Characterization of high frequency welded aluminium microfin tube for heat exchangers

Abstract

An aluminium alloy tube produced using linear high frequency welding of a strip consisting of a 3xxx-series alloy core with an embossed inner part and a thin 7xxx-series outer clad layer has been investigated in this work. Characterization techniques such as scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, optical microscopy, and X-ray tomography have been utilized to understand the change in microstructure due to embossing and welding process. It is found that welding creates a high-quality joint without any observable flaws along the weld. The weld region contains a deformed microstructure as a result of compression applied during welding. The width of this plastically deformed region is 150–200 μm. On both sides adjacent to the deformed weld region there are approximately 250–300 μm-wide partially recrystallized heat-affected zones. The rest of the tube retains the deformed microstructure of the embossed strip. The microhardness of the welded tube follows the microstructural variations, with higher values in the deformed regions and lower values in the partially recrystallized heat-affected zones. The influence of the manufacturing process on the observed microstructural characteristics is discussed.