity of fine shrinkage pits appear in the billet surface when the withdrawal rate is 100 mm.min-1, and the above defects in the billet surface can be eliminated completely when the withdrawal rate is above 150 mm.min-1. But when the withdrawal rate is too fast (250 mm.min-1), the primary a grains, except the ones in the billet center, have not enough time for ripening due to the high silidification rate, and will solidify as the dendrite structure. When the withdrawal rate is between 150 - 200 mm.min-1, the dendritic growth of the primary a grains is effectively inhibited, and a billet of AISi7Mg alloy with a smooth surface and homogeneous, fine, non-dendritic grains can be obtained.展开更多
Electro-pulse modification(EPM) was used to change the dendritic structure of AlSi7Mg alloy to globular one.The effects of the modified temperature,electro-pulse frequency and time on the solidified structure were exa...Electro-pulse modification(EPM) was used to change the dendritic structure of AlSi7Mg alloy to globular one.The effects of the modified temperature,electro-pulse frequency and time on the solidified structure were examined.The results show that these parameters play an important role in the solidified microstructures.That is to say,under the same modified temperature,the solidified microstructure will be improved greatly with the increase of electro-pulse frequency and time,but when they exceed to limit values,the solidified microstructure will become worse,resulting from the decrease of the ratio of nucleation.The experimental results indicate that the suitable modified temperature of AlSi7Mg alloy is 720 °C,and the appropriate electro-pulse frequency and time are 5 Hz and 40 s,respectively.Then the microstructures produced by suitable EPM process were reheated at temperatures between liquidus and solidus,the primary-Al grains ripen further and become more spherical,which is favorable to the semi-solid forming of AlSi7Mg alloy.展开更多
Slurry processing experiments were performed with AlSi7Mg0.6 to identify the globularization mechanisms.The melt sample water quenched slightly above the liquidus point is predominantly dendritic while that cooled int...Slurry processing experiments were performed with AlSi7Mg0.6 to identify the globularization mechanisms.The melt sample water quenched slightly above the liquidus point is predominantly dendritic while that cooled into the semi-solid temperature range internally via stirring the melt with a rotating cylindrical block of the alloy itself becomes fully globular.The globules are much smaller when internal cooling and stirring are employed longer to achieve higher solid fractions before casting.Coarse dendrite fragments of various sizes are revealed,in the case of stirring after an initial fraction of solid is first formed without the benefit of additional internal cooling.展开更多
Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500℃ and strain rates between 0.05 and 5 s^(-1) to explore the progressive dynamic recrystallization(DRX)and texture behavio...Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500℃ and strain rates between 0.05 and 5 s^(-1) to explore the progressive dynamic recrystallization(DRX)and texture behaviors.The DRX behavior of the alloy manifested two distinct stages:Stage 1 at strain of≤2 and Stage 2 at strains of≥2.In Stage 1,there was a slight increase in the DRXed grain fraction(X_(DRX))with predominance of discontinuous DRX(DDRX),followed by a modest change in X_(DRX) until the transition to Stage 2.Stage 2 was marked by an accelerated rate of DRX,culminating in a substantial final X_(DRX) of~0.9.Electron backscattered diffraction(EBSD)analysis on a sample in Stage 2 revealed that continuous DRX(CDRX)predominantly occurred within the(121)[001]grains,whereas the(111)[110]grains underwent a geometric DRX(GDRX)evolution without a noticeable sub-grain structure.Furthermore,a modified Avrami’s DRX kinetics model was utilized to predict the microstructural refinement in the Al-7Mg alloy during the DRX evolution.Although this kinetics model did not accurately capture the DDRX behavior in Stage 1,it effectively simulated the DRX rate in Stage 2.The texture index was employed to assess the evolution of the texture isotropy during hot-torsion test,demonstrating significant improvement(>75%)in texture randomness before the commencement of Stage 2.This initial texture evolution is attributed to the rotation of parent grains and the substructure evolution,rather than to an increase in X_(DRX).展开更多
The microstructures and corrosion behavior of AlSi5 CulMg alloy modified with different contents of La were investigated.Optical microscopy observations showed that the microstructures of AlSi5 Cu1 Mg-xLa(x = 0, 0.3, ...The microstructures and corrosion behavior of AlSi5 CulMg alloy modified with different contents of La were investigated.Optical microscopy observations showed that the microstructures of AlSi5 Cu1 Mg-xLa(x = 0, 0.3, 0.6, and 0.9 wt%) alloy transformed from coarse cellular to fine cellular as the content of La increased from 0 to 0.9 wt%. The results of electrochemical measurement and immersion test in 3.5 wt% NaCl solution showed that the corrosion resistance of AlSi5 CulMg-xLa alloy strongly depended on its microstructures. The AlSi5 Cu1 Mg-0.6 La sample exhibited the highest corrosion resistance due to its fine cellular structure and the cathode phases coated by the La element. The covering film of La hindered the corrosion electron flowing between the cathode and the anode. As a result, the corrosion current density of the AlSi5 CulMg-0.6 La alloy was only about 40% that of the matrix alloy in the electrochemical measurement.展开更多
Numerous studies have addressed the advantages of wire arc additive manufacturing for manufacturing aluminum alloys. However, the role of Ti content in aluminum alloys has rarely been discussed. Herein, the effect of ...Numerous studies have addressed the advantages of wire arc additive manufacturing for manufacturing aluminum alloys. However, the role of Ti content in aluminum alloys has rarely been discussed. Herein, the effect of Ti content on the microstructure and properties of Al–7 Si–0.6 Mg alloys was studied. The alloys were deposited via wire arc additive manufacturing and were examined through optical microscopy(OM), scanning electron microscopy(SEM), and electronic universal testing. The results show that the increase of Ti content gradually promotes the increase of the secondary dendrite arm spacing and also has an increasing tendency to form pores defect in the as-deposited alloys. The change of titanium content also affects the difference between horizontal and vertical direction properties of the alloy. The alloy with a Ti content of 0.112 wt% exhibits the best comprehensive properties. There is no difference in its horizontal and vertical direction properties. The tensile strengths, yield strengths, and elongation of this alloy(T6) along the vertical and horizontal axis are 356 and 355 MPa, 307 and308 MPa, and 8.5% and 8.0%, respectively.展开更多
Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning el...Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning electron micro- scopy (SEM).By utilizing a Sieverts apparatus,the hydrogenation and dehydrogenation properties of Mg85Zn5Ni10 powders were measured systematically.XRD and SEM results indicated that the Mg85Zn5Ni10 alloy powders contained the major phase Mg,the eutectic Mg-Mg2Ni and Mg-MgZn2 mixtures.The possible reaction pathway can be inferred as follows:Mg +Mg2Ni +MgZn2 +H2←→MgH2+Mg2NiH4 +MgZn2,indicating that MgZn2 did not react with H2. After activation,the Mg85Zn5Ni10 alloy powders could absorb 5.4 wt.% hydrogen reversibly and held an excellent hydrogenation kinetics at a relatively low temperature.At 360 ℃,the alloy powders desorbed 5.351 wt.% hydrogen in 264 s.However,it only had fast dehydrogenation kinetics above 300 ℃.The existence of MgZn2 contributed to improving the kinetic properties.During the hydriding and dehydriding,the formed cracks and defects promoted the kinetics and thermodynamic properties.The activation energy for dehydrogenation was 75.514 kJ/mol.The enthalpy change values of hydrogenation and dehydrogenation were calculated to be -73.064 kJ/mol and 76.674 kJ/mol,respectively,indicating that melting with Ni and Zn could improve the thermodynamic property of Mg slightly.展开更多
The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poure...The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AISi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.展开更多
基金the fund of Beijing Municipal Science and Technology Commission(Z181100003318001)。
文摘The AlSi7Mg alloy was fabricated by selective laser melting(SLM),and its microstructure and properties at different building directions after heat treatment were analyzed.Results show that the microstructure of SLM AlSi7Mg samples containes three zones:fine grain zone,coarse grain zone,and heat affected zone.The fine-grain regions locate inside the molten pool,and the grains are equiaxed.The coarse-grain regions locate in the overlap of molten pools.After T6 treatment,the microstructure at the molten pool boundary is still the network eutectic Si,but the network structure becomes discrete,and is composed of intermittent,chain-like eutectic Si particles.The yield strength at three directions(xy,45°,z direction)of the AlSi7Mg alloy samples fabricated by SLM is improved after T6 heat treatment.The fracture mechanism of the samples is a mixed ductile and brittle fracture before heat treatment and ductile fracture after heat treatment.
基金This work was financially supported by the National High-Tech Research and Development Program of China (No.G2002AA336080) and the National Natural Science Foundation of China (No.50374012).
文摘The effect of different pouring heights and evenly soaking process in the liquidus and solidus range on the solidified microstructure of AlSi7Mg alloy has been studied. The results show that if the pouring temperature is 630 or 650℃ and the pouring height is 40 mm, the microstructure of the solidified melt is not homogeneous and there are many rosette-like primary α-Al grains. But if the pouring height is increased to 400 mm, the solidified microstructure becomes more homogeneous and favorable to obtain spherical primary α-Al grains in the solidified melt. With further being evenly soaked in the liquidus and solidus range for some time, the temperature difference between the melt center and the melt periphery can be controlled within ±2℃ and the primary α-Al grains will evolve into more spherical grains. The theoretical analysis indicates that the higher pouring height promotes the melt flow motion and makes the temperature field in the melt more homogeneous and restrains the large rosette primary α-Al grains. This flow motion can also promote the ripening effect and the primary α-Al grains in the melt are gradually changed into spherical grains. It can be concluded from the experiments that pouring at an appropriate superheat and from a proper height is a good new method for preparing the semisolid slurry of AlSi7Mg alloy, its process control is easy and the preparation cost is lower.
基金the National Natural Science Foundation of China (No. 50374031)the Aviation Science Foundation of Liaoning Province (No. 20054003)+1 种基金the Education Committee of Liaoning Province (No. 05L415)the Research Foundation of the Experimental Center of SYNU.]
文摘Semi-solid ingots of an A1SiTMg alloy were obtained using the method of near liquidus casting. Their microstructures exhibit the characteristics of free, equiaxed, and non-dendrite, which are required for semi-solid forming. The influences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is freer than that with graphite mould.
基金The authors would like to thank the National 863 Plan of China for financial support under Grant No 715-012-0040.
文摘The effect of different pouring temperatures and different pouring heights, the distance between the mouth of the pouring ladle and the top of the mold, on the microstructure of AlSi7Mg alloy have been researched in the paper. When the pouring temperature is close to the liquidus temperature, the primary alpha -Al in 'the billets of AlSi7Mg alloy solidified into spherical and nodular fine grains distributed homogeneously. The optimum pouring temperature for semi-solid AlSi7Mg billet with spherical or nodular primary alpha -Al is 615 degreesC. At the same pouring temperature, the higher the pouring ladle, the more easily the spherical and nodular primary alpha -Al obtained in the semi-solid AlSi7Mg billet. When the pouring temperature is close to the liquidus temperature and the pouring ladle is relatively high, it is the great cooling rate, the flow of the molten allay caused by pouring and the large simultaneous solidification region induced by the near liquidus temperature, that promote the formation of spherical or nodular primary cr-Al.
基金financially supported by the the National Natural Science Foundation of China(Nos.51801079 and 52001140)the Natural Science Foundation for Young Scientists of Jiangsu,China(Nos.BK20180985 and BK20180987)the Open Foundation of Zhenjiang Key Laboratory for High Technology Research on Marine Functional Films(No.ZHZ2019001)。
文摘Many studies have investigated the selective laser melting(SLM)of AlSi10Mg and AlSi7Mg alloys,but there are still lack of researches focused on Al-Si-Mg alloys specifically tailored for SLM.In this work,a novel high Mg-content AlSi8Mg3 alloy was specifically designed for SLM.The results showed that this new alloy exhibited excellent SLM processability with a lowest porosity of 0.07%.Massive lattice distortion led to a high Vickers hardness in samples fabricated at a high laser power due to the precipitation of Mg_(2)Si nanoparticles from theα-Al matrix induced by high-intensity intrinsic heat treatment during SLM.The maximum microhardness and compressive yield strength of the alloy reached HV(211±4)and(526±12)MPa,respectively.After aging treatment at 150℃,the maximum microhardness and compressive yield strength of the samples were further improved to HV(221±4)and(577±5)MPa,respectively.These values are higher than those of most known aluminum alloys fabricated by SLM.This paper provides a new idea for optimizing the mechanical properties of Al-Si-Mg alloys fabricated using SLM.
基金supported by the National High-Tech Research and Development Program of China (No.2006AA03Z115)the National Basic Research Priorities Program of China (No.2006CB605203)the National Natural Science Foundation of China (No.50374012)
文摘The semisolid AlSi7Mg alloy slurry with large capacity was prepared by low superheat pouring and week traveling-wave electromagnetic stirring. The effects of electromagnetic stirring power and frequency on the shape and distribution of primary α-A1 grains in the AlSi7Mg alloy slurry were discussed. The experimental results show that the AlSi7Mg alloy slurry with fine and spherical primary α-A1 grains distributed homogeneously can be obtained. Under the condition of low superheat pouring and week traveling-wave electromagnetic stirring, when the pouring temperature is 630℃, raising the stirring power or frequency appropriately can gain a better shape of primary α-Al grains; but if the stirring power or frequency is increased to a certain value (1.72 kW or10 Hz), the shape of primary α-A1 grains cannot be obviously improved and spherical primary α-Al grains distributed homogeneously can be still obtained.
基金This work was financially supported by the National Nature Science Foundation of China (No. 50374012), the National High-Tech Research and Development Program of China (863 Program) (No. 2006AA03Z115), and the National key Basic Research Foundation of China (No.2006CB605203).
文摘The effects of pouring temperature and short electromagnetic stirring with low strength on the microstructures of AlSi7Mg alloy were investigated. The results show that if liquid AlSi7Mg alloy is poured at 630 or 650℃, many primary α-Al grains in the solidified melt are rosette-like, and only a small number of them are spherical. However, if liquid AlSi7Mg alloy is poured at a lower superheat and meanwhile is stirred by an electromagnetic field at a low power for a short time, then most primary α-Al grains in the solidified melt become spherical, and only a few are rosette-like. The theoretical analysis indicates that the strengthened melt flow motion induced by the short electromagnetic stirring makes the temperature field more homogeneous in the melt, which is poured at a lower superheat, and makes the primary α-Al grains deposit in a larger region at the same time, so this new solidification kinetic condition leads to the microstructure of spherical primary α-Al grains. The experiments also demonstrate that pouring at an appropriate superheat and stirring by an electromagnetic field at a low power for a short time is a good new method for preparing the semi-solid slurry or billet of AlSi7Mg alloy.
基金supported by the Postdoctoral Foundation of Northeastern University and the National High Technology Research and Development Program of China(Grant No.2009BAE80B01)
文摘To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi- solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill (DC) casting is simpler and more effective. In this study, the billets of AISi7Mg alloy were prepared by low- superheat DC casting at various withdrawal rates. The effect of withdrawal rate on the surface quality of the billets was investigated, and the evolution mechanism of the microstructural morphology in the billets was analyzed. The results show that the periodic corrugations and a large quantity of fine shrinkage pits appear in the billet surface when the withdrawal rate is 100 mm.min-1, and the above defects in the billet surface can be eliminated completely when the withdrawal rate is above 150 mm.min-1. But when the withdrawal rate is too fast (250 mm.min-1), the primary a grains, except the ones in the billet center, have not enough time for ripening due to the high silidification rate, and will solidify as the dendrite structure. When the withdrawal rate is between 150 - 200 mm.min-1, the dendritic growth of the primary a grains is effectively inhibited, and a billet of AISi7Mg alloy with a smooth surface and homogeneous, fine, non-dendritic grains can be obtained.
基金Project(07KJD460007) supported by the Educational Science Foundation of Jiangsu Province,China
文摘Electro-pulse modification(EPM) was used to change the dendritic structure of AlSi7Mg alloy to globular one.The effects of the modified temperature,electro-pulse frequency and time on the solidified structure were examined.The results show that these parameters play an important role in the solidified microstructures.That is to say,under the same modified temperature,the solidified microstructure will be improved greatly with the increase of electro-pulse frequency and time,but when they exceed to limit values,the solidified microstructure will become worse,resulting from the decrease of the ratio of nucleation.The experimental results indicate that the suitable modified temperature of AlSi7Mg alloy is 720 °C,and the appropriate electro-pulse frequency and time are 5 Hz and 40 s,respectively.Then the microstructures produced by suitable EPM process were reheated at temperatures between liquidus and solidus,the primary-Al grains ripen further and become more spherical,which is favorable to the semi-solid forming of AlSi7Mg alloy.
基金the State Planning Organization of Turkey for the financial support
文摘Slurry processing experiments were performed with AlSi7Mg0.6 to identify the globularization mechanisms.The melt sample water quenched slightly above the liquidus point is predominantly dendritic while that cooled into the semi-solid temperature range internally via stirring the melt with a rotating cylindrical block of the alloy itself becomes fully globular.The globules are much smaller when internal cooling and stirring are employed longer to achieve higher solid fractions before casting.Coarse dendrite fragments of various sizes are revealed,in the case of stirring after an initial fraction of solid is first formed without the benefit of additional internal cooling.
基金partly supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1C1C1005726)Technology development Program (No. RS-2023-00220823) funded by the Ministry of SMEs and Startups (MSS, Korea)+1 种基金the Electronics Technology Development Project (No. 20026289) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea)partly supported by the research grant of the Kongju National University in 2022
文摘Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500℃ and strain rates between 0.05 and 5 s^(-1) to explore the progressive dynamic recrystallization(DRX)and texture behaviors.The DRX behavior of the alloy manifested two distinct stages:Stage 1 at strain of≤2 and Stage 2 at strains of≥2.In Stage 1,there was a slight increase in the DRXed grain fraction(X_(DRX))with predominance of discontinuous DRX(DDRX),followed by a modest change in X_(DRX) until the transition to Stage 2.Stage 2 was marked by an accelerated rate of DRX,culminating in a substantial final X_(DRX) of~0.9.Electron backscattered diffraction(EBSD)analysis on a sample in Stage 2 revealed that continuous DRX(CDRX)predominantly occurred within the(121)[001]grains,whereas the(111)[110]grains underwent a geometric DRX(GDRX)evolution without a noticeable sub-grain structure.Furthermore,a modified Avrami’s DRX kinetics model was utilized to predict the microstructural refinement in the Al-7Mg alloy during the DRX evolution.Although this kinetics model did not accurately capture the DDRX behavior in Stage 1,it effectively simulated the DRX rate in Stage 2.The texture index was employed to assess the evolution of the texture isotropy during hot-torsion test,demonstrating significant improvement(>75%)in texture randomness before the commencement of Stage 2.This initial texture evolution is attributed to the rotation of parent grains and the substructure evolution,rather than to an increase in X_(DRX).
基金supported financially by the National Natural Science Foundation of China (No. 51364035)the Natural Science Foundation of Jiangxi Province (No. 20171BAB206034)
文摘The microstructures and corrosion behavior of AlSi5 CulMg alloy modified with different contents of La were investigated.Optical microscopy observations showed that the microstructures of AlSi5 Cu1 Mg-xLa(x = 0, 0.3, 0.6, and 0.9 wt%) alloy transformed from coarse cellular to fine cellular as the content of La increased from 0 to 0.9 wt%. The results of electrochemical measurement and immersion test in 3.5 wt% NaCl solution showed that the corrosion resistance of AlSi5 CulMg-xLa alloy strongly depended on its microstructures. The AlSi5 Cu1 Mg-0.6 La sample exhibited the highest corrosion resistance due to its fine cellular structure and the cathode phases coated by the La element. The covering film of La hindered the corrosion electron flowing between the cathode and the anode. As a result, the corrosion current density of the AlSi5 CulMg-0.6 La alloy was only about 40% that of the matrix alloy in the electrochemical measurement.
基金financially supported by the National Key R&D Program of China(No.2018YFB1106300-5)。
文摘Numerous studies have addressed the advantages of wire arc additive manufacturing for manufacturing aluminum alloys. However, the role of Ti content in aluminum alloys has rarely been discussed. Herein, the effect of Ti content on the microstructure and properties of Al–7 Si–0.6 Mg alloys was studied. The alloys were deposited via wire arc additive manufacturing and were examined through optical microscopy(OM), scanning electron microscopy(SEM), and electronic universal testing. The results show that the increase of Ti content gradually promotes the increase of the secondary dendrite arm spacing and also has an increasing tendency to form pores defect in the as-deposited alloys. The change of titanium content also affects the difference between horizontal and vertical direction properties of the alloy. The alloy with a Ti content of 0.112 wt% exhibits the best comprehensive properties. There is no difference in its horizontal and vertical direction properties. The tensile strengths, yield strengths, and elongation of this alloy(T6) along the vertical and horizontal axis are 356 and 355 MPa, 307 and308 MPa, and 8.5% and 8.0%, respectively.
基金National Natural Science Foundations of China (51761032,51471054 and 51871125).
文摘Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning electron micro- scopy (SEM).By utilizing a Sieverts apparatus,the hydrogenation and dehydrogenation properties of Mg85Zn5Ni10 powders were measured systematically.XRD and SEM results indicated that the Mg85Zn5Ni10 alloy powders contained the major phase Mg,the eutectic Mg-Mg2Ni and Mg-MgZn2 mixtures.The possible reaction pathway can be inferred as follows:Mg +Mg2Ni +MgZn2 +H2←→MgH2+Mg2NiH4 +MgZn2,indicating that MgZn2 did not react with H2. After activation,the Mg85Zn5Ni10 alloy powders could absorb 5.4 wt.% hydrogen reversibly and held an excellent hydrogenation kinetics at a relatively low temperature.At 360 ℃,the alloy powders desorbed 5.351 wt.% hydrogen in 264 s.However,it only had fast dehydrogenation kinetics above 300 ℃.The existence of MgZn2 contributed to improving the kinetic properties.During the hydriding and dehydriding,the formed cracks and defects promoted the kinetics and thermodynamic properties.The activation energy for dehydrogenation was 75.514 kJ/mol.The enthalpy change values of hydrogenation and dehydrogenation were calculated to be -73.064 kJ/mol and 76.674 kJ/mol,respectively,indicating that melting with Ni and Zn could improve the thermodynamic property of Mg slightly.
基金The work was supported by the National Hitech Research Foundation of China under grant No. G2002AA336080 by the National Natural Science Foundation of China under grant No. 50374012.
文摘The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AISi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.