Abstract

Friction Stir Welding (FSW) is a new solid state welding technique which is characterized by its ability to join the difficult-to-weld alloys, notably aluminum alloys. Microstructural studies revealed that FSW produces fine grain structure within the weld nugget due to the extensive plastic deformation and dynamic recrystallization (DRX) associated with it. Further studies hypothetically suggested that thermo-mechanical processing using friction stir can be used as a technique to create ultra-fine grain structure for superplastic forming (SPF). Yet, a more practical and economic suggestion indicated the suitability of combining FSW with SPF technologies in a way similar to the existing combination of diffusion bonding (DB) and SPF.In this research, FSW was applied to DRX Al-Cu-Li alloy (AA 2095) with 2 average grain size, prepared for SPF. To measure the retention of the room temperature mechanical properties and superplastic behavior (SPB), FSW conditions were prepared to experimentally and statistically evaluate the effect of the two main process parameters (tool rotation speed,feed rate). Macro- and microstructural investigations of the weld conditions were carried out, as well as in the post heat treated condition. Microhardness profiles were developed to examine the hardness distribution within the weld zone. Room temperature tension testing was carried out for the as-welded, naturally aged, and artificially aged conditions to assess the effect of FSW on the mechanical properties compared to the as-received DRX sheets. High temperature testing was carried out using constant strain rate tensile testing to study the impact of weld parameters, as well as other SPF parameters (strain rate and temperature) on the elongation-to-failure and the strain rate sensitivity of the material. Potential linking between the measured power and heat input during welding and the mechanical properties was also explored. Experimental work revealed that aluminum alloys are readily weldable using FSW. Retention of mechanical properties was observed to a great extent, either in the as-welded or the postheat treated conditions. Most importantly is the retention or in fact the improvement of SPB exhibited within the stir zone. The examined process parameters (tool rotation speed, feed rate) had an interaction rather than an individual impact on the as-welded microstructure and room temperature mechanical properties. However, weld sections in the post heat treated condition showed that the interaction effect ceased to exist after heat treatment, and the effect of individual parameters became significant. Microstructure of the heat treated welds showed abnormal grain growth taking place within the weld. Moreover, the tool rotation speed showed to be the more decisive parameter for structural refinement as revealed by the experimental and statistical analysis.

School

School of Sciences and Engineering

Department

Mechanical Engineering Department

Degree Name

MS in Mechanical Engineering

Date of Award

6-1-2004

Online Submission Date

2-3-2013

First Advisor

Hanadi G. Salem

Committee Member 1

Mohamed Raafat El Koussy

Committee Member 2

Mahmoud Farag

Committee Member 3

Ezzat Fahmy

Document Type

Thesis

Extent

186 p

Rights

The American University in Cairo grants authors of theses and dissertations a maximum embargo period of two years from the date of submission, upon request. After the embargo elapses, these documents are made available publicly. If you are the author of this thesis or dissertation, and would like to request an exceptional extension of the embargo period, please write to thesisadmin@aucegypt.edu

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