No abstract

Metal matrix composites (MMCs) play a vital role in today’s engineering industries. Stir casting is one of the most inexpensive methods for the production of particulate reinforced metal matrix composites. However there are few problems encountered in stir casting such as the problem of poor wettability of the reinforcement particles in the matrix metal. The reinforcement particles have the tendency to either settle at the bottom of the crucible or they tend to float at the top of molten metal. This is due to the greater surface tension of the molten metal. Various techniques are available to improve the wettability of the ceramic particles in metal matrix which includes Particle treatment, Particle coating and Addition of alloying agent. In this work, Magnesium (Mg) was used as the alloying element to improve the wettability of SiC particles in the Al matrix. Mg is used to reduce the surface tension of molten aluminum (Al) thus promoting proper wetting. To understand the effect of Mg on improving the wettability of SiC in aluminum matrix, different weight percentages of SiC particles reinforced aluminum alloy 6061(AA6061) based MMCs were fabricated in stir casting method by adding Mg as alloying element. The cast specimens were subjected to microstructural analysis, tension tests and hardness tests. Results showed that addition of Mg with SiC in AA6061 matrix significantly improved the wetting between Al and SiC; subsequently MMCs possessed enhanced mechanical properties.

Aluminium reinforced with SiC, Al2O3 and B4C etc. possesses an attractive combination of properties such as high wear resistance, high strength to weight ratio and high specific stiffness. Among the various reinforced materials used for aluminium, B4C has outperformed all others in terms of hardening effect. Particle size reduction of B4C is found to have positive impact on the material hardness. In the view of physical properties, B4C has less density than that of SiC and Al2O3, which makes it an attractive reinforcement for aluminium and its alloys for light weight applications. In this work, Al nano B4C composite prepared by ultrasonic cavitation method was machined by Abrasive assisted electrochemical machining using cylindrical copper tool electrodes with SiC abrasive medium. In this paper, attempts have been made to model and optimize process parameters in Abrasive assisted Electro-Chemical Machining of Aluminium-Boron carbide nano composite. Optimization of process parameters is based on the statistical techniques using Response Surface Methodology with four independent input parameters such as voltage, current, abrasive concentration and feed rate were used to assess the process performance in terms of material removal rate and surface finish. The obtained results were compared with abrasive assisted electro chemical machining of Aluminium-Boron carbide micro composite and the effect of particle size on the process parameters was analyzed.

Magnesium alloys are used in many applications, particularly in orthopaedic implants are very difficult to machine by conventional processes because of their complex 3D structure and limited slip system at room temperature. Hence there is an inherent need for alternative processes for machining such intricate profiles. Electric Discharge Machining is growing rapidly in tool rooms, die shops and even in general shop floors of modern industries to facilitate complex machining for difficult-to-machine materials and provide better surface integrity. Therefore, the use of electric discharge machining on ZM21 magnesium alloy is attempted in this paper. Nanographite powder is added for machining zone to enhance the electrical conductivity of EDM oil by way it improves the machining performance. Machining parameters such as the current, pulse on time and pulse off time were process parameters to explore their effects on the material removal rate and tool wear rate. It is observed that, an increased material removal rate was due to the enhanced electrical and thermal conductivity of the EDM oil.

The effect of microstructure and chemistry of passive films on the kinetics of passive layer growth and passivity breakdown of some Ti-based alloys, namely Ti-6Al-4V, Ti-6Al-7Nb and TC21 alloys was studied. The rate of pitting corrosion was evaluated using cyclic polarization measurements. Chronoamperometry was applied to assess the passive layer growth kinetics and breakdown. Microstructure influence on the uniform corrosion rate of these alloys was also investigated employing Tafel extrapolation and dynamic electrochemical impedance spectroscopy. Corrosion studies were performed in 0.9% NaCl solution at 37 oC, and the obtained results were compared with ultrapure Ti (99.99%). The different phases of the microstructure were characterized by X-ray diffraction and scanning electron microscopy. Chemical composition and chemistry of the corroded surfaces were studied using X-ray photoelectron analysis. For all studied alloys, the microstructure consisted of α matrix, which was strengthened by β phase. The highest and the lowest values of the β phase’s volume fraction were recorded for TC21 and Ti-Al-Nb alloys, respectively. The uniform corrosion rate and pitting corrosion resistance (Rpit) of the studied alloys were enhanced following the sequence: Ti-6Al-7Nb < Ti-6Al-4V << TC21. The corrosion resistance of Ti-Al-Nb alloy approached that of pure Ti. The obvious changes in the microstructure of these alloys, together with XPS findings, were adopted to interpret the pronounced variation in their corrosion rates.