Thermal Efficiency and Material Properties of Friction Stir Channelling Applied to Aluminium Alloy AA5083

Abstract

The Friction Stir Channelling (FSC) is a novel advanced solution for producing internal closed channels along any desired path with a constant or continuously modified shape along the path in a single manufacturing step. The channels are formed by continuous extraction of part of the stirred processed material into external flash. In this work, the performance of channels with the same shape and dimensions but produced by FSC and milling respectively, are compared using an experimental calorimeter setup with a focus on the influence of the geometrical features of the channels on the thermal efficiency. The investigation is implemented in a plate of AA5083-H111, with a thickness of 10 mm. The material properties of the channels produced by FSC are investigated with a microhardness field and optical microscopic analysis, assessing the thermomechanically processed and heat affected zones. The mechanical resistance of the channels produced by FSC is evaluated with an application of internal pressure up to 380 bar. The results show that the FSC enhanced the heat transfer by about 45 % compared with smoother milled channels. The optical microscopy shows evidence of a good consolidation of the solid state joining mechanisms activated during the FSC, with a small reduction of the hardness around the channel in the stirred zone and heat affected zone, being assisted by a harder top region at the ceiling of the channel.

A review on friction stir-based channeling

“…In friction stir-based channeling, each wall of the channel is resulted with unique and distinct surface roughness features. [62,57,66,70,77] Figure 23 shows differences in surface roughness within channel's walls. [57,70,77] These differences in surface roughness are greatly influenced by the processing characteristics of friction stir-based channeling.…”

“…[51] Figure 23. Surface features of channel manufactured by friction stir channeling (a-d) cross-section of channel with four different sides, [77] (e) X-ray microcomputed tomography of channel, [70] (f) Channel surfaces and its confocal laser scanning microscopy for channel. [57] channel is resulted from deposited material where higher surface roughness is obtained.…”

“…It is also suggested that, improved performance of HFSC channels results in extending the life of electronic components that undergo complex and demanding heat loading cycles during service. Karvinen et al [77] concluded that channels produced by FSC without shoulder-workpiece clearance improve performance by 45% of heat transfer capacity with turbulent air cooling as compared to the milled channels, despite of increased pressure loss of 36%. Salminen et al [91] found that channels produced by FSC without shoulder-workpiece clearance are better in terms of heat transfer rate and cooling power ability despite of high pressure difference, as compared to channel produced by milling ( Figure 25).…”

“…The grain coarsening is expected in this variant due to processing conditions in high heat input with low pressure consolidation by shoulder-workpiece clearance, whereas higher hardness in ceiling zone is observed in other variants of HFSC and FSC without shoulder-workpiece clearance. The hardness variations across the cross-section are mapped in literature of [57,66,77] as shown in Figure 27 for variants of HFSC and FSC without shoulder-workpiece clearance. On contrary to the hardness of ceiling zone in case of FSC with shoulderworkpiece clearance, it can be seen that the hardness on the ceiling zone is higher as compared to the base material in both the cases of FSC without shoulderworkpiece clearance and HFSC.…”

Monitoring of the mechanical load and thermal history during friction stir channelling under constant position and constant force control modes

“…They have also found that the influence of the tool shoulder on the channel formation increases along with the channel length. Channels produced by FSC and tested by Karvinen et al [9] were able to withstand an internal pressure up to 380 bar and results using air as cooling media showed that the FSC enhanced the heat transfer by about 45 % compared with smoother milled channels. A recent addition to these techniques is the Hybrid Channelling (HC), which enables simultaneous welding and channelling, in one action, of multiple metal components from similar or dissimilar materials and geometries.…”