Type of Document	Thesis
Author	Conn, John Edward
Author's Email Address	conn@eng.fsu.edu
URN	etd-07092004-122436
Title	An OIM Study of Some Superplastic Aluminum Alloys
Degree	Master of Science
Department	Mechanical Engineering, Department of
Advisory Committee	Advisor Name Title Chiang Shih Committee Member Namas Chandra Committee Member Peter Kalu Committee Member
Keywords	EBSD Texture Superplasticity Aluminum OIM
Date of Defense	2004-07-01
Availability	unrestricted
Abstract Earlier work by Ghandi and Raj on aluminum alloy D19 showed that it exhibited a unique superplastic behavior, which was termed “subgrain superplasticity”. The grain boundary misorientation distribution data presented in this work relied only on transmission electron microscopy (TEM) of the as-received materials. The advent of computer aided microscopy techniques such as Orientation Imaging Microscopy (OIM) demands that a comprehensive characterization of this alloy be carried out. In the current work, OIM was used to obtain the microstructure, microtexture and grain boundary character distribution of superplastic alloys D17, D19, 7475 and non-superplastic alloy 5052 in both as-received and annealed conditions. Annealing of alloys D17, D19, and 5052 was carried out at 460oC for 60 min, which is the general condition used for soaking these materials before the commencement of superplastic deformation. On the other hand, alloy 7475 was annealed at 516oC for 60 min. Additional analysis was carried out on these materials by using nano-indentation testing to obtain their Young’s modulus and hardness values. With the exception of alloy 5052, which was essentially unrecrystallized, the other alloys were either partially recrystallized (alloys D17 and D19), or fully recrystallized (alloy 7475) in the as-received condition. The degree of recrystallization for these materials was determined via a metallography-OIM technique to be 17.5%, 28%, 26% and 83%, respectively. The predominant texture components for alloys D17 and D19 were {110}<112> brass, {112}<111> copper, and {123}<634> S, while brass was the only major texture component in alloy 7475. Although {100}<001> cube, {013}<100> cubeRD and {110}<001> goss were the dominant texture components in alloy 5052, it was nevertheless unrecrystallized. Upon annealing, there was a decrease in deformation textures and increase in recrystallization textures in these alloys, with the exception of alloy D17. This work showed that the use of texture components as the sole means of assessing the degree of recrystallization could be very misleading. The analysis of the grain boundary character distributions, revealed that the three superplastic alloys (D17, D19 and 7475) exhibited a high population of {110} planes, and intermediate/low populations of {100} and {111} planes, all in the as-received condition. There was no discernable consistent pattern in the annealed materials. The use of the nano-indentation testing provided reliable values for the Young’s modulus of the materials. In regards to alloys D17 and D19, it was seen that the annealed materials had lower Young’s modulus values than the as-received materials, specifically at a depth of 2000nm and an indenter loading rate of 150mN/min. At a distance of ~3mm from the edge, the values of modulus were seen to somewhat stabilize to approximately 70GPa for annealed alloy D17, and 90GPa for annealed alloy D19. The same trend was exhibited for hardness at a distance of ~2mm away from the edge.
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