INVESTIGATION OF THE DECOMPOSITION AND PRECIPITATION IN SUPERSATURATED AI-Mg ALLOYS.

Abstract

For Al-Mg alloys (Al+0.82, Al+1.84, Al+3.76, Al+5.74 and Al+12.81 at. % Mg) have been selected for this study. From the electrical resistivity measurements it is concluded that the resistivity increment of Al-Mg alloys (in a solid solution state) is proportional to the atomic fractional constituents (Mg and Al) as !J.pall 64.66 c(1-c) -tOcm. In addition, both the temperature

coefficient of resistivity, a and the relaxation time of the all

free electrons <: all

in the alloys diminish with increasing the

solute Mg concentration in the alloy.

As the electrical resistivity results fit fairly with the Bloch-Gruneisen model, the dependence of both the scattering power, and the Deby temperature e on the magnesium

concentration has been identified. In other words, increases as

C increases due .cto the contribution of electron-impurity Mg

'scattering. The percentage increase due electron-impurity scattering per one atomic percent Mg has been determined as 12.99 %. In contrast, the Debye temperature e decreases as the Mg

concentration increases.

The microhardness results showed that the solid solution hardening obeys the relation !J.HV = 135.5 c0 •778 MPa which is s Mg

comparable to the theory of solid solution hardening for all

alloys; !J.HV "'Co.s-o. 67 . s

The combined results of the microhardness, HV, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM)