Abstract
Electrical resistivity is one characteristic and important physical property of a metal, and it is sensitive to the composition and microstructure. The relationship between resistivity and composition and microstructure makes resistivity a useful tool in materials research, such as non-destructive evaluation and monitoring precipitation kinetics. However, this needs a good understanding of how composition and microstructure influence resistivity, which is currently lack in Mg alloys. Therefore, a systematic investigation of the resistivity of Mg alloys is necessary. Mg-Al, Mg-Gd, Mg-Sn and Mg-Zn series alloys with different solute content are prepared for the current investigation. The resistivity of these alloys in the as-cast, solution treated, and aged status are measured at different temperatures to study the influence of temperature, composition and microstructure on the resistivity. In situ measurements are also conducted to study the resistivity changes during isothermal ageing of Mg alloys. The results show that Mg alloys have a positive temperature coefficient of resistivity (TCR). The TCR varies from different solute content, which demonstrate the deviation from Matthiessen’s rule in Mg alloys. When the alloys are solution treated, the following equation can describe the relationship between resistivity and solute contents: ρ(T)=ρMg(T)+δ(T)×c ρ(T) is the resistivity of the alloy under a certain temperature, ρMg(T) is the resistivity of pure Mg, δ(T) is the coefficient, and c is the concentration of the solute. δ(T) depends on both the temperature and the type of solute. The reason for the increment is the lattice distortion caused by the solute elements. When the alloys are aged, a phenomenological formula can describe the relationship between the resistivity and the volume fraction of precipitates： 𝜌𝑒𝑓𝑓=𝜌𝛼*(1+1/2𝑉𝛽)/(1−𝑉𝛽) 𝜌𝑒𝑓𝑓 is the effective resistivity, 𝑉𝛽 is the volume fraction of the precipitates, 𝜌𝛼 is the resistivity of the 𝛼-Mg matrix. With the help of this formula, resistivity can be used to quantify the precipitation kinetics of binary magnesium alloys.
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