共查询到20条相似文献,搜索用时 31 毫秒
1.
Y. V. V. R. S. Murty T. Z. Kattamis O. F. Devereux 《Metallurgical and Materials Transactions B》1973,4(11):2575-2580
The morphological and kinetic nature of corrosion of directionally solidified aluminum-4.5 wt pct copper alloy in the as-cast,
solutionized and solutionized-and-aged conditions in air-saturated aqueous 3.5 wt pct NaCl solution were evaluated. In the
solutionized and solutionized-and-aged conditions the intergranular attack and pitting are similar to those occurring in solutionized
wrought alloys; the extent of attack at long times increases with increasing severity of solidification rate. The as-cast
alloy exhibits a cored dendritic structure with significant formation of interdendritic nonequilibrium eutectic. Extensive
inter dendritic corrosion of the α-phase containing more than 3.2 wt pct copper is seen; α containing less than 3.2 wt pct
copper and the θ-Al2Cu phase are cathodic. Corrosion of the as-cast alloy is parabolic with time and increases with increasing severity of solidification
rate in proportion to the amount of nonequilibrium second phase. 相似文献
2.
C. Gonzalez J. Genesca O. Alvarez J. A. Juarez-Islas 《Metallurgical and Materials Transactions A》2003,34(12):2991-2997
In the present research, Al-Zn-Mg alloys were vacuum induction melted and gravity cast into steel molds. Ingots were microstructurally
and electrochemically characterized to evaluate their performance as Al-sacrificial anodes for cathodic protection of structures
exposed to marine environments. The microstructure observed in as-cast ingots consisted mainly of α-Al dendrites with 0.68 to 2.25 vol pct of τ phase in α-Al matrix and eutectic in interdendritic regions. After heat treatment, the presence of the τ phase increased up to 5 vol pct. Electrochemical efficiencies obtained in Al alloys showed maximum values of 73 and 87 pct
in as-cast ingots and heat-treated ingots, respectively. In order to contribute to the development of Al-Zn-Mg anodes, the
Al-5.3 at. pct Zn-6.2 at. pct Mg (Al-12 wt pct Zn-5.4 wt pct Mg) alloy was monitored to identify the temperature changes as
it cools through phase transformation intervals. Growth temperatures of the phases present in this alloy were employed to
predict the structure growing at fixed growth velocity. Predictions of variation of solute concentration with growth velocity
in α-Al dendrites were included, too. The results of these analyses help to select alloy composition and to control microstructure
in order to develop a new generation of Al-sacrificial anodes free of In and Hg. 相似文献
3.
W. J. Boettinger L. Bendersky J. G. Early 《Metallurgical and Materials Transactions A》1986,17(5):781-790
Rapidly solidified powders of Al-8 wt pct Fe exhibit four distinct microstructures with increasing particle diameter in the
size range of 5 μm to 45 μm: microcellular α-Al; cellular α-Al; a-Al + Al6Fe eutectic; and Al3Fe primary intermetallic structure. Small powder particles (~10 μm or less) undercool significantly prior to solidification
and typically exhibit a two-zone microcellular-cellular structure in individual powder particles. In the two-zone microstructure,
there is a transition from solidification dominated by internal heat flow during recalescence with high growth rates (microcellular)
to solidification dominated by external heat flow and slower growth rates (cellular). The origin of the two-zone microstructure
from an initially cellular or dendritic structure is interpreted on the basis of growth controlled primarily by solute redistribution.
Larger particles experience little or no initial undercooling prior to solidification and do not exhibit the two-zone structure.
The larger particles contain cellular, eutectic, or primary intermetallic structures that are consistent with growth rates
controlled by heat extraction through the particle surface (external heat flow). 相似文献
4.
5.
A. K. Mukhopadhyay 《Metallurgical and Materials Transactions A》1998,29(13):979-987
The deleterious effects of Fe-bearing constituent particles on the fracture toughness of wrought A1 alloys have been known.
Recent studies have shown that the presence of Fe-bearing, constituent particles is also determental to the nature and growth
of the hard anodic oxide coating formed on such materials. The present study, using a combination of scanning electron microscopy
(SEM), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA), was made to examine the influence
of the nature of the Fe-bearing particles on the hard anodizing behavior of AA 7075 extrusion products containing varying
amounts of Si, Mn, and Fe impurities. It was found that, in the alloy containing 0.25 wt pct Si, 0.27 wt pct Mn, and 0.25
wt pct Fe, the Fe-bearing constituent particles are based on the Al12(FeMn)3Si phase (bcc with α=1.260 nm). These particles survive the hard anodizing treatment, add resistance to the electrical path,
causing a rapid rise in the bath voltage with time, and cause a nonuniform growth of the anodic oxide film. In the materials
containing 0.05 wt pct Si, 0.04 wt pct Mn, and 0.18 wt pct Fe, on the other hand, the formation of the Al12(FeMn)3Si-based phase is suppressed, and two different Fe-bearing phases, based on Al−Fe−Cu−Mn-based (simple cubic with a=1.265 nm) and Al7Cu2Fe, respectively form. Neither the Al−Fe−Cu−Mn-based phase nor the Al7Cu2Fe-based phase survive the hard anodizing treatment, and this results in a steady rise in the bath voltage with time and a
relatively uniform growth of the anodic oxide film. Consideration of the size of the Fe-bearing, particles reveals that the
smaller the particle, the more uniform the growth of the anodic oxide film. 相似文献
6.
D. G. Konitzer B. C. Muddle H. L. Fraser 《Metallurgical and Materials Transactions A》1983,14(10):1979-1988
A Ti-8 at. pct Al-4 at. pct Y alloy has been cast in small quantities and subjected to laser surface melting treatments in
an effort to produce a uniform distribution of fine-scale dispersoids by internal oxidation. The microstructures of both as-cast
and laser-modified material have been characterized using transmission electron microscopy, energy dispersive X-ray spectroscopy,
and convergent beam electron diffraction, and the identity and distribution of second phase dispersoids established. An ability
to refine significantly the dendritic structure of the as-cast alloy by laser surface treatment is demonstrated. The matrix
phase of the modified alloy is martensitic α′, in contrast to the α phase of the as-cast material. The interdendritic phase
observed in both as-cast and laser-modified material and the fine-scale dispersed particles (50 to 70 nm) in the as-cast alloy
are shown to be rich in Y, with a structure consistent with that of the oxide Y2O3. Dispersoids within the laser modified zone are typically 8 to 20 nm in diameter and show a tendency to form preferentially
at interlath boundaries of the martensite. The origins of these structures and their potential effects on the mechanical properties
of the alloy are discussed briefly. 相似文献
7.
Guangxin Wu Jieyu Zhang Qian Li Kuochih Chou Xiaochun Wu 《Metallurgical and Materials Transactions B》2012,43(1):198-205
The microstructure and thickness of 55 pct A1-Zn-1.6 pct Si-0.2 pct RE coatings during continuous hot-dip on Q235 steel were
investigated in this work. The experimental results revealed that the intermetallic layer was composed of the Fe2Al5, FeAl3, and α-FeAlSi phases. The results of thermodynamic calculations with Pandat software package (CompuTherm, LLC, Madison, WI) indicated
that FeAl3 and α(β)-FeAlSi phase precipitated during the period of temperature cooling, which was consistent with experimental result. Then,
the thickness of intermetallic layer was characterized. It was shown that the thickness of intermetallic layer decreased after
0.2 wt pct RE was added. Finally, a first-principles calculation was performed to interpret the effect mechanism of RE on
the thickness of intermetallic layer. The results indicated that La substitution in Fe2Al5 and FeAl3 phases could grab electronic charges from Al atoms and weaken the formation of Fe-Al compounds. 相似文献
8.
Frank W. Gayle Alexander J. Shapiro Francis S. Biancaniello William J. Boettinger 《Metallurgical and Materials Transactions A》1992,23(9):2409-2417
Isothermal sections of the Al-Cu-Fe equilibrium phase diagram at temperatures from 680 °C to 800 °C were determined in the
region with 50 to 75 at. pct Al and 0 to 25 at. pct Fe using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS)
techniques. This re- gion includes the face-centered icosahedral phase (Ψ-Al6Cu2Fe) which has unprecedented struc- tural perfection and no apparent phason strain. The icosahedral phase has equilibrium phase
fields with four distinct phases at 700 °C and 720 °C (β-Al(Fe, Cu), λ-Al13Fe4, ω-Al7Cu2Fe, and liquid) and three phases at 680 °C(β, ω, and λ) and 800 °C (β, λ, and liquid). The B2 ordered β phase has considerably greater solubility for Cu than previously
reported, extending from AlFe to ∼Al50Fe5Cu45. The equilibrium range of composition for the icosahedral phase at these temperatures was determined, and a liquidus projection
is proposed. 相似文献
9.
Joonyeon Chang Inge Moon Chongsool Choi 《Metallurgical and Materials Transactions A》1998,29(7):1873-1882
Analytical transmission electron microscopy and thermal analysis of as-extruded Al-4.7 pct Zn-2.5 pct Mg-0.2 pct Zr-X wt pct Mn alloys, with Mn contents ranging from 0.5 to 2.5 wt pct, were carried out to elucidate the microstructural change
and accompanying mechanical properties during subsequent heat treatments. The as-extruded alloy was fabricated from rapidly
solidified powder and consisted of a fine, metastable manganese dispersoid and the ternary eutectic T phase (Al2Mg3Zn3). Solution heat treatment resulted in the formation of the stable Al6Mn phase and complete dissolution of the T phase. Formation of stable Al6Mn was made by two routes: by phase transition from metastable Mn dispersoids which already existed, and from the supersaturated
solid solution by homogeneous nucleation. The density of the Al6Mn phase increased with the addition of manganese, while the shape and average size remained unchanged. A significant increase
in the hardness was observed to coincide with the formation of the Al6Mn phase. Similarly, the tensile strength increased further after the aging treatment, and the increment was constant over
the content of Mn in the alloy, which was explained by the contribution from the same amount of precipitates, MgZn2. Results of thermal analysis indicated that the dissolution of the T phase started near 180 °C and that formation of Al6Mn occurred at about 400 °C, suggesting that further enhancement of strength is possible with the modification of the heat-treatment
schedule. 相似文献
10.
Cubic (L12) ternary zirconium trialuminides macroalloyed with Cu(Al5CuZr2), Mn(Al66Mn9Zr25), and Cr(Al67Cr8Zr25) (atomic percent) and doped with 50 and 100 ppm boron were fabricated by induction melting. Their as-cast microstructures
are characterized by a small amount of porosity (1 to 2 pct) and second phase (2 to 3 pct). Boron seems to slightly enhance
porosity (up to 3.3 pct) in Al5CuZr2 +100 ppm B alloy, and it also promotes some compositional inhomo-geneity in Al66Mn9Zr25 alloy. Vickers microhardness and compressive properties at room temperature (RT), peak strength temperature (500 °C to 600
°C) and 900 °C were investigated. Microcracking development was also investigated in Al5CuZr2 +100 ppm boron alloy exhibiting a stepped load-deflection curve. Vickers microhardness strongly depends on load, similarly
to boron-free cubic ternary zirconium and titanium trialuminides, and increases in a systematic way with increasing boron
content which seems to indicate a solid solution strengthening effect. At RT, 0.2 pct offset yield strength is not increased
by the boron doping in most of the alloys studied except for Al66Mn9Zr25 + 50 ppm B alloy. Permanent deformation (apparent ductility) at ultimate compressive strength is not enhanced by boron doping.
In Al5CuZr2 +100 ppm B alloy microcracks start nucleating and proliferating in the elastic region of load-deflection curve in characteristic
“bursts” accompanied by a “click” sound and the appearance of a discernible step on the load-deflection curve. Pre-existing
pores are observed to be active centers of microcracking. 相似文献
11.
Hongseok Choi Milton Jones Hiromi Konishi Xiaochun Li 《Metallurgical and Materials Transactions A》2012,43(2):738-746
In this study, an ultrasonic cavitation based dispersion technique was used to fabricate Al-7Si-0.3Mg alloyed with Cu and
reinforced with 1 wt pct Al2O3 nanoparticles, in order to investigate their influence on the mechanical properties and microstructures of Al-7Si-0.3Mg alloy.
The combined addition of 0.5 pct Cu with 1 pct Al2O3 nanoparticles increased the yield strength, tensile strength, and ductility of the as-cast Al-7Si-0.3Mg alloy, mostly due
to grain refinement and modification of the eutectic Si and θ-CuAl2 phases. Moreover, Al-7Si-0.3Mg-0.5Cu-1 pct Al2O3 nanocomposites after T6 heat treatment showed a significant enhancement of ductility (increased by 512 pct) and tensile strength
(by 22 pct). The significant enhancement of properties is attributed to the suppression of pore formation and modification
of eutectic Si phases due to the addition of Al2O3 nanoparticles. However, the yield strength of the T6 heat-treated nanocomposites was limited in enhancement due to a reaction
between Mg and Al2O3 nanoparticles. 相似文献
12.
Y. L. Liu Z. Q. Hu Y. Zhang C. X. Shi 《Metallurgical and Materials Transactions B》1993,24(5):857-865
In this work, the solidification and segregation behaviors of 8090 Al-Li alloy have been investigated with differential thermal
analysis (DTA) and the metallographic-electron microprobe method. The results show that 8090 Al-Li alloy has a much more complex
solidification path than Al-Li binary alloy due to the addition of many alloying elements and the presence of impure elements.
Solidification begins at about 635 °C with the reaction of L → α-Al + L′, and this reaction goes on to termination. The alloying
element Cu and impure elements Fe and Si have a strong segregation tendency. During solidification, Cu segregates to the interdendrite
and finally forms α-Al + T2 eutectic. As a result, the solidification temperature range is greatly extended. Iron and Si form the insoluble constituents
Al7Cu2Fe, AlLiSi,etc., although their concentrations in the alloy are quite low. With the increase of Fe content, there is a eutectic reaction
of α-Al/Al3Fe at about 595 °C. The formation of insoluble constituents is influenced by both concentrations of impure elements in the
alloy and the cooling rate. 相似文献
13.
An investigation of the influence of processing variables on mechanical properties and phase development for a Ti-60 wt pct
Ta (Ti-28.5 at. pct Ta) alloy was conducted. The alloy was hot-rolled, subjected to heat-treatment temperatures above the
β (bcc) transus (1 hour at 700 °C, 800 °C, or 900 °C), and water quenched. All heat treatment produced a combination of metastable
β (bcc) and metastable α″ (orthorhombic martensite), with the amount of retained β essentially independent of heat treatment, ranging from 20 to 33 vol pct. Deformation of as-rolled and heat-treated tension
specimens showed an anomalous leveling of the stress-strain curve in the stress-strain curves at low strains. X-ray diffraction
(both simple 2ϑ diffractometry and texture analysis) on both deformed and undeformed material determined that the leveling of the stress-strain
curve was a result of the β→α″ martensitic transformation. The stress required to initiate the transformation increased with prequench temperature. This
was determined to be due to the presence of athermal ω. Grain growth kinetics have been determined in the course of this work. 相似文献
14.
W. Khalifa F. H. Samuel J. E. Gruzleski 《Metallurgical and Materials Transactions A》2004,35(10):3233-3250
Systematic inoculation experiments were carried out to study the influence of various inclusions on the nucleation of the
α-Al phase in Al-Si-Fe alloys at different cooling rates. The results showed that in dilute alloys, containing less than 1.5
pct Si+Fe, almost all the inclusion types have high percentages of occurrence within the α-Al phase, indicating that nucleation can be promoted on the surface of such inclusions. In a hypoeutectic Al-Si alloy containing
6.3 pct Si, the inclusion particles of MgO, TiB2, TiC, α-Al2O3, and SiC become mostly inactive nucleants and are pushed to the interdendritic regions because of the dominating poisoning
effect of Si. The current results were used successfully to explain the efficiency differences between the commercial grain
refiners in the hypoeutectic Al-Si alloys. Silicon is observed to preferentially segregate to the liquid-Al/inclusion interfaces
so as to lower the free energy of such interfaces. A theoretical analysis of the poisoning effect of Si showed that Si segregation
to the liquid/nucleant interface alters the interfacial energy balance so that the catalytic efficiency of the nucleant particles
is dramatically reduced. Careful analysis showed that the poisoning effect of Si in the hypoeutectic alloy is overcome when
the nucleant particles have active surface characteristics, as represented by the high catalytic potencies of γ-Al2O3, CaO, and Al4C3 particles in nucleating the α-Al phase of the hypoeutectic Al-Si alloy. Although some inclusions have comparable or higher occurrence levels than TiB2 in the α-Al phase, they cannot be used as efficient nucleants because of either their poor wettability with liquid aluminum or their
chemical reactivity, which can change the alloy chemistry. 相似文献
15.
Noam Bernstein Ramasis Goswami Ronald L. Holtz 《Metallurgical and Materials Transactions A》2012,43(6):2166-2176
Alloying Al with Mg can improve its structural properties but also can lead to the formation of grain-boundary precipitates
of β-Mg2Al3 that lead to failure by intergranular fracture and corrosion. Simulating the properties of the β phase is difficult because
it has a complex structure with more than 1000 atoms per unit cell. We approximate the experimental β structure by the β′
structure, which has about 300 atoms per unit cell, and we compute the fracture behavior of the material from density functional
theory calculations of relevant surface and interface energies. We report also on experimental measurements of the orientation
and fracture properties of the α-Al(Mg)–β-Mg2Al3 interface and compare them with the atomistic simulations. We have computed the surface energy of face-centered cubic α-Al
with up to 10 at. pct Mg, as well as the decohesion energy of β′-Mg2Al3 and the interfacial decohesion energy between β′-Mg2Al3 and pure α-Al with geometry similar to that observed experimentally. We find that the β′-Mg2Al3 decohesion energy is nearly isotropic and is lower than the pure Al surface energy and the α-Al–β′-Mg2Al3 interface decohesion energy. This result is consistent with the experimental observations of fracture within the β phase
rather than at the α-Al(Mg)–β-Mg2Al3 interface or within the α-Al(Mg) phase. 相似文献
16.
P. K. Rohatgi R. C. Sharma K. V. Prabhakar 《Metallurgical and Materials Transactions A》1975,6(2):569-575
Al-10.98 pct Si-4.9 pct Ni ternary eutectic alloy was unidirectionally solidified at growth rates from 1.39μm/sec to 6.95μm/sec.
Binary Al-Ni and Al-Si eutectics prepared from the same purity metals were also solidified under similar conditions to characterize
the growth conditions under the conditions of present study. NiAl3 phase appeared as fibers in the binary Al-Ni eutectic and silicon appeared as irregular plates in the binary Al-Si eutectic.
However, in the ternary Al-Si-Ni eutectic alloy both NiAl3 and silicon phases appeared as irregular plates dispersed in α-Al phase, without any regular repctitive arrangement. The
size and spacing of NiAl3 and Si platelets in cone shaped colonies decreased with an increase in the growth rate of the ternary eutectic. Examination
of specimen quenched during unidirectional solidification indicated that the ternary eutectic grows with a non-planar interface
with both Si and NiAl3 phases protruding into the liquid. It is concluded that it will be difficult to grow regular ternary eutectic structures
even if only one phase has a high entropy of melting. The tensile strength and modulus of unidirectionally solidified Al-Si-Ni
eutectic was lower than the chill cast alloys of the same composition, and decreased with a decrease in growth rate. Tensile
modulus and strength of ternary Al-Si-Ni eutectic alloys was greater than binary Al-Si eutectic alloy under similar growth
conditions, both in the chill cast and in unidirectionally solidified conditions. 相似文献
17.
Microstructure and its development in Cu-Al-Ni alloys 总被引:2,自引:0,他引:2
The microstructure of as-cast Cu-AI-Ni alloys, based on copper containing 9 to 10 wt pct Al and up to 5 wt pct Ni, has been
examined. The development of the microstructure on continuous cooling has also been investigated. For alloys with 9.2 to 9.3
wt pct Al, and less than 1 wt pct Ni, the as-cast microstructure consists of proeutectoid α solid solution, α + γ2 eutectoid, and martensitic β. If the nickel content is more than 2.5 wt pct, the α + γ2 eutectoid is replaced by α + β
2
′
eutectoid, and no martensitic β is observed in the as-cast alloys. The morphologies of the β
2
′
and γ2 eutectoid phases are similar; both have the Kurdjumov-Sachs (K-S) orientation relationship with the a phase. Two eutectoid
reactions, involving β to α + γ2 and β to α + β′2, have been observed in an alloy containing 9.7 wt pct Al and 2.7 wt pct Ni. When both eutectoid reactions occur, the Nishiyama-Wassermann
(N-W) orientation relationship exists between γ2 or β
2
′
and the α phase. During continuous cooling, proeutectoid α solid solution is the first phase to precipitate from the high-temperature
β phase. The β to α + β
2
′
eutectoid reaction starts at higher temperatures than the β to α + γ2 reaction. Tempering of the as-cast alloys results in the elimination of the martensitic β.
Y.S. SUN formerly Research Associate with the Manchester Materials Science Centre. 相似文献
18.
Cu-10 Ni alloy suffers from accelerated corrosion in sulphide-polluted seawater. New copper alloys containing 29% Zn, 10Ni
and 3 or 5% Mn have been found to be more corrosion resistant than Cu-10Ni alloys in sulphide polluted synthetic seawater.
The studies were carried out in synthetic seawater (ASTM D 114–75) and sulphide was added through Na2S (1 gpl ≈ 41ppm S2−). Testing was carried out using cathodic and anodic potentiodynamic polarization methods. Corrosion product film formed on
the Cu-29Zn-10Ni-5Mn alloy in sulphide polluted synthetic seawater was characterized using SEM and XRD. The film was found
to contain Cu2O, Cu2S, NiS and ZnS. Better corrosion resistance of new alloys as compared to that of Cu-10Ni alloy is attributed to formation
of ZnS, a bad conductor, in the film and incorporation of Mn3+ cations in Cu2O and Cu2S lattice. 相似文献
19.
R. K. Singh Raman 《Metallurgical and Materials Transactions A》2004,35(8):2525-2531
The article presents new findings on the influence of microstructural changes on corrosion behavior of magnesium alloy AZ91
in chloride solution, with a particular attention to the role of the β phase (Mg17Al12) and the surrounding Al-rich-α area. The as-cast alloy was subjected to solutionizing and aging heat treatments, in order to incorporate variation in morphology
and distribution of the intermetallic β phase and the surrounding Al-rich-α (also known as eutectic α). Although previous workers have ascribed the higher corrosion resistance of a fine-grained alloy to the formation of the
finely distributed β phase, the present work suggests that it is the ratio of the β phase to the Al-rich-α that governs the localized corrosion of the aged alloy. Corrosion characteristics were investigated by immersion and electrochemical
tests. Surface microtopography, optical microscopy, and scanning electron microscopy (SEM) were employed to characterize the
localized corrosion. 相似文献
20.
The effect of quenching condition on the mechanical properties of an A356 (Al-7 wt pct Si-0.4 wt pct Mg) casting alloy has
been studied using a combination of mechanical testing, differential scanning calorimetry (DSC), and transmission electron
microscopy (TEM). As the quench rate decreases from 250 °C/s to 0.5 °C/s, the ultimate tensile strength (UTS) and yield strength
decrease by approximately 27 and 33 pct, respectively. The ductility also decreases with decreasing quench rate. It appears
that with the peak-aged condition, both the UTS and yield strength are a logarithmic function of the quench rate,i.e., UTS orσ
y
=A logR +B. The termA is a measure of quench sensitivity. For both UTS and yield strength of the peak-aged A356 alloy,A is approximately 32 to 33 MPa/log (°C/s). The peak-aged A356 alloy is more quench sensitive than the aluminum alloy 6063.
For 6063,A is approximately 10 MPa/log (°C/s). The higher quench sensitivity of A356 is probably due to the high level of excess Si.
A lower quench rate results in a lower level of solute supersaturation in the α-Al matrix and a decreased amount of excess
Si in the matrix after quenching. Both of these mechanisms play important roles in causing the decrease in the strength of
the peak-aged A356 with decreasing the quench rate. 相似文献