Abstract
This work investigates the benefits of having an aluminum (Al) busbar with welded copper (Cu) ends, and evaluates the force relaxation phenomena of a pre-loaded bolt joint on Cu versus Al, under cyclic thermal loading. The results show a force relaxation rate 50% lower in the Cu-bolted joint compared with the one in Al. The core of this research is the weldability analysis of Al-Cu butt joints made by friction stir welding (FSW). The materials are AA1050 H14/24 and Cu OF 04 with thickness of 6 mm. Temperature monitoring during the FSW cycle emphasize how heat generation depends mostly on local internal viscoplastic deformation. Tensile, bending, and microhardness tests were used to establish the mechanical properties. Optical microscope and scanning electron microscopy were used to characterize the microstructure. Joining mechanisms in the weld were investigated using energy-dispersive X-ray spectroscopy. The FSW resulted in 85% tensile strength efficiency compared to the Al base material, and 97% electrical conductivity efficiency compared to an ideal bimetallic component made of the same materials with no contact resistance. Electrical resistance of the FSW is 200 times lower than the electrical contact resistance between the Al-Cu materials while under high compressive force.
Highlights
Various industries constantly strive to improve their competitiveness, with higher performance products made with efficient processes with low environmental impact
The maximum temperature in Cu at 15.8 mm distance from the center of the stirred zone is 293.7 °C while the maximum temperature in Al at the same distance from the stirred zone is 219.5 °C. These facts emphasize that differently from what some authors consider in their heat generation models [4, 25], the bulk of the heat is not generated due to the friction dissipation at the sliding interfaces, but in the internal energy dissipation inherent to the viscoplastic deformation of the material flow imposed by the tool geometry
The investigation of the bimetallic friction stir welding (FSW) joint between the plates with thickness of 6 mm, made of AA1050-H14/24 and Cu-OF-04 FSW, with the manufacturing of Al busbar with welded Cu ends in mind, delivered the following main results:
Summary
Various industries constantly strive to improve their competitiveness, with higher performance products made with efficient processes with low environmental impact. The IMCs are defined as solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents [18] They are generally very stable, brittle, and with a high fusion temperature, causing a problem in the welding of dissimilar materials, both in fusion and solid-state welding. The Al material in the FSW joint was selected to maximize the electrical conductivity (where σCu-OF ≅ 100% IACS; σAA1050 ≅ 61% IACS; and σAA6101 ≅ 43% IACS), because there is no need for higher mechanical resistance, as provided by AA6101-T4, when the busbar ends are made of Cu. During the FSW, the temperatures were monitored. The electrical resistance of the Al-Cu weld and contacting Al-Cu components under different clamping force levels was assessed using a microhmmeter
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