Abstract

Aluminum's many exceptional properties promote it to be as a strong candidate for several applications in the aerospace, automotive, building and packaging industries to name a few. As a result, strengthening Aluminum has been the interest of many researchers over the time. The most commonly followed approaches are alloying and thermal treatments. However, recently, refining the internal structure of materials until reaching the nano-scale range to improve their mechanical properties has been fostered. Specifically speaking, research adopting this approach on various metals has yielded promising results. One of the techniques used to produce nanostructured Aluminum powders, which is the one employed in this research, is mechanical milling. Aluminum powders were mechanically milled using a high-energy ball mill under argon atmosphere for several milling durations up to 12 hours. The effect of the process control agent used during milling was investigated to determine the suitable amount to be used for best achievable mechanical behavior. Both X-ray diffraction patterns and scanning electron micrographs have revealed the establishment of nanostructured Aluminum by mechanical milling. Bulk samples were synthesized by powder metallurgy. The success of the process of powder consolidation was determined by examining the degree of densification through density measurements. The effect of mechanical milling on the bulk samples has been studied by evaluating the tensile and compressive behaviors of the developed material. The material after milling for 12 hours exhibited a tensile strength that is four folds that of the starting powders. But this elevated strength was at the cost of sacrificing the ductility of the material. Nevertheless, under compressive loading the material behaved in a ductile manner in addition to the improved strength. Peaks for secondary phases have been noticed in the X-ray diffraction patterns for the bulk samples after mechanical milling. The types of these phases remain undetermined, although high suspects of oxides and carbides exist, that might have contributed to the material strengthening. Transmission electron micrographs have ascertained achieving a nanocrystalline structure after milling for 12 hours. The poor ductility of the milled Aluminum acts as a barrier that hinders the utility of the material since almost all the applications require an amount of ductility within certain margins for shaping, manufacturing, and so forth. Hence, post-extrusion annealing was conducted on additional samples in an attempt to improve the ductility. This has been proved quite successful, but still the achieved ductility is nowhere near the range that can help commercialize the newly developed material. It was also remarkable that annealing didn't result in sacrificing the acquired strength; on the contrary, the tensile strength of the material was noticed to have increased. Another approach to compromise the strength and ductility of mechanically milled Aluminum was to mix soft as-received Aluminum powders with the Aluminum powders mechanically milled for 12 hours to produce bi-modally structured Aluminum composite. Two mixing techniques were tried out that are turbula mixer and the high-energy ball mill. Using turbula mixer yielded disappointing results by demonstrating a weak bond between the two constituents. Conversely, using the ball mill for mixing allowed a strong bond to form between the constituents leading to enhancing the ductility of mechanically milled Aluminum for 12 hours without depressing the strength beyond the acceptable range.

Department

Mechanical Engineering Department

Degree Name

MS in Mechanical Engineering

Date of Award

2-1-2012

Online Submission Date

January 2012

First Advisor

Esawi, Amal M. K.

Document Type

Thesis

Extent

NA

Library of Congress Subject Heading 1

nostructured materials industry.

Library of Congress Subject Heading 2

Metal powders industry.

Rights

The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy.

IRB

Not necessary for this item

Comments

I would like to start my dissertation by acknowledging all those who have helped me reach the point of actually writing my dissertation. First, I would love to express my deep gratitude to my supervisor, Professor Amal M. K. Esawi who has continuously nourished me with her guidance and experience. Second, I am deeply thankful for the Youssef Jameel Sciences and Technology Research Center (YJSTRC), at the American University in Cairo for providing all the facilities, and materials as well as the fincial support needed for this research to be accomplished. In addition to the persol help that I received from the YJSTRC team and particularly Abdel Hamid Mostafa, Ahmed Abdel-Gawad, Ahmed El-Ghazaly, Ehab Salama, Hany Salib, Mi Mikhael, Mohamed Taher, Mohie El-din Safwat and Radwa Raafat. Also, special thanks to Ms. Hady Hussein and Mr. Rami Wasfi for their invaluable technical assistance. Third, I am really grateful for Professor Hadi Salem for her unconditiol caring and encouragement throughout my years at AUC. Fourth, I am extremely appreciative to my dear friends, Irene Samy and Mohamed Hegazy, who have always been beside me during my downfalls when I was just about to give up and helped me rise up again and follow the path to where I am today. Also, thanks to Ahmed Hossam who has helped me on a very short notice while writing my dissertation to catch up with my tight schedule. Fifth, thanks to all the laboratory engineers and technicians (Eng. Khaled Eraqi, Hussein, Mohamed, Saeed, Magdy, and Sobhy) who have contributed hugely to getting this research done smoothly. Sixth, thanks to the department of chemistry at AUC and specially Mr. Emad Farag for conducting the XRD alysis for the samples. Seventh, thanks to Durametal Industries, the Egyptian company for wear resistant steels for supplying me with tooling at no cost to carry out this research. Last and foremost, my beloved family, I can never thank you enough, not in a million years. Thank you my mother for your care, attention, and prayers, thank you for bearing with me and enthusing me during my worst times and never letting me fall. Thank you my father for you have always been my inspiration. Thank you my brother, Ibrahim, for supporting and encouraging me. Thank you all for believing in me.

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