Micro-forming Ability of Ultrafine-Grained Magnesium Alloy Prepared by High-ratio Differential Speed Rolling

초록

An ultrafine grained Mg-9Al-1Zn magnesium alloy with the mean grain size less than 1 mu m was produced by using high-ratio differential speed rolling. The processed alloy exhibited excellent superplasticity at relatively low temperatures. The micro-forming tests were carried out using a micro-forging apparatus with micro V-grooved shaped dies made of silicon and the micro-formability was evaluated by means of micro-formability index, R-f (=A(f)/A(g), A(f): formed and inflowed area into the V-groove, A(g): area of the V-groove). The Rf value increased with temperature up to 280 degrees C and then decreased beyond 300 degrees C. The decrease of the R-f value at 300 degrees C was attributed to the accelerated grain coarsening. Increasing the micro-forging pressure increased the R-f values. At a given die geometry, die filling ability decreased as the die position moved away from the die center to the end. FEM simulation predicted this behavior and a method of improving this problem was proposed.

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