Microstructure Analysis of Al–5.5at%Mg Alloy Semi-solid Slurry by Weck’s Reagent

Abstract

Spheroidization of Al grains is required for the production of semi-solid slurry by either a partial solidification route or partial melting route. In this research, Al–5.5at%Mg alloy with dendrite structure was plastically deformed with 33 % compression and partially melted in a semi-solid state in order to obtain globular solid grains. Color etching method by Weck’s reagent (distilled water 100 mL; KMnO4 4 g; NaOH 1 g) was used for microstructure observation. During microstructure evolution of compressed specimen, the deformed dendrite changed gradually to the spheroidal shape due to the partial melting at the semi-solid temperature range. In the optical micrograph of the etched specimen, the microstructure was revealed with different color and contrast. The original shape of the spheroidal Al grains at the semi-solid state could be visualized clearly in the quenched microstructure. The solid fractions were measured for the entire semi-solid temperature ranging from 585 to 625 °C. By eliminating the growth layer of Al grains formed during water quenching, the solid fractions were evaluated accurately.