Solid State Communications, Vol. 86, No. 10, pp. 679-683, 1993. 0038-1098/93 $6.00 + .OO Printed in Great Britain. Pergamon Press Ltd ELECTRICAL AND MICROHARDNESS STUDIES ON Al-Mg ALLOYS A. Gaber, N. Atify, A.Y. Abdel-Latief and M.S. Mostafa Physics Department, Faculty of Science, Assiut University, Assiut, Egypt zyxwvutsrqponmlkjihg (Received 9 December 1992; accepted for publication 24 February1993 by P.H. Dederichs) The effect of Mg content on some of the electrical parameters and the microhardness of Al-Mg alloys has been investigated. Namely, the dependence of the temperature coefficient of resistivity, aall, the electronic relaxation time, rail, and the electron-impurity scattering power, Aq, on the Mg content in the alloys has been studied. On the other hand, the influence of dissolved Mg on the microhardness of Al- Mg alloys has been evaluated. In addition, the decomposition behaviour of the sunersaturated Al-Mg alloys has been followed and characterized. * 1. INTRODUCTION SINCE the electrical resistivity and the micro- hardness are sensitive parameters to the structural transformations of the supersaturated alloys, they have been widely used to follow the G.P. zones formation and the subsequent precipitation in Al- Mg alloys [l-5]. Depending on the type of such precipitates, i.e. coherent or incoherent in the base matrix, an increase in the microhardness will occur or not, respectively [6]. On the other hand, the early state decomposition and formation of G.P. zones is accompanied by an increase in the electrical resistivity of the given alloy and, in contrast, large precipitates are accompanied by a decrease in the resistivity. In the present work, in addition to tracing the decomposition process in Al-Mg dilute alloys, the dependence of the temperature coefficient of resistivity on the Mg concentration in the alloy has been studied. Furthermore, from the resistivity results during the continuous heating of the alloys, the effect of Mg concentration, C, on the Debye temperature, 8, and electron-impurity scattering power has been investigated. 2. EXPERIMENTAL PROCEDURES Specimens of Al, _ cMgc alloys, where C is the atomic fraction of the dissolved Mg (C = 0.0, 0.006, 0.025 and 0.045), were prepared using Al (99.98%) and pure Mg (99.9%). The main impurities in the prepared alloys are Fe and Si of maximum content of 0.008 and 0.02 wt%, respectively. Strips of 0.5 x 2 x 35mm3 from the prepared alloys were used for electrical resistivity measure- ments. These measurements were carried out by the conventional four-wire method using Philips com- puterized system 21. The uncertainty of such system was *0.012%. Disc-shaped specimens of 25mm diameter and 3 mm thickness were prepared for the microhardness measurements. Vickers microhardness, HV (0.49 N load and 10 s period) has been measured by the usual method previously described elsewhere [7]. 3. RESULTS AND DISCUSSION 3.1. Electrical Resistivity M easurements 3.1 .l. Dependence of temperature coeficient of resistivity aaIl and the relaxation time, r,~. on the Mg content C. For dilute binary alloys, in a solid solution state, the electrical resistivity, paa( T), can be given by (Matthiessen’s rule) Pall(T) = BC(1 - C) + PT, (1) where ,K( 1 - C) represents the temperature-inde- pendent residual resistivity arising from scattering power of electrons on the static impurities, and pT is the temperature-dependent term arising from the scattering power of electrons on the dynamic deviations from crystal perfection (phonons). It has been shown in a previous work [8] that at room temperature %ll/~ = m/T = l/I1 + PC0 - C>lPr). (2) Here, for dilute Al-Mg alloys, o, T and ~1, ~~11 are the temperature coefficients of resistivity and the electronic relaxation time for pure Al and Al-Mg alloys, respectively. According to equation (l), the measured resistivity of the specimens at room temperature is represented against C( 1 - C) (Fig. 1). 679