Viscous flow behaviour of Zn–Al eutectoid alloy

Strain and shear viscosity were measured for Zn–Al eutectoid alloy, while continuously changing temperature. The minimum shear viscosity accompanied by the eutectoid change process was observed. The stress dependence of the strain rate and the heating rate dependence of minimum values of the shear viscosity were investigated. It is found that the relation between strain rate and the stress in the temperature region of the phase transition obeys Newtonian viscous flow law. The viscous flow behaviour of Zn–Al alloy in the temperature region of phase transition can be explained by the size and property of the phase interface. Comparing the activation energy of the phase transition with that of the viscous flow of the phase interface, it is found that the fluidity of phase interface is likely to be a primary factor influencing phase transition process. In a previous work, the minimum viscosity was observed in glass transition and crystallisation process of amorphous Pd–Cu–Si alloy. According to these results, it is shown that the minimum viscosity occurring in structural transition has some universality.