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1.
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
2.
The torsional vibration damping of Mg-4.5 Ce alloys has been correlated with the texture orientation resulting from the method
of fabrication. Forged and forged-plus-swaged alloys at vibratory stress levels of 1500 psi exhibit specific damping capacities,
respectively, of 6 and 11 times that of an extruded alloy of similar composition. Pole figures show that the basal planes
are oriented preferentially in the extruded alloys with a 20 deg tilt to the axis of the extrusion, while the basal planes
are generally parallel to the rod axis for forged or forged-plus-swaged alloys. The correlations indicate that the major source
of damping in these hexagonal magnesium alloys is stress-induced anelastic shear on the basal planes (probably by dislocation
motion). 相似文献
3.
Equal-channel angular pressing (ECAP) is used to refine grains and to change the texture of the initial pressed Mg-0.49% Al-0.47% Ca alloy rod in order to study the possibility of increasing the low-temperature ductility of the alloy. ECAP is performed at 300°C in six passes at a total true logarithmic strain ε = 6.8 according to route B C . As a result, an ultrafine-grained structure with a grain size of 2–5 μm forms. The initial texture of the pressed rod is characterized by the [12 11] axial orientation parallel to the pressing direction. After ECAP, the texture changes its type and is characterized by a set of preferred orientations that represent basal planes located at an angle of 40°–50° with respect to the pressing direction. An analysis of the generalized Schmid factors, which were calculated for the main operating deformation systems with allowance for the critical shear stresses in them and the volume fractions of the preferred orientations, indicates that the texture caused by ECAP affects the decrease in the strength properties of the alloy measured at room temperature and the increase in the low-temperature ductility of the alloy. 相似文献
4.
Equal-channel angular pressing (ECAP) of am MA2-1 alloy according to routes A and Bc is used to study the possibility of increasing
the low-temperature deformability of the alloy due to grain refinement and a change in its texture. To separate the grain
refinement effect from the effect of texture on the deformability of the alloy, samples after ECAP are subjected to recrystallization
annealing that provides grain growth to the grain size characteristic of the initial state (IS) of the alloy. Upon ECAP, the
average grain size is found to decrease to 2–2.4 μm and the initial sharp axial texture changes substantially (it decomposes
into several scattered orientations). The type of orientations and the degree of their scattering depend on the type of ECAP
routes. The detected change in the texture is accompanied by an increase in the deformability parameters (normal plastic anisotropy
coefficient R, strain-hardening exponent n, relative uniform elongation δ u) determined upon tensile tests at 20°C for the states of the alloy formed in the IS-4A-4Bc and IS-4Ao-4B cO sequences. The experimental values of R agree with the values calculated in terms of the Taylor model of plastic deformation in the Bishop-Hill approximation using
quantitative texture data in the form of orientation distribution function coefficients with allowance for the activation
of prismatic slip, especially for ECAP routes 4B c and 4B cO. When the simulation results, the Hall-Petch relation, and the generalized Schmid factors are taken into account, a correlation
is detected between the deformability parameter, the Hall-Petch coefficient, and the ratio of the critical shear stresses
on prismatic and basal planes. 相似文献
5.
Ca was added to Mg-1Zn and Mg-6Zn alloys to modify their texture, and the origin of texture modification by Ca addition has been investigated. It shows that Mg-1Zn-1Ca (ZX11) and Mg-6Zn-1Ca (ZX61) alloy sheets in the as-rolled condition show the textures having a splitting of basal poles toward the rolling direction and a splitting of basal poles toward the transverse direction, respectively. An analysis of the microstructure in the as-rolled condition shows that two different types of twins become active during rolling, double twins for ZX11 and tension twins for ZX61, suggesting that double twinning and tension twinning promote a splitting of basal poles toward the rolling direction (ZX11) and transverse direction (ZX61), respectively. On the other hand, after annealing, both alloy sheets show a weakened texture characterized by a splitting of basal poles toward the transverse direction. During annealing, the growth of tension twin-oriented grains occurs, resulting in the texture having a splitting of basal poles toward the transverse direction in both alloys. These alloys show not only higher yield strength but also better stretch formability than Al 5052 alloy, showing their potential as highly formable Mg sheet alloys. 相似文献
6.
Current commercial magnesium extrusion alloys do not offer desirable combinations of strength, ductility, and extrusion speed
for automotive structural applications. The effect of small additions of cerium (Ce) to pure magnesium (Mg) and Mg-3 pct Al
alloy extruded tubes has been studied. The results suggest that 0.2 pct Ce addition can significantly improve the extrudability
and mechanical properties of the Mg extrusions. The improvement in mechanical properties is due to grain refinement and dispersion
strengthening provided by the Mg 12Ce particles and the beneficial texture obtained. Higher Ce contents further increase strength, but significantly reduce ductility
and cause excessive surface oxidation during extrusion. The beneficial effect of 0.2 pct Ce on mechanical properties of pure
Mg is not observed when it is added to Mg-3 pct Al alloy, due to the higher affinity of Ce to Al to form the Al 11Ce 3 phase in the Mg-Al-Ce ternary alloys. The Mg-0.2 pct Ce alloy is a promising base alloy for further development in automotive
applications; however, Al should be avoided in Mg-Ce–based extrusion alloys. 相似文献
7.
Commercial purity aluminum was deformed by equal channel angular pressing (ECAP) using steel dies producing two different
shear strains of either 1.15 or 0.60 in each pass. Two sets of samples were selected for study, of which the first set consists
of aluminum billets repeatedly deformed without changing orientation (process A) up to three passes using first die. The second
set of samples was equal channel angular pressed (ECAPed) using the second die up to 10 passes adopting process B c, where samples were rotated by 90 deg between successive passes. The flow patterns were revealed by optical metallography.
Tensile strength and hardness were measured. The ECAPed samples were isochronally-annealed and recrystallization behavior
was studied by microscopy and Vickers hardness measurements. Refinement of grain size, substructure, and texture was studied
by transmission electron microscopy (TEM) and orientation imaging microscopy (OIM). The results show that flow patterns are
complex and distinct from simple shear. Strain is higher at the outer surfaces, highest at the bottom surface, and intermediate
in the middle of the billet. The work piece strain hardens significantly in first pass with an attendant drop in ductility.
The degree of strengthening reduces in subsequent passes. The high defect density introduced during the initial passes leads
to grain refinement to an ultrafine level and advantageously the material regains ductility. The refinement in microstructure
obtained after two to three passes is stable up to 250 °C. The flow patterns are very similar to those obtained by physical
modeling in our earlier studies using plasticine. Equiaxed ultrafine-grained structure (average grain size = 0.53 μm) was obtained after ECAP at an equivalent shear strain of 6.0.
This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part
of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred on December 15–16, 2006 in Mumbai, India.
相似文献
8.
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
9.
In the present investigation, wear performance of equal channel angular pressing (ECAP) processed cast Al–Zn–Mg alloys under dry sliding wear conditions was studied against a steel disc. Initially, Al–Zn–Mg alloys (with 5, 10, 15% zinc and 2% magnesium) were ECAP processed. After ECAP, grain size was reduced and enhancement in the hardness was observed. Wear resistance of the alloys increased after ECAP processing. Wear resistance of the alloys also increased when the quantity of the zinc was increased in the alloys. But, wear resistance of all three alloys decreased with increase in the load and the sliding speed. Coefficient of friction of the alloys decreased after ECAP processing. Coefficient of friction of the alloys also decreased when the quantity of the zinc was increased in the alloys. Coefficient of friction of all three alloys increased with increase in the load and the sliding speed. Irrespective of the alloy composition and applied load, worn surfaces of the cast and homogenized samples were composed of plastic deformation, scratches and micro-ploughing. On the other hand, in ECAP processed samples, morphology of the worn surfaces depended on the applied load. Abrasive wear is the main wear mechanism perceived in cast and homogenized samples at all loads. While in ECAP processed samples, the wear mechanism shifted from adhesive and oxidation wear to abrasive wear with increase in the load. Formation of oxide layers on the surface of the sample increased with increase in the ECAP passes. In ECAP processed samples, transfer of iron content from the disc to the sample surface was identified. 相似文献
10.
Ultrafine-grained (UFG) Mg-3Al-1Zn (AZ31) alloys with gain sizes ranging from 0.46 to 3.22 μm were prepared by equal channel angular pressing (ECAP) and annealing. The deformation structure of UFG AZ31 alloy resulting
from uniaxial compression was studied by optical and electron microscopy. The deformation was noted to proceed with the development
of shear bands (SBs), which has not been reported in an UFG hcp metal. Characterization of these SBs was performed, and comparison
with the SBs formed in UFG bcc and fcc metals was given. { 10[`1]2} \{ 10\bar{1}2\} tension twins inside SBs were found in all specimens compressed, irrespective of the grain size. Discussion on the limiting
grain size of twinning in the UFG AZ31 alloy is also given. 相似文献
11.
Mg-2Al-0.5Mn alloys with 0-0.5% Zn and 0.5%-1.0% La-Ce misch metal (MM) were prepared by metal mould casting method. Effect of alloying elements Zn and MM on microstructures were investigated by X-ray diffraction, optical microstructure and scanning electron microscope. The results showed that Zn and MM additions led to an obvious grain refinement. Addition of 0.5% Zn resulted in about 30% reduction in grain size for Mg-2Al-0.5Mn alloys, while 0.5% MM addition caused about 40% reduction in grain size. The t... 相似文献
12.
Grain size effects on three generations of twins were investigated in extruded Mg-4 wt pct Li (-1 wt pct Al) alloys using electron-backscatter diffraction. Samples with three distinct grains sizes, yet the same texture and applied strain were analyzed. With these variables fixed, we show that compression and double twinning decrease substantially with decreasing grain size. We find that compression twinning exhibits a stronger grain size effect than tension twinning, whereas the compression twinning to double twinning transition is independent of grain size. 相似文献
13.
Sheet samples of Mg-8Li,Mg-8Li-3Al,Mg-8Li-3AlSi and Mg-8Li-5AlSi alloys were obtained by hot rolling.Optical microscope,microhardness tester,nanoindentor,X-ray diffractometer and electrochemical analyzer were adopted to investigate the microstructures,micro-mechanical properties and corrosion resistance.Roller was preheated to 150°C before rolling process,and rolling reduction designed was about20% per pass with a total rolling reduction of 84%.The rolled plates were annealed at 200°C for 120 min.The tensile tests were performed at room temperature.Experimental results showed that both the strength and corrosion resistance of theα+βdual-phase of Mg-Li alloy were significantly improved with adding Al-Si elements.The strength enhancement was attributed to the solid solution of Al into theα-Mg matrix and into theβ-Li matrix as well as to the precipitation strengthening of Mg2 Si particles.Besides,the dendrite grains ofα-Mg transformed to equiaxed ones with addition of Al into alloy Mg-Li. 相似文献
14.
Significant grain refinement was achieved in rare earth (RE) containing aeronautic magnesium alloy ZE41A through equal-chan-nel angular pressing (ECAP) using rotary die at 603 K. Influence of ECAP pass number on its microstructure change and corrosion behavior was investigated by optical microscope (OM)/scanning electron microscope (SEM) observation and potentiostatic polarization tests in aque-otis solution of NaCl, respectively. The results showed that ultrafine equiaxial grains (about 2.5 μm) were obtained over 16 passes due to plastic-induced grain refinement accommodated by dynamic recrystallization. The lower corrosion current density and nobler corrosion po-tential correlated with large number of pressing passes were attributed to the low tendency toward localized corrosion with broken secondary phase after homogenization on ultrafine-grained Mg matrix. The multi-pass ECAP method made the ZE41A aeronautic magnesium alloy more attractive since severe plastic deformation may significandy improve its corrosion resistance besides superior mechanical properties. 相似文献
15.
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
16.
The deformation behavior of textured ultrafine-grained (UFG) and fine-grained (FG) Mg-3Al-1Zn alloy compressed along the easy-glide
orientation was studied. It was found that severe strain localization within very thin shear bands (SBs) caused the loss of
ductility in UFG Mg-3Al-1Zn alloy. Increasing grain size increases the width of SBs, which decreases the degree of strain
localization. The reason for the occurrence of severe strain localization in textured UFG Mg-3Al-1Zn alloy is proposed. 相似文献
17.
在Mg-6Al-1Zn合金的基础上添加不同质量分数的Y(分别为0%,0.5%,0.9%,1.4%),制备了4种实验合金,研究了Y的添加对合金组织性能的影响。通过X射线衍射、金相显微镜、扫描电镜、电子探针等手段分析了Mg-6Al-1Zn合金添加Y后组织结构的变化。研究结果表明,添加了不同含量Y的合金中都出现了一种新相Al2Y相。随着Y含量的增加,Al2Y相数量增多而Mg17Al 12相则减少。Y能细化合金铸态及挤压态显微组织,其细化作用在添加了0.9%Y的镁合金中尤为明显。铸态合金室温拉伸试验表明:该合金具有最佳的综合力学性能。当Y含量添加至1.4%时,Al2Y相变得粗大且出现团聚现象而导致了拉伸性能的下降。经过挤压后,合金的力学性能大幅度上升。 相似文献
18.
This study developed the reciprocating extrusion method to refine the inclusions and grain structure of Al-5.8Mg-0.23Mn alloys
to enhance their strength and superplasticity without prior homogenization treatment. Alloy cast billets were extruded with
an extrusion ratio of 10:1 at 450 °C for one, five, or ten passes. The grain size was reduced to 4.6 μm, and the coarse inclusions refined to 2 μm, after ten passes. A subgrain structure was formed in the interior of the fine grains, indicating that dynamic recrystallization
occurred during extrusion. In this study, dynamic recrystallization in the billet was repeatedly induced by a number of extrusion
passes until a limiting grain size was obtained. Thereafter, dynamic recrystallization was no longer activated because grain
boundary sliding, instead of dislocation gliding, accommodated the deformation strain required for extrusion. The alloys extruded
in ten-passes extrusion were found to be stronger and more ductile than commercial Al-Mg alloys and showed improved superplastic
behavior at 500 °C not only from low to high strain rate but also with a small flow stress of less than 30 MPa. These advantages
demonstrate that reciprocating extrusion can produce Al-Mg alloys with improved mechanical properties making them good candidates
for high-strain-rate superplastic forming. 相似文献
19.
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 during in 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 (Al 2CuMg) 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
20.
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
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