Effect of Sr addition on an Al-7Si-10 vol.% SiCp cast composites GARCIA-HINOJOSA, J. A; GONZALEZ, C. R; JUAREZ, J. I ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
09/2004, Letnik:
382, Številka:
1-2
Journal Article
Recenzirano
The effect of additions of Sr (in the range 0.05-0.5%) on the microstructural characteristics of Al-7 wt.% Si-10 vol.% SiC, composites have been studied. Optical microscopy (OM), SEM, EDS, WDS ...microanalysis techniques and X-ray diffraction powder techniques have been used for the characterization of the composites. It was found that Sr concentrations between 0.05 and 0.20 facilitates incorporation of higher volume fraction of SiC particles and also does not contribute to the overall modification of the matrix. However, at higher wt.% of Sr, Sr-rich compounds were found. These Strontium rich compounds were located at the matrix-ceramic interface.
An addition of Ti or Ti/B is an accepted technique to produce cast aluminum alloys having fine grain size and superior mechanical properties. Present investigation focuses on the role of grain ...refinement treatment on the SiC particle distribution in Al-7
wt.% Si-10
vol.% SiCp cast composites and also on the degree of refinement of matrix microstructure. Composites manufactured by vortex method were treated with three different commercial grain refiners namely; K
2TiF
6 salt, Al–6Ti and Al–5Ti–1B master alloys. Microstructural characteristics including nature of distribution of SiCp in the matrix, grain size and dendritic arm spacing have been studied. It was found that complete dewetting of the SiCp and consequently their rejection from the melt takes place when the composite was treated with K
2TiF
6 salt. Improved distribution of SiCp in the matrix of composites was observed when the melt was treated with either Al–6Ti or Al–5Ti–1B master alloy. Composite melt treated with Al–5Ti–1B master alloy show excellent combination of matrix grain refinement and uniform SiCp distribution.
The effect of Cr additions on the Al-20Si-5Fe alloy, produced by means of two different solidification methods is presented and discussed. The modification of iron intermetallics and the ...microstructural refinement through suction casting were also assessed. Several Al−20Si−5Fe−xCr (x = 1.0, 3.0 and 5.0 wt%) alloy ingots were prepared by arc melting furnace (AMF). Rods of each alloy were produced by copper mold suction casting under Ar atmosphere. The elemental chemical analysis was performed by X-ray fluorescence spectrometry (XRF). The microstructure of all samples was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructural analysis revealed the presence of α−Al, eutectic silicon (SiE), primary silicon (SiP), Al3FeSi2 and Al95Fe4Cr phases. The microhardness and compressive properties were measured in order to correlate the microstructural changes with Cr additions. The acicular Al3FeSi2 intermetallic compound (2D) obtained by conventional solidification was found to be a plate-like structure (3D). The highest microhardness value was found for the alloys with the 5 wt% Cr (220 HV) in conventional solidification. However, for suction casting, the highest microhardness was 192 HV for the 3 wt% Cr. Although the microhardness dropped with the suction casting, the compressive plasticity of the alloy did increase considerably (>300%), being the microstructural homogeneity the main contributor to the ductility behavior.
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•A plate-like morphology was found for the Al3FeSi2 intermetallic.•The 3 wt% of Cr addition represents the thresholds for the Al3FeSi2 intermetallic compound formation.•The additions of Cr showed that above 3 wt% the microstructure tended to be rather similar for suction casting.•Due to the microstructural homogeneity, the compressive plasticity of the 3 wt% Cr alloy increased above 300%.
A study on the microstructure, microhardness, and corrosion behavior of A413/Al2O3 composites has been carried out. Composites with 5, 10, and 15 wt.% of Al2O3 were produced by powder metallurgy (PM) ...method. Electrochemical techniques including potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy were use to evaluate the corrosion behavior in 3.5 wt.% NaCl solution. Detailed electronic microscopy studies revealed that the surface of composites has a fairly uniform distribution of Al2O3 particles and a slight porosity content ranging from 2.59 to 3.83 % whereas X-ray diffraction patterns indicated the presence of the main phases Al, Si, along with reinforcement Al2O3 phase. The microhardness of the samples improved with the addition of alumina as reinforcement, obtaining the highest microhardness value for the composite A413-15 wt.% Al2O3 (104.5 HV). Electrochemical tests showed that the corrosion rate of the samples increased as the weight percent of Al2O3 increased, where the unreinforced A413 alloy exhibited the lowest corrosion rate. Corrosion process was charge controlled and remained unaltered by the addition of reinforcement. After the corrosion test, the composites evidence a type of localized corrosion such as crevice due to the galvanic effects between the A413 alloy matrix and the Al2O3d particles.
The corrosion behaviour of A413/SiC composites with different SiC contents (5, 10, and 15 wt.%) was evaluated through electrochemical techniques in 3.5 wt.% NaCl solution. For this purpose, ...composites were produced by the mechanical alloying technique. In addition to this, X-ray diffraction and by Scanning electronic microscope studies were performed. It was found that the addition of SiC increased both density and porosity. Electrochemical tests showed that the corrosion resistance of unreinforced A413 alloy was improved with the addition of 5% SiC but the addition of either 10 or 15 % SiC was detrimental. The corrosion products film developed on top of unreinforced A413 alloy and composite containing 5 % SiC consisted basically of protective Al2O3, alumina layer, whereas that formed on top of composites containing either 10 or 15 % SiC contained less Al as well as Fe and Cr making them less protective.
The corrosion behavior of the A356 (0, 5, 10, and 15 wt.%) SiC composites produced by mechanical alloying (MA) and uniaxially pressing/sintering route was studied through electrochemical and surface ...analysis techniques in 3.5 wt.% NaCl. The corrosion behavior of the samples was investigated by using electrochemical techniques. The corrosion resistance for the unreinforced A356 aluminum alloy was higher than the composites, however, when the A356 aluminum alloy was reinforced with SiC particles, composites were susceptible to a localized type of corrosion at the matrix/SiC particles interface. This made that although the passive zone for composites was wider with a pitting potential value slightly higher than those for base alloy, passivation current density was higher.
This work shows the results obtained of the microstructural analysis by optical microscopy (OM) and scanning electron microscopy (SEM-EDX) and its relationship with the mechanical properties of ...Al–7Si–0.5Cu, Al–7Si–1.5Cu, Al–7Si–0.5Ni and Al–7Si–1.0Ni cast alloys. These cast alloys were manufactured in two conditions: nonmodified and modified with 0.02
wt.% Sr, in order to evaluate the effect of the Sr on the eutectic phase morphology. Results indicated that Sr presence produce a good modification rating of the eutectic phase in the case of Al–7Si–Cu cast alloys and their mechanical properties were increased in as cast condition. However the massive eutectic microconstituent NiAl
3 of Al–Si–Ni cast alloys was not affected by Sr presence, and their mechanical properties were not improved.
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