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1.
Metastable fcc phase with highly ductile nature has been found in melt-quenched Mn-Al-C alloys instead of extremely brittle
equilibrium phases. This formation range is limited to about 9 to 22 at. pct Al and about 3.0 to 6.5 at. pct C. Further, the
fee phase wires with circular cross section have been manufactured by an in-rotating-water spinning method. The wire diameter
is in the range of 70 to 150 μm diameter and the average grain size is about 3 μm. The Vickers hardness, yield strength, and
tensile strength of the wires increase with aluminum and carbon content and reach about 285 DPN, 560 MPa, and 960 MPa, respectively,
for Mn74.5Al20.5C5-Elongation increases with decrease in aluminum and carbon, and the highest value is about 28 pct for Mn-13.5 pct Al-4 pct
C alloy. The cold-drawing to about 60 pct reduction in area results in a very significant increase of tensile strength from
260 to 1460 MPa, through a remarkable work-hardening effect. Thus, the use of the in-rotating-water spinning method, being
a new type of rapid quenching technique, is very useful to endow the manganese-base alloy wires exhibiting high strength combined
with good ductility. 相似文献
2.
A method has been developed to produce grain sizes as small as 5 μm in alloys of β-CuAlNi. The alloys were of eutectoid composition
and a procedure was developed for determining the composition of a eutectoid alloy having any required value for transition
temperature (M
s
). The thermo-mechanical treatment involved two sequential stages of warm rolling followed by recrystallization. The alloys
produced were single phase β-type with no second phase being present. Characteristic two-stage stress-strain curves were obtained
for most of the specimens. It was generally found that the tensile strength and strain to failure increased with decreasing
grain size according to a Hall-Petch type relationship down to a grain size of 5 μm. A fracture strength of 1200 MPa and a
fracture strain of 10 pct were obtained in the best alloy. It was found that the major recovery mode, whether pseudoelastic
or strain-memory, did not have any significant effect on the total recovery obtained. Recovery properties were not affected
significantly by decreasing grain size, and 86 pct recovery could still be obtained at a grain size of around 10 μm. Grain
refinement improved the fatigue life considerably, possibly due to the high ultimate fracture stress and ductile fracture
mode. A fatigue life of 275,000 cycles could be obtained for an applied stress of 330 MPa and a steady state strain of 0.7
pct. At fine-grain sizes most of the fractures were due to transgranular-type brittle fracture and micro void-type ductile
fracture, depending on the alloy composition. It was suggested that the difference between the alloys was due to differences
in oxygen segregation at the grain boundaries. 相似文献
3.
F. S. Lin S. B. Chakrabortty E. A. Starke 《Metallurgical and Materials Transactions A》1982,13(3):401-410
The microstructure and tensile properties of two A1-3 wt pct Li-2 wt pct Cu-0.2 wt pct Zr alloys, one Cd-free and one containing
0.2 wt pct Cd, have been investigated. The Cd-free alloy remained unrecrystallized for all solutionizing treatments studied,
whereas a special treatment had to be developed to prevent recrystallization during solutionizing of the 0.2 wt pct Cd alloy.
In combination with cadmium, zirconium either enters into, or nucleates on, the course Al7Cu2Fe and T2 phases during high temperature annealing. This reduces the volume fraction of small coherent Al3Zr particles in the matrix which normally inhibits recrystallization. Consequently, a low temperature anneal to precipitate
Al3Zr is necessary prior to high temperature solutionizing in order to prevent recrystallization in the Cd-containing alloy.
Unlike its effect in lower lithium, higher copper content aluminum alloys, cadmium does not significantly affect the nucleation
of the strengthening precipitates. If anything, cadmium has a detrimental effect on the age hardening response of this alloy,
since it increases the formation of coarse Al-Cu-Li equilibrium phases at grain and subgrain boundaries and thus removes some
of the copper and lithium from participating in the formation of the strengthening precipitates T1 and δ′. Subgrain boundary fracture occurred during tensile tests of both alloys in the unrecrystallized condition; however,
transgranular fracture occurred in tests of the partially recrystallized 0.2 wt pct Cd alloy. Both types of fractures are
believed due to a form of strain localization associated with precipitate free zones and shearable precipitates.
Formerly with the Fracture and Fatigue Research Laboratory, Georgia Institute of Technology, Atlanta, GA 相似文献
4.
M. B. Winnicka Ph.D. Candidate R. A. Varin 《Metallurgical and Materials Transactions A》1992,23(11):2963-2972
The present article reports and discusses the results of the microstructural characterization of various modifications of
Ll2 trialuminides containing various titanium contents, including the first ever report on their degree of ordering. The Ll2 trialuminide alloys Al3Ti + X, where X = Cu, Fe, Cr, and Mn were studied. The as-cast structure contains a very low level of porosity, and the amount
of second phase depends on the particular alloy. After homogenization, the second phase is reduced in almost all the alloys
to the level less than 0.5 pct, except for the Mn-high Ti alloy in which it remains at about 20 pct and its composition is
67.9 ± 0.6 at. pct Al, 2.2 ± 0.6 at. pct Mn, and 29.9 ± 0.3 at. pct Ti. In almost all the alloys, porosity after homogenization
increases about twofold, except in the Al3Ti + Cr alloy in which it remains at almost the as-cast level. Limited transmission electron microscopic observations have
revealed the existence of very fine (≈10 nm) unidentified precipitates in the homogenized Al3Ti + Cu alloy. The homogenized Al3Ti + Cr and Mn alloys have greater lattice parameters than the Al3Ti + Fe and Cu alloys. It is also found that the long-range order parameterS of the ho- mogenized Ll2 Al3Ti + X alloys dramatically decreases with increasing titanium content. 相似文献
5.
Microstructures,mechanical properties,and electrical resistivity of rapidly quenched Fe-Cr-Al alloys
T. Naohara A. Inoue T. Minemura T. Masumoto K. Kumada 《Metallurgical and Materials Transactions A》1982,13(3):337-343
By the rapid quenching technique, ductile supersaturated ferrite solid solution with high hardness and strength as well as
unusual electrical properties has been found in Fe-Cr-Al ternary system. This formation range is limited to less than about
35 at. pct Cr and 23 at. pct Al. The ferrite phase has fine grains of about 10 μm in diameter. Their hardness, yield strength,
and tensile fracture strength increase with increase in the amounts of chromium and aluminum, and the highest values reach
about 290 DPN, 720 MPa, and 740 MPa. These alloys are so ductile that no cracks are observed even after closely contacted
bending test. The good strength and ductility remain almost unchanged on tempering for one hour until heated to about 923
K where a large amount of Cr2Al compound begins to precipitate preferentially along the grain boundaries of the ferrite phase. The room-temperature resistivity
increases with increasing chromium and aluminum contents and reaches as high as 1.86 μ Ώ m for Fe50Cr30Al20 alloy. Also, the temperature coefficient of resistivity in the temperature range between room temperature and 773 K decreases
with increasing chromium and aluminum contents and becomes zero in the vicinity of 20 to 30 at. pct Cr and 15 at. pct Al.
Thus, the present alloys may be attractive as fine gauge high-resistance and/or standard-resistance wires and plates because
of the unusual electrical properties combined with high strength and good ductility.
formerly with the Research Staff of Tohoku University
formerly Graduate Student of Tohoku University, 相似文献
6.
The microstructure and tensile behavior of an Al-3Cu-l.6Li-0.8Mg-0.2Zr alloy, produced by splatquenched powder metallurgy
processing, were studied. The alloy exhibited homogeneous deformation, both in bulk samples and duringin situ TEM studies. This is in contrast to the strain localization that is frequently observed in Mg-free Al-Cu-Li-X alloys. The
difference in deformation mode is attributed to a fine distribution of Ś (Al2CuMg) which precipitates up to the grain boundaries. A processing treatment involving 2 pct stretch prior to aging resulted
in a yield strength of 555 MPa, a reduction in area of 29 pct, and a strain to fracture of 8.8 pct. This represents an attractive
improvement in specific properties compared with 7075-T76 having a similar texture. 相似文献
7.
Ti57−x
Cu15Ni14Sn4+x
Nb10 (x = 0, 5, or 10) alloys were prepared by copper mold casting. At Sn = 4 at. pct, a dendrite/ultrafine-structured multicomponent
alloy was obtained, which exhibits 1271 MPa yield strength, 77 GPa Young’s modulus, and 2 pct plasticity at room temperature
for 3-mm-diameter samples. The cooling rate significantly affects the as-cast microstructure and the mechanical properties.
For 5-mm-diameter samples, the alloy exhibits 1226 MPa yield strength, 63 GPa Young’s modulus, and 2.5 pct plasticity. At
Sn = 9 at. pct, Ti-, Sn-, and Nb-rich particles precipitate primarily. This near-hypereutectic alloy composition leads to
the precipitation of intermetallics, which deteriorate the mechanical properties and result in the coexistence of ductile
and brittle fracture mechanisms. At Sn = 14 at. pct, the alloy composition is completely in the intermetallic region, thus
inducing the formation of Ti2Cu, Ti2Ni, and Ti3Sn intermetallics. The alloy becomes very brittle because the intermetallic compounds dominate the fracture process. 相似文献
8.
Although Al-Li-Cu alloys showed initial promise as lightweight structural materials, implementation into primary aerospace
applications has been hindered due in part to their characteristic anisotropic mechanical and fracture behaviors. The Air
Force recently developed two isotropic Al-Li-Cu-X alloys with 2.1 wt pct Li and 1.8 wt pct Li designated AF/C-489 and AF/C-458,
respectively. The elongation at peak strength was less than the required 5 pct for the 2.1 wt pct Li variant but greater than
10 pct for the 1.8 wt pct Li alloy. The objectives of our investigations were to first identify the mechanisms for the large
difference in ductility between the AF/C-489 and AF/C-458 alloys and then to develop an aging schedule to optimize the microstructure
for high ductility and strength levels. Duplex and triple aging practices were designed to minimize grain boundary precipitation
while encouraging matrix precipitation of the T1 (Al2CuLi) strengthening phase. Certain duplex aged conditions for the AF/C-489 alloy showed significant increases in ductility
by as much as 85 pct with a small decrease of only 6.5 and 2.5 pct in yield and ultimate tensile strength, respectively. However,
no significant variations were found through either duplex or triple aging practices for the AF/C-458 alloys, thus, indicating
a very large processing window. Grain size and δ′ (Al3Li) volume fraction were determined to be the major cause for the differences in the mechanical properties of the two alloys. 相似文献
9.
Mayank Agarwal Avtar Singh Rajeev Srivastava 《Transactions of the Indian Institute of Metals》2018,71(5):1091-1098
Tensile properties and fracture behaviors of silicon rich LM6 aluminum alloy were investigated in details for as cast alloy and modified by LM6 powdery-chip capsules. The obtained results showed that 20% modified LM6 cast composite ensured the excellent tensile properties (tensile strength of 203 MPa with 3.8% elongation). An impressive increase in the elongation (6.8%) was found for 25% modified cast composite with good ultimate tensile strength, 6.2% higher than unmodified (182 MPa). Characterization of the casts and fracture surfaces were carried out to study the effect of reinforcement particles. An influence of un-melted chip structure was observed inside the cavities and on fractured surfaces. The XRD results showed that cast consisted of inter-metallics of AlO2, Al2Si and Al4Si. It was attributed to micro-cracks prevalently propagated along the broken eutectic silicon particles and some rejected solid particles on the fractured surfaces with ductile and inter-granular fracture. Debonding and cracking of silicon particles were also detected on the fractured surface of the specimens. 相似文献
10.
The formation mechanism of nanoscale Al3Fe phase in Al-1Fe (wt pct) alloy during rheo-extrusion was investigated, and the mechanical property of the prepared alloy was also measured. The results show that the average length of Al3Fe phase in Al-1Fe alloy prepared by rheo-extrusion is 300 nm, which is much more refined than the needlelike Al3Fe phase in as-cast Al-1Fe alloy (50 μm). In rheo-extrusion, Al3Fe phase formed by eutectic reaction is bonelike, but it could be continuously refined by the shear deformation in the wheel groove, in equal channel angular flow, and in expansion extrusion mold. The total equivalent strain of the shear deformation is higher than 4.82. The tensile strength and elongation of Al-1Fe alloy prepared by rheo-extrusion are 135 MPa and 30 pct, respectively. The tensile strength of Al-1Fe alloy prepared by rheo-extrusion is 58.8 pct higher than that of as-cast Al-1Fe alloy, and the elongation is 19 pct higher than that of as-cast Al-1Fe alloy. Compared with as-cast Al-1Fe alloy, the improvements of tensile strength and elongation caused by shear deformation in rheo-extrusion are higher than the reported improvements induced by rare earth modification. 相似文献
11.
The present article describes an investigation of the microstructure and tensile properties of cast Al-Li-Mg alloys with very
low densities, in the range 2.3 to 2.4 Mg/m3. Low density is achieved by adding Li and Mg in excess of the solubility limit, which prevents subsequent dissolution of
the Al2LiMg particles that form during solidification. A simple model developed during the course of this research allows prediction
of the volume fraction of Al2LiMg and alloy density from alloy composition. The model was used to select two alloy compositions for detailed investigation:
A112Li6Mg and A116Li8Mg. The microstructures of the cast alloys consist of coarse Al2LiMg particles embedded in an Al matrix containing Al3Li particles. Both alloys exhibit low tensile elongation in the as-cast condition. Additional processing steps were used to
modify the microstructural characteristics thought to be responsible for the low tensile elongation of the ascast alloys.
The A116Li8Mg alloy, with an Al2LiMg volume fraction of 0.25, does not exhibit increased tensile elongation as a result of processing, and the brittle nature
of this material is attributed to the high volume fraction of the Al2LiMg phase. The A112Li6Mg alloy, with an Al2LiMg volume fraction of 0.13, exhibits a remarkable increase in tensile elongation after extrusion, an effect attributed to
fragmentation and dispersal of a three-dimensional (3-D) network of the intermetallic phase in the as-cast alloy. 相似文献
12.
F. G. Wilson B. R. Knott C. D. Desforges 《Metallurgical and Materials Transactions A》1978,9(2):275-282
Several alloys based on Fe-25Cr-6Al and Fe-25Cr-11Al (wt pct) with additions of yttrium, Al2O3, and Y2O3 have been prepared by mechanical alloying of elemental, master alloy and oxide powders. The powders were consolidated by
extrusion at 1000°C with a reduction ratio of 36:1. The resulting oxide contents were all approximately either 3 vol pct or
8 vol pct of mixed Al2O3-Y2O3 oxides or of Al2O3. The alloys exhibited substantial ductility at 600°C: an alloy containing 3 vol pct oxide could be readily warm worked to
sheet without intermediate annealing; an 8 vol pct alloy required intermediate annealing at 1100°C. The 3 vol pct alloys could
be recrystallized to produce large elongated grains by isothermal annealing of as-extruded material at 1450°C, but the high
temperature strength properties were not improved. However, these alloys, together with some of the 8 vol pct materials, could
be more readily recrystallized after rod (or sheet) rolling; sub-stantially improved tensile and stress rupture properties
were obtained following 9 pct rod rolling at 620°C and isothermal annealing for 2 h at 1350°C. In this condition, the rup-ture
strengths of selected alloys at 1000 and 1100°C were superior to those of competitive nickel-and cobalt-base superalloys.
The oxidation resistance of all the alloys was ex-cellent.
F. G. WILSON and C. D. DESFORGES, formerly with Fulmer Re-search Institute 相似文献
13.
Farzad Khodabakhshi Abdolreza Simchi Amirhossein Kokabi Martin Nosko Peter Švec 《Metallurgical and Materials Transactions A》2014,45(9):4073-4088
Annealed and wrought AA5052 aluminum alloy was subjected to friction stir processing (FSP) without and with 3 vol pct TiO2 nanoparticles. Microstructural studies by electron backscattered diffraction and transmission electron microscopy showed the formation of an ultra-fine-grained structure with fine distribution of TiO2 nanoparticles in the metal matrix. Nanometric Al3Ti and MgO particles were also observed, revealing in-situ solid-state reactions between Al and Mg with TiO2. Tensile testing at different strain rates determined that FSP decreased the strain rate sensitivity and work hardening of annealed Al-Mg alloy without and with TiO2 nanoparticles, while opposite results were obtained for the wrought alloy. Fractographic studies exhibited that the presence of hard reinforcement particles changed the fracture mode from ductile rupture to ductile-brittle fracture. Notably, the failure mechanism was also altered from shear to tensile rupture as the strain rate increased. Consequently, the fracture surface contained hemispherical equiaxed dimples instead of parabolic ones. 相似文献
14.
Design of quaternary Ir-Nb-Ni-Al refractory superalloys 总被引:2,自引:0,他引:2
X. H. Yu Y. Yamabe-Mitarai Y. Ro H. Harada 《Metallurgical and Materials Transactions A》2000,31(1):173-178
We propose a method for developing new quaternary Ir-Nb-Ni-Al refractory superalloys for ultra-high-temperature uses, by mixing
two types of binary alloys, Ir-20 at. pct Nb and Ni-16.8 at. pct Al, which contain fcc/L12 two-phase coherent structures. For alloys of various Ir-Nb/Ni-Al compositions, we analyzed the microstructure and measured
the compressive strengths. Phase analysis indicated that three-phase equilibria—fcc, Ir3Nb-L12, and Ni3Al-L12—existed in Ir-5Nb-62.4Ni-12.6Al (at. pct) (alloy A), Ir-10Nb-41.6Ni-8.4Al (at. pct) (alloy B), and Ir-15Nb-20.8Ni-4.2Al (at.
pct) (alloy C) at 1400 °C; at 1300 °C, three phase equilibria—fcc, Ir3Nb, and Ni3Al—existed in alloys A and C and four-phase equilibria—fcc, Ir3Nb, Ni3Al, and IrAl-B2—existed in alloy B. The fcc/L12 coherent structure was examined by using transmission electron microscopy (TEM). At a temperature of 1200 °C, the compressive
strength of these quaternary alloys was between 130 and 350 MPa, which was higher than that of commercial Ni-based superalloys,
such as MarM247 (50 MPa), and lower than that of Ir-based binary alloys (500 MPa). Compared to Ir-based alloys, the compressive
strain of these quaternary alloys was greatly improved. The potential of the quaternary alloys for ultra-high-temperature
use is also discussed. 相似文献
15.
Aluminum matrix composites: Fabrication and properties 总被引:7,自引:0,他引:7
Aluminum alloy matrix composites containing 1 to 30 wt pct of fibrous and particulate nonmetals varying in size from 0.06
μm to 840 μm were fabricated. The composites were cast into cylindrical molds for friction and wear tests, hot extrusion and
tensile tests. The distribution of the nonmetals in the cast ingots was homogeneous. Friction and wear tests were done on
a pin (52100 bearing steel) and dish type machine without lubrication. It was found that composites containing ∼10 wt pct
or more of SiC, TiC, Si3N4, Al2O3, glass, solid waste slag, and silica sand wear less than the pure matrix alloy, but have slightly higher average coefficients
of friction. Wear in composites containing soft particles, especially MgO and boron nitride was higher than the pure matrix
alloy. The average coefficient of friction of all the composites was in the range of 0.35 to 0.58. Increasing the sliding
velocity reduced this range to ∼ 0.4 to 0.45. The longitudinal tensile properties of the extruded composites (with the exception
of loss of ductility in some cases) are comparable to that of the matrix alloys. Improvements in strength or ductility were
noted. For example, addition of 15 wt pct of 3 μm size Al2O3 particles raised the yield and ultimate strength of the Al-4 pct Cu-0.75 pct Mg alloy matrix from 227 to 302 MPa, and 356
to 403 MPa, respectively. The corresponding percent elongation decreased from 25.8 to 12.5. The fact that the various composites
can be readily cast and hot formed suggests a variety of engineering applications.
AKIRA SATO, formerly Visiting Scientist at Massachusetts Institute of Technology, Cambridge. 相似文献
16.
In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), electrochemical and mechanical stretch methods. The results indicated that β-Mg17Al12 phase decreased and Al2Gd3 and Al0.4GdMn1.6 phase existed after Gd addition. Because of the Gd addition, the grain of AM50 magnesium alloy was refined significantly, which improved the tensile strength of AM50 magnesium alloy. The decreasing of β phase improved the corrosion resistance of the magnesium alloy. The fracture mechanism of the Gd modified AM50 magnesium alloy was quasi-cleavage fracture. The corrosion residual strength(CRS) of AM50 magnesium alloy was improved after 1 wt.% Gd addition. 相似文献
17.
K. Sharifian M. Emamy K. Tavighi S. E. Vaziri Yeganeh 《Metallurgical and Materials Transactions A》2014,45(12):5344-5350
In this investigation, the effect of hot extrusion process has been studied on the microstructure and tensile properties of aluminum matrix composite containing different amounts (10, 15, and 20 wt pct) of Al4Sr intermetallic phase. Microstructural examinations assessed by scanning electron microscopy revealed that hot extrusion breaks large Al4Sr particles and reduces their length tremendously. It was also found that although the addition of Al4Sr content in the composite reduces ultimate tensile strength and elongation values, hot extrusion improves tensile results significantly. Remarkable result of this study was concerned with significant improvement in the toughness of hot-extruded Al-10 wt pct Al4Sr composite in which elongation values raised up to 22 pct. Therefore, optimum amount of Al4Sr intermetallic in the composite was found to be 10 wt pct. Fractographic examinations revealed that hot extrusion encourages ductile mode of fracture by introducing homogeneous distribution of fine dimples on the fracture surface of the composites. 相似文献
18.
A. Inoue S. Furukawa M. Hagiwara T. Masumoto 《Metallurgical and Materials Transactions A》1987,18(5):621-628
Ni-based amorphous wires with good bending ductility have been prepared for Ni75Si8B17 and Ni78P12B10 alloys containing 1 to 2 at. pct Al or Zr by melt spinning in rotating water. The enhancement of the wire-formation tendency
by the addition of Al has been clarified to be due to the increase in the stability of the melt jet through the formation
of a thin A12O3 film on the outer surface. The maximum wire diameter is about 190 to 200 μm for the Ni-Si (or P)-B-Al alloys and increases
to about 250 μm for the Ni-Si-B-Al-Cr alloys containing 4 to 6 at. pct Cr. The tensile fracture strength and fracture elongation
are 2730 MPa and 2.9 pct for (Ni0.75Si0.08B0.17
99Al1) wire and 2170 MPa and 2.4 pct for (Ni0.78P0.12B0.1)99Al1 wire. These wires exhibit a fatigue limit under dynamic bending strain in air with a relative humidity of 65 pct; this limit
is 0.50 pct for a Ni-Si-B-Al wire, which is higher by 0.15 pct than that of a Fe75Si10B15 amorphous wire. Furthermore, the Ni-base wires do not fracture during a 180-deg bending even for a sample annealed at temperatures
just below the crystallization temperature, in sharp contrast to high embrittlement tendency for Fe-base amorphous alloys.
Thus, the Ni-based amorphous wires have been shown to be an attractive material similar to Fe- and Co-based amorphous wires
because of its high static and dynamic strength, high ductility, high stability to thermal embrittlement, and good corrosion
resistance. 相似文献
19.
The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class
of forged damage-tolerant niobium aluminide (Nb3Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti
(10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic percentages
unless stated otherwise. The 10Ti and 25Ti alloys exhibit fracture toughness levels between 10 and 20 MPa√m at room temperature.
Fracture in these alloys occurs by brittle cleavage fracture modes. In contrast, a ductile dimpled fracture mode is observed
at room-temperature for the alloy containing 40 at. pct Ti. The 40Ti alloy also exhibits exceptional combinations of room-temperature
strength (695 to 904 MPa), ductility (4 to 30 pct), fracture toughness (40 to 100 MPa√m), and fatigue crack growth resistance
(comparable to Ti-6Al-4V, monolithic Nb, and inconnel 718). The implications of the results are discussed for potential structural
applications of the 40Ti alloy in the intermediate-temperature (∼700 °C to 750 °C) regime. 相似文献
20.
The effect of Mg on the microstructure and mechanical behavior of Al-Si-Mg casting alloys 总被引:3,自引:0,他引:3
C. H. Caceres C. J. Davidson J. R. Griffiths Q. G. Wang 《Metallurgical and Materials Transactions A》1999,30(10):2611-2618
The microstructure and tensile behavior of two Al-7 pct Si-Mg casting alloys, with magnesium contents of 0.4 and 0.7 pct,
have been studied. Different microstructures were produced by varying the solidification rate and by modification with strontium.
An extraction technique was used to determine the maximum size of the eutectic silicon flakes and particles. The eutectic
Si particles in the unmodified alloys and, to a lesser extent, in the Sr-modified alloys are larger in the alloys with higher
Mg content. Large Fe-rich π-phase (Al9FeMg3Si5) particles are formed in the 0.7 pct Mg alloys together with some smaller β-phase (Al5FeSi) plates; in contrast, only β-phase plates are observed in the 0.4 pct Mg alloys. The yield stress increases with the Mg content, although, at 0.7 pct
Mg, it is less than expected, possibly because some of the Mg is lost to π-phase intermetallics. The tensile ductility is less in the higher Mg alloys, especially in the Sr-modified alloys, compared
with the lower Mg alloys. The loss of ductility of the unmodified alloy seems to be caused by the larger Si particles, while
the presence of large π-phase intermetallic particles accounts for the loss in ductility of the Sr-modified alloy. 相似文献