Equal channel angular pressing (ECAP) process of copper electrodes for resistance spot brazing application

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Date
2007
Authors
Tran, Thi Thien Ly
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Abstract
This research was performed to investigate the influence of ECA pressing step on the workability of copper electrode used for resistance spot brazing application. The as- received copper material was characterized using optical microscope observation and X- Ray fluorescence analysis. It was then annealed at 600OC for 48 hours followed by ECA pressing using the die with inner angle of 120O and outer angle of 35O. The billets were processed by four passes using route BC. After each pass, the billets were examined for cracks and polished again before continued for the next pass. Scanning electron microscope was used to characterize the ECA pressed material microstructure and microhardness distribution in transverse and longitudinal sections. The electrical conductivity of ECA pressed samples was also examined. The results showed a significant increase in microhardness value of samples. After four passes, the microhardness observed was 158Hv and 160 Hv referring to transverse and longitudinal section compared to the microhardness of 60Hv of the as- annealed sample. After four passes, the grain size had been reduced from 110μm to the ultrafine fibrous structure of 290nm, in the transverse view. There was also a significant change in electrical conductivity. The electrical conductivity of 1.5X108 (Ohm-m)-1 was achieved compared to 6.00X107 (Ohm-m)-1 of pure copper standard conductivity. The working performance of processed copper as electrode in resistance spot brazing was studied in comparison to the copper-chrome electrode. The microstructure measurement of brazed joints, the shear tensile strength and microhardness profile observation over the brazing area were evaluated and studied. The processed copper electrode showed an ability to produce comparable joint quality by means of load at break in shear tensile test and produced relatively good shear strength. The optimum brazing condition for each type of electrode was also established.
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Master
Keywords
Materials and Mineral Resources Engineering , Equal channel angular pressing (ECAP) , Copper electrodes , Spot brazing
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