A modification of Mg2Si in the hypereutectic Mg-4%Si alloy（mass fraction） with Sr was investigated.Two types of Mg2Si in the alloys were found：polygonal primary Mg2Si and Chinese script type eutectic Mg2Si.Adding A...A modification of Mg2Si in the hypereutectic Mg-4%Si alloy（mass fraction） with Sr was investigated.Two types of Mg2Si in the alloys were found：polygonal primary Mg2Si and Chinese script type eutectic Mg2Si.Adding Al-10% Sr master alloy to the Mg-4%Si alloy clearly reduced the average size of primary Mg2Si and changed the morphology of eutectic Mg2Si from Chinese script type to polyhedral or fine fibre shape.The refinement of primary Mg2Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles.The modification of eutectic Mg2Si results from the dissolved Sr,which alters the preferred growth manner of the eutectic.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 effects of Sm additions （0, 0.5 wt.%, 1.0 wt.%and 1.5 wt.%） on the eutectic Si and β-Al5FeSi phases of ADC12 as-cast alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and di...The effects of Sm additions （0, 0.5 wt.%, 1.0 wt.%and 1.5 wt.%） on the eutectic Si and β-Al5FeSi phases of ADC12 as-cast alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and differential thermal analysis （DTA）. The experimental results showed that Sm was an effective modifying agent for the eutectic Si of ADC12 alloy, when 1.0 wt.%-1.5 wt.%Sm was added to the alloy, the coarse acicular eutectic Si was modified into fine particle or short rod structure. Moreover, the appropriate addition of Sm （about 1.0 wt.%） had marked effects on shortening the length of needle-likeβ-Al5FeSi phase. Whereas, Sm was less effective on modifying the needle-likeβ-iron to the Chinese script or sphericalα-iron phase. The modification mecha-nism was also discussed.展开更多
Trace amount of Sr(0.05 wt.%)was added into the hypoeutectic Al−Si(3−12 wt.%Si)alloys to modify their microstructure and improve thermal conductivity.The results showed that the thermal conductivity of hypoeutectic Al...Trace amount of Sr(0.05 wt.%)was added into the hypoeutectic Al−Si(3−12 wt.%Si)alloys to modify their microstructure and improve thermal conductivity.The results showed that the thermal conductivity of hypoeutectic Al−Si alloys was improved by Sr modification,and the increment and increasing rate of the thermal conductivity gradually increased with Si content increasing.The improvement of thermal conductivity was primarily related to the morphology variation of eutectic Si phases.In Sr-modified Al−Si alloys,the morphology of eutectic Si phases was a mixed morphology of fiber structure and fine flaky structure,and the proportion of the fine flaky eutectic Si phases gradually decreased with Si content increasing.Under the Si content reaching 9 wt.%,the proportion of fine flaky eutectic Si phases was nearly negligible in Sr-modified alloys.Correspondingly,the increment and increasing rate of thermal conductivity of Sr-modified alloys reached the maximum and tended to be stable.展开更多
This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of prim...This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of primary Mg2 Si particles was achieved with the addition of 0.4 wt% Bi. Increasing Bi beyond 0.4 wt%resulted in a loss of modification, possibly due to the formation of Al8 MgB iS i4 compound before the precipitation of the primary Mg2 Si. Additionally, the structure of the pseudo-eutectic Mg2 Si was transformed from plate to fibrous, which was consistent with decrease of growth temperature extracted from the cooling curve thermal analysis. Addition of Bi had an effect on the morphology of Al5 Fe Si（β）, Al2Cu（θ） and Al5Cu2Mg8Si6（Q） intermetallic compounds. The tensile strength, elongation percentage, impact toughness, and hardness increased by 6%, 13%, 75%, and 23%, respectively, due to modification of both the primary and eutectic Mg2 Si crystals. The tensile and impact fracture surfaces showed fewer decohered particles in the Bi-treated composite. The enhancement in wear resistance of the Bi-treated composite could be attributed to solid lubricant function of insoluble soft Bi phase and modification effects on Mg2 Si particles.展开更多
The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experi...The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experiment, the optimal modification effect was obtained with an addition of about 0.5 wt.% La. The size of the primary phase MgzSi was considerably reduced to 25μm or less and the morphology was modified from a coarse dendritic shape to a polyhedral shape. However, when the addition of La increased to 0.8 wt.% or higher, the primary Mg2Si grew into a coarse dendritic morphology again. Moreover, it was found that some LaSi2 compounds were formed during solidification and the amount of the compounds appeared to increase gradually with increasing La content.展开更多
The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-scrip...The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-script shaped Mg2Si phase in the AZ61-0.7Si alloy.By adding 0.06wt.%-0.12wt.%Sr to AZ61-0.7Si alloy,the Mg2Si phase in the alloy can be changed from the initial coarse Chinese-script shape to fine granule and/or irregular polygonal shapes.Accordingly,the Sr-containing AZ61-0.7Si alloy exhibits higher tensile and creep properties than the AZ61-0.7Si alloy without Sr modification.The mechanism on modification and refinement of the Mg2Si phase in Sr-containing AZ61-0.7Si alloy is possibly related to the following two aspects:(1)adding Sr may form the Al4Sr phase which can serve as the heterogeneous nucleus for the Mg2Si particles and/or(2)adding Sr may lower the onset crystallizing temperature and increase the undercooling level.展开更多
The effect of rare earth （RE） elements on the morphologies and sizes of Si phases in the hypereutectic A1-Si alloys modified with P was investigated. The results show that the addition of La element to the hypereute...The effect of rare earth （RE） elements on the morphologies and sizes of Si phases in the hypereutectic A1-Si alloys modified with P was investigated. The results show that the addition of La element to the hypereutectic A1-Si alloys can enhance the effect of P element on the modification of the primary Si phases. In the multiplex modification of RE-P, the primary Si phase is refiner and the shape of the eutectic Si is changed from long needle-like to short rod-like. Moreover, the agglomeration rate of the primary Si phase is slowed greatly. Even the melt is held for 6 h, the average size of the primary Si phase is still satisfied. The results analyzed by scanning electron microscope （SEM） indicate that La is richer at A1-Si interface than that in α-A1 or primary Si phase. The higher the La content in the A1-Si interface, the smaller the primary Si phase.展开更多
The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dis...The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element.The length of Chinese script type Mg_(2)Si phase was reduced from 110 to 50μm with increasing Ce content to 1.6 wt.%.The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi_(2)phase,which could serve as the heterogeneous nucleation of Mg_(2)Si phase due to the small lattice mismatch of 7.97%.The modification of Mg_(2)Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg_(2)Si phase and CeSi_(2)promoted the nucleation of Mg_(2)Si phase.With increasing Ce content from 0 wt.%to 1.6 wt.%,the YS,UTS and EL at 150℃were improved from 67.7 MPa,91.2 MPa and 1.6%to 84.2 MPa,128 MPa and 7.5%,respectively.展开更多
P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P an...P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon. The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.展开更多
Effect of P-Na united modification on Al-22%Si-1.0%Cu-0.5%Mg-0.5%Mn alloy was studied. The results show that the refining effect of P-Na addition on primary silicon is superior to that of P and the former could modify...Effect of P-Na united modification on Al-22%Si-1.0%Cu-0.5%Mg-0.5%Mn alloy was studied. The results show that the refining effect of P-Na addition on primary silicon is superior to that of P and the former could modify eutectic silicon at the same time. Effects of P-Na modification on crystallization and microstructure of hypereutectic Al-Si alloys were studied with Electron-Scanning Microscope, Electron-Probe and X-ray diffractometer. The modification mechanism represents that on one hand, the primary silicon is refined by AlP as heterogeneous nucleus; on the other hand, when Na is added at the same time, P atoms are difficult to diffuse in the melt, and then enrichs on the growing faces of silicon phase. Moreover, a SiP compound was also discovered in Si crystals, which prevents the growth of silicon phase and refines the primary silicon.展开更多
Hypereutectic Al-17.5Si （wt pct） and Al-25Si （wt pct） alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hype...Hypereutectic Al-17.5Si （wt pct） and Al-25Si （wt pct） alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.展开更多
The refining effect and mechanism of Sb on Mg2Si and the microstructure of the matrix were investigated.The results indicate that there are Mg3Sb2 particles in the composites with the addition of Sb,and Mg3Sb2 can pro...The refining effect and mechanism of Sb on Mg2Si and the microstructure of the matrix were investigated.The results indicate that there are Mg3Sb2 particles in the composites with the addition of Sb,and Mg3Sb2 can promote the formation of fine polygonal type Mg2Si by providing nucleation site.Meanwhile,the grain size of Sb modified alloy is finer than that of the matrix. The improved microstructure results in the improvement of mechanical properties.The ultimate tensile strength is increased by 12.2%with the addition of 0.8%Sb.展开更多
The modification effects of ytterbium(Yb), Na_3PO_4 and Yb + Na_3PO_4 on primary Mg_2Si phase in Mg-4Si alloys were investigated by means of X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy...The modification effects of ytterbium(Yb), Na_3PO_4 and Yb + Na_3PO_4 on primary Mg_2Si phase in Mg-4Si alloys were investigated by means of X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) analysis in this work. The results indicate that the morphology of the primary Mg_2Si phase apparently changes from coarse dendrites to fine dispersive polygonal particles and the mean size decreases from 276.6 μm to 7.1 μm, with combined modification of 0.8wt.% Yb and 2.64 wt.% Na_3PO_4. Such a morphological evolution results in improvement in the ultimate tensile strength and elongation of the alloys as compared to the base alloy. This may be attributed to the formation of the YbP particles that acted as the heterogeneous nucleation substrates for the primary Mg_2Si particles, resulting in a refined distribution of these precipitates. The results of XRD examination show that there was no reaction between Si and Yb or Na_3PO_4. Solo addition of Yb or Na_3PO_4 into the melt has no real modification effect on the microstructure, but the primary Mg_2Si particles and α-Mg phases become coarser than that in the unmodified alloy.展开更多
The modification effect of La addition on the microstructural characteristics of hypereutectic Al 17%Si alloys was studied. Microstructures were examined using conventional optical microscopy and electron probe X ray ...The modification effect of La addition on the microstructural characteristics of hypereutectic Al 17%Si alloys was studied. Microstructures were examined using conventional optical microscopy and electron probe X ray microanalyzer. The morphology of Si crystal was evaluated by quantitative metallographical analysis. The results indicate that simultaneous modification to both primary and eutectic Si crystals is obtained by the addition of pure rare earth metal La in the hypereutectic Al 17%Si alloys while the optimal effect of La is obtained at a rather large scale. La begins to form intermetallic compound when its concentration exceeds approximately 1%, which appears as dark platelets in etched specimens. Electron probe X ray microanalysis experiment shows that La rich platelet could be represented as Al 1Si 2La 2 consisting of LaSi 2 and some unknown ternary Al x Si y La phase.展开更多
The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated. It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into ...The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated. It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into Al-24Si melt and the average primary Si grain size is decreased below 47 μm from original 225 μm. It is also found that the TiC particles in the melt coming from Al8Ti2C can improve the modification effect of the Al-P master alloy. When the content of TiC particles in the Al-24Si melt is 0.03%, the improvement reaches the maximum and keeps steady with increasing content of TiC particles. Modification effect occurs at 50 min after the addition of the Al-P master alloy and TiC particles, and keeps stable with prolonging holding time.展开更多
The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr s...The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-likeβ-Al-5FeSi phases （β-compound） into the fibrousα-Al-8Fe-2Si （α-compound）.The additions of Sr and Sr/Mg were less effective to modify theβ-compound into theα-compound,while the eutectic Si was fully modified into the fibrous morphology.A small secondary dendrite arm spacing （DAS） was found in the Sr-added,Cr-added and Sr/Cr-added alloys,especially in a steel mold.The Sr,Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously.A sludge phase was found in the addition of Cr-added,Sr/Cr-added and Mg-added alloys,especially in the graphite mold casting.The volume fraction ofβ-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify theβ-compound for the recycled Al-Si-Fe based alloys.展开更多
In order to improve mechanical properties of Mg_(2)Si/Al composites,Eu element was added to mod-ify Mg_(2)Si morphology,and T6 heat treatment was used to control Mg_(2)Si morphology and precipitate strengthening phase...In order to improve mechanical properties of Mg_(2)Si/Al composites,Eu element was added to mod-ify Mg_(2)Si morphology,and T6 heat treatment was used to control Mg_(2)Si morphology and precipitate strengthening phase.Microstructure and morphology of Mg_(2)Si were observed by synchrotron X-ray to-mography and TEM,and first-principles calculations were also performed to testify the effect of Eu mod-ification.Results show that the size of primary Mg_(2)Si particles decreases and eutectic Mg_(2)Si phase trans-forms from lamellar to fibrous by Eu addition.After heat treatment,sharp angles of primary Mg_(2)Si par-ticles passivate,and eutectic Mg_(2)Si dissolves and appears to be short dot-like.Meanwhile,nano-sizedβ"phase precipitates in the matrix.For morphology of Mg_(2)Si with Eu modification,TEM results show that Eu impedes the growing of Mg_(2)Si,which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg_(2)Si{100}facet.The adsorption and suppression growing of Mg_(2)Si transform the morphology of Mg_(2)Si and thus improve the elongation.UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%,which improved 81%and 200%compared to the as-cast Al-15%Mg_(2)Si composite.The strengthening mechanism mainly results from precipitation strengthening of nano-sizedβ"precipitates in the heat-treated composite.展开更多
The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive...The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...展开更多
Surfaces of AISI 304 austenitic stainless steel plates nitrided by plasma immersion ion implantation （PⅢ） technology were studied by means of Auger electron spectroscopy （AES） and X-ray photoelectron spectroscopy...Surfaces of AISI 304 austenitic stainless steel plates nitrided by plasma immersion ion implantation （PⅢ） technology were studied by means of Auger electron spectroscopy （AES） and X-ray photoelectron spectroscopy （XPS） to determine the effect of the nitriding process on the surface and subjacent layers. Elemental compositions obtained by AES and XPS at varying depths indicate that the saturation of N is relatively constant as a function of depth, indicating the reliability of PⅢ technology for substirface saturation. It is concluded that the concentrations of both Cr and O increase with depth, the subjacent oxide is driven by the Ar^＋ sputtering process used to access the lower layers, and then N is bound to Cr.展开更多
基金Project(2011BAE22B00) supported by the National Key Technology R&D Program of ChinaProjects(ZR2010EQ021,ZR2010EL013) supported by the Natural Science Foundation of Shandong Province,China
文摘A modification of Mg2Si in the hypereutectic Mg-4%Si alloy（mass fraction） with Sr was investigated.Two types of Mg2Si in the alloys were found：polygonal primary Mg2Si and Chinese script type eutectic Mg2Si.Adding Al-10% Sr master alloy to the Mg-4%Si alloy clearly reduced the average size of primary Mg2Si and changed the morphology of eutectic Mg2Si from Chinese script type to polyhedral or fine fibre shape.The refinement of primary Mg2Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles.The modification of eutectic Mg2Si results from the dissolved Sr,which alters the preferred growth manner of the eutectic.
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Project supported by National Natural Science Foundation of China(51165032,51364035)Department of Education of JiangxiProvince(GJJ13203)+2 种基金Innovative Group of Science and Technology of College of Jiangxi Province(00008713)Jiangxi Province Education Commission Foundation(GJJ13203)University-industry Cooperation Plan of Non-party Experts and Doctor of Nanchang (2012-CYH-DW-XCL-002) for financial support
文摘The effects of Sm additions （0, 0.5 wt.%, 1.0 wt.%and 1.5 wt.%） on the eutectic Si and β-Al5FeSi phases of ADC12 as-cast alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and differential thermal analysis （DTA）. The experimental results showed that Sm was an effective modifying agent for the eutectic Si of ADC12 alloy, when 1.0 wt.%-1.5 wt.%Sm was added to the alloy, the coarse acicular eutectic Si was modified into fine particle or short rod structure. Moreover, the appropriate addition of Sm （about 1.0 wt.%） had marked effects on shortening the length of needle-likeβ-Al5FeSi phase. Whereas, Sm was less effective on modifying the needle-likeβ-iron to the Chinese script or sphericalα-iron phase. The modification mecha-nism was also discussed.
基金Project(2013B090500091)supported by Industry-University-Research Combined Project of Guangdong Province,ChinaProject(20180358)supported by the Shenzhen Jiansheng Technology Inc.Cooperation Project,China。
文摘Trace amount of Sr(0.05 wt.%)was added into the hypoeutectic Al−Si(3−12 wt.%Si)alloys to modify their microstructure and improve thermal conductivity.The results showed that the thermal conductivity of hypoeutectic Al−Si alloys was improved by Sr modification,and the increment and increasing rate of the thermal conductivity gradually increased with Si content increasing.The improvement of thermal conductivity was primarily related to the morphology variation of eutectic Si phases.In Sr-modified Al−Si alloys,the morphology of eutectic Si phases was a mixed morphology of fiber structure and fine flaky structure,and the proportion of the fine flaky eutectic Si phases gradually decreased with Si content increasing.Under the Si content reaching 9 wt.%,the proportion of fine flaky eutectic Si phases was nearly negligible in Sr-modified alloys.Correspondingly,the increment and increasing rate of thermal conductivity of Sr-modified alloys reached the maximum and tended to be stable.
文摘This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of primary Mg2 Si particles was achieved with the addition of 0.4 wt% Bi. Increasing Bi beyond 0.4 wt%resulted in a loss of modification, possibly due to the formation of Al8 MgB iS i4 compound before the precipitation of the primary Mg2 Si. Additionally, the structure of the pseudo-eutectic Mg2 Si was transformed from plate to fibrous, which was consistent with decrease of growth temperature extracted from the cooling curve thermal analysis. Addition of Bi had an effect on the morphology of Al5 Fe Si（β）, Al2Cu（θ） and Al5Cu2Mg8Si6（Q） intermetallic compounds. The tensile strength, elongation percentage, impact toughness, and hardness increased by 6%, 13%, 75%, and 23%, respectively, due to modification of both the primary and eutectic Mg2 Si crystals. The tensile and impact fracture surfaces showed fewer decohered particles in the Bi-treated composite. The enhancement in wear resistance of the Bi-treated composite could be attributed to solid lubricant function of insoluble soft Bi phase and modification effects on Mg2 Si particles.
基金Project supported by the Science and Technology of Heilongjiang Province (GC05A209)the Science and Technology of Harbin (2005AA5CG046)
文摘The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experiment, the optimal modification effect was obtained with an addition of about 0.5 wt.% La. The size of the primary phase MgzSi was considerably reduced to 25μm or less and the morphology was modified from a coarse dendritic shape to a polyhedral shape. However, when the addition of La increased to 0.8 wt.% or higher, the primary Mg2Si grew into a coarse dendritic morphology again. Moreover, it was found that some LaSi2 compounds were formed during solidification and the amount of the compounds appeared to increase gradually with increasing La content.
基金supported by the National Natural Science Funds for Distinguished Young Scholar in China(No.50725413)the Major State Basic Research Development Program of China(973)(No.2007CB613704)+1 种基金the Natural Science Foundation Project of CQ CSTC(No.2007BB4400)Chongqing Science and Technology Commission in China(No.2006AA4012-9-6).
文摘The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-script shaped Mg2Si phase in the AZ61-0.7Si alloy.By adding 0.06wt.%-0.12wt.%Sr to AZ61-0.7Si alloy,the Mg2Si phase in the alloy can be changed from the initial coarse Chinese-script shape to fine granule and/or irregular polygonal shapes.Accordingly,the Sr-containing AZ61-0.7Si alloy exhibits higher tensile and creep properties than the AZ61-0.7Si alloy without Sr modification.The mechanism on modification and refinement of the Mg2Si phase in Sr-containing AZ61-0.7Si alloy is possibly related to the following two aspects:(1)adding Sr may form the Al4Sr phase which can serve as the heterogeneous nucleus for the Mg2Si particles and/or(2)adding Sr may lower the onset crystallizing temperature and increase the undercooling level.
基金supported by the National Natural Science Foundation of China （Grant No.50075051）
文摘The effect of rare earth （RE） elements on the morphologies and sizes of Si phases in the hypereutectic A1-Si alloys modified with P was investigated. The results show that the addition of La element to the hypereutectic A1-Si alloys can enhance the effect of P element on the modification of the primary Si phases. In the multiplex modification of RE-P, the primary Si phase is refiner and the shape of the eutectic Si is changed from long needle-like to short rod-like. Moreover, the agglomeration rate of the primary Si phase is slowed greatly. Even the melt is held for 6 h, the average size of the primary Si phase is still satisfied. The results analyzed by scanning electron microscope （SEM） indicate that La is richer at A1-Si interface than that in α-A1 or primary Si phase. The higher the La content in the A1-Si interface, the smaller the primary Si phase.
基金supported by the Major Science and Technology projects in Qinghai province (2018-GX-A1)Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (Grant No. 2013M3A6B1078874)+1 种基金funded by Shanghai Science and Technology Committee (Grant No. 18511109302)the National Natural Science Foundation of China (Grant No. 51825101)
文摘The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element.The length of Chinese script type Mg_(2)Si phase was reduced from 110 to 50μm with increasing Ce content to 1.6 wt.%.The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi_(2)phase,which could serve as the heterogeneous nucleation of Mg_(2)Si phase due to the small lattice mismatch of 7.97%.The modification of Mg_(2)Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg_(2)Si phase and CeSi_(2)promoted the nucleation of Mg_(2)Si phase.With increasing Ce content from 0 wt.%to 1.6 wt.%,the YS,UTS and EL at 150℃were improved from 67.7 MPa,91.2 MPa and 1.6%to 84.2 MPa,128 MPa and 7.5%,respectively.
文摘P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon. The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.
文摘Effect of P-Na united modification on Al-22%Si-1.0%Cu-0.5%Mg-0.5%Mn alloy was studied. The results show that the refining effect of P-Na addition on primary silicon is superior to that of P and the former could modify eutectic silicon at the same time. Effects of P-Na modification on crystallization and microstructure of hypereutectic Al-Si alloys were studied with Electron-Scanning Microscope, Electron-Probe and X-ray diffractometer. The modification mechanism represents that on one hand, the primary silicon is refined by AlP as heterogeneous nucleus; on the other hand, when Na is added at the same time, P atoms are difficult to diffuse in the melt, and then enrichs on the growing faces of silicon phase. Moreover, a SiP compound was also discovered in Si crystals, which prevents the growth of silicon phase and refines the primary silicon.
基金supported by the National Key Technology R&D Program of China(No.2009BAE80B00)
文摘Hypereutectic Al-17.5Si （wt pct） and Al-25Si （wt pct） alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.
基金Project（50765005）supported by the National Natural Science Foundation of China
文摘The refining effect and mechanism of Sb on Mg2Si and the microstructure of the matrix were investigated.The results indicate that there are Mg3Sb2 particles in the composites with the addition of Sb,and Mg3Sb2 can promote the formation of fine polygonal type Mg2Si by providing nucleation site.Meanwhile,the grain size of Sb modified alloy is finer than that of the matrix. The improved microstructure results in the improvement of mechanical properties.The ultimate tensile strength is increased by 12.2%with the addition of 0.8%Sb.
基金financially supported by the Fundamental Research Funds for Central Universities(Grant No.:XDJK2015B001)
文摘The modification effects of ytterbium(Yb), Na_3PO_4 and Yb + Na_3PO_4 on primary Mg_2Si phase in Mg-4Si alloys were investigated by means of X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) analysis in this work. The results indicate that the morphology of the primary Mg_2Si phase apparently changes from coarse dendrites to fine dispersive polygonal particles and the mean size decreases from 276.6 μm to 7.1 μm, with combined modification of 0.8wt.% Yb and 2.64 wt.% Na_3PO_4. Such a morphological evolution results in improvement in the ultimate tensile strength and elongation of the alloys as compared to the base alloy. This may be attributed to the formation of the YbP particles that acted as the heterogeneous nucleation substrates for the primary Mg_2Si particles, resulting in a refined distribution of these precipitates. The results of XRD examination show that there was no reaction between Si and Yb or Na_3PO_4. Solo addition of Yb or Na_3PO_4 into the melt has no real modification effect on the microstructure, but the primary Mg_2Si particles and α-Mg phases become coarser than that in the unmodified alloy.
文摘The modification effect of La addition on the microstructural characteristics of hypereutectic Al 17%Si alloys was studied. Microstructures were examined using conventional optical microscopy and electron probe X ray microanalyzer. The morphology of Si crystal was evaluated by quantitative metallographical analysis. The results indicate that simultaneous modification to both primary and eutectic Si crystals is obtained by the addition of pure rare earth metal La in the hypereutectic Al 17%Si alloys while the optimal effect of La is obtained at a rather large scale. La begins to form intermetallic compound when its concentration exceeds approximately 1%, which appears as dark platelets in etched specimens. Electron probe X ray microanalysis experiment shows that La rich platelet could be represented as Al 1Si 2La 2 consisting of LaSi 2 and some unknown ternary Al x Si y La phase.
文摘The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated. It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into Al-24Si melt and the average primary Si grain size is decreased below 47 μm from original 225 μm. It is also found that the TiC particles in the melt coming from Al8Ti2C can improve the modification effect of the Al-P master alloy. When the content of TiC particles in the Al-24Si melt is 0.03%, the improvement reaches the maximum and keeps steady with increasing content of TiC particles. Modification effect occurs at 50 min after the addition of the Al-P master alloy and TiC particles, and keeps stable with prolonging holding time.
文摘The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-likeβ-Al-5FeSi phases （β-compound） into the fibrousα-Al-8Fe-2Si （α-compound）.The additions of Sr and Sr/Mg were less effective to modify theβ-compound into theα-compound,while the eutectic Si was fully modified into the fibrous morphology.A small secondary dendrite arm spacing （DAS） was found in the Sr-added,Cr-added and Sr/Cr-added alloys,especially in a steel mold.The Sr,Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously.A sludge phase was found in the addition of Cr-added,Sr/Cr-added and Mg-added alloys,especially in the graphite mold casting.The volume fraction ofβ-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify theβ-compound for the recycled Al-Si-Fe based alloys.
基金the National Natural Science Foun-dation of China(No.U21A2042)the National Science Fund for Distinguished Young Scholars of China(No.51825401).
文摘In order to improve mechanical properties of Mg_(2)Si/Al composites,Eu element was added to mod-ify Mg_(2)Si morphology,and T6 heat treatment was used to control Mg_(2)Si morphology and precipitate strengthening phase.Microstructure and morphology of Mg_(2)Si were observed by synchrotron X-ray to-mography and TEM,and first-principles calculations were also performed to testify the effect of Eu mod-ification.Results show that the size of primary Mg_(2)Si particles decreases and eutectic Mg_(2)Si phase trans-forms from lamellar to fibrous by Eu addition.After heat treatment,sharp angles of primary Mg_(2)Si par-ticles passivate,and eutectic Mg_(2)Si dissolves and appears to be short dot-like.Meanwhile,nano-sizedβ"phase precipitates in the matrix.For morphology of Mg_(2)Si with Eu modification,TEM results show that Eu impedes the growing of Mg_(2)Si,which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg_(2)Si{100}facet.The adsorption and suppression growing of Mg_(2)Si transform the morphology of Mg_(2)Si and thus improve the elongation.UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%,which improved 81%and 200%compared to the as-cast Al-15%Mg_(2)Si composite.The strengthening mechanism mainly results from precipitation strengthening of nano-sizedβ"precipitates in the heat-treated composite.
基金the Natural Science Foundation of Jiangxi Province (No. 0650047)the Science and Technology Program of the Education Department of Jiangxi Province,China(No.GJJ08268).
文摘The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...
文摘Surfaces of AISI 304 austenitic stainless steel plates nitrided by plasma immersion ion implantation （PⅢ） technology were studied by means of Auger electron spectroscopy （AES） and X-ray photoelectron spectroscopy （XPS） to determine the effect of the nitriding process on the surface and subjacent layers. Elemental compositions obtained by AES and XPS at varying depths indicate that the saturation of N is relatively constant as a function of depth, indicating the reliability of PⅢ technology for substirface saturation. It is concluded that the concentrations of both Cr and O increase with depth, the subjacent oxide is driven by the Ar^＋ sputtering process used to access the lower layers, and then N is bound to Cr.
