MICRO-ALLOYED HIGH-PURITY ALUMINUM FOR LOW-TEMPERATURE CONDUCTOR APPLICATIONS

The development of micro-alloyed high-purity aluminum for low-temperat ure superconductor stabilizer applications is described. The base alum inum is 99.9998% pure; the micro-alloy levels range from 5 up to 90 wt ppm. Individual elements are added to the base in binary form; the so lute elements used are B, Ca, Ce, Ga or Y. The effects of solute eleme nts and solute concentration on electrical, mechanical, and crystallog raphic properties and on cyclic-strain resistivity degradation at 4.2 K are presented. The addition of low levels of various elements change s these properties with minimal effects on resistivity, and alloyed ma terials exhibit lower levels of cyclic-strain resistivity degradation than the base high-purity aluminum. Our results show that this improve ment in resistivity degradation is closely related to grain refinement resulting from the addition of solute elements and sample preparation procedures. Optical micrographs show the presence of particles that o ccurred as a result of micro-segregation during the initial solidifica tion.