High-strength and high-RRR Al-Ni alloy for aluminum-stabilized superconductor

The precipitation type aluminum alloys have excellent performance as the increasing rate in electric resistivity with additives in the precipitation state is considerably low, compared to that of the aluminum alloy with additives in the solid-solution state. It is possible to enhance the mechanical strength without remarkable degradation in residual resistivity ratio (RRR) by increasing content of selected additive elements. Nickel is the suitable additive element because it has very low solubility in aluminum and low increasing rate in electric resistivity, and furthermore, nickel and aluminum form intermetallic compounds which effectively resist the motion of dislocations. First, Al-0.1wt%Ni alloy was developed for the ATLAS thin superconducting solenoid. This alloy achieved high yield strength of 79 MPa (R.T.) and 117 MPa (4.2 K) with high RRR of 490 after cold working of 21% in area reduction. These highly balanced properties could not be achieved with previously developed solid-solution aluminum alloys. In order to achieve higher strength than the above, Al-Ni alloys of up to 2.0 wt% Ni content were investigated. Al-2.0wt%Ni alloy achieved yield strength of 120 MPa (R.T.) and 167 MPa (4.2 K) with RRR of 170 after cold working of 20% in area reduction.