Evaluation of Mechanical and Microstructural Properties of Al-SiC/Gr Particulate Produced by Stir Casting Technique

Stir casting is an economical process for the production of aluminum matrix composites. There are many parameters in this process, which affect the final microstructure and mechanical properties of the composites. In this study, micron-sized SiC and Gr particles were used as reinforcement to fabricate Al-SiC/Gr composites at holding temperature of 700 ± 5 °C for 5 min at 350 rev/min stirring speed. The evaluation of the mechanical properties of the composites show improvement compared with pure aluminum-matrix. The Scanning Electron Microscope (SEM) of the as-cast composites shows that the vortex formations within the melt eliminates the agglomeration of the particles and improve the wettability phenomenon.

Investigating the Hall-Petch Constants for As-Cast and Aged AZ61/CNTs Metal Matrix Composites and Their Role on Superposition Law Exponent

AZ61/carbon nanotubes (CNTs) (0, 0.1, 0.5, and 1 wt.%) composites were successfully fabricated by using the stir-casting method. Hall–Petch relationship and superposition of different strengthening mechanisms were analyzed for aged and as-cast AZ61/CNTs composites. Aged composites showed higher frictional stress (108.81 MPa) than that of as-cast (31.56 Mpa) composites when the grain size was fitted directly against the experimentally measured yield strength. In contrast, considering the superposition of all contributing strengthening mechanisms, the Hall–Petch constants contributed by only grain-size strengthening were found (σ0 = 100.06 Mpa and Kf = 0.3048 Mpa m1/2) for as-cast and (σ0 = 87.154 Mpa and Kf = 0.3407 Mpa m1/2) for aged composites when superposition law exponent is unity. The dislocation density for the as-cast composites was maximum (8.3239 × 1013 m−2) in the case of the AZ61/0.5 wt.%CNT composite, and for aged composites, it increased with the increase in CNTs concentration and reached the maximum value (1.0518 × 1014 m−2) in the case of the AZ61/1 wt.%CNT composite.

Dehydrogenation of AlSi7Fe1 Melt during In Situ Composite Production by Oxygen Blowing

The technology of producing a composite material in situ envisages the pre-saturation of an AlSi7Fe1 melt with hydrogen; afterwards, the melt is blown with oxygen until the hydrogen dissolved in the melt is burned out. The hydrogen content was researched during the manufacturing process of the composite material; before oxygen blowing, and at incomplete and complete burning out of the dissolved hydrogen. The interrelation between the absorbed hydrogen content and the aluminum oxide fraction was identified. A mathematical model was proposed which demonstrated that during the saturation process of the melt with oxide particles, hydrogen was absorbed on their surface as a layer close to monoatomic, which does not lead to the realization of the pores’ heterogeneous nucleation mechanism. Due to this, castings produced from the researched composite material are leakless. Incomplete burning out of hydrogen dissolved in the melt leads to the formation of significant hydrogen porosity. The proposed method of prevention of gas porosity in cast composites is an alternative to the conventional one and offers not only the purging of the melt from oxide inclusions but, on the contrary, a significant increase in their specific surface, which allows for the reduction in hydrogen content on the inclusion surface to the monoatomic level.

Electrochemical behavior of A356 Al alloy and its vortex and squeeze composites containing ZrO2 in 3.5 % NaCl solution

Corrosion of A356 Al alloy and its composites reinforced by ZrO2 and prepared by vortex and squeeze casting was studied in 3.5 % NaCl solution using poteniodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results of polarization and EIS indicated that the corrosion resistance of the vortex cast composites increases with the increasing in the vol. % of ZrO2 up to 20 % then decreases again at 30 % in the chloride solution. Also, the corrosion resistance of the squeeze cast composites increases as the squeeze pressure increases due to decreasing the porosity within these composites. Additional, the SEM micrographs well-showed that the defects and notches which appeared on the surface of the mechanically polished vortex cast composite were diminished due to growth of a protective passive film on the composite in the chloride solution. Also, the squeeze cast composite is covered by a thick passive film and less exposure to corrosion in comparing with surface of the vortex cast composite. Energy dispersive spectroscopy (EDS) spectra found out the presence of a passive aluminium oxide layer on the A356 Al alloy/ZrO2 composites.

A Study on Particle Weight Fraction and Extrusion on the Mechanical Properties and Microstructural Evaluation of Al-Cu/Fly Ash Composite

Fly ash is the waste product coming out from thermal power plant is an increasingly urgent problem due to its storage and disposal. At the same time Metal Matrix composites (MMCs) reinforced with ceramic particles such as SiC, Al2O3 and B4C has their partial use in engineering application due to higher cost. The study focuses on the Al-Cu alloy reinforced fly ash particles produced by stir casting followed by hot extrusion. The composites produced by incorporation of fly ash reinforcements by varying 2%, 4%, 6%, 8% and 10wt% is hot extruded with an extrusion temperature of 400°C, extrusion rate of 5mm/s and extrusion ratio of 1.77:1. The extrusion composites have been evaluated based on the investigation of mechanical properties and microstructure. The results showed that, the amount of porosity increased with increasing the percentage of fly ash reinforcements in stir cast and the extruded composites is almost gratis from porosity. Hardness and tensile strength of composites increases with increases in percentage of reinforcement by stir and extruded composites. But extruded composites show better mechanical properties than stir cast composites. Wear test under different loads and for 45 minutes duration have been conducted on both cast and extruded composites. The worn surfaces have been observed under Scanning electron microscope (SEM) to understand the mechanism of wear. Extruded composites possess lower wear rates under all studied loads with constant sliding velocities when compared with cast composites. Microstructural study using SEM shows that the fly ash particulates in the molten matrix forms strong matrix reinforcement interface and their distribution might have led to the increase in mechanical properties of the composites due to fine grain structure during extrusion and dislocation density in the matrix.