Επίδραση της ηλεκτροχημικής διάβρωσης στη δομική ακεραιότητα κραμάτων αλουμινίου υπο μηχανική κυκλική φόρτιση (Master thesis)

Τσιβιλτίδης, Χαράλαμπος


In the context of this dissertation, the study of mechanical properties and mechanical behavior in dynamic loads was carried out aluminum alloys 7075 - Τ6 & 7075 - Τ7 with the parallel implementation of non - destructive evaluation (NDE), infrared thermography (IR) and acoustic emission (AE), to which targeted electrochemical corrosion was subjected. The reason for choosing studying aluminum alloy 7075 is that they are one of the most widely used building materials in aeronautics due to their competitive mechanical endurance and corrosion resist in relation to ferrous alloys. The purpose of this dissertation was to correlate the degree of wear of the aluminum samples through electrochemical corrosion, with their mechanical behavior in dynamic loads and degradation of the fatigue limit or endurance limit. The theoretical background is presented in the first part of this dissertation with the main pillars the mechanical behavior of mechanical components mainly in static and dynamic loads, the nature of corrosion and in particular electrochemical corrosion, the importance of aluminum as a structural material nowadays as well as the theory of non - destructive evaluation techniques specializing in infrared thermography and acoustic emission. The theoretical background was the tool to conduct conclusions during the presentation of the results of each experiment. The second part presents extensively the experimental process followed by references to corresponding bibliographic studies. More specifically, in making experiments aluminum samples, with specific geometric specifications, have undergone heat treatments according to standards Τ651 and Τ731 in order to achieve complete homogenization and uniformity in the distribution of their alloys elements in order to enhance their mechanical and physical properties. The above reinforcement was confirmed by Brinell macro - hardness tests as well as static tensile tests. Subsequently, 7075 - T651 aluminum samples were coated with transparent nail polish and three uniform cavities on their outer surface were created through the head of the Brinell macro - hardness. Then they underwent electrochemical corrosion by the use of potentiodynamic polarization causing severe damage to the individual cavities. Optical observation of the corroded cavities was performed using white light profilometry to determine their geometric characteristics. Subsequently, the corroded specimens underwent dynamic loads in order to evaluate their mechanical behavior as well as the effect of the degree of corrosion on it. Finally, an innovative apparatus was applied to quickly determine the endurance limit (fatigue limit) developed in the laboratory, in combination with the non - destructive evaluation methods mentioned above, in order to study the effect of the corroded cavities of the aluminum samples on it. Finally, the third part analyzes the results of the experimental process and are interpreted based on the theoretical background. According to the results of the present dissertation, it appears that the effect of electrochemical corrosion on the structural integrity and mechanical behavior of the 7075 - T651 aluminum alloys on dynamic stresses is worthy of study. Instead, thermal treatments enhance both the mechanical and corrosive behavior of 7075 alloy alloys. In particular, eroded areas constitute stress concentration points that affect the mechanical strength and behavior of the specimens in the application of dynamic loadings. The influence of corrosion is detected both by the failure mechanism and by the determination of the fatigue limit through thermography and acoustic emission diagrams.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Πολυτεχνική Σχολή. Τμήμα Μηχανικών Επιστήμης Υλικών
Subject classification: Ηλεκτροχημική ανάλυση
Keywords: Ηλεκροχημική διάβρωση,Κράμματα αλουμινίου 7075,Μηχανική συμπεριφορά,Κόπωση,Θερμογραφία,ΑΕ
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/29408
Appears in Collections:Διατριβές Μεταπτυχιακής Έρευνας (Masters)

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