Manas Kumar Mondal

Study of Microstructure Evolution during Semi-Solid Processing of an In-Situ Al Alloy Composite

In the present work, effect of pouring temperature (650°C, 655°C, and 660°C) on semi-solid microstructure evolution of in-situ magnesium silicide (Mg2Si) reinforced aluminum (Al) alloy composite has been studied. The shear force exerted by the cooling slope during gravity driven flow of the melt facilitates the formation of near spherical primary Mg2Si and primary Al grains. Shear driven melt flow along the cooling slope and grain fragmentation have been identified as the responsible mechanisms for refinement of primary Mg2Si and Al grains with improved sphericity. Results show that, while flowing down the cooling slope, morphology of primary Mg2Si and primary Al transformed gradually from coarse dendritic to mixture of near spherical particles, rosettes, and degenerated dendrites. In terms of minimum grain size and maximum sphericity, 650°C has been identified as the ideal pouring temperature for the cooling slope semi-solid processing of present Al alloy composite. Formation of spheroidal grains with homogeneous distribution of reinforcing phase (Mg2Si) improves the isotropic property of the said composite, which is desirable in most of the engineering applications.

Microstructural characterisation of novel 6351 Al–Al4SiC4 in-situ composite

Abstract 6351 Al–Al4SiC4 composite has been developed through stir casting route by incorporation of fine TiC powder in 6351 Al melt. Simultaneous effects of the generation of in-situ particles (Al4SiC4 and Al3Ti) and grain refinement were observed. The in-situ generated Al4SiC4 particles were found to act as nucleation sites for primary α (causing grain refinement) along with engulfment effect promoting uniform particle distribution. As the volume fraction of Al4SiC4 particles increased, the dendritic solidification was suppressed (more equiaxed grains appeared) and overall grain size of the matrix decreased. Besides, the precipitation of Al3Ti occurred at the dislocation enriched region. Accordingly, hardness of the composite was improved with increasing content of Al4SiC4 particles.

Microstructural evolution and hardness property of in situ Al–Mg2Si composites using one-step gravity casting method

ABSTRACT In the present investigation, Al–X wt-% Mg2Si (X = 0, 5, 10, 15 and 20) in situ composites are successfully synthesised by one-step gravity casting technique. Commercially pure Al, Mg and Si are used as raw materials. Microstructural evaluation and correlation of micro- and bulk hardness properties have been studied on developing composites. The composites consist of mainly three phases: matrix (α-Al), reinforcing (primary Mg2Si) and binary eutectic (Al–Mg2Si) phase. Primary Mg2Si particles are formed by pseudo-eutectic transformation during solidification and surrounded by matrix and binary eutectic phase. It is found that Mg2Si concentration has a significant impact on morphology and volume per cent of the above-mentioned phases. Primary Mg2Si particles’ size and volume per cent increase with increasing wt-% of Mg2Si. Volume per cent of individual phases and Mg2Si concentration have great impact on hardness properties of composites. Bulk hardness increases with increasing wt-% of Mg2Si concentration, but micro-hardness of primary Mg2Si particle decreases slightly. Mg2Si concentration also has significant impact on micro-hardness of individual phases.

Dry sliding wear behaviour of a novel 6351 Al-Al4SiC4 composite at high loads

In this research work the dry sliding wear behaviour of 6351 Al alloy and 6351 Al based composites possessing varying amount of (2–7 vol%) insitu Al4SiC4 reinforcement was investigated at low sliding speed (1 m s−1) against a hardened EN 31 disk at higher loads (44 N and 68.7 N). In general, at higher loads, the wear mechanism involved microcutting and microploughing abrasion. In most occasions, Al4SiC4 reinforced 6351 Al based composites exhibited much higher wear rate (lower wear resistance) than the unreinforced 6351Al alloy. This was mainly attributed to the removal of reinforcement particle through microcutting abrasion process that resulted in cavitation and subsequent microploughing abrasion for rapid removal of material from surface. This is on contrary to the authors previous research work, where at lower loads (24.5 N or below), Al4SiC4 particles stood tall to enhance wear resistance of 6351 Al-Al4SiC4 composite.

Modelling of flow behaviour in a LD vessel by an impinging gas jet

Present study is focused towards development of computational fluid dynamic model of oxygen impingement in the melt pool in case of LD (basic oxygen converter) steelmaking process. 1/30th scaled down model of the 100 ton LD converter has been developed and flow simulation has been performed based on volume of fluid technique, using Fluent as solver engine. Simulation of the steel bath and oxygen is carried out by using water and air, respectively. Effect of process variables on the LD steelmaking practice has been studied and the findings ascertain penetration depth of the oxygen jet into the liquid (metal) pool as a strong function of bath (lance) height, gas flow rate and nozzle exit diameter. Furthermore, an equation is developed by carrying out regression analysis using results obtained from numerical simulation. The study also provides insight into the surface deformation modes, their onsets and transition regimes, which originates due to the gas impingement into the melt pool. Finally, the computed results are compared with the experimental findings for selected cases and good agreement has been found.

A Pure Implicit Finite Difference-Based Modeling Approach for Prediction of the Hardenability of Eutectoid Steel

In this work, an independent pure implicit finite difference-based modeling approach has been adopted for the determination of the hardenability of eutectoid steel. In this model, cooling curves were generated by solving transient heat transfer equations through discretization with pure implicit finite difference scheme in view of constant effective thermophysical properties of AISI-1080 steel. The cooling curves were solved against the 50% transformation nose of the time–temperature–transformation diagram in order to predict hardening behavior of AISI-1080 steel in terms of hardenability parameters (Grossmann critical diameter, DC; and ideal critical diameter, DI) and the variation of the ratio of the unhardened core diameter (Du) to diameter of steel bar (D). Furthermore, a relationship is established between the Grossmann critical diameter and the heat transfer coefficient. The hardenability predicted by the developed model was found to match reasonably with that obtained through the chemical composition method. Therefore, the model developed in the present work can be used for direct determination of DC, DI, and Du without resorting to any rigorous experimentation.