Browsing by Author "Preetham Kumar, G.V.P."

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Microstructure and Mechanical Properties of Cast Al-5Zn-2Mg Alloy Subjected to Equal-Channel Angular Pressing
(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Manjunath, G.K.; Preetham Kumar, G.V.P.; Udaya Bhat, K.; Huilgol, P.
In the present work, cast Al-5Zn-2Mg alloy was processed through equal-channel angular pressing (ECAP) in route BC up to four number of passes. Microstructure and mechanical properties were investigated on processed and unprocessed materials. In cast condition, the material was composed of dendritic structure. After homogenization treatment, large-sized grains were observed. After ECAP processing, significant grain refinement was observed. After ECAP processing, high-density dislocations and high degree of misorientation between the grains were observed. In cast material, rod-shaped precipitates were observed, while, after ECAP processing, spherical-shaped precipitates were observed. ECAP processing leads to a noticeable improvement in the mechanical properties of the material. After four passes, 122% improvement in the microhardness and 135% improvement in the ultimate tensile strength of the material were observed. After three passes, a slight decrease in the mechanical properties was observed. This is attributed to the dissolution of the metastable ?? phase, annihilation of dislocations, dynamic recrystallization and texturing during ECAP processing. Brittle fracture mode was observed in tensile testing cast and homogenized samples. After ECAP processing, fracture mode was changed into shear fracture mode. © 2018, ASM International.
Microstructure and mechanical properties of ZA27 based SiC reinforced composite processed by multi directional forging
(Institute of Physics Publishing helen.craven@iop.org, 2018) Anjan, B.N.; Preetham Kumar, G.V.P.
Influence of multi directional forging (MDF) on microstructural and mechanical properties of ZA27/SiC 5 weight percentage (Wt%) composites were investigated. Stir casting technique followed by squeezing process was adopted for synthesis of composite. MDF process was conducted at 100 °C and 200 °C upto strain of 0.54 and 1.09 respectively. Microstructure analysis was carried out using optical microscopy, scanning electron microscopy and energy dispersive spectrometry. SiC particles were fairly distributed and some clusters were also observed. Density of composite decreased with the reinforcement of SiC particles as compared with ZA27 alloy, however porosity which was existing as casting defect was reduced by MDF process. Average grain size of 200-250 nm and 1 ?m was achieved for MDF processed sample at 100 °C upto 3 passes and at 200 °C upto 6 passes respectively. Addition of SiC particles and adoption of MDF technique improved the vickers hardness of composites. Ultimate tensile strength of ZA/SiC composite has increased from 380 MPa to 395 and 432 MPa respectively with 54 and 37 percentage of elongation to failure. Improvement in hardness and tensile strength is due to strain hardening and grain refinement. Ductility of MDF processed ZA27/SiC composite is attributed to uniform distribution of ultrafine equiaxed grain and micro constituents. © 2018 IOP Publishing Ltd.
Precipitate evolution during severe plastic deformation of cast Al-Zn-Mg alloys and their thermal stability
(Institute of Physics Publishing helen.craven@iop.org, 2019) Manjunath, G.K.; Huilgol, P.; Preetham Kumar, G.V.P.; Bhat, K.U.
In the current investigation, an effort was made to understand the precipitate evolution process during equal channel angular pressing (ECAP) of an alloy composed of only aluminium, zinc and magnesium. For this purpose, three different compositions of cast Al-Zn-Mg alloys were selected and ECAP processed in route BC upto four passes. Microstructural observations indicated that, ECAP processing leads to refined structure possessing high density dislocations and large amount of grains with high angle grain boundaries. The precipitate volume in the alloys increased with increase in the zinc quantity in the alloy. Microstructural characterization through transmission electron microscope (TEM) and differential scanning calorimeter (DSC) revealed that, processing by ECAP results in structure having stable ? phase precipitates without the presence of GP zones and intermediate ?? phase precipitates. Thereby demonstrates that, ECAP process accelerates the precipitation kinetics and also shifts the morphology of the precipitates. Higher mechanical properties were noticed in the alloy containing large quantity of MgZn2 precipitates. © 2018 IOP Publishing Ltd.