Abstract
The results of annealing on the residual resistance ratio (RRR) of five (5) composite aluminum cryoconductor wires and mechanical properties on fifteen (15) aluminum cryoconductor wires are presented. The independent variables of the study include the wire diameter, number of pure aluminum filaments, initial filament RRR, matrix alloy composition and manufacturing method. The dependent variables for the annealing study include annealing temperature, annealing time and cooling rate. This investigation is primarily undertaken to determine the optimum post manufacturing heat treatment and to learn about the sensitivity of wire RRR to variations in the heat treatment schedule. Wires are annealed to remove crystal defects and allow recovery, recrystallization and grain growth to proceed. The removal of crystal defects will increase the RRR as a function of time and temperature. At the same time recovery is taking place, filament contamination is occurring by the diffusion of impurity atoms (Fe, Ce, Si, Mg, etc.) from the alloy matrix. The result of these two situations is a RRR vs. time curve that exhibits a maximum. The optimum annealing temperature for the five (5) wires is approximately 400'C, and the optimum annealing time lies between 5 to 200 minutes. This broad range in annealing times is caused by physical differences in wire types and sample variability. Sample variability is defined as the electrical or mechanical property differences between adjacent samples of the same wire type. Values of RRR are dependent on the number of filaments, the purity of the matrix and filament purity. RRR results cover a range from 750 to 2242 when annealed at 400'C for 20 minutes In general, single filament cryoconductors show larger RRR values compared to the four (4) filament conductors. Yield strength, ultimate tensile strength and percent elongation on fifteen (I 5) cryoconductor wires are also examined at room temperature and 4.2K. Results show cryoconductors which appear to have high RRR values are usually the weakest. Other highlights in this thesis include a post annealing recovery study, computerized data acquisition source code and RRR probe construction design details.
Sundby, Paul C. (1994). Measurements of electrical and mechanical properties of aluminum composite cryoconductors. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -S9573.