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speeds, zone lengths and numbers of passes were tried to know the optimum refining conditions. The impurity content was estimated from the residual resistivity, and the highest resistance ratio in bulk R300/R4.2 obtained in the present work was 50000.

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The residual electrical resistivity of dilute aluminium-silver foils with thicknesses of 30-1300 mu m has been measured. The silver concentration is 0.01-0.1 at.%, and three heat treatments are used, referred to here as furnace cooling, air quenching and quenching followed by aging. The resistivities of foils show various features consistent with the presence of Guinier-Preston (GP) zones. A strong enhancement of surface resistivity rho s (=foil resistivity-bulk resistivity) is found in these foils: rho s increases with solute concentration and becomes about 4-5 times as large as that in the solid solution and in Fuchs-Sondheimer theory. The enhanced rho s decreases to about a half upon aging for six days at 350 K after quenching from 871 K. These results strongly suggest that anisotropy in GP zone scattering enhances rho s.