Masters Theses


Wei Yuan


"Efforts to reduce vehicle weight and improve safety performance have resulted in increased application of light-weight aluminum alloys and a recent focus on the weldability of these alloys. Friction stir spot welding (FSSW) is a solid state welding technique (derivative from friction stir welding (FSW), which was developed as a novel method for joining aluminum alloys). During FSSW, the frictional heat generated at the tool-workpiece interface softens the surrounding material, and the rotating and moving pin causes material flow. The forging pressure and mixing of the plasticized material result in the formation of a solid bond region. The present work investigated the effect of tool designs and process parameters on microstructure and mechanical properties of friction stir spot welds. Different tool designs were compared and process parameters were optimized for specific aluminum alloy 6016 (AA6016) based on lap-shear test. Effect of paint-bake cycle on weld properties was also studied. Different failure modes for welds were proposed and discussed. Material flow during FSSW using a step spiral pin was studied by decomposing the welding process and examining dissimilar alloys spot welds which allowed a visualization of material flow based on their differing etching characteristics. The formation and control of a skew "Y" shape oxide layer was investigated. The movement of upper and bottom sheet material, and their mixing during FSSW were observed"--Abstract, page iv.


Mishra, Rajiv S.

Committee Member(s)

Miller, F. Scott, 1956-
Dharani, Lokeswarappa R.


Materials Science and Engineering

Degree Name

M.S. in Materials Science and Engineering


Friction Stir Linc, Inc.
National Science Foundation (U.S.)
General Motors Corporation


Missouri University of Science and Technology

Publication Date


Journal article titles appearing in thesis/dissertation

  • Effect of tool design and process parameters on properties of friction stir spot welds.
  • Material flow during friction stir spot welding


xi, 66 pages

Note about bibliography

Includes bibliographical references.


© 2008 Wei Yuan, All rights reserved.

Document Type

Thesis - Open Access

File Type




Subject Headings

Friction stir welding
Aluminum alloys -- Welding
Electric welding -- Equipment and supplies
Welded joints
Tools -- Design
Shear (Mechanics)

Thesis Number

T 10253

Print OCLC #


Electronic OCLC #