Microstructural aspects and fracture behavior of A356/357 alloys - An overview

The microstructural aspects of cast A356/357 alloys are strongly dependent on the magnesium content, modification, grain refinement, cooling rate, porosity and heat treatment. On the other hand, the fracture behavior of these alloys depends on the size and shape of eutectic silicon particles and iron-rich intermetallics. Magnesium content increases both the matrix strength and eutectic particle size but decreases the ductility. The combined effect of modification and grain refinement improves the overall mechanical properties. Increasing the cooling rate refines the eutectic Si particles, iron-rich intermetallics, aspect ratio and improves ductility. Porosity defect is detrimental to mechanical properties and an increased level of porosity is reported to accompany the modification of A356/357 cast alloys. Cast A356/357 aluminium alloys are strengthened by heat treatment processes to attain desirable mechanical properties. The fracture behavior of Al-Si-Mg alloys depends on silicon particle cracking. The damage process takes place due to particle cracking, microcrack formation and growth and local linkage of microcracks. This paper presents an overview on the microstructural aspects and fracture behavior of A356/A357 alloys.