Conference Papers

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Author: search.filters.author.Valder, J.

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    Effect of thermal and surface chemical treatment on the cyclic oxidation behavior of 7039 aluminum alloy used in aerospace armor applications
    (Elsevier Ltd, 2020) Fageehi, Y.; Saminathan, S.; Venugopal, G.; Valder, J.; Kumar, H.; Ravishankar, K.S.
    7039 Aluminum alloy is subjected to artificial aging (T6 treatment) at temperatures namely 80, 100, 120, 140, 160 °C for various time periods up to 100 h. Based on the Brinell Hardness measurements the artificially aged alloys are categorized into three groups namely under aged, peak aged and overaged based. The specimens from the alloy groups are further subjected to cyclic oxidation measurements at temperatures namely 100, 200 and 300 °C. The cyclic oxidation measurements in atmospheric air, revealed that the pre temperature history of the artificially aged alloy has an influence on the cyclic oxidation behavior of the 7039 Aluminum alloy as the under aged alloy showed greater tendency for cyclic oxidation. A surface chemical treatment is employed to coat the alloy by CeO2ceramic coating through chemical bath technique. Cyclic oxidation tests, X-RD and SEM analysis of the 7039 Aluminum alloy specimens with and without ceramic coatings are carried out. Interestingly, the ceramic coated 7039 Aluminum alloy showed greater resistance to oxidation when compared to that of artificially aged alloy specimens. © 2020 Elsevier Ltd. All rights reserved.
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    Effect of plastic strain and processing routes on the hardness of as-cast aluminum
    (American Institute of Physics Inc. subs@aip.org, 2020) Valder, J.; Rijesh, R.; Kumar, P.; Saminathan, S.; Raju, K.; Surendranathan, A.O.
    In the present study, Equal Channel Angular Pressing (ECAP) of commercially pure aluminum (Al) in the cast form was carried out at room temperature for assessing its hardness by different routes and passes. The different routes employed in the present investigation are A, BA, BC and C. The Al specimens were pressed by a die of 150° channel angle without back pressure with Molybdenum disulfide (MoS2) as the lubricant. ECAP has significantly improved the hardness of Al in the subsequent passes. It has been observed that the hardness has been increased after first pass at room temperature from 47 VHN in the annealed condition to 54 VHN and after the second pass the hardness value has been increased to 56, 57, 62 and 56 VHN for routes A, BA, BC and C respectively. The increase in the hardness may be attributed to the severe fragmentation of microstructure of cast Al and the change in the orientation of the specimen from one pass to the next pass. After one pass, the dendritic microstructure of cast Al has been distorted by the shear stress developed during deformation. The processing by different routeswith number of passes has further refined the microstructure leading to a better hardness in the cast Al. © 2020 Author(s).