Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study...Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study, the CDS was employed to prepare hypereutectic Al-20%Si(mass fraction) alloy using Al-30%Si and pure Al of different temperatures. The mixing rate was controlled using three small crucibles with a hole of different diameters in their bottom. The effect of mixing rate and temperature on the microstructure of the primary Si-phase during the mixing of molten Al and Al-30%Si was studied. The results showed that when the diameter of the small crucible bottom hole is 16 mm, a higher mass mixing rate 0.217 kg·s-1 would results in a lower stream velocity 0.414 m·s-1. Conversely a lower mass mixing rate 0.114 kg·s-1(the diameter of the small crucible bottom hole is 8 mm) would result in a higher fluid stream velocity 0.879 m·s-1. A lower mass mixing rate would be better to refine the primary Si than a higher mass mixing rate. Meanwhile, the morphology and distribution of primary Si could also be improved. Especially, when Al-30%Si alloy at 820 °C was mixed with pure Al at 670 °C in the case of a mass mixing rate of 0.114 kg·s-1 and a pouring temperature of 680 °C, the average size of the primary Si phase would be only 18.2 μm. Its morphology would mostly be octahedral and the primary Si would distribute uniformly in the matrix microstructure. The lower mass mixing rate(0.114 kg·s-1) will enhance the broken tendency of Al-30%Si steam and the mixing agitation of resultant melt, so the primary Si phase can be better refined.展开更多
Al-Si pistons are frequently damaged by burning piston top surface due to elevated combustion temperature, and by rubbing the first ring groove against the engine cylinder liner. To prevent piston from these damages, ...Al-Si pistons are frequently damaged by burning piston top surface due to elevated combustion temperature, and by rubbing the first ring groove against the engine cylinder liner. To prevent piston from these damages, some technologies were invented, such as mounting high Ni cast iron ring around the first ring groove in Al alloy piston body and thermal resistant steel on piston top surface, and fabricating Al composite pistons by squeeze casting for enhancing the whole or local piston performance. In this paper, composite pistons locally reinforced with in situ primary Si and primary Mg2Si particles are fabricated by centrifugal casting. The microstructure characteristics, hardness and wear resistance of the composite piston are investigated and the motion characteristic of the in situ particles in centrifugal field is analyzed. The results of the experiments show that primary Si and Mg2Si particles mix up with each other in melt and segregate at the regions of piston top and piston ring grooves under the effect of centrifugal force. Particulate reinforced regions have a higher hardness and better wear resistance compared with the unreinforced regions and this performance increases after heat treatment. The analysis result of particle movement shows that, primary Si and primary Mg2Si particles move at approximately the same velocity in the centrifugal field, because of the growth of primary Si and fusion after colliding between primary Si particles, which compromised the velocity difference of primary Si and primary Mg2Si particles caused by the difference of their densities. Research results have some theory significance and applicative value of project in development of new aluminum matrix composites piston products.展开更多
The structure and mechanical properties of a new type of Al-based discontinuous gradient composites prepared by using the ternary AI-19Si-5Mg alloys as the raw material adopting the centrifugal casting method were inv...The structure and mechanical properties of a new type of Al-based discontinuous gradient composites prepared by using the ternary AI-19Si-5Mg alloys as the raw material adopting the centrifugal casting method were investigated. Structurally, the composites are divided into two zones: a reinforced zone with the high volume fraction of primary Si and Mg2Si particles and an unreinforced zone with no or a few particles. In the reinforced zone, the primary particles are evenly distributed, with the sizes of the primary Si particles 80-120 μm, and that of primary Mg2Si particles 20-50 μm. The properties test results show the reinforced zone has higher Rockwell hardness and better wear resistance than the unreinforced zone, due to the complementary reinforcement relationship between the primary Si and Mg2Si particles and their high volume fraction.展开更多
In this paper, the serpentine channel pouring process for preparing a semi-solid A390 alloy slurry and refining the primary Si grains of the A390 alloy, was used. The effects of the pouring temperature, the cooling wa...In this paper, the serpentine channel pouring process for preparing a semi-solid A390 alloy slurry and refining the primary Si grains of the A390 alloy, was used. The effects of the pouring temperature, the cooling water flow and the number of the curves on the size of the primary Si grains in the semi-solid A390 alloy slurry were investigated. The results show that the pouring temperature, the cooling water flow and the number of the curves have a major effect on the size and the distribution of primary Si grains. Under the experimental condition of the four-curve copper channel whose cooling water flow was 500 L·h-1 and the pouring temperature was 690 oC, the primary Si grains of the semi-solid A390 alloy slurry were refined to the greatest extent and the lath-like grains were changed into granular ones. Additionally, the equivalent grain diameter and the average shape factor of the primary Si grains of the satisfactory semi-solid A390 alloy slurry are 18.6 μm and 0.8, respectively. Further, the refinement mechanism of the primary Si grains through the serpentine channel pouring process was analyzed and discussed. In summary, the primary Si nuclei could be easily precipitated due to the chilling effect of the channel inner wall, thus the primary Si grains were greatly refined. Meanwhile, the subsequent alloy melt fluid also promoted the separation of primary Si grains from the inner wall, further refining the primary Si grains.展开更多
The electromagnetic directional solidification(DS)phase separation experiments of high silicon 90 wt.%Si–Ti alloy were performed under various pulling-down speeds.The results showed that Si enriched layer,Si+TiSi_(2)...The electromagnetic directional solidification(DS)phase separation experiments of high silicon 90 wt.%Si–Ti alloy were performed under various pulling-down speeds.The results showed that Si enriched layer,Si+TiSi_(2)-rich layer and Si–Ti–Fe alloy layer appeared successively in axial direction of ingot after electromagnetic DS of 90 wt.%Si–Ti alloy melt at different pulling-down speeds.Separation of primary Si and segregation mechanism of metal impurities(Fe)during the electromagnetic DS process were controlled by pulling-down speed of ingot and electromagnetic stirring.When pulling-down speed was 5μm/s,minimum thickness of the Si enriched layer was 29.4 mm,and the highest content of primary Si in this layer was 92.46 wt.%;meanwhile,the highest removal rate of Fe as metal impurity was 92.90%.The type of inclusions in the Si enriched layer is determined by Fe content of segregated Si enriched layer.When the pulling-down speed was 5μm/s,the inclusions in the Si enriched layer were TiSi_(2).Finally,when the pulling-down speed reached greater than 5μm/s,the inclusions in the Si enriched layer evolved into TiSi_(2)+τ_(5).展开更多
AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the m...AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the morphologies of AlP crystals were studied comprehensively by experimental observation and theorical prediction.It is found that AlP collected from an Al-0.03 P melt could be divided into two categories:spinel twin crystals and non-twin crystals.During the nucleation process,these two kinds of AlP crystals triggered morphologically templated nucleation of primary Si phase,resulting in the formation of hexagonal primary Si twin and octahedral non-twin crystals,respectively.As such,the percentage of primary Si twin crystals in the experimental Al-18 Si alloy was also increased obviously after the morphologically templated nucleation via Al P.The morphologically templated nucleation also eliminated the dendritic growth of primary Si phase and the formation of hopper structures inside primary Si,forcing primary Si to maintain to be faceted solid crystals through layer-by-layer growing mechanism.The insight into morphologically templated nucleation offers a new view in understanding the mechanism of heterogeneous nucleation of primary Si phase on AlP nuclei.展开更多
A pulse magnetic field(PMF)was applied on the hypereutectic A1-23%Si alloy of different temperature range(830-780 ℃,830-730 ℃,830-700 ℃,780-700 ℃,730-700 ℃)during its solidification processing.The influence of pu...A pulse magnetic field(PMF)was applied on the hypereutectic A1-23%Si alloy of different temperature range(830-780 ℃,830-730 ℃,830-700 ℃,780-700 ℃,730-700 ℃)during its solidification processing.The influence of pulse magnetic field on the size and distribution of primary Si was studied.The results show that,the primary Si is very coarse strip,distributs non-unifromly and gathers at the edge of the sample when the alloy solidifies under the condition of no PMF.By applying PMF can significantly refine the primary Si,and make the primary Si distribute uniformly.There has no significant effect on the refinement of primary Si when PMF applied from 830 ℃ to 780 ℃,indicating that PMF has no outstanding effect on the high temperature liquid metal.Applying PMF from 50 ℃ above the liquidus to 30 ℃ below the liquidus(i.e.from liquid to the initial nucleation stage)can get the best refinement result.The refining mechanism of the pulse magnetic field on the solidification structure of Ai-23%Si alloy was discussed,展开更多
An Al-Si-P master alloy has been developed by an in-situ reaction and the electron probe microanalyzer (EPMA) results show that there are many pre-formed AlP particles contained in the master alloy. Silicon introduc...An Al-Si-P master alloy has been developed by an in-situ reaction and the electron probe microanalyzer (EPMA) results show that there are many pre-formed AlP particles contained in the master alloy. Silicon introduced into the system plays an important role in remarkably improving the distribution and content of AlP particles due to their similar crystal structure and lattice parameters. ZL109 alloys have shown fast modification response to the addition of 0.5% Al-15Si-3.5P master alloy at 720℃, with a mass of primary Si precipitating in size of about 15 μm. Also, coarse primary Si grains in AI-30Si alloy can be refined dramatically from 150 μm to 37 μm after the addition of 2.0% Al-15Si-3.5P master alloy at 850℃. The P recovery of the Al-15Si-3.5P master alloy is much higher than that of a Cu-8.5P master alloy due to the pre-formed AlP particles.展开更多
The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xS i alloys(x = 15, 17.5, 22 wt%) was investigated in this study. Results show that microstructure of the hypereutectic A...The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xS i alloys(x = 15, 17.5, 22 wt%) was investigated in this study. Results show that microstructure of the hypereutectic Al-x Si alloys was obviously improved by squeeze casting. The amount of coarse primary Si phase decreased, while that of fine primary α-Al dendrites increased with the increase of squeeze casting pressure. Due to the decrease of coarse primary Si particles, cracking of the matrix was reduced, whilst the fine microstructure, and mechanical properties of the squeeze casting alloys were improved. Compared with gravity casting alloys, mechanical properties of the hypereutectic Al-xS i alloys solidified at 600 MPa were improved significantly. Hardness of the squeeze casting hypereutectic Al-(15, 17.5, 22 wt%) Si alloys was improved by 15.91%, 12.23%, 17.48%, ultimate tensile strength was improved by 37.85%, 32.27%, 22.74%,and elongation was improved by 55.83%, 167.86%, 126.76%, respectively. Due to the uniform distribution of Si phases in squeeze casting Al-x Si alloys, their wear resistance was markedly enhanced.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51064017 and 51464031)
文摘Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study, the CDS was employed to prepare hypereutectic Al-20%Si(mass fraction) alloy using Al-30%Si and pure Al of different temperatures. The mixing rate was controlled using three small crucibles with a hole of different diameters in their bottom. The effect of mixing rate and temperature on the microstructure of the primary Si-phase during the mixing of molten Al and Al-30%Si was studied. The results showed that when the diameter of the small crucible bottom hole is 16 mm, a higher mass mixing rate 0.217 kg·s-1 would results in a lower stream velocity 0.414 m·s-1. Conversely a lower mass mixing rate 0.114 kg·s-1(the diameter of the small crucible bottom hole is 8 mm) would result in a higher fluid stream velocity 0.879 m·s-1. A lower mass mixing rate would be better to refine the primary Si than a higher mass mixing rate. Meanwhile, the morphology and distribution of primary Si could also be improved. Especially, when Al-30%Si alloy at 820 °C was mixed with pure Al at 670 °C in the case of a mass mixing rate of 0.114 kg·s-1 and a pouring temperature of 680 °C, the average size of the primary Si phase would be only 18.2 μm. Its morphology would mostly be octahedral and the primary Si would distribute uniformly in the matrix microstructure. The lower mass mixing rate(0.114 kg·s-1) will enhance the broken tendency of Al-30%Si steam and the mixing agitation of resultant melt, so the primary Si phase can be better refined.
文摘Al-Si pistons are frequently damaged by burning piston top surface due to elevated combustion temperature, and by rubbing the first ring groove against the engine cylinder liner. To prevent piston from these damages, some technologies were invented, such as mounting high Ni cast iron ring around the first ring groove in Al alloy piston body and thermal resistant steel on piston top surface, and fabricating Al composite pistons by squeeze casting for enhancing the whole or local piston performance. In this paper, composite pistons locally reinforced with in situ primary Si and primary Mg2Si particles are fabricated by centrifugal casting. The microstructure characteristics, hardness and wear resistance of the composite piston are investigated and the motion characteristic of the in situ particles in centrifugal field is analyzed. The results of the experiments show that primary Si and Mg2Si particles mix up with each other in melt and segregate at the regions of piston top and piston ring grooves under the effect of centrifugal force. Particulate reinforced regions have a higher hardness and better wear resistance compared with the unreinforced regions and this performance increases after heat treatment. The analysis result of particle movement shows that, primary Si and primary Mg2Si particles move at approximately the same velocity in the centrifugal field, because of the growth of primary Si and fusion after colliding between primary Si particles, which compromised the velocity difference of primary Si and primary Mg2Si particles caused by the difference of their densities. Research results have some theory significance and applicative value of project in development of new aluminum matrix composites piston products.
基金Funded by the National Natural Science Foundation of China(No.51201140)the Fundamental Research Funds for the Central Universities(No.XDJK2010C007)
文摘The structure and mechanical properties of a new type of Al-based discontinuous gradient composites prepared by using the ternary AI-19Si-5Mg alloys as the raw material adopting the centrifugal casting method were investigated. Structurally, the composites are divided into two zones: a reinforced zone with the high volume fraction of primary Si and Mg2Si particles and an unreinforced zone with no or a few particles. In the reinforced zone, the primary particles are evenly distributed, with the sizes of the primary Si particles 80-120 μm, and that of primary Mg2Si particles 20-50 μm. The properties test results show the reinforced zone has higher Rockwell hardness and better wear resistance than the unreinforced zone, due to the complementary reinforcement relationship between the primary Si and Mg2Si particles and their high volume fraction.
基金supported by the National Basic Research Program of China(2011CB606300)the National Natural Science Foundation of China(5077400)
文摘In this paper, the serpentine channel pouring process for preparing a semi-solid A390 alloy slurry and refining the primary Si grains of the A390 alloy, was used. The effects of the pouring temperature, the cooling water flow and the number of the curves on the size of the primary Si grains in the semi-solid A390 alloy slurry were investigated. The results show that the pouring temperature, the cooling water flow and the number of the curves have a major effect on the size and the distribution of primary Si grains. Under the experimental condition of the four-curve copper channel whose cooling water flow was 500 L·h-1 and the pouring temperature was 690 oC, the primary Si grains of the semi-solid A390 alloy slurry were refined to the greatest extent and the lath-like grains were changed into granular ones. Additionally, the equivalent grain diameter and the average shape factor of the primary Si grains of the satisfactory semi-solid A390 alloy slurry are 18.6 μm and 0.8, respectively. Further, the refinement mechanism of the primary Si grains through the serpentine channel pouring process was analyzed and discussed. In summary, the primary Si nuclei could be easily precipitated due to the chilling effect of the channel inner wall, thus the primary Si grains were greatly refined. Meanwhile, the subsequent alloy melt fluid also promoted the separation of primary Si grains from the inner wall, further refining the primary Si grains.
基金the Sichuan Science and Technology Program(2021YJ0548)Panzhihua Science and Technology Project(2020CY-G-15)+1 种基金Research Project of Panzhihua University(2020ZD002)Project of Sichuan Key Laboratory for comprehensive utilization of vanadium and titanium resources(2019FTSZ06,2020FTSZ01).
文摘The electromagnetic directional solidification(DS)phase separation experiments of high silicon 90 wt.%Si–Ti alloy were performed under various pulling-down speeds.The results showed that Si enriched layer,Si+TiSi_(2)-rich layer and Si–Ti–Fe alloy layer appeared successively in axial direction of ingot after electromagnetic DS of 90 wt.%Si–Ti alloy melt at different pulling-down speeds.Separation of primary Si and segregation mechanism of metal impurities(Fe)during the electromagnetic DS process were controlled by pulling-down speed of ingot and electromagnetic stirring.When pulling-down speed was 5μm/s,minimum thickness of the Si enriched layer was 29.4 mm,and the highest content of primary Si in this layer was 92.46 wt.%;meanwhile,the highest removal rate of Fe as metal impurity was 92.90%.The type of inclusions in the Si enriched layer is determined by Fe content of segregated Si enriched layer.When the pulling-down speed was 5μm/s,the inclusions in the Si enriched layer were TiSi_(2).Finally,when the pulling-down speed reached greater than 5μm/s,the inclusions in the Si enriched layer evolved into TiSi_(2)+τ_(5).
基金Financial supports from Innovate UK(grant number 11019)National Natural Science Foundation of China(grant number 51571133,51731007 and 52071189)。
文摘AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the morphologies of AlP crystals were studied comprehensively by experimental observation and theorical prediction.It is found that AlP collected from an Al-0.03 P melt could be divided into two categories:spinel twin crystals and non-twin crystals.During the nucleation process,these two kinds of AlP crystals triggered morphologically templated nucleation of primary Si phase,resulting in the formation of hexagonal primary Si twin and octahedral non-twin crystals,respectively.As such,the percentage of primary Si twin crystals in the experimental Al-18 Si alloy was also increased obviously after the morphologically templated nucleation via Al P.The morphologically templated nucleation also eliminated the dendritic growth of primary Si phase and the formation of hopper structures inside primary Si,forcing primary Si to maintain to be faceted solid crystals through layer-by-layer growing mechanism.The insight into morphologically templated nucleation offers a new view in understanding the mechanism of heterogeneous nucleation of primary Si phase on AlP nuclei.
基金Item Sponsored by National Natural Science Foundation of China[No.51074048]Fundamental Research Funds for the Central Universities[N110408002]
文摘A pulse magnetic field(PMF)was applied on the hypereutectic A1-23%Si alloy of different temperature range(830-780 ℃,830-730 ℃,830-700 ℃,780-700 ℃,730-700 ℃)during its solidification processing.The influence of pulse magnetic field on the size and distribution of primary Si was studied.The results show that,the primary Si is very coarse strip,distributs non-unifromly and gathers at the edge of the sample when the alloy solidifies under the condition of no PMF.By applying PMF can significantly refine the primary Si,and make the primary Si distribute uniformly.There has no significant effect on the refinement of primary Si when PMF applied from 830 ℃ to 780 ℃,indicating that PMF has no outstanding effect on the high temperature liquid metal.Applying PMF from 50 ℃ above the liquidus to 30 ℃ below the liquidus(i.e.from liquid to the initial nucleation stage)can get the best refinement result.The refining mechanism of the pulse magnetic field on the solidification structure of Ai-23%Si alloy was discussed,
基金supported by the National Science Fund for Distinguished Young Scholars (No. 50625101)the Key Project of Science and Technology Research of the Ministry of Education of China (No. 106103)
文摘An Al-Si-P master alloy has been developed by an in-situ reaction and the electron probe microanalyzer (EPMA) results show that there are many pre-formed AlP particles contained in the master alloy. Silicon introduced into the system plays an important role in remarkably improving the distribution and content of AlP particles due to their similar crystal structure and lattice parameters. ZL109 alloys have shown fast modification response to the addition of 0.5% Al-15Si-3.5P master alloy at 720℃, with a mass of primary Si precipitating in size of about 15 μm. Also, coarse primary Si grains in AI-30Si alloy can be refined dramatically from 150 μm to 37 μm after the addition of 2.0% Al-15Si-3.5P master alloy at 850℃. The P recovery of the Al-15Si-3.5P master alloy is much higher than that of a Cu-8.5P master alloy due to the pre-formed AlP particles.
基金support from the National Natural Science Foundation of China(Grant No.51674168)Shenyang Application Basic Research Fund(Grant No.F14-231-1-23)
文摘The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xS i alloys(x = 15, 17.5, 22 wt%) was investigated in this study. Results show that microstructure of the hypereutectic Al-x Si alloys was obviously improved by squeeze casting. The amount of coarse primary Si phase decreased, while that of fine primary α-Al dendrites increased with the increase of squeeze casting pressure. Due to the decrease of coarse primary Si particles, cracking of the matrix was reduced, whilst the fine microstructure, and mechanical properties of the squeeze casting alloys were improved. Compared with gravity casting alloys, mechanical properties of the hypereutectic Al-xS i alloys solidified at 600 MPa were improved significantly. Hardness of the squeeze casting hypereutectic Al-(15, 17.5, 22 wt%) Si alloys was improved by 15.91%, 12.23%, 17.48%, ultimate tensile strength was improved by 37.85%, 32.27%, 22.74%,and elongation was improved by 55.83%, 167.86%, 126.76%, respectively. Due to the uniform distribution of Si phases in squeeze casting Al-x Si alloys, their wear resistance was markedly enhanced.