共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Cao C. Zhang H. Cao Y.A. Chang S. Kou 《Metallurgical and Materials Transactions A》2010,41(3):706-716
The susceptibility of Mg-Al-Sr alloys to hot tearing during permanent mold casting was investigated using constrained rod
casting (CRC) in a steel mold. The alloys included Mg-xAl-1.5Sr and Mg-xAl-3Sr, where x = 4, 6, or 8 wt pct. The hot-tearing susceptibility (HTS) was determined based on the widths and locations of the cracks
in the rods. With the Mg-xAl-1.5 Sr alloys, the HTS decreased significantly with increasing Al content. With the Mg-xAl-3Sr alloys, the trend was similar but not as significant. At the same Al content, the HTS was significantly lower at 3 wt pct
Sr than at 1.5 wt pct Sr. To help understand the HTS of these alloys, the solidification path and phase fractions were calculated
for each alloy. The HTS was found to increase with increasing fraction solid at the end of primary solidification. 相似文献
2.
The microstructure evolution of impulse atomized powders of Al-0.61 wt pct and Al-1.90 wt pct Fe compositions have been investigated
with a scanning electron microscope, transmission electron microscope, neutron diffraction, and backscattering electron diffraction
(EBSD). Both hypoeutectic and hypereutectic compositions demonstrated similar macrostructure (i.e., primary α-Al dendrites/cells with eutectic Al-Fe intermetallics decorated at the dendritic/cellular walls). Selected area electron
diffraction (SAED) analysis and SAED pattern simulation identified the eutectic Al-Fe intermetallic as AlmFe (m = 4.0-4.4). This is verified by neutron diffraction analysis. Cubic texture was observed by EBSD on the droplets with dendritic
growth direction close to 〈111〉. The possible reasons are discussed. 相似文献
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Heat treatments were performed using an isothermal bainitic transformation (IBT) temperature compatible with continuous hot-dip
galvanizing on two high Al–low Si transformation induced plasticity (TRIP)-assisted steels. Both steels had 0.2 wt pct C and
1.5 wt pct Mn; one had 1.5 wt pct Al and the other had 1 wt pct Al and 0.5 wt pct Si. Two different intercritical annealing
(IA) temperatures were used, resulting in intercritical microstructures of 50 pct ferrite (α)-50 pct austenite (γ) and 65 pct α-35 pct γ. Using the IBT temperature of 465 °C, five IBT times were tested: 4, 30, 60, 90, and 120 seconds. Increasing the IBT time
resulted in a decrease in the ultimate tensile strength (UTS) and an increase in the uniform elongation, yield strength, and
yield point elongation. The uniform elongation was higher when using the 50 pct α-50 pct γ IA temperature when compared to the 65 pct α-35 pct γ IA temperature. The best combinations of strength and ductility and their corresponding heat treatments were as follows:
a tensile strength of 895 MPa and uniform elongation of 0.26 for the 1.5 pct Al TRIP steel at the 50 pct γ IA temperature and 90-second IBT time; a tensile strength of 880 MPa and uniform elongation of 0.27 for the 1.5 pct Al TRIP
steel at the 50 pct γ IA temperature and 120-second IBT time; and a tensile strength of 1009 MPa and uniform elongation of 0.22 for the 1 pct Al-0.5 pct
Si TRIP steel at the 50 pct γ IA temperature and 120-second IBT time. 相似文献
5.
A. Munitz V. Y. Zenou C. Cotler M. Talyanker 《Metallurgical and Materials Transactions A》1997,28(4):1035-1046
The impact of cooling rates on the microstructure of Al-U alloys was studied by optical, scanning electron, and transmission
electron microscopy. A variety of solidification techniques were employed to obtain cooling rates ranging between 3 × 10−2 and 106 K/s. High-purity uranium (99.9 pct) and high-purity aluminum (99.99 pct), or “commercially pure” type Al-1050 aluminum alloys
were used to prepare Al-U alloys with U concentration ranging between 3 and 22 wt pct. The U concentration at which a coupled
eutectic growth was observed depends on the cooling rates imposed during solidification and ranged from 13.8 wt pct for the
slower cooling rates to more than 22 wt pct for the fastest cooling rates. The eutectic morphology and its distribution depends
on the type of aluminum used in preparing the alloys and on the cooling rates during solidification. The eutectic in alloys
prepared from pure aluminum was evenly distributed, while for those prepared from Al-1050, the eutectic was unevenly distributed,
with eutectic colonies of up to 3 mm in diameter. Two lamellar eutectic structures were observed in alloys prepared from pure
aluminum containing more than 18 wt pct U, which solidified by cooling rates of about 10 K/s. One structure consisted of the
stable eutectic between UAl4 and Al lamella. The other structure consisted of a metastable eutectic between UAl3 and Al lamella. At least three different eutectic morphologies were observed in alloys prepared from Al-1050. 相似文献
6.
W. Kasprzak D. Sediako M. Walker M. Sahoo I. Swainson 《Metallurgical and Materials Transactions A》2011,42(7):1854-1862
In-situ neutron diffraction and thermal analysis techniques were used simultaneously to evaluate the kinetics of the nonequilibrium
solidification process of an Al-19 pct Si binary alloy. Feasibility studies concerning the application of neutron diffraction
for advanced solidification analysis were undertaken to explore its potential for high resolution phase analysis coupled with
fraction solid/liquid analysis of phase constituents. Neutron diffraction patterns were collected in a stepwise mode during
solidification between 983 K and 793 K (710 °C and 520 °C). The variation of intensity of the diffraction peaks was analyzed
and compared to the results of conventional cooling curve analysis. Neutron diffraction was capable of detecting nucleation
of the Si phase (primary and eutectic), as well as the Al phase during Al-Si eutectic nucleation. Moreover, neutron diffraction
indicated the possibility of detecting the presence of Si peaks at near liquidus temperature and premature nucleation of α-Al prior to Al-Si eutectic temperature. The solid and liquid volume fractions were determined based on the change of intensity
of neutron diffraction peaks over the solidification interval. Overall, the volume fraction determined was in good agreement
with the results of the cooling curve thermal analysis, as well as calculations using the FactSage software. The potential
of neutron diffraction for high resolution melt analysis required for advanced studies of grain refining, eutectic modification,
etc. was illustrated. This study will help us better understand the solidification mechanism of Al-Si alloys used for various
casting component applications. 相似文献
7.
G. -X. Wang B. Dogan F. -Y. Hsu H. -J. Klaar M. Dahms 《Metallurgical and Materials Transactions A》1995,26(3):691-701
Two ternary TiAl-based alloys with chemical compositions of Ti-46.4 at. pct Al-1.4 at. pct Si (Si poor) and Ti-45 at. pct
Al-2.7 at. pct Si (Si rich), which were prepared by reaction powder processing, have been investigated. Both alloys consist
of the intermetallic compounds y-TiAl, α2-Ti3Al, and ξ-Ti5(Si, Al)3. The microstructure can be described as a duplex structure(i.e., lamellar γ/α2 regions distributed in γ matrix) containing ξ precipitates. The higher Si content leads to a larger amount of ξ precipitates
and a finer y grain size in the Si-rich alloy. The tensile properties of both alloys depend on test temperature. At room temperature
and 700 °C, the tensile properties of the Si-poor alloy are better than those of the Si-rich alloy. At 900 °C, the opposite
is true. Examinations of tensile deformed specimens reveal ξ-Ti5(Si, Al)3 particle debonding and particle cracking at lower test temperatures. At 900 °C, nucleation of voids and microcracks along
lamellar grain boundaries and evidence for recovery and dynamic recrystallization were observed. Due to these processes, the
alloys can tolerate ξ-Ti5(Si, Al)3 particles at high temperature, where the positive effect of grain refinement on both strength and ductility can be utilized. 相似文献
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The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through
microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct
Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct
Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal
analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples,
and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases
was measured using the image analysis technique. The results show that Ni mainly participates as Al3Ni, Al9FeNi, and Al3CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al9FeNi the only Ni-rich phase, and Al12(Fe,Mn)3Si2 appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents. 相似文献
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J. A. Taylor G. B. Schaffer D. H. StJohn 《Metallurgical and Materials Transactions A》1999,30(6):1651-1655
The mechanism by which iron causes casting defects in the AA309 (Al-5 pct Si-1.2 pct Cu-0.5 pct Mg) may be related to the
solidification sequence of the alloy. Superimposing calculated segregation lines on the liquidus projection of the ternary
Al-Si-Fe phase diagram suggests that porosity is minimized at a critical iron content when solidification proceeds directly
from the primary field to the ternary Al-Si-βAl5FeSi eutectic point. Solidification via the binary Al-βAl5FeSi eutectic is detrimental to casting integrity. This hypothesis was tested by comparing the critical iron content observed
in the standard AA309 alloy to that of a high-silicon (10 pct Si) variant of this alloy. 相似文献
13.
H. Kamguo Kamga D. Larouche M. Bournane A. Rahem 《Metallurgical and Materials Transactions A》2010,41(11):2844-2855
Solidification of B206 aluminum alloys with additions of iron and silicon was studied to investigate their combined effect
on the formation and precipitation of intermetallics, particularly Fe-rich phases. Iron is precipitated mainly by either β(CuFe) or α(MnFe) phases, or both depending of the iron and silicon content, as well as the cooling rate. It was found that in alloys
having up to 0.3 wt pct Fe, the precipitation of β(CuFe) phase can be largely suppressed if the ratio Si/Fe is close to 1 and the cooling rate is moderately high. The low mobility
of the large facets of the β(CuFe) platelets is likely the cause limiting the amount of this phase, especially when the iron atoms have the possibility
to be captured by another phase, in this case, the α(MnFe) phase. 相似文献
14.
T. S. Prasanna Kumar K. Narayan Prabhu 《Metallurgical and Materials Transactions B》1991,22(5):717-727
Heat flow at the metal/chill interface of bar-type castings of aluminum base alloys was modeled as a function of thermophysical
properties of the chill material and its thickness. Experimental setup for casting square bars of Al-13.2 pct Si eutectic
and Al-3 pet Cu-4.5 pct Si long freezing range alloys with chill at one end exposed to ambient conditions was fabricated.
Experiments were carried out for different metal/chill combinations with and without coatings. The thermal history at nodal
locations in the chill obtained during the experiments was used to estimate the interface heat flux by solving a one-dimensional
Fourier heat conduction equation inversely. Using the data on transient heat flux q, the heat flow at the casting/chill interface
was modeled in two steps: (1) The peak in the heat flux curve qmax was modeled as a power function of the ratio of the chill thickness d to its thermal diffusivity a, and (2) the factor (q/qmax) X α0.05 was also modeled as a power function of the time after the solidification set in. The model was validated for Cu-10 pct Sn
-2 pct Zn alloy chill and Al-13.2 pct Si and Al-3 pct Cu-4.5 pct Si as the casting alloys. The heat flux values estimated
using the model were used as one of the boundary conditions for solidification simulation of the test casting. The experimental
and simulated temperature distributions inside the casting were found to be in good agreement.
Formerly Assistant Professor with Karnataka Regional Engineering College 相似文献
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C. M. Dinnis J. A. Taylor A. K. Dahle 《Metallurgical and Materials Transactions A》2006,37(11):3283-3291
Sand-cast plates were used to determine the effect of iron and manganese concentrations on porosity levels in Al-9 pct Si-0.5
pct Mg alloys. Iron increased porosity levels. Manganese additions increased porosity levels in alloys with 0.1 pct Fe, but
reduced porosity in alloys with 0.6 and 1 pct Fe. Thermal analysis and quenching were undertaken to determine the effect of
iron and managanese on the solidification of the Al-Si eutectic. At high iron levels, the presence of large β-Al5FeSi was found to reduce the number of eutectic nucleation events and increase the eutectic grain size. The preferential formation
of α-Al15Mn3Si2 upon addition of manganese reversed these effects. It is proposed that this interaction is due to β-Al5FeSi and the Al-Si eutectic having common nuclei. Porosity levels are proposed to be controlled by the eutectic grain size
and the size of the iron-bearing intermetallic particles rather than the specific intermetallic phase that forms. 相似文献
17.
18.
Per Skjerpe 《Metallurgical and Materials Transactions A》1987,18(2):189-200
The Al−Fe and Al−Fe−Si particles formed during DC-casting of an Al-0.25 wt pct Fe-0.13 wt pct Si alloy have been examined.
The particles were analyzed by transmission electron microscopy (TEM) and energy dispersive spectroscopy of X-rays (EDS).
Crystal faults were studied by high resolution electron microscopy (HREM). Samples for electron microscopy were taken at various
positions in the ingot,i.e., with different local cooling rates during solidification. At a cooling rate of 6 to 8 K/s the dominating phases were bcc
α-AlFeSi and bct Al
m
Fe. The space group of bcc α-AlFeSi was verified to be Im3. Superstructure reflections from Al
m
Fe were caused by faults on {110}-planes. At a cooling rate of 1 K/s the dominating phases were monoclinic Al3Fe and the incommensurate structure Al
x
Fe. In Al3Fe, stacking faults on {001} were frequently observed. The structure of Al
x
Fe is probably related to Al6Fe. Some amounts of other phases were detected. For EDS-analysis, extracted particles mounted on holey carbon films were examined.
Extracted particles were obtained by dissolving aluminum samples in butanol. Accurate compositions of various Al−Fe−Si phases
were determined by EDS-analysis of extracted crystals. 相似文献
19.
The constitution of the ternary system Al-Cr-Ti is investigated over the entire composition range using X-ray diffraction
(XRD), energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) up to 1500 °C, and metallography. Solid-state
phase equilibria at 900 °C are determined for alloys containing ≤75 at. pct aluminum and at 600 °C for alloys containing >75 at. pct
Al. A reaction scheme linking these solid-state equilibria with the liquidus surface is presented. The liquidus surface for
≤50 at. pct aluminum is dominated by the primary crystallization field of bcc β(Ti,Cr,Al). In the region >50 at. pct Al, the ternary L12-type phase τ forms in a peritectic reaction p
max at 1393 °C from L + TiAl. Furthermore, with the addition of chromium, the binary peritectic L + α(Ti,Al) = TiAl changes into an eutectic L = α(Ti,Al) + TiAl. This eutectic trough descends monotonously through a series of transition reactions and ternary peritectics
to end in the binary eutectic L = Cr7Al45 + (Al). 相似文献