Equilibrium solid solubility of nickel to aluminum re-investigated by resistometry

Trace nickel addition improved a property of aluminum bonding wire. Recently some investigators reported equilibrium solid solubility of Ni to Al smaller than previous values. Therefore, its re-investigation is necessary. Wire and sheet of Al-Ni dilute alloys were prepared with total impurity contents less than 15 ppm. After heat treatments at temperatures above 523 K, electrical resistivity was measured at 77 K and 300 K by four contacts DC potentiometry and density-mass method size factor. Resistivity at 77 K, ρD77, after solution treatments showed a good linear relation to Ni contents up to 310ppm. The 438ppmNi specimen of the highest content showed a smaller ρD77 than the straight line, suggesting incomplete dissolution of Ni. Contribution per unit concentration of Ni to the ρD77, ΔρD77Ni, was 10.4±0.2 nΩm/mass%. Resistivity values at 300 K, ρD300, were at maximum only 1.7% higher than that of ideally pure aluminum. Though linearity of the line was poor, Δρ300Ni was 8.86±1.09nΩm/ mass% and still higher than the Fink et al.'s value. The equilibrium solubility of Ni determined at temperatures ranging 723K to 913K is expressed as C eqNi/mass% = 1.36×104exp(-1. 16×104/T), giving maximum solubility about 20% lower than Fink et al.'s.