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Master's Dissertation
DOI
10.11606/D.3.2018.tde-10042018-134754
Document
Author
Full name
Saul Hissaci de Souza
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2018
Supervisor
Committee
Padilha, Angelo Fernando (President)
Fernandes, Ricardo do Carmo
Lima, Nelson Batista de
Title in Portuguese
Cinética de amolecimento da liga de alumí­nio AA 7075 durante recozimento após laminação a frio.
Keywords in Portuguese
Alumínio
Ligas leves
Recristalização
Abstract in Portuguese
O presente trabalho apresenta um estudo sobre o amolecimento após laminação e recozimento da AA 7075, uma liga de alumínio endurecível por precipitação . As amostras recebidas no estado T6 foram caracterizadas com auxílio das técnicas de microscopia óptica de luz polarizada, microscopia eletrônica de varredura, espectroscopia de raios X por dispersão de energia, difração de raios X, condutividade elétrica e dureza Vickers . As amostras foram então separadas em dois grupos. O primeiro sofreu um tratamento térmico de solubilização (485°C por 5 horas) enquanto o segundo foi submetido a um tratamento de superenvelhecimento (300°C por 5 horas) e, em seguida, ambos os grupos de amostras tratadas foram novamente caracterizadas pelas técnicas descritas anteriormente (exceto microscopia óptica) e laminadas a frio. Durante a etapa de laminação, constatou-se a dificuldade em causar deformação plástica na amostra solubilizada. Optou-se em conduzir o estudo com as amostras superenvelhecidas, que foram laminadas com reduções de 45%, 75% e 90% em espessura. A seguir, estas foram submetidas a tratamentos isotérmicos e isócronos com o objetivo de estudar a cinética de amolecimento das amostras deformadas a frio. As amostras superenvelhecidas e deformadas em 45% em redução de espessura, apresentaram somente indícios de início de recristalização (nas amostras tratadas a partir de 250°C por 1 hora) via EBSD, sendo que a maior parte do amolecimento pode ser explicada pelo mecanismo de recuperação. Além disso, a cinética de amolecimento das amostras recozidas nesse grupo apresentaram boa concordância com a lei logarítmica proposta por Kulhmann (1948) e (coincidentemente) também com o consolidado modelo JMAK. As amostras superenvelhecidas e deformadas em 75% e 90% apresentaram comportamento similar (isso é, principalmente recuperação) para recozimentos realizados em temperaturas de até 350°C por uma hora. Recozimentos realizados a 400°C promoveram a recristalização total das amostras desse grupo para tempos inferiores a 15 minutos. Dessa forma, não foi possível estudar a cinética de recristalização para esse segundo grupo de amostras.
Title in English
Softening behavior during annealing of col-rolled aluminium alloy 7075.
Keywords in English
AA 7075
Aluminium alloys
Recovering
Recrystallization
Abstract in English
This work presents a study about the softening after cold rolling and annealing of aluminium alloy AA 7075. Firstly, polarized light optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, electrical conductivity and Vickers hardness have been used at the starting material (T6). The samples were then separated in two groups. The former underwent a solubilization heat treatment (485°C for 5 hours) whilst the latter underwent an overaging treatment to grow up the existing precipitates (300°C for 5 hours). Both groups of treated samples were again characterized by the techniques described above (except optical microscopy). In the rolling stage, the difficulty in straining the solubilized sample and the relative ease for doing so to the overaged sample was verified. It was therefore decided to conduct the study with the samples of the second group, which were 45%, 75% and 90% rolled in thickness reduction. Then, they underwent isothermal and isochronous treatments in order to study its softening kinetics by Vickers hardness measurements, polarized light optic microscopy and EBSD. The overaged and rolled samples (45% in thickness reduction) didn't present evidences of recrystallization except by very few grains found via EBSD (in samples treated from 250 ° C for 1 hour). So, most of the observed softening can be explained by recovery. In addition, the softening kinetics of the annealed samples in this group showed good agreement with the logarithmic law proposed by Kulhmann (1948) and (coincidentally) also with the consolidated JMAK model. The overaged samples that underwent thickness reduction of 75% and 90% showed a similar behavior (that is, mainly recovery) for annealing at temperatures up to 350 ° C. Annealing at 400 ° C promoted total recrystallization of the samples from this group (75% and 90% in thickness reduction) in less than 15 minutes. Thus, it was not possible to study the kinetics of recrystallization for this second group of samples.
 
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Publishing Date
2018-04-10
 
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