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1.
The effects of extrusion ratio and alloying addition on the microstructure of Mg-0.2 wt pct Ce alloys are investigated by
electron backscatter diffraction. The results show that in this alloy, texture randomization does not occur at high or low
extrusion ratios but at a ratio of 25:1 at 400 °C. When extruded at the same temperature and extrusion ratio, Ca addition
to Mg results in a weak nonbasal texture. In contrast, Mg-Al and Mg-3 wt pct Al-0.2 wt pct Ce alloys do not exhibit texture
modification in single-pass extrusion. In the Mg-Al-Ce alloy, Ce and Al form Al 11Ce 3 particles, leaving little Ce solute in the matrix. The texture modifications in Mg-Ce or Mg-Ca alloys are related to the
nature of the solid solution and consistent with dynamic strain aging during extrusion. 相似文献
2.
Pure magnesium and two binary alloys, Mg-1 wt pct Al and Mg-1.4 wt pct Gd, have been prepared with comparable grain sizes
and textures. The alloys have been tensile tested at various strain rates and temperatures to examine the strain rate sensitivity
(SRS). It has been found that Mg and Mg-Al show increasing SRS with increasing deformation temperatures. The Mg-Gd alloy showed
decreasing SRS with increasing deformation temperatures and exhibited a negative SRS at 200 °C and 250 °C. Above these temperatures,
the SRS returned to a positive value. The elongation to fracture was not effected by the SRS, and it has been concluded that
for the alloys and conditions examined, the influences of mechanical twinning and dynamic recrystallization dominate the elongation
behavior, rather than the SRS. 相似文献
3.
This article describes the creep and microstructure of Mg-Al-Ca-based magnesium alloys (designated as ACX alloys, where A
stands for aluminum; C for calcium; and X for strontium or silicon) developed for automotive powertrain applications. Important
creep parameters, i.e., secondary creep rate and creep strength, for the new alloys are reported. Creep properties of the new alloys are significantly
better than those of the AE42 (Mg-4 pct* Al-2 pct RE**) alloy, which is the benchmark creep-resistant magnesium die-casting
alloy. Creep mechanisms for different temperature/stress regimes are proposed. A ternary intermetallic phase, (Mg,Al) 2Ca, was identified in the microstructure of the ACX alloys and is proposed to be responsible for the improved creep resistance
of the alloys.
All concentrations in wt. pct, unless otherwise stated.
RE stands for a combination of rare earth elements, i.e., misch metal, in this case. 相似文献
5.
Tensile tests were carried out at 123 K to 373 K (–150 °C to 100 °C) on pure Mg, Mg-3.0 mass pct (2.71 at. pct) Al alloy,
and Mg-0.06 mass pct (0.036 at. pct) Ca alloy. Little decrease occurred in the yield stress of the pure Mg and the Mg-Ca alloy
with increasing temperature from 223 K to 373 K (–50 °C to 100 °C). For the Mg-Al alloy, however, its yield stress decreased
with increasing temperature from 223 K to 373 K (–50 °C to 100 °C). Analyses based on the existing solid-solution strengthening
theories, focusing on the athermal component of stress, revealed that the dominant strengthening mechanism is the shear modulus
effect for the Mg-Ca alloy and the chemical interaction for the Mg-Al alloy. It is suggested that the shear modulus effect
is dominant at a low concentration and the chemical interaction is dominant at a high concentration for Mg alloys. 相似文献
6.
The impact of micro-alloying on tensile behavior at strain rates in various ranges is examined using five types of extruded Mg-0.3 at. pct Mn–0.1 at. pct X ternary alloys, where X is selected as a common element, Al, Li, Sn, Y or Zn. Microstructural observations reveal that the average grain size of these extruded alloys is between 1 and 3 μm, and these micro-alloying elements segregate at grain boundaries. In room temperature tensile and compression tests, these results show that the mechanical properties and deformation behavior are influenced by the micro-alloying element, even as a small addition of 0.1 at. pct. Mg–Mn–Y and Mg–Mn-Zn alloys show higher strength and smaller strain rate sensitivity (m-value) among the present alloys, owing to the rate-controlling mechanism as dislocation slip. On the other hand, the Mg–Mn–Li alloy exhibits the largest elongation to failure in tension and the highest strain rate sensitivity, associated with high contribution of grain boundary sliding to deformation. These differences are due to the grain boundary segregation of the micro-alloying elements. Compared to the common Mg alloys, the present ternary alloys also show a trade-off relationship between strength and ductility, which is similar to that of the well-known Mg alloys; however, these properties of the Mg–Mn system ternary alloys could be controlled via the type of micro-alloying elements with a chemical content of 0.1 at. pct. 相似文献
7.
An investigation has been made into the solidification behavior and microstructural evolution of AM50, AM70, and AM90 alloys
during rheo-diecasting, their processibility, and the resulting mechanical properties. It was found that solidification of
AM series alloys under intensive melt shearing in the unique twin-screw slurry maker during rheo-diecasting gave rise to numerous
spheroidal primary magnesium (Mg) particles that were uniformly present in the microstructure. As a result, the network of
the β-Mg 17Al 12 phase was consistently interrupted by these spheroidal and ductile particles. Such a microstructure reduced the obstacle
of deformation and the harmfulness of the β-Mg 17Al 12 network on ductility, and therefore improved the ductility of rheo-diecast AM alloys. It was shown that, even with 9 wt pct
Al, the elongation of rheo-diecast AM90 still achieved (9 ± 1.2) pct. Rheodiecasting thus provides an attractive processing
route for upgrading the alloy specification of AM series alloys by increasing the aluminum (Al) content while ensuring ductility.
Assessment of the processibility of AM series alloys for semisolid processing showed that high Al content AM series alloys
are more suitable for rheo-diecasting than low Al content alloys, because of the lower sensitivity of solid fraction to temperature,
the lower liquidus temperature, and the smaller interval between the semisolid processing temperature and the complete solidification
temperature. 相似文献
8.
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
9.
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 Al 2O 3 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 Al 2O 3 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-CuAl 2 phases. Moreover, Al-7Si-0.3Mg-0.5Cu-1 pct Al 2O 3 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 Al 2O 3 nanoparticles. However, the yield strength of the T6 heat-treated nanocomposites was limited in enhancement due to a reaction
between Mg and Al 2O 3 nanoparticles. 相似文献
11.
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.
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 (Al 9FeMg 3Si 5) particles are formed in the 0.7 pct Mg alloys together with some smaller β-phase (Al 5FeSi) 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
13.
The electrochemical codeposition of Mg and Li at an aluminium electrode in LiCl-KCl (50:50 wt pct) melts containing different
concentrations of MgCl 2 at 893 K (620 °C) to form Al-Li-Mg alloys was investigated. Cyclic voltammograms showed that the potential of Li metal deposition
at an Al electrode, before the addition of MgCl 2, is more positive than that of Li metal deposition at an Mo electrode, which indicated the formation of an Al-Li alloy. The
underpotential deposition of magnesium at an aluminium electrode leads to the formation of Al-Mg alloys, and the succeeding
underpotential deposition of lithium on predeposited Al-Mg alloys leads to the formation of Al-Li-Mg alloys. Chronopotentiometric
measurements indicated that the codeposition of Mg and Li occurs at current densities lower than −0.668 A cm −2 in LiCl-KCl-MgCl 2 (8 wt pct) melts at an aluminium electrode. The chronoamperometric studies indicated that the onset potential for the codeposition
of Mg and Li is −2.000 V, and the codeposition of Mg and Li at an aluminium electrode is formed into Al-Li-Mg alloys when
the applied potentials are more negative than −2.000 V. X-ray diffraction and inductively coupled plasma analysis indicated
that Al-Li-Mg alloys with different lithium and magnesium contents were prepared via potentiostatic and galvanostatic electrolysis. The microstructure of typical dual phases of the Al-Li-Mg alloy was characterized
by an optical microscope and by scanning electron microscopy. The analysis of energy dispersive spectrometry showed that the
elements of Al and Mg distribute homogeneously in the Al-Li-Mg alloy. The lithium and magnesium contents of Al-Li-Mg alloys
can be controlled by MgCl 2 concentrations and by electrolytic parameters. 相似文献
14.
Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace
and automotive applications because of their low density and superior specific properties. This article presents a liquid
mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional
foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial
reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters
and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this
work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid
excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding
are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied
and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite,
based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength
and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to
the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding,
in the fracture process of the composite. 相似文献
15.
This study examined the microstructural evolution and castability of Al–Mg–Si ternary alloys with varying Si contents. Al–6Mg–xSi alloys (where x = 0, 1, 3, 5, and 7; all compositions in mass pct) were examined, with Al–6 mass pct Mg as a base alloy. The results showed that in the ternary alloys with Si ≤ 3 pct, the solidification process ended with the formation of eutectic α-Al–Mg2Si phases generated by a univariant reaction. However, in the case of ternary alloys with Si > 3 pct, solidification was completed with the formation of α-Al–Mg2Si–Si ternary eutectic phases generated by a three-phase invariant reaction. In addition to the eutectic Mg2Si phases, the primary Mg2Si phases formed in each of the ternary alloys, and the size of both sets of phases increased with increasing Si content. The two-phase eutectic α-Al–Mg2Si nucleated from the primary Mg2Si phases. The inoculated Al–6Mg–1Si alloy had the smallest grain size. Moreover, the grain-refining efficacy of the Al–5Ti–B master alloy in the ternary alloys decreased with increasing Si content in the alloys. Despite the poisoning effect of Si on the potency of TiB2 compounds in the inoculated Al–6Mg–1Si alloy, the grain size of the alloy was slightly smaller than that of the Al–6Mg binary alloy. This resulted from the increasing growth restriction factor (induced by Si addition) of the Al–6Mg–1Si alloy. In terms of the castability, the examined alloys showed different levels of susceptibility to hot tearing. Among the alloys, the ternary Al–6Mg–5Si alloy exhibited the highest susceptibility to hot tearing, whereas the Al–6Mg–7Si exhibited the lowest. The severity of hot tearing initiated by the unraveling of the bifilm was determined by the freezing range, grain size, and the amount of eutectic phases at the end of the solidification process. 相似文献
16.
The solidification microstructure and mechanical properties of as-cast Mg-Al-Sn alloys have been investigated using computational
thermodynamics and experiments. The as-cast microstructure of Mg-Al-Sn alloys consists of α-Mg, Mg 17Al 12, and Mg 2Sn phases. The amount of Mg 17Al 12 and Mg 2Sn phases formed increases with increasing Al and Sn content and shows good agreement between the experimental results and
the Scheil solidification calculations. Generally, the yield strength of as-cast alloys increases with Al and Sn content,
whereas the ductility decreases. This study has confirmed an early development of Mg-7Al-2Sn alloy for structural applications
and has led to a promising new Mg-7Al-5Sn alloy with significantly improved strength and ductility comparable with commercial
AZ91 alloy. 相似文献
17.
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
19.
Mg-9Li-3Al- xSr (LA93- xSr, x = 0, 1.5, 2.5, and 3.5 wt pct) alloys were cast and extruded at 533 K (260 °C) with an extrusion ratio of 28. The microstructure and mechanical response are reported and discussed paying particular attention to the influence of extrusion and Sr content on phase composition, strength, and ductility. The results of the current study show that LA93- xSr alloys contain both α-Mg (hcp) and β-Li (bcc) matrix phases. Moreover, the addition of Sr refines the grain size in the as-cast alloys and leads to the formation of the intermetallic compound (Al 4Sr). Our results show significant grain refinement during extrusion and almost no influence of Sr content on the grain size of the extruded alloys. The microstructure evolution during extrusion is governed by continuous dynamic recrystallization (CDRX) in the α-Mg phase, whereas discontinuous dynamic recrystallization (DDRX) occurs in the β-Li phase. The mechanical behavior of the extruded LA93- xSr alloy is discussed in terms of grain refinement and dislocation strengthening. The tensile strength of the extruded alloys first increases and then decreases, whereas the elongation decreases monotonically with increasing Sr; in contrast, hardness increases for all Sr compositions studied herein. Specifically, when Sr content is 2.5 wt pct, the extruded Mg-9Li-3Al-2.5Sr (LAJ932) alloy exhibits a favorable combination of strength and ductility with an ultimate tensile strength of 235 MPa, yield strength of 221 MPa, and an elongation of 19.4 pct. 相似文献
20.
An Al-3 pct Mg-0.2 pct Sc alloy was fabricated by casting and subjected to equal-channel angular pressing to reduce the grain
size to ∼0.2 μm. Very high tensile elongations were achieved in this alloy at temperatures over the range from 573 to 723
K, with elongations up to >2000 pct at temperatures of 673 and 723 K and strain rates at and above 10 −2 s −1. By contrast, samples of the same alloy subjected to cold rolling (CR) yielded elongations to failure of <400 pct at 673
K. An analysis of the experimental data for the equal-channel angular (ECA)—pressed samples shows consistency with conventional
superplasticity including an activation energy for superplastic flow which is within the range anticipated for grain boundary
diffusion in pure Al and interdiffusion in Al−Mg solid solution alloys.
MINORU NEMOTO, formerly Professor, Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University. 相似文献
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