Study on Tensile Behavior of High Vacuum Die-Cast AlSiMgMn Alloys

The tensile behavior of high vacuum die-cast AlSiMgMn alloys at as-cast and T6 heat-treated conditions was investigated with in situ SEM. For the alloys at both conditions, the cracks initiated from small subsurface gas pores with several microns. For the as-cast alloys, slip bands and plastic deformation were obvious in the a-Al grains. The cracks expanded rapidly within the eutectics. After the T6 heat-treatment, the eutectic regions were separated by alpha-Al grains and the eutectic Si particles became globular shape. Hence the elongation improved significantly but the UTS decreased due to decrease of eutectic fractions. The crack grew with connecting the voids between the aluminum matrix and particles. The a-Fe intermetallics in as-cast status were prone to cause microcracks. Though the shape of intermetallics was hardly changed by the T6 treatment, the denency of microcrack formation on them decreased.