Masters Theses

Keywords and Phrases

Lap joints; Friction stir welding (FSW)

Abstract

"Friction stir welding (FSW) of thin plate lap-joints promises to reduce production time, improve joint stiffness and reduce the total weight of the aircraft by eliminating rivet fasteners. FSW does not, however, eliminate the crevice corrosion issue that is created when two plates are joined, which have an overlapped area (faying surface) with a finite gap between the plate surfaces.

The purpose of this research is to seal the faying surface gap using a low melting Al-Ge eutectic alloy, which melts and fills the faying surface gap during the FSW process. Heat generated during the FSW process is expected to melt the sealant material. The Al-Ge sealant is meant to inhibit the formation of a concentration corrosion cell (crevice corrosion) by preventing the penetration of the corrosive electrolyte into the faying surface gap. Binary Al-Ge eutectic and ternary Al-Ge-Sr based alloys were investigated in terms of fusibility and bonding behavior with 7075-T6 alloy in a simple lap joint configuration.

Sealants were applied by air plasma spray (APS). Pulverized powders, less than 53 µm in diameter, were APS coated on the plate along the tool path making a uniform coating thickness of 70 µm. An uncoated plate was lapped with the coated plate to sandwich the APS coating. FSW was then performed to join the two plates and melt the sealant.

This research shows that with current tool design, sealants only partially fill the faying surface gap and melting of the sealants were restricted to regions below the tool shoulder diameter. Complete sealing of the faying surface will require a FSW tool having a large shoulder diameter that extends across the entire faying surface.

A new mechanism of material transport for FSW was discovered during the course of this research. It was found that the low melting eutectic was capable of penetrating the base material grain structure and facilitated the removal of grains. These grains were later deposited within the faying surface. This newly discovered mechanism might help to explain microstructural development and strength variations within friction stir welded structures"--Abstract, page iii.

Advisor(s)

Van Aken, David C.

Committee Member(s)

Mishra, Rajiv S.
Fahrenholtz, William

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Metallurgical Engineering

Comments

The author is thankful to the Boeing Company, Advanced Manufacturing Research and Development for funding this research.

Publisher

University of Missouri--Rolla

Publication Date

Summer 2003

Pagination

xvi, 131 pages

Note about bibliography

Includes bibliographical references (pages 122-130).

Rights

© 2003 Yoshihide Kato, All rights reserved.

Document Type

Thesis - Restricted Access

File Type

text

Language

English

Subject Headings

Friction weldingJoints (Engineering)AluminumGermanium

Thesis Number

T 8340

Print OCLC #

54893253

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