Speaker
Description
To achieve Net Zero CO2 Emissions by 2050, aircraft industries are conducting extensive studies for future aircraft using new technologies such as hydrogen aircraft and electric aircraft. Since those new aircraft should carry liquid Hydrogen, its cryogenic temperature of 20K could be expected to be used as a coolant for the efficient fan motor and generator. Super-high-purity aluminum is a promising conductor material for cryogenic electric aircraft because of its excellent electrical and thermal conductivity and lightweight. However, pure Aluminum shows very soft and weak yield strength, which makes it difficult the wire-drawing to small diameters. In addition, general solders using conventional tin alloy would not be acceptable because of the existence of the passivation thin film on the surface of pure Aluminum.
In this study, we have successfully fabricated the copper-clad super-high-purity aluminum ultrafine wires 0.05 mm in diameter, which are smaller than human hair. An initial simple billet was prepared in which a super-high-purity aluminum rod (5N5) 6.0 mm in diameter was inserted into the pure copper tube with 8.0 mm outer and 6.4 mm inner diameters. The aluminum rods and copper tube were carefully cleaned using the ultrasonic bath before assembling the billet in the clean booth of class 1,000 (USA Fed. Std. 209E). The rotary swaging was applied at the beginning of area reduction and then the continuous diamond die-drawing was applied using the slip-typed multi-die drawing machine. There was no wire breakage on the cold drawing from 8.0 mm to 0.05 mm. The maximum drawing speed was 800m/min, which is comparable to the mass-production speed of general electro-copper fine wires. The volume fraction of super-high-purity aluminum on 0.05 mm wire is approximately 54%, and the maximum tensile strength and elongation at room temperature are 342 MPa and 2.4%, respectively. Resistivity from room temperature (300K) to 10K has been measured by a DC four-probe method and RRR (residual resistivity ratio, 300K/20K) will be reported.
