抄録
In order to increase the elongation of T6-heat treated JIS AC4C alloy squeeze castings, the effects of Srmodification and grain-refinement by titanium addition on the tensile properties were investigated by varying the secondary dendrite arm spacing between 15 to 30 μm as the coarseness of solidified structures. The effects of Sr-modification and Ti-refinement on the elongation were hardly observed when the structure was fine as a result of rapid solidification. The elongation of castings decreased as the solidified structures became coarser when no molten metal treatment was performed. However, the elongation was increased by Sr-modification. Moreover, the elongation increased more when Ti-refinement in addition to Sr-modification was performed. It was also clarified that the elongation improved with the formation of fine eutectic silicon particles which are hard to crack. In addition, the crack advanced zigzag not only through the Al-Si eutectic region but also across dendrites which grew in a curve due to the cored structure of the segregated titanium.
