マチーセン則経験式によるAl-Si鋳造合金の比抵抗とサイズファクター

抄録

A relation between the resistance ratio (R=ρ₃₀₀/ρ₇₇) and the resistivity at 77K (ρ₇₇) deduced from Matthiessen's rule and empirically determiend for commercial pure aluminium was applied to Al-1-15%Si cast alloys. ρ_M77 and size factor M.F. according to Matthiessen's rule were calculated from the resistance ratio R using the empirical relation. Both the geometrical size factor G.F. and resistivity ρ_G77 obtained using the conventional method were compared with the M.F. and ρ_M77•ρ_M77 was always smaller than ρ_G77, and well corresponded to the change in solute Si concentration caused by heat treatment. Volume fraction of precipitated Si approximately estimated from a ratio of the two size factors, M.F./G.F., was nearly 3 times higher than that estimated from the ρ_M77 and Si content. To explain this large discrepancy, the current screened areas (S.A.) was proposed to exist in front and behind of precipitated Si particles. The increase in M.F./G.F. during isochronal heat treatment could be qualitatively explained by the decrease in the S.A. resulting from the rapid dissolution of smaller Si particles. Taking account of the effects of shape and distribution of Si particles on the S.A., the change in the contribution of precipitates to the resistivity is also understood.