Abstract:Superplastic uniaxial tensile tests of coarse-grained LY12 are conducted. Large elongation to fracture is obtained at 10^-4 s^-1 and 10^-1 s^-1 strain rates, while elongation to fracture is low at intermediate strain rates. Analysis of the SEM fracture surface shows that amorphous matter at the grain boundary plays a dominant role in coarse-grained superplastic behaviors. At higher strain rates, the amorphous matter layer is thin and the grains and sub-structure size decrease during the grains extruding and turning around among each other so that exhibit good superplastic characteristics. In this case, few cavities form and mechanical properties at room temperature are good. At lower strain rates, nearly all grains are covered with thick amorphous matter layer which makes grain boundary sliding more easily and enhances superplastic deforming ability, but many cavities tend to form and mechanical properties at room temperature deteriorate. At intermediate strain rates, grains cant become very fine and amorphous matter layer at the grain boundary is not very thick, hence a samll quantity of cavities forms and the specimens exhibit a decrease in superplastic characteristics.

Key words: LY12 alloy; coarse grains; superplastic deformation; grain boundary; amorphous matter