Effects of Sr Addition and Heat Treatment on the Morphology of Eutectic Si in the Al-12Si Die Casting Alloys

초록

Die cast Al-Si alloy includes the eutectic Si in coarse, acicular form leading to stress concentration. Accordingly, its application as structural alloy has been limited. Various ways to modify the morphology of eutectic Si have been proposed and developed in order to improve the mechanical property of the alloys. As one of them, trace addition of Sr has been considered. The alloy also has been limited in heat treatment because the formation of surface defects by agglomeration of pores during solution treatment. CSIRO, Australian laboratory, suggested a solution treatment to avoid the formation of the defects. The solution treatment is performed for15 min. at the temperature range from 440℃ to 530℃. A380 alloy, one of Al-Si die cast alloys, is solution treated for 15 min. at 490℃ and aged at 150℃ after the quenching. The aim of this study is to investigate the effects of Sr addition and heat treatment on the variation of morphology of eutectic Si in the Al–12Si die casting alloys. The morphology of eutectic Si for each alloy is observed by scanning electron microscopy (SEM). The Solution treat is conducted for 15 min. at 485℃ and artificial aged at 150℃ after the quenching. Tensile test is carried out to investigate effect of the morphology of eutectic Si on tensile properties of the alloys.