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1.
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
2.
A metallographic study of the porosity and fracture behavior in unidirectionally solidified end chill castings of 319.2 aluminum
alloy (Al-6.2 pct Si-3.8 pct Cu-0.5 pct Fe-0.14 pct Mn-0.06 pct Mg-0.073 pct Ti) was carried out using optical microscopy
and scanning electron microscopy (SEM) to determine their relationship with the tensile properties. The parameters varied
in the production of these castings were the hydrogen (∼0.1 and ∼0.37 mL/100 g Al), modifier (0 and 300 ppm Sr), and grain
refiner (0 and 0.02 wt pct Ti) concentrations, as well as the solidification time, which increased with increasing distance
from the end chill bottom of the casting, giving dendrite arm spacings (DASs) ranging from ∼15 to ∼95 /im. Image analysis
and energy dispersive X-ray (EDX) analysis were employed for quantification of porosity/microstructural constituents and fracture
surface analysis (phase identification), respectively. The results showed that the local solidification time(viz. DAS) significantly influences the ductility at low hydrogen levels; at higher levels, however, hydro-gen has a more pronounced
effect (porosity related) on the drop in ductility. Porosity is mainly observed in the form of elongated pores along the grain
boundaries, with Sr increasing the porosity volume percent and grain refining increasing the probability for pore branching.
The beneficial effect of Sr modification, however, improves the alloy ductility. Fracture of the Si, β-Al5FeSi, α- Al15(Fe,Mn)3Si2, and Al2Cu phases takes place within the phase particles rather than at the particle/Al matrix interface. Sensitivity of tensile properties
to DAS allows for the use of the latter as an indicator of the expected properties of the alloy. 相似文献
3.
M. Ravi U. T. S. Pillai B. C. Pai A. D. Damodaran E. S. Dwarakadasa 《Metallurgical and Materials Transactions A》2002,33(2):391-400
The effect of Fe content (0.2 to 0.6 pct) on the microstructure and mechanical properties of a cast Al-7Si-0.3Mg (LM 25/356)
alloy has been investigated. Further, 1 pct mischmetal (MM) additions (a mixture of rare-earth (RE) elements) were made to
these alloys, and their mechanical properties at room and at elevated temperatures (up to 200 °C) were evaluated. A structure-property
correlation on this alloy was attempted using optical microstructure analysis, fractographs, X-ray diffraction, energy-dispersive
analysis of X-rays (EDX), and quantitative metallography by image analysis. An increase in Fe content increased the volume
percentage of Fe-bearing intermetallic compounds (β and π phases), contributing to the loweryield strength (YS), ultimate tensile strength (UTS), percentage elongation, and higher
hardness. An addition of 1 pct MM to the alloys containing 0.2 and 0.6 pct Fe was found to refine the microstructure; modify
the eutectic silicon and La, Ce, and Nd present in the MM; form different intermetallic compounds with Al, Si, Fe, and Mg;
and improve the mechanical properties of the alloys both at room and elevated temperatures. 相似文献
4.
M. Ravi U. T. S. Pillai B. C. Pai A. D. Damodaran E. S. Dwarakadasa 《Metallurgical and Materials Transactions A》1996,27(5):1283-1292
This article deals with the effect of 0.25-1.5 wt pct mischmetal (MM) addition on the mechanical properties, microstructure,
electrical conductivity, and fracture behavior of cast Al-7Si-0.3Mg (LM 25/356) alloy. Modification of eutectic silicon by
MM is compared with strontium modification in terms of microstructure, mechanical properties, and fading behavior. Loss of
magnesium encountered on holding the molten alloy and its resultant effect on mechanical properties of alloys modified with
MM and Sr are compared with those in the unmodified alloy. 相似文献
5.
A new process for the preparation and casting of metal-particulate non-metal composites is described. Particulate composites
of ceramic oxides and carbides and an Al-5 pet Si-2 pct Fe matrix were successfully prepared. From 10 to 30 wt pct of A12O3, SiC, and up to 21 wt pct glass particles, ranging in size from 14 to 340 ώ were uniformly distributed in the liquid matrix
of a 0.4 to 0.45 fraction solid slurry of the alloy. Initially, the non-wetted ceramic particles are mechanically entrapped,
dispersed and prevented from settling, floating, or agglomerating by the fact that the alloy is already partially solid. With
increasing mixing times, after addition, interaction between the ceramic particles and the liquid matrix promotes bonding.
Efforts to mix the non-wetted particles into the liquid alloy above its liquidus temperature were unsuccessful. The composite
can then be cast either when the metal alloy is partially solid or after reheating to above the liquidus temperature of the
alloy. End-chilled plates and cylindrical slugs of the composites were sand cast from above the liquidus temperature of the
alloy. The cylindrical slugs were again reheated and used as starting material for die casting. Some of the reheated composites
possessed “thixotropy.” Distribution of the ceramic particles in the alloy matrix was uniform in all the castings except for
some settling of the coarse, 340ώ in size, particles in the end-chilled cast plates. 相似文献
6.
Minoru Furukawa Patrick B. Berbon Terence G. Langdon Zenji Horita Minoru Nemoto Nikolai K. Tsenev Ruslan Z. Valiev 《Metallurgical and Materials Transactions A》1998,29(1):169-177
Experiments were conducted to determine the age-hardening characteristics and the mechanical properties of an Al-5.5 pct Mg-2.2
pct Li-0.12 pct Zr alloy processed by equal-channel angular (ECA) pressing to give a very fine grain size of ∼1.2 μm. The results show that peak aging occurs more rapidly when the grain size is very fine, and this effect is interpreted in
terms of the higher volume of precipitate-free zones in the fine-grained material. Mechanical testing demonstrates that the
ECA-pressed material exhibits high strength and good ductility at room temperature compared to conventional Al alloys containing
Li. Elongations of up to ∼550 pct may be achieved at an elevated temperature of 603 K in the ECA-pressed condition, thereby
confirming that, in this condition, the alloy may be a suitable candidate material for use in superplastic forming operations. 相似文献
7.
S. S. Sreeja Kumari R. M. Pillai B. C. Pai K. Nogita A. K. Dahle 《Metallurgical and Materials Transactions A》2006,37(8):2581-2587
The effect of Ca addition on the microstructure, physical characteristics (density/porosity), and mechanical properties (tensile
and impact strength) has been investigated in an Al-7Si-0.3Mg-xFe (x=0.2, 0.4, and 0.7) alloy. The size of Al-Fe intermetallic platelets (β-Al5FeSi) increased with increasing Fe content. The addition of Ca modified the eutectic microstructure and also reduced the size
of intermetallic Fe-platelets, causing improved elongation and impact strengths. A low level of Ca addition (39 ppm) reduced
the proosity of the alloys. The tensile strength was decreased marginally with Ca addition. However, Ca addition improved
the ductility of the alloy by 18.3, 16.7, and 44 pct and the impact strength by 44, 48, and 15.8 pct for Fe contents of 0.2,
0.4, and 0.7 pct, respectively. 相似文献
8.
The effects of squeeze casting process on microstructure and flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy were investigated and the hot-compression tests of gravity casting and squeeze casting alloy were carried out at 350-500°C and 0.001-5s-1.The results show that microstructures of Al-17.5Si-4Cu-0.5Mg alloys were obviously improved by squeeze casting.Due to the decrease of coarse primary Si particles,softα-Al dendrite as well as the fine microstructures appeared,and the mechanical properties of squeeze casting alloys were improved.However,when the strain rate rises or the deformation temperature decreases,the flow stress increases and it was proved that the alloy is a positive strain rate sensitive material.It was deduced that compared with the gravity casting alloy,squeeze casting alloy(solidified at 632 MPa)is more difficult to deform since the flow stress of squeeze casting alloy is higher than that of gravity casting alloy when the deformation temperature exceeds 400°C.Flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy can be described by a hyperbolic sine form with Zener-Hollomon parameter,and the average hot deformation activation energy Q of gravity casting alloy and squeeze casting alloy is 278.97 and 308.77kJ/mol,respectively. 相似文献
9.
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
10.
11.
L. del Castillo H. M. Hu E. J. Lavernia Y. Wu 《Metallurgical and Materials Transactions A》1999,30(5):1381-1389
High-Li alloys, with the composition Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr, were synthesized using a spray deposition technique (wt. pct, X=0∼1.5). The microstructure of the spray-deposited Al-Li alloys consisted of equiaxed grains with an average grain size in
the range from 20 to 50 μm. The grain-boundary phases were fine and discrete. The spray-deposited and thermomechanically processed materials were isothermally
heat treated at 150 °C and 170 °C to investigate the age-hardening kinetics. It was noted that the spray-deposited Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr alloys exhibited relatively sluggish aging behavior. The peak-aged condition was achieved at 170 °C in
the range from 20 to 90 hours. It was noted that Cu increases the hardness of alloys during aging. Moreover, the influence
of Cu on age-hardening kinetics is marginal. The mechanical properties of the spray-deposited and extruded Al-Li alloys were
studied in the underaged, peak-aged, and overaged conditions. For example, the peak-aged yield strength, tensile strength,
and ductility of Al-3.8Li-1.0Cu-1.0Mg-0.4Ge-0.2Zr are 455 MPa, 601 MPa, and 3.1 pct, respectively. Moreover, an increase in
the Cu content of the alloy led to improvements in strength, with only slight changes in ductility, for Cu contents up to
1.0 wt pct. Beyond this range, an increase in Cu content led to decreases in both strength and ductility. 相似文献
12.
Sliding wear behavior of some Al-Si alloys: Role of shape and size of Si particles and test conditions 总被引:1,自引:0,他引:1
B. K. Prasad K. Venkateswarlu O. P. Modi A. K. Jha S. Das R. Dasgupta A. H. Yegneswaran 《Metallurgical and Materials Transactions A》1998,29(11):2747-2752
In this investigation, effects of the shape and size of silicon particles have been studied on the sliding wear response of
two Al-Si alloys, namely, LM13 and LM29. The LM13 alloy comprised 11.70 pct Si, 1.02 pct Cu, 1.50 pct Ni, 1.08 pct Mg, 0.70
pct Fe, 0.80 pct Mn, and remainder Al. The LM29 alloy contained 23.25 pct Si, 0.80 pct Cu, 1.10 pct Ni, 1.21 pct Mg, 0.71
pct Fe, 0.61 pct Mn, and remainder Al. Wear tests were conducted under the conditions of varying sliding speed and applied
pressure. The alloys were also characterized for their microstructural features and mechanical properties. The presence of
primary silicon particles in the alloy led to a higher hardness but lower tensile properties. Further, refinement in the size
of the primary particles improved the mechanical properties of the alloy system. The wear behavior of the alloys was influenced
by the presence of primary Si particles and was a function of their size. Samples with refined but identical microconstituents
(e.g., pressure cast vs gravity cast LM29 in terms of the size of primary Si particles and dendritic arm spacing) exhibited better wear characteristics.
Their overall effect was further controlled by the test conditions. It was observed that test conditions leading to the generation
of an optimal degree of frictional heating offer the best wear resistance. This was attributed to the reduced microcracking
tendency of the alloy system otherwise introduced by the Si particles. The reduced microcracking tendency in turn allows the
Si phase to carry load more effectively and impart better thermal stability to the alloy system. This caused improved wear
resistance under the circumstances. Further, the primary Si particles improved the wear resistance of the alloy system (e.g., gravity-cast LM29 vs gravity-cast LM13) under high operating temperature conditions. Additional thermal stability and protection offered to the
matrix by the primary Si phase, under the conditions of reduced microcracking tendency, were the reasons for the improved
wear characteristics of the alloy system. Conversely, a reverse effect was produced at low operating temperatures in view
of the predominating microcracking tendency. The study suggests that shape, size, microcracking tendency, and thermal stability
of different microconstituents greatly control the mechanical and tribological properties of these alloys. The extent of effective
load transfer between the phases plays an important role in this regard. Further, the overall effect of these factors is significantly
governed by the test conditions. 相似文献
13.
F. Zhou Z. Lee S. R. Nutt E. J. Lavernia 《Metallurgical and Materials Transactions A》2005,36(6):1587-1594
The microstructural evolution during annealing of a cryogenically ball-milled Al-7.5Mg-0.3Sc (in wt pct) was examined using
differential scanning calorimetry and transmission electron microscopy (TEM). The as-milled alloy was a supersaturated fcc
solid solution with an average grain size of ∼25 nm and heterogeneous grain morphologies and size distributions. Calorimetric
measurements at a constant heating rate of 32 K/min indicated two exothermic events in association with recovery from 100
°C to 240 °C and recrystallization from 300 °C to 450 °C. Prior to recrystallization, the precipitation of Al3Sc may occur at low annealing temperatures producing a nonuniform dispersion of approximately spherical particles with diameters
of 4 to 5 nm. Recrystallization gave rise to heterogeneous microstructures with bimodal grain size distributions, which may
result from the heterogeneity of microstructure in the as-milled state. The heterogeneous microstructures of the recrystallized
Al-Mg-Sc alloy were similar to those observed in the recrystallized Sc-free Al-Mg alloy. 相似文献
14.
Robert A. Ayres 《Metallurgical and Materials Transactions A》1977,8(3):487-492
A considerable enhancement of the tensile ductility in a commercial Al-4 pct Mg alloy is observed during deformation at elevated
temperatures (up to 250°C) and slow strain rates. Total elongations of ∼175 pct at 250°C were obtained compared to 27 pct
at ambient temperature. Much of this ductility was a result of large increases with temperature in the post uniform or diffuse
necking strain. Measurements of strain rate sensitivity,m, as a function of strain, strain rate, and temperature showed thatm near fracture was linearly related to total elongation. The mechanisms controllingm in this Al-4 pct Mg alloy were dynamic strain aging at the lower temperature range and dynamic recovery at the higher temperatures.m was found to be a function of strain only when the relative fraction of dynamic recovery was greater than ∼35 pct. A comparison
ofm as measured in pure aluminum and in the commercial Al-4 pct Mg alloy suggests that Mg additions can significantly increasem during dynamic recovery. 相似文献
15.
16.
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
17.
18.
19.
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
20.
The effects of impurity element of Fe and microelements of Zn, Cr and Ti on the constituents,dispersoids, grain size, mechanical properties and formability of Al-1.3Mg-1.2Si-0. 6Cu-0. 3Mn alloy were investigated in the present work by analyzing microstructures, phase composition, mechanical tests. The resuits indicated that with the increase of Fe content, the insoluble constituents increased, and the mechanical properties and r15 of alloy sheets debased, which can be recovered by the addition of microelements Zn, Cr and Ti. Al-1.3Mg-1.2Si-0. 6Cu-0. 3Mn alloy sheets in the T4 temper are difficult to strengthen with paint -bake treatment in automobile factory. 相似文献