Influence of freezing rate on microstructure and electrochemical properties of Mg-2%Ga alloys

Abstract

Equilibrium freezing curve of Mg-2%Ga (mass fraction) alloy was calculated by CALPHALD method. Microstructures of the melted Mg-2%Ga alloys solidified by iron and copper moulds, respectively, were investigated using OM and SEM. Electrochemical properties of the Mg-2%Ga alloys with different freezing rates were measured by galvanostatic, potentiodynamic and electrochemical impedance spectroscopy tests. The results show that solidification by copper mould leads to intergranular Mg 5Ga 2 compounds with small size and large number density. Less adsorbent of Mg + and oxide corrosion products occur on the surface of the Mg-2%Ga alloys solidified by copper mould, producing lower corrosion current density of 1.8×10 −5 mA/cm 2. In the galvanostatic tests with 100 mA/cm 2 current density, more negative stable potential of −1.604 V exists in the Mg-2%Ga alloys solidified by iron mould due to the lower freezing rate, which leads to smaller inductive and capacity time constants as well as shorter activity time and better electrochemical activity.