マグネシウム合金での抵抗比(ρ300/ρ77)と比抵抗の関係

Dependence of resistivity of solid solution ρss on solute concentration and temperature of measurement was considered. In relatively dilute solid solution, ρss can be approximated by a linear function of solute concentration C. Deviation from Matthiessen's Rule (DMR) defined by change in dρ/dT with C can be replaced by temperature dependence of dρ/dC(≡Δρ), change in ρ with C. Using difference e = ΔρT2-ΔρT1 and ratio η = ΔρT2/ΔρT1 of Δρ at two different temperatures T1 and T2 (T1solid solution at T1K) and resistance ratio R = ρT2/ρT1 are obtained.ρSST1=(ρPURET2-ρPURET1+Cbeb+Ccec)/(R-1) ρSST1=[ρPURET2-ρPURET1ηb+CcΔρcT1(ηc-ηb)]/(R-ηb), where ρPURE is ρ of idealy pure solvent metal. For solid solution of high concentration, replacing C to f (X), an appropriate function of atomic fraction X, and Δρ to Δρf(X) based on the f (X), similar expressions as above two relations can be obtained. The R-ρ relations in commercial magnesium alloy AZ91 were investigated comparing with those calculated from reported ρ values. The Δρ of Al in Mg is smaller at 300K than at 77K and DMR is negative, however, Zn in Mg appears to show a positive DMR. As an empirical R-ρ relation applicable to ρ changes resulted from aging and solution treatment of AZ91 alloy, 52<ρ77/nΩ•m= [69.1/(R-0.77)]-13.8<138 is recommended.