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1.
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
2.
Microstructural examination of the Al-5.3Mg-2.4Si-0.6Mn-1.0Fe alloy in the die-cast condition revealed that a significant number of the primary α-AlFeMnSi intermetallic particles were found inside both the coarse α-Al dendrite fragments formed in the shot sleeve and the fine α-Al grains formed in the die cavity. The heterogeneous nucleation of α-Al phase on primary α-AlFeMnSi intermetallic particle was further investigated experimentally. 3-Dimension (3D) scanning electron microscopy ultramicrotomy revealed that the probability of finding at least one primary α-AlFeMnSi intermetallic particle inside each α-Al grain was almost 90 pct. The detailed microstructural analysis identified the primary α-AlFeMnSi intermetallic particle as the α-Al 12(Fe,Mn) 3Si composition with a body-centered cubic structure and a lattice parameter of a = 1.265 nm. It was found that the primary α-Al 12(Fe,Mn) 3Si intermetallic particle had a faceted morphology with {110} planes exposed as its natural surfaces. High resolution transmission electron microscopy further confirmed that the crystallographic orientation relationship between α-Al 12(Fe,Mn) 3Si intermetallic particle and α-Al phase was: [111] α-AlFeMnSi//[110] Al and (1 \( \overline{1} \) 0) α-AlFeMnSi~6 deg from (1 \( \overline{1} \) 1) α-Al, and the corresponding interface between two phases could be confirmed as a semi-coherent interface with a lattice misfit of 2.67 pct at 933 K (660 °C), which was considerably smaller than the theoretical limit (5.7 pct) for epitaxial nucleation. Finally, based on these experimental evidences and the epitaxial nucleation model, we concluded that the primary α-Al 12(Fe,Mn) 3Si intermetallic particles were both potent and effective nucleating substrates for the α-Al phase. 相似文献
3.
The influence of solidification rate on the solution-treatment response has been investigated for an Al-7Si-0.3Mg alloy and an Al-8Si-3Cu-0.5Mg alloy. The concentrations of Mg, Cu, and Si in the matrix after different solution-treatment times were measured using a wavelength dispersive spectrometer. All Mg dissolves into the matrix for the Al-Si-Mg alloy when solution treated at 803 K (530 °C) because the π-Fe phase is unstable and transforms into short β-Fe plates which release Mg. The Q-Al 5Mg 8Cu 2Si 6 phase do not dissolve completely at 768 K (495 °C) in the Al-Si-Cu-Mg alloy and the concentration in the matrix reached 0.22 to 0.25 wt pct Mg. The distance between π-Fe phases and Al 2Cu phases was found to determine the solution-treatment time needed for dissolution and homogenization for the Al-Si-Mg alloy and Al-Si-Cu-Mg alloy, respectively. From the distance between the phases, a dimensionless diffusion time was calculated which can be used to estimate the solution-treatment times needed for different coarsenesses of the microstructure. A model was developed to describe the dissolution and homogenization processes. 相似文献
4.
Hypereutectic Al?CSi alloys are used in components that require high resistance wear and corrosion, good mechanical properties, low thermal expansion and less density. The size and morphology of hard primary silicon particles present in Al?CSi alloys greatly influences the mechanical properties. Addition of Mg leads to formation of intermetallic Mg 2Si phases, which contributes towards the properties of high silicon alloy as well as alters the nature and quantity of primary silicon formed. The high silicon alloy subjected to centrifugal casting leads to the formation of functionally gradient material, which provides variation in spatial and continuous distribution of primary phases in a definite direction exhibiting selective properties and functions within a component. The present study is to evaluate the effect of Mg on solidification microstructures of homogenous and functionally graded A390 aluminium alloys. The addition of Mg from 3 to 5?% in A390 alloy using Al?C20Mg master alloy has shown a transformation from primary silicon rich matrix to Mg 2Si rich matrix. Centrifugal casting shows the gradient distribution of primary silicon and Mg 2Si phases towards the inner periphery of the casting. 相似文献
5.
A novel hypereutectic die casting Al-Si-Mg alloy with relatively high Mg content was developed. The optimized microstructure of the alloy is characterized by a fine dispersion of eutectic Si and Mg 2Si particles in an α-Al matrix which is devoid of primary silicon particles. Of the several modifiers used to refine the coarse morphology of the Mg 2Si particles, an optimum combination of strontium and misch metal yielded the best results. The refined microstructure after a standard T6 heat treatment accounts for the enhanced room temperature tensile properties of castings made from this alloy. 相似文献
6.
Based on the densification of the spray-formed hypereutectic Al-Si (hyper-AS) alloys, the microstructural evolution, mechanical properties, as well as the failure are studied in this investigation. The appropriate process and parameters for the densification of the deposits are gained from the thermomechanical simulation. Besides of the spray-formed Al-25Si-5Fe-3Cu (3C) alloy, the microstructures of other spray-formed alloys with Mn/Cr addition are stable without coarsening of the refined α-Al(Fe,TM)Si (TM = Mn/Cr/(Mn+Cr)) particles, which can improve the heat resistance. Especially, a great number of the submicrosized α-Al(Fe,TM)Si phases are observed in the hot-extruded TM-containing alloys. The critical ranges of the major parameter TM/Fe mass ratios that can affect the formation of the α-Al(Fe,TM)Si phases in the cast or spray-formed hyper-AS alloys are severally determined. The structure and lattice constant of the refined α-Al(Fe,TM)Si phases also are characterized. The mechanical properties of the current extruded hyper-AS alloys at room or elevated temperatures are close to or higher than some commercial alloys or other published results. Therefore, the hyper-AS alloys can be proposed as new lightweight, heat-resistant, and high-strength alloys, which can be used in the complex working conditions, such as advanced engine systems. The main reason for the enhanced properties would be the formation of a large quantity of microsized/submicrosized α-Al(Fe,TM)Si phases and abundant dislocations, which can greatly reinforce the matrix and transform the brittle fracture of the needle-like Fe-bearing phases into ductile fracture. 相似文献
7.
In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1?×?10 ?4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al 12Mg 17, Al 3Mg 2, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al 3Mg 2 caused brittle fracturing. 相似文献
8.
The Al ― Mg ― Si phase diagram was studied and the formation conditions for a regular two-phase eutectic structure (α-Al + Mg 2Si) were established. Concentration limits were found for optimum alloy compositions with maximum melting point (~595°C) and a narrow (or zero) melting (crystallization) range (less than 5°C). The structures of these alloys are formed by Mg 2Si monocrystal fibers and lamellae with a high degree of ordering, located in the aluminum matrix. 相似文献
10.
In the present investigation, Al–X?wt-% Mg 2Si ( X?=?0, 5, 10, 15 and 20) in situ composites are successfully synthesised by one-step gravity casting technique. Commercially pure Al, Mg and Si are used as raw materials. Microstructural evaluation and correlation of micro- and bulk hardness properties have been studied on developing composites. The composites consist of mainly three phases: matrix ( α-Al), reinforcing (primary Mg 2Si) and binary eutectic (Al–Mg 2Si) phase. Primary Mg 2Si particles are formed by pseudo-eutectic transformation during solidification and surrounded by matrix and binary eutectic phase. It is found that Mg 2Si concentration has a significant impact on morphology and volume per cent of the above-mentioned phases. Primary Mg 2Si particles’ size and volume per cent increase with increasing wt-% of Mg 2Si. Volume per cent of individual phases and Mg 2Si concentration have great impact on hardness properties of composites. Bulk hardness increases with increasing wt-% of Mg 2Si concentration, but micro-hardness of primary Mg 2Si particle decreases slightly. Mg 2Si concentration also has significant impact on micro-hardness of individual phases. 相似文献
11.
A series of Al-5 wt pct Si alloys with Yb additions (up to 6100 ppm) have been investigated using thermal analysis and multiscale microstructure characterization techniques. The addition of Yb was found to cause no modification effect to a fibrous morphology involving Si twinning; however, a refined plate-like eutectic structure was observed. The Al 2Si 2Yb phase was observed with Yb addition level of more than 1000 ppm. Within the eutectic Al and Si phases, the Al 2Si 2Yb phase was also found as a precipitation from the remained liquid. No Yb was detected in the α-Al matrix or plate-like Si particle, even with Yb addition up to 6100 ppm. The absence of Yb inside the eutectic Si particle may partly explain why no significant Si twinning was observed along {111} Si planes in the eutectic Si particle. In addition, the formation of the thermodynamic stable YbP phases is also proposed to deteriorate the potency of AlP phase in Al alloys. This investigation highlights to distinguish the modification associated with the ever present P in Al alloys. We define modification as a transition from faceted to fibrous morphology, while a reduction of the Si size is termed refinement. 相似文献
12.
The microstructural evolution and mechanical properties of an AC8A/12 vol Pct A1 2O 3 (sf) composite fabricated by squeeze casting were characterized. Thermal treatments included the normal T6 temper and thermal
exposure at 150 °C, 250 °C, 300 °C, and 350 °C for 400 hours. The predominant strengthening phase in the matrix appeared to
be β′ (Mg 2Si) needles. Bulk pure Si particles and dendrites were commonly seen. Large particles, termed as B-type phase, might include hexagonal Al 3(Ni, Cu, Fe, Si, Mg) 2 and orthorhombic Al 3(Ni, Cu, Fe, Si, Mg) phases. Both the Si and B dispersoids were not obviously affected by artificial aging at 150 °C to 350 °C. In certain cases, large cubic β (Mg 2Si) particles, hexagonal Q′ or Q (Al 4Cu 2Mg 8Si 7) precipitates, and numerous small Al particles inside Si dispersoids were also seen. No interfacial reaction product was
observed along the fiber/ matrix interface even after long exposure at 350 °C. Amorphous SiO 2 gels, which were used as a binder during fabrication, were occasionally observed. The tensile and fatigue behavior of the
AC8A alloys and composites after the preceding thermal exposures were evaluated over the temperature range of 25 °C to 350
°C. The composites showed similar strength as the matrix alloy at room temperature but exhibited higher strength at temperatures
above 250 °C, with the sacrifice of the lower ductility. The strength levels of both the alloys and composites were significantly
reduced after long thermal exposure, especially for temperatures higher than 250 °C. The loss of strength after long-term
exposure at elevated temperatures may be attributed to age-softening of the matrix. 相似文献
13.
Al-Si alloys are materials that have been developed over the years to meet the increasing demands of the automotive industry
for smaller, lighter-weight, high-performance components. An important alloy in this respect is the 319 alloy, wherein silicon
and copper are the main alloying elements, and magnesium is often added in automotive versions of the alloy for strengthening
purposes. The mechanical properties are also ameliorated by modifying the eutectic silicon structure (strontium being commonly
employed) and by reducing the harmful effect of the β-Al 5FeSi iron intermetallic present in the cast structure. Magnesium is also found to refine the silicon structure. The present
study was undertaken to investigate the individual and combined roles of Mg and Sr on the morphologies of Si, Mg 2Si, and the iron and copper intermetallics likely to form during the solidification of 319-type alloys at very slow (close
to equilibrium) cooling rates. The results show that magnesium leads to the precipitation of Al 8Mg 3FeSi 6, Mg 2Si, and Al 5Mg 8Cu 2Si 6 intermetallics. With a strontium addition, dissolution of a large proportion of the needle-like β-Al 5FeSi intermetallic in the aluminum matrix takes place; no transformation of this phase into any other intermetallics (including
the Al 15(Fe,Mn) 3Si 2 phase) is observed. When both Mg and Sr are added, the diminution of the β-Al 5FeSi phase is enhanced, through both its dissolution in the aluminum matrix as well as its transformation into Al 8Mg 3FeSi 6. The reactions and phases obtained have been analyzed using thermal analysis, optical microscopy, image analysis, and electron
microprobe analysis (EMPA) coupled with energydispersive X-ray (EDX) analysis. 相似文献
14.
The current investigation reports detailed study on the microstructural evolution in the suction cast hypereutectic Ti 71Fe 29?x Sn x alloys during Sn addition with x = 0, 2, 2.5, 3, 3.85, 4.5, 6, and 10 at. pct and the solidification of these ternary alloys using SEM and TEM. These alloys have been prepared by melting high-purity elements using vacuum arc melting furnace under high-purity argon atmosphere. This was followed by suction casting these alloys in the water-cooled split Cu molds of diameters, ? = 1 and 3 mm, under argon atmosphere. The results indicate the formation of binary eutectic between bcc solid solution ??-Ti and B2 FeTi in all alloys. ??-Ti undergoes eutectoid transformation, ??-Ti ?? ??-Ti + FeTi, during subsequent solid-state cooling, leading to formation of hcp ??-Ti and FeTi. For alloys x < 2, the primary FeTi forms from the liquid before the formation of eutectic with minute scale Ti 3Sn phase. For alloys with 2 ?? x ?? 10, the liquid is found to undergo ternary quasi-peritectic reaction with primary Ti 3Sn, L+Ti 3Sn ?? ??-Ti+FeTi, leading to formation of another kind of FeTi. In all the other alloy compositions (3.85 ?? x ?? 10), Ti 3Sn and FeTi dendrites are observed in the suction cast alloys with profuse amount of Ti 3Sn being formed for alloys with x ?? 4.5. The current study conclusively proves that the liquid undergoes ternary quasi-peritectic reaction involving four phases, L + Ti 3Sn ?? ??-Ti + FeTi, which lies at the invariant point Ti 69.2±0.8Fe 27.4±0.7Sn 3.4±0.2 (denoted by P). Below P, there is one univariant reaction, i.e., L ?? ??-Ti + FeTi for all alloy compositions, whereas above P, liquid undergoes one of the univariant reactions, i.e., L + ??-Ti ?? Ti 3Sn (Sn = 2, 2.5, 3, and 4.5 at. pct) or L + FeTi ?? Ti 3Sn for alloys (Sn = 6, 10 at. pct). For alloy with Sn = 3.85 at. pct, the ternary quasi-peritectic reaction is co-operated by two monovariant eutectic reactions, i.e., L ?? ??-Ti + FeTi below P and L ?? FeTi + Ti 3Sn above P. Detailed microstructural information allows us to construct liquidus projection of the investigated alloys. The results are critically discussed in the light of available literature data. 相似文献
16.
The effect of Mn on the microstructure of electromagnetic stirred hypereutectic Al-22Si-2Fe (% w/w) alloys was studied. The results show that the alloy with a Mn/Fe ratio zero, contained plentiful α-Al 4FeSi 2 phases existing as mainly intermetallic compounds in the solidified microstructures by electromagnetic stirring (EMS) process. With EMS process, the alloy with 0.61 % Mn contained acicular β-Al 5(Fe, Mn)Si, δ-Al 4(Fe, Mn)Si 2 and blocky α-Al 15(Fe, Mn) 3Si 2 phases in the solidification microstructure of the stirred A1 alloy. As the Mn/Fe ratio increased to 1, intermetallic compounds were mainly in the form of blocky and fine α-Al 15(Fe, Mn) 3Si 2 phases in the microstructure. The intermetallic compounds were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. The acicular δ-Al 4(Fe, Mn)Si 2 and blocky α-Al 15(Fe, Mn) 3Si 2 phases were also analyzed by transmission electron microscopy. 相似文献
17.
Phase transformations in the Al–Ca–Mg–Si system in the region of aluminum–magnesium alloys are investigated using the Thermo-Calc program. The liquidus projection of the quaternary system is constructed with a Mg content of 10% and it is shown that phases Al4Ca, Mg 2Si, and Al 2CaSi 2 can crystallize (in addition to the aluminum solid solution (Al)) depending on the calcium and silicon concentrations. The crystallization character of quaternary alloys is investigated with the help of a polythermal cross section calculated at concentrations of 10% Mg and 84% Al. Based on the analysis of phase transformations occurring in alloys of this section, the presence of the Al–Al 2CaSi 2–Mg 2Si quasi-ternary section in the Al–Ca–Mg–Si system was assumed. Three experimental alloys were considered from a quantitative analysis of the phase composition, notably, Al–10% Ca–10% Mg–2% Si, Al–4% Ca–10% Mg–2% Si, and Al–3% Ca–10% Mg–1% Si. Metallographic investigations and electron-probe microanalysis were performed using a TESCAN Vega 3 scanning electron microscope. Critical temperatures are determined using a DSC Setaram Setsys Evolution differential calorimeter. The experimental results agree well with the calculated data; in particular, a peak at t ~ 450°C is revealed for all alloys in curves of the nonequilibrium solidus and invariant eutectic reaction L → (Al) + Al 4Ca + Mg 2Si + Al 3Mg 2. It is established that the structure of the Al–3% Ca–10% Mg–1% Si alloy is closest to the eutectic alloy. It is no worse that the AMg10 alloy in regards to density and corrosion resistance and even surpasses it in hardness, which allows us to consider this alloy as the basis for the development of a new cast material: “natural composites.” 相似文献
18.
The microstructural factors such as type, area fraction, morphology, distribution, and size of second phases in as-cast and homogenized 7055 aluminum alloy and the influence of impurity content variations have been investigated by using optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). In as-cast microstructures, the dominant second phases of η [Mg(Al, Cu, Zn) 2] with extended solubility of Cu and Al, a small amount of impurity phases of Al 7Cu 2Fe and Al 3Fe with a little solubility of Cu and Si, and trace Mg 2Si are identified. The variations of Fe and Si contents have no significant influence on the area fraction of η phases, but the area fraction of Fe-rich phase decreases from 0.231 to 0.102 pct with Fe content decreasing from 0.080 to 0.038 wt pct. Decreasing Fe contents reduces the size parameters of Fe-rich phases and refines their morphology correspondingly. After being homogenized at 753 K (480 °C) for 24 hours, η phases are largely dissolved, but the coarse impurity phases are insoluble. Compared with as-cast microstructures, the area fraction and composition of Fe-rich phases change a little but their morphologies are slightly coarsened. 相似文献
19.
Lap joints of aluminum alloy A6061-T6 and AZ31B magnesium alloy were produced by cold metal transfer welding with Al-5 %Si filler metal. Four heat inputs designated as A (175 J/mm), B (185 J/mm), C (195 J/mm) and D (205 J/mm) were used during the process and the joints made were subjected to analysis of microstructure, mechanical properties and corrosion behaviour. The thickness of the fusion line (diffusion layer) varied from 3 to 12 µm depending on the heat input. It was also found that the joints made using the heat input of 205 J/mm exhibited highest tensile strength of 360 N/mm, least tensile stress in the weld and better pitting corrosion resistance. Electron microscopy study of the weld revealed the presence of β′-Mg 2Si, Al 6Mn and β-Al 3Mg 2 particles. X-ray diffraction study in the weld revealed the formation of γ-Al 12Mg 17 and β-Al 3Mg 2 phase with Mg 2Si strengthening precipitates. Tensile failure occurred at the fusion line near magnesium. 相似文献
20.
A357 hypoeutectic alloy is a heat-treatable Al-Si-Mg system with a nominal composition of Al-7 pct Si and about 0.6 pct Mg
have widespreaded applications, especially in the aerospace and automotive industries. The purpose of this study was to determine
the influences of Be and Fe content on the microstructure and mechanical properties of A357.0 alloys. Distinct morphologies
were discerned between Be-containing and Be-free alloys. The Be-free alloys contain larger amount of iron-bearing phases with
Mg than in Be-containing alloys. The addition of Be can change the plateletlike structure of iron-bearing phases to a comparatively
harmless round nodular form. Also, the amounts of iron-rich phases are significantly lower and the silicon particles are smaller
and more spherical in the Be-containing alloys. Small amounts of Be in A357.0 caused significant increases in the precipitation
kinetics of Mg 2Si. It was found that the addition of Be lowers the ternary and binary eutectic melting point. The amount of Mg available
to form the major strengthening phase Mg 2Si is increased promoting the tensile strength of A357.0 casting. The tensile properties were improved with decreasing Fe
content and the addition of Be. The effect is more apparent in the higher Fe alloys than that in the lower Fe alloys. 相似文献
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