List of Tables
Chapter 4 End forming behaviour of FSPed Al 6063-T6 tubes at different tool
4.1 Methodology
4.1.1 FSP of tube
The material used for the present work is AA 6063-T6, which has been used in as- received condition. A T6 heat treatment has been applied in the base material by the manufacturer. The outer diameter of tube is 50.8 mm and thickness is 3.17 mm. The chemical composition (% wt) of the alloy is: Si-0.496 %, Fe-0.149 %, Mg-0.549 %, Cu- 0.008 %, Ti-0.009 %, Cr-0.002 %, Ni-0.007 %, V-0.011 %, Zn-0.002 %, Others<0.084
%, and Al-balance.
Single pass FSP of aluminium tubes has been conducted using a specially fabricated tool on a 5-axis friction stir welding machine. To support the tube against the large amount of forces applied by the tool holder, it is supported by a mandrel, located inside the tube. The diameter of mandrel is almost equal to inside diameter of the tube.
The length of mandrel is larger than the length of the tube. The length of the tube used for FSP is 100 mm, while the length of the mandrel is 140 mm. Two capsules with threaded internal diameter are engaged with the mandrel. Both ends of mandrel are threaded up to a length of 25 mm at their ends. The designing of the capsule has been done in such a way that some part of it is covering the tube, so in this way tube, mandrel and capsules are providing a locking mechanism for tube. The tube has been processed up to a length of 65 mm. The schematic of the experimental set-up along with nomenclature of parts, the actual processing set-up, and the final processed tube are shown in Fig. 4.1.
Chapter 4
Fig. 4.1 FSP of tubes, (a) schematic of processing set-up for FSP of tubes, parts (1: base plate, 2: support plate, 3: slot, 4: inside rod, 5: movable angle plate, 6: capsule, 7:
mandrel, 8: tube, 9: fixed angle plate, 10: FSP starts, 11: FSP ends, 12 and 13: bolts), (b) actual experimental set-up showing the processing operation, and (c) final FSPed tube
A tool with circular shoulder profile and a cylindrical tapered pin made of non- consumable H13 tool-steel has been used for the processing purpose. The shoulder diameter and shoulder length of the tool is 25 mm. The pin height is 2.9 mm. The diameter of the pin at its base is 4.5 mm and at its tip is 2.45 mm. The positioning of the tube on the base plate along with mandrel (not seen in the picture, since it is inside the tube) and capsules can be observed. Two angle plates have been kept at the opposite ends of mandrel-tube-capsule assembly and one through hole has been done in the mandrel and angle plates. One circular rod of particular dimension passes through this hole and bolted at the both ends with angle plates, such that any vibration of the set-up during processing can be avoided and processing could be conducted smoothly.
End forming of tubes have been conducted with defect free processed zones. To decide the defect free range, a tube has been processed, in which the rotational speed kept on varied from 500 rpm at one end to 1900 rpm at the other end. The other parameters such as tool traverse speed, tool plunge depth and tool tilt angle are kept constant at 90 mm/min, 3 mm and 2° respectively. The constant value of traverse speed has been decided by past experiences for defect free welding in case of traverse speed for 6xxx series aluminium alloys. Plunge depth has been kept at 3 mm such that a sufficient thickness of the tube could be penetrated and defects such as microscopic voids and other
Chapter 4 root defects (kissing bond) could be avoided which happens due to lack of penetration. A
tool tilt angle of 2° has been used.
After the processing has been completed, the tube has been taken out of the experimental set-up carefully. For metallographic examination, the entire processed length has been sectioned into suitable sizes of prescribed lengths perpendicular to processing direction. The sectioned specimen has been ground using standard procedures and polished with different grades of emery paper on a disc polishing machine. After the polishing is completed, the material is polished with velvet sheet (with 1μm particle size diamond). Finally, to reveal the macrostructure, etching is done with Keller‟s reagent (H2O: 190ml, HNO3: 5ml, HF: 3 ml, HCl: 2ml). The same procedure has been followed for grain size evaluation of processed zone later. Macrograph examination has been done at a low magnification of 10×. Micrograph examination has been done at a higher magnification of 20×. Some of the macrographs have been shown in Table 4.1.
Table 4.1 Macrographs of processed samples at different tool rotational speeds
S. No. Tool rotational speed (ω, rpm) Tool welding speed (v,
mm/min.)
Macrograph of weld cross-section Defect and quality
1. ω=566
v=90
Tunnel, defective
2. ω=830
v=90 Pin hole, defective
3. ω=1050
v=90 Worm hole, defective
4. ω= 1200
v=90 Defect-free
5. ω=1307
v=90 Defect-free
6. ω=1535
v=90 Defect-free
7. ω=1775
v=90 Rough surface,
defective
Chapter 4 It is observed from the macrographs that at lower rotational speed, below 1100
rpm, and higher rotational speeds, above 1600 rpm, tunnel defect, pin hole defect, worm hole defect and rough surfaces are observed at rotational speeds of 566 rpm, 830 rpm, 1050 rpm and 1775 rpm, due to inadequate or excessive heat input. So, for actual processing trials, the tool rotational speeds decided are 1200 rpm, 1350 rpm and 1500 rpm which lies in the defect free range of 1100 rpm to 1600 rpm and the same is confirmed from the macrographs (Table 4.1). A substantial gap between the two levels of tool rotational speeds has been maintained such that their effect on end forming behaviour could be identified.
Totally sixteen processing trials have been conducted for each rotational speed.
Out of sixteen processed tubes for each rotational speed, four each will be utilized for expansion, reduction and beading and the two each will be utilized for tensile testing as well as plastic strain ratio, „r‟ value, calculation of processed zone. In total, 49 welding trials have been conducted. The scheme of utilization of sixteen tubes for a rotational speed has been shown in the form of flow chart (Fig. 4.2). Each experiment has been conducted twice to check the repeatability.
Fig. 4.2 Flow-chart of utilization of tubes for end forming operation