Effect of bi- and trimodal size distribution on the superficial hardness of Al/SiCp composites prepared by pressureless infiltration

The effect of particle size distribution on the superficial hardness of Al/SiCp composites prepared by pressureless infiltration, as well as on the microhardness and fracture toughness (KIC) of particulate silicon carbide (SiCp) was investigated. Preforms with 0.6 volume fraction of SiC powders (10, 68 and 140 μm) with monomodal, bimodal and trimodal distribution were infiltrated with the alloy Al–15.52 Mg–13.62 Si (wt.%) in argon followed by nitrogen at 1100 °C for 60 min. Results show that density behaves linearly with increase in particle-size-distribution whilst superficial hardness, microhardness and fracture toughness exhibit all a parabolic behavior. Superficial hardness behavior can be explained by the combined effect of work-hardening in the alloy matrix and particle-to-particle impingement. Due to the highly covalent nature of SiC, the parabolic response shown by microhardness and KIC cannot be attributed to a dislocation mechanism as in strain-hardening.The effect of particle size distribution on the superficial hardness of Al/SiCp composites prepared by pressureless infiltration, as well as on the microhardness and fracture toughness (KIC) of particulate silicon carbide (SiCp) was investigated. Preforms with 0.6 volume fraction of SiC powders (10, 68 and 140 μm) with monomodal, bimodal and trimodal distribution were infiltrated with the alloy Al–15.52 Mg–13.62 Si (wt.%) in argon followed by nitrogen at 1100 °C for 60 min. Results show that density behaves linearly with increase in particle-size-distribution whilst superficial hardness, microhardness and fracture toughness exhibit all a parabolic behavior. Superficial hardness behavior can be explained by the combined effect of work-hardening in the alloy matrix and particle-to-particle impingement. Due to the highly covalent nature of SiC, the parabolic response shown by microhardness and KIC cannot be attributed to a dislocation mechanism as in strain-hardening

Effect of SiCp multimodal distribution on pitting behavior of Al/SiCp composites prepared by reactive infiltration

The effect of coated-SiCp multimodal-size-distribution on the pitting behavior of Al/SiCp composites was inves- tigated. α-SiC powders (10, 54, 86, and 146 μm) were properly mixed and coated with silica to produce porous preforms with 0.6 volume fraction of the reinforcement with monomodal, bimodal, trimodal, and cuatrimodal size distribution. The preforms were infiltrated with the alloy Al–13 Mg–1.8Si (wt.%) in argon followed by nitrogen at 1100 oC for 60 min. The composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after cyclic polarization measurements in 0.1 M NaCl de-aerated solu- tions. Results show that whereas corrosion and passivation potentials are not influenced with increase in SiCp particle size distribution, favorably, the susceptibility to pitting corrosion decreases. This beneficial effect is ascribed to the smaller area of the alloy matrix exposed to the chloride solution with augment in particle size distribution, substantially when going from monomodal to bimodal SiCp particle size distribution

Microstructure and Mechanical Properties of Al/Sicp Composites with Multimodal Size Distribution of Reinforcements

Abstract. The effect of particle size distribution and particle size ratio of SiCp in SiCp/SiO2 preforms on the microstructure, microhardness of SiCp reinforcements, modulus of rupture, and superficial hardness of Al/SiCp composites produced by pressureless infiltration has been investigated. SiCp/SiO2 preforms in the form of plates (4cm x 3cm x 0.5cm) have been pressureless infiltrated by the alloy Al-15.52 Mg-13.62 Si (wt. %) at 1100 oC for 60 min under inert atmosphere. SiC powders with average particle size of 10, 68 and 140 μm are mixed with SiO2 powders and preforms of 40 % porosity with unimodal, bimodal and trimodal size distributions are prepared by uniaxial compaction. The bimodal (small: large) and trimodal (small: medium: large) preforms are prepared with different particle size ratios in the following levels: 1:1, 3:1, 1:3, 2:2:2, 3:2:1, 3:1:2. Results from characterization by XRD, SEM and energy dispersive X-ray spectrometry show that the typical microstructure of the composites contains the MgAl2O4 (spinel), AlN and MgO phases formed during processing as well as partially reacted silica, SiC, Si and Al. It is found that the density, reinforcement microhardness, modulus of rupture and superficial hardness of the composites increase all with wider particle size distribution. However, whilst the modulus of rupture is mainly affected on going from unimodal and bimodal to trimodal distribution, superficial hardness and microhardness are mostly influenced on going from unimodal to bimodal and trimodal distribution

Microstructure and Mechanical Properties of Al/SiC Composites with Multimodal Size Distribution of Reinforcements

The effect of particle size distribution and particle size ratio of SiC in SiC/SiO2 preforms on the microstructure, microhardness of SiC reinforcements, modulus of rupture and superficial hardness of Al/SiC composites produced by pressureless infiltration has been investigated. SiC/SiO2 preforms in the form of plates (4cm x 3cm x 0.5 cm) have been pressureless infiltrated by the alloy Al-15.52 Mg-13.62 Si (wt%) at 1100°C fro 60 min under inert atmosphere. SiC powders with average particle size of 10, 68 an 140 micras are mixed withy SiO2 powders an preforms of 40% porosity with unimodal, bimodal and trimodal size distribuitions are prepared by uniaxial compactation. The bimodal (small:large) and trimodal (small:medium:large) preforms are prepared with differents particles sizes ratiosin the following levels: 1:1, 3:1.1:3. 2:2:2, 3:2:1, 3:1:2. Results from characterization by XRD, SEM and energy dispersive X-ray spectrometry show that the typical microstructure of the composites contains the MgAl2O4 (spinel), AlN and MgO phases formed during processing as well as particlly reacted silica, SiC, SI and Al. It is found that the density, reinforcements microhardness, modulus of rupture and superficial hardness of the composites increase all with winder particle size distribution. However, whilst the modulus of rupture is mainly affected on going from unimodal and bimodal to trimodal distribution, superficial hardness and microhardness are mostly influenced on going from unimodal to bimmodal adn trimodal distribution

Young’s modulus of Al/SiCP/MgAl2O4 composites with different particle size distribution of reinforcements

The effect of particle size distribution of SiC particulate reinforcements coated with colloidal SiO2 on Young ́s modulus of Al/SiCp/MgAl2O4 composites fabricated by reactive infiltration was investigated. Composites were prepared from porous preforms of silica-coated α- SiC powders of 10, 54, 86, and 146 μm, 0.6 volume fraction of reinforcements and particle size distribution from monomodal to cuatrimodal. Infiltration tests with the alloy Al-13.3Mg-1.8Si (wt. %) were carried out in Ar→N2 atmosphere at 1100oC for 60 min. The composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition to density and residual porosity measurements, Young ́s modulus was evaluated by ultrasonic techniques. Results show that with increase in particles size distribution, residual porosity decreases and density and Young ́s modulus of the composites are improved, the latter from 185.39 ±3.6 to 201.93 ±2.3 GPa. This is attributed to the increased metal-ceramic interfaces and to an enhanced matrix-reinforcement load transmission

Young’s modulus of Al/SiCP/MgAl2O4 composites with different particle size distribution of reinforcements

The effect of particle size distribution of SiC particulate reinforcements coated with colloidal SiO2 on Young ́s modulus of Al/SiCp/MgAl2O4 composites fabricated by reactive infiltration was investigated. Composites were prepared from porous preforms of silica-coated α- SiC powders of 10, 54, 86, and 146 μm, 0.6 volume fraction of reinforcements and particle size distribution from monomodal to cuatrimodal. Infiltration tests with the alloy Al-13.3Mg-1.8Si (wt. %) were carried out in Ar→N2 atmosphere at 1100oC for 60 min. The composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition to density and residual porosity measurements, Young ́s modulus was evaluated by ultrasonic techniques. Results show that with increase in particles size distribution, residual porosity decreases and density and Young ́s modulus of the composites are improved, the latter from 185.39 ±3.6 to 201.93 ±2.3 GPa. This is attributed to the increased metal-ceramic interfaces and to an enhanced matrix-reinforcement load transmission

Effect of Mg Alloying Addition on Dissolution Behavior of Oxide Films in Al-Si-Mg Alloys

Cyclic polarization measurements were carried out for Al-10%Si- X%Mg (X: 3%, 6% and 9.5%) alloys in borate solutions with and without additions of 50 mM NaCl. The voltammetric response exhibited some features of oxide film growth consistent with the high field conduction model. However, higher currents and distortions in the voltammetric wave shape compared to those for pure Al were ascribed to a possible incorporation of alloying elements in the oxide film, rendering it more defective, and to the strong electrochemical activity of Mg2Si particles.Cyclic polarization measurements were carried out for Al-10%Si- X%Mg (X: 3%, 6% and 9.5%) alloys in borate solutions with and without additions of 50 mM NaCl. The voltammetric response exhibited some features of oxide film growth consistent with the high field conduction model. However, higher currents and distortions in the voltammetric wave shape compared to those for pure Al were ascribed to a possible incorporation of alloying elements in the oxide film, rendering it more defective, and to the strong electrochemical activity of Mg2Si particles

The Activity of Silicon Carbide Particles in Al-Based Metal Matrix Composites Revealed by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is used to image variations in electrochemical activity over the surface of an aluminum-based metal matrix composite (MMC) in contact with buffered or unbuffered neutral solutions. The composite consists of an Al - 13.5% Si - 9% Mg alloy matrix and reinforcing silicon carbide particles (SiCp). Feedback mode SECM imaging using ferrocenemethanol as a redox mediator in 0.1 M NaCl solution and in buffer solution (pH 6.8) revealed that the SiC particles are electrochemically active. The data suggest that the electronic conductivity at these sites is higher than that of the Al2O3 film covering the alloy matrix surface. The reduction of dissolved oxygen on the silicon carbide particles was investigated by in situ SECM images of samples and current vs. tip-substrate distance curves. The results with samples of SiCp/Al composites immersed in distilled water alone or in either 0.1 M NaCl or boric acid/borax buffer containing ferrocenemethanol as mediator demonstrate that the silicon carbide particles are conductive and act as local cathodes for the reduction of oxygen