Bellambettu Chandrasekhara Pai

Physical, Mechanical, and Tribological Attributes of Stir-Cast AZ91/SiCp Composite

In the present investigation, composites with silicon carbide particle (SiCp) as reinforcement and AZ91 magnesium alloy as matrix have been synthesized using liquid metal stir-casting technique with optimized processing conditions. The composites with good particle distribution in the matrix, and better grain refinement and good interfacial bonding between the matrix and reinforcement have been obtained. The effect of SiCp content on the physical, mechanical, and tribological properties of Mg-based metal matrix composite (MMC) is studied with respect to particle distribution, grain refinement, and particle/matrix interfacial reactions. The electrical conductivity, coefficient of thermal expansion, micro- as well as macro-hardness, tensile and compressive properties, and the fracture behavior of the composites along with dry sliding wear of the composites have been evaluated and compared with the base alloy.

Developments in Solidification Processing of Functionally Graded Aluminium Alloys and Composites by Centrifugal Casting Technique

Centrifugal casting is one of the potential solidification processing techniques used for producing near-net shaped symmetrical cast components with improved properties. The emergence of new class of functionally graded materials has propelled this technique for the fabrication of engineering components and structures with graded property. The specific properties obtained by the use of functionally graded metal matrix composites (FGMMC) are high temperature surface wear resistance, surface friction and thermal properties, adjustable thermal mismatching, reduced interfacial stresses, increased adhesion at metal–ceramic interface, minimized thermal stresses and increased fracture toughness and crack retardation. Among various processing techniques available for the fabrication of FGMMC, centrifugal casting has emerged as the simplest and cost effective technique for producing large size engineering components of FGMMC. The present paper gives an overview on the developments in use of centrifugal processing technique for processing various functionally graded aluminium alloys and composites. The influence of various process and solidification parameters on microstructure and properties of graded alloys and composites are described.

Microstructural evolution and mechanical properties of misch metal added Mg-Si alloys

Effect of misch metal additions (0.3, 0.6, 0.9 and 1.2 wt%) on the refinement of Mg2Si phase in Mg-1.15Si alloy has been studied and compared with the base alloy. MM addition effectively refines the microstructure by breaking the α-Mg halos and lamellar eutectic phase and the maximum refinement is obtained for 0.6 MM addition. For higher MM additions (0.9 and 1.2 wt%), the refinement effect gets reduced and the formation of RE-Si compound is dominated. Improved tensile properties are obtained with the addition of MM and are attributed to the refinement of microstructure and the presence RE-Si compound. The tensile properties obtained are correlated with the microstructure and mirofractomechnisms.

Effect of Sb, Sn and Pb Additions on the Microstructure and Mechanical Properties of AZ91 Alloy

This article presents the effect of individual addition of Sb, Sn and Pb on the precipitation sequence at room as well as high temperature tensile properties of AZ91 alloy. The results show grain refinement, formation of Mg3Sb2 and Mg2Sn phases when Sb and Sn are added to AZ91 alloy. Lamellar precipitate is significantly suppressed while Pb added. Improved room and high temperature tensile properties are observed in Sb and Sn addition. Maximum tensile properties are noticed with AZ91 alloy having 0.5 wt.% Sb addition.

Fabrication and Characterization of Short Carbon Fiber Reinforced AZ91 Mg Alloy Composites

Short carbon fiber reinforced AZ91 magnesium alloy matrix composites have been made by stir casting technique. The microstructure and the fibre matrix interfacial region of the composites characterized using optical and scanning electron microscopes reveal uniform distribution of fiber in the matrix and good interfacial bonding respectively. Increase in compressive strength values are observed with increase in fiber content where as the room and high temperature (150°C) strength properties are found to decrease marginally. The microfractograph of the tensile fractured surface reveals mixed type of fracture.

Processing and Microstructure of Magnesium In Situ Composite with Titanium and Boron Based Reinforcement

The present work is aimed to investigate the in-situ TiB/TiB2 particle formation in Mg and Mg-Al alloy via the chemical reaction between Mg, Al, K2TiF6 and KBF4. The feasibility to produce the Mg and Mg-Al matrix with in-situ TiB2 and TiB particles have been studied with respect to processing parameters. The XRD, optical microscopy and SEM-EDX analyses have been carried out on the synthesised composites. Significant improvement in the hardness values are obtained for the in-situ composite compared to the base alloys.

Formation of Electroless Ni-B Coating on Boron Carbide Particles for Composite Processing

The present investigation is on formation of a uniform coating of Ni-B coating on the surface of B4C particle by electroless technique by varying process parameters and pH of the coating bath. The coating characteristics observed on majority of pH conditions on activated particles were mesh-like and at higher pH 12 the coated surface characteristics changes to patch like morphology. At lower alkaline condition there was not enough time for co-deposition to occur and the co-deposits appeared along with the coated particles. The studies with varying pH showed that pH 8 gives uniform coating of the entire particles surface with Ni-B and above which higher amount of co-deposited particles of Ni-B is also observed.

Microstructure and Properties of Stir Cast AZ91 Mg Alloy – SiCp Composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. Using stir casting process, AZ91 magnesium alloy metal matrix composites have been produced with different weight percentages (5, 10, 15, 20 and 25) of silicon carbide particles (SiCp) addition. Microstructural characterization reveals uniform distribution of SiC particles with good interfacial bonding between the matrix and reinforcement. Electrical conductivity and Co-efficient of Thermal Expansion (CTE) measurements carried out on these composites have yielded better properties. Improved mechanical properties such as hardness, ultimate tensile strength, and compressive strength are obtained. The microfracture mechanisms involved during tensile fracture is analyzed and correlated with the properties obtained.

Grain Refinement Mechanism in Al–4B Master Alloy Added Pure Mg

Al–4B master alloy has been prepared by the reaction of fluoride salt KBF4 with molten Al and different amounts of this master alloy (0.5, 1, 1.5 and 2 wt%) has been added to pure Mg to study in detail its effect on the grain refinement of pure Mg. Considerable reduction in grain size from 1300 to 210μm is obtained and maximum reduction is observed with 2 wt% master alloy addition. The grain refinement is caused by both the growth restriction effect of Al and the presence of potent AlB2 nucleant particles. Improvement in mechanical properties is obtained with Al–4B master alloy and is attributed to increase in grain boundary area due to the grain refinement and the particle strengthening due to AlB2.

Effects of gadolinium addition on the microstructure and mechanical properties of Mg–9Al alloy

This research aims to study the significance of Gd addition (0wt%–2wt%) on the microstructure and mechanical properties of Mg–9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg–9Al alloy contained two phases, α-Mg and β-Mg17Al12. Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al2Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg–9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg–9Al–2.0Gd alloy exhibited the smallest grain size (181 μm) and the highest dislocation density (5.1 × 1010 m−2) among the investigated compositions, the Mg–9Al–1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al2Gd phase was uniformly distributed and present in abundance in Mg–9Al–1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg–9Al–2.0Gd.