Auswirkung von Elementvariationen auf die Wärmebehandlung und Eloxierbarkeit von EN AW 7075

Translated title of the contribution: Effect of element variation on the heat treatment and anodising of EN AW 7075

Franz Waldsam

Research output: ThesisMaster's Thesis

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Abstract

For aluminum alloys, both the individual chemical composition, as well as the microstructure caused by heat treatment influence the contained phases and affect attainable hardness and ability to anodize. In order to enable an investigation of the described correlations generally used EN AW-7075 wrought alloys (AlZn5,5MgCu) with a standardized content of zinc, magnesium, copper and other accompanying elements are processed by different specific treatments. Before starting the actual anodizing the deliberate variation of main alloy elements within the standard specification by melting and the different solution and precipitation processing are essential for the examination of the material behavior. At the beginning of this work, there is an overview of properties, application areas and manufacturing ways of EN AW-7075 and a detailed description of the possible methods of treatment with focus on anodizing. In addition, a research on the impact of different microstructures on the current state of knowledge is included. Related alloying elements and different annealing treatments are the most important part. The solution annealing, the cold ageing and especially the artificial ageing at elevated temperatures are the main focus of investigation. The practical part of the thesis first illustrates the alloy production and sample preparation (cutting, grinding...). Specific computer programs simplify the design of experiments and support all alloying calculations. Analyses by using spectroscopy are additionally used to achieve the required alloy mixture. It should be noted that the samples aren’t rolled in any way during the whole process. Finally the hardening takes place. Then the calculated ageing curves of the alloy samples provide information about the structure-related hardening behavior. Afterwards the desired heat treatment conditions can be set more selectively. The anodizing itself takes place in a laboratory-scaled aggregate under steady state conditions. The uniform anodizing of the solution annealed and precipitated sample plates results in the analysis of the surfaces by oxide thickness measurements, optical microscopy and scanning electron microscopy. The examination of the results shows a direct dependence of maximum achievable oxide layer thickness to existing microstructural condition. Fully dissolved elements contained in the 7075 alloy affect the artificial layer growth of anodizing less critical and the thickest anodic coatings are made possible. The optimal chemical composition for maximum layer thickness lies in the upper level of the allowed copper content. However hardness maxima only occur after precipitation by ageing and at the highest zinc and copper values according to the standard. In summary, the production of dense oxide layers is nevertheless possible.
Translated title of the contributionEffect of element variation on the heat treatment and anodising of EN AW 7075
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Antrekowitsch, Helmut, Supervisor (internal)
  • Schlögl, Carina, Co-Supervisor (internal)
Award date18 Dec 2015
Publication statusPublished - 2015

Bibliographical note

embargoed until null

Keywords

  • aluminum
  • AW 7075
  • anodizing
  • oxide layer
  • heat treatment
  • element variation
  • casting
  • solution annealing
  • artificial ageing
  • oxide thickness measurement
  • hardness profile

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