- Title
- Study of the interrelationship between weld geometry, process variables and joint intergrity for friction processed AA6082-T6 aluminium
- Creator
- Samuel, Darren Alton Graham
- Subject
- Friction welding -- Research Pressure welding
- Subject
- Welding
- Date Issued
- 2014
- Date
- 2014
- Type
- Thesis
- Type
- Doctoral
- Type
- DPhil
- Identifier
- http://hdl.handle.net/10948/48058
- Identifier
- vital:40467
- Description
- This work presents a broad overview of the successful development of friction taper stud welding (FTSW) in 25mm thick AA6082-T6 sections. It covers the selection of geometry and process parameters, the development of data logging equipment, energy input results and interpretations. Research was carried out to develop the FTSW process for application in 25mm AA6082-T6 sections. The development and application of the FTSW process addresses the need to fill blind holes in thick aluminium sections for the repair of incorrectly drilled holes, friction stir welding exit holes and defects in critical components. During welding, frictional torque, rotational speed, axial force, near interface temperature of the tapered hole and welding time was recorded. This data was used to calculate energy input and energy input rates throughout a weld, enabling the effect of process parameters to be linked to energy, temperature, microhardness and static joint strength. Results of preliminary experiments are included in the study that were used for the design of a process parameter test window for FTSW in AA6082-T6, as no parameters were available to indicate a starting point for the research. The effect of process parameters on the static joint strength at the base of the tapered hole are presented; using a parallel sided stud and tapered hole configuration. This addresses one of the pressing issues facing FTSW of AA6082-T6, namely the lack of bonding at the bottom of the blind hole. A final process parameter matrix is designed based on the process development welds and is presented and discussed. In addition, the use of a non-consumable heat sink was investigated to prevent the premature collapse of the stud during welding and was shown to be critically important to the FTSW of AA6082-T6. To achieve good sidewall bonding a hole taper angle of 60° is required, this having been shown during visual evaluation of development welds. Stud taper angles between 2° and 5° less than the taper angle of the hole were identified as the range within which good FTSW can be made. With this geometry, at no stage during welding did the body of the stud shear off from the weld interface due to softening, thereby preventing collapse of the stud and formation of poorly bonded regions at the sidewall of the hole. The absence of shearing off of the weld interface during plunge was shown to be a good indicator of appropriate geometry and can be linked to welds made with high hole and stud taper angles and high axial force ramp up rates. The large hole and stud diameter relative to the depth of the hole and the large taper angle of the hole further aid in keeping the weld nugget rotating in the hole, promoting plasticization of the sidewall. Axial force ramp up rate was found to be the main critical success factor in an AA6082-T6 FTSW. Without control of this parameter the body of the stud will heat and detrimentally soften during plunge. It was established that good FTSW in AA6082-T6 cannot be made without the use of preheat to overcome the heat dissipation during welding, and is directly linked to improved energy input characteristics. Energy input as well as energy input rate were directly linked to static tensile strength and softening in the HAZ. The angle of the stud has been related to the energy input rate limit of the stud body, with increasing stud taper angles enabling the stud to withstand a higher energy input rate, allowing the weld interface to propagate up the hole at a slower rate, promoting plasticization of the sidewall. This study has successfully made good FTSW in 25mm thick AA6082-T6, in a 60°, 20mm deep tapered hole. Process parameters and ranges that produce FTSW exhibiting the required characteristics were identified by this study.
- Format
- xviii, 322 leaves
- Format
- Publisher
- Nelson Mandela Metropolitan University
- Publisher
- Faculty of Engineering, the Built Environment and Technology
- Language
- English
- Rights
- Nelson Mandela Metropolitan University
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | PhD Darren Alton Graham Samuel.pdf | 27 MB | Adobe Acrobat PDF | View Details Download |