Viscous behavior of (Sn61.9Pb38.1)100 -xREx (x = 0, 0.1, 0.3, 1 wt%) solder alloys

Abstract The viscous behavior of (Sn 61.9 Pb 38.1 ) 100− x RE x ( x = 0 , 0.1, 0.3, 1 wt%) solder alloys has been investigated by a torsional oscillation viscometer. The structural transition temperature T ′ increases with increasing addition of RE elements. Above T ′ , the viscosities of melts increase with increasing addition of RE, and are fitted well with the Arrhenius equation. The time dependence of viscosity at the measured temperature below T ′ follows the exponential relaxation function and reflects the process of the structural transition in the melt, which can be considered as the thermodynamic equilibrium process. The thermodynamic equilibrium relaxation time τ eq increases with both the equilibrium viscosity η eq and the discrepancy in viscosity (Δ η ), between the initial state and the equilibrium state. However, it decreases with the measured temperature T . The size of clusters in the melts increases with increasing of viscosity and is restricted by the thermodynamic equilibrium conditions.