The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr(wt.%) alloys in as-cast, solution treated(T4) and aged(T6) conditions were studied by means of immersion test and electrochemical measurements in 5wt.% NaCl solution saturated with Mg(OH)_2. It was observed that the corrosion rate in the T4 condition was lower than that of the as-cast and T6 conditions by both sand casting and permanent mold casting with the same order of as-cast>T6>T4; while the corrosion resistance of the permanent mold casting is superior to the sand casting. The morphologies of the corrosion products are similar porous structures consisting of tiny erect flakes perpendicular to the corroded surface of the alloy, irrespective of the heat treatment conditions. Especially, the corrosion film in T4 condition is more compact than that in the other two conditions. In addition, the severer corrosion happening to the as-cast condition is correlated with the galvanic corrosion between the matrix and the eutectic compounds; while improved corrosion resistance for the T4 and T6 conditions is ascribed to the dissolution of the secondary eutectic compounds. The measured corrosion current densities of Mg-10Gd-3Y-0.5Zr alloys in as-cast, T4, and T6 conditions are 36 μA?cm^(-2), 10 μA?cm^(-2), and 33 μA?cm^(-2), respectively. The proposed equivalent circuit [Rs(CPE_1(R_t(R_fCPE_2))] by Zview software matches well with the tested electrochemical impedance spectra(EIS) data.
In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification,and the samples of semi-solid slurry were taken by the rapid quenching method.The results show that fine and sphericalα-Mg particles can be obtained under rotating gas bubble stirring treatment.The process parameters such as gas flow rate,cooling rate and rotation speed have significant influence on the morphology of primary solid particles.After rotating gas bubble stirring treatment,the higher the particle density,the finer and rounder the primaryα-Mg particles.The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.
