Date of Award

2016

Document Type

Open Access Thesis

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Anthony P. Reynolds

Abstract

Friction stir welding (FSW) is a solid-state joining process that utilizes a non-consumable, rotating tool to plunge into abutting faces and transverse along the weld path. Material nearby the tool is softened by frictional heat generated via local friction and plastic deformation. Severe plastic deformation of the interface along with a state of hydrostatic pressure results in creation of a joint by metallurgical bonding. Because the temperature of the material during the welding process is below that of the melting point, FSW has numerous advantages over conventional fusion welding. Friction consolidation (FC) is also a solid-state process that uses a rotating die to soften and consolidate initially well divided charge (chips or metal waste). FC can produce fully consolidated bulk material from low-cost precursors such as metal chips, scraps or even powders. It may be more economical, efficient and convenient than conventional melting and casting recycle process. This thesis focuses on the friction stir weldability of titanium 15 molybdenum alloy (Ti 15Mo) as well as friction consolidation of commercially pure titanium alloy (CP Ti) and Ti 15Mo with an emphasis on FSW of Ti 15Mo. For Ti 15Mo welds, the correlation between the control parameters such as forge force, tool rotation rate and travel speed, and response variables like, torque, weld power and weld energy are investigated by empirical observation and numerical calculations. Extensive experiments and calculations are carried out and the result shows that that joint quality weld strength and grain size in the weld nugget are significantly affected by the control parameters. For the part of friction consolidation of CP Ti and Ti 15Mo, ultra-high Vickers hardness and tensile strength are found in the fully consolidated disk. Multiple experiments and methods were performed to examine and characterize this abnormal mechanical and metallurgical response. Possible explanations are also talked about in this thesis.

Rights

© 2016, Dawei Li

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