The impact energies of A356 aluminum-silicon alloys have been measured using a Charpy impact tester. The Charpy specimens have been machined from cast plates with the same geometry and produced in sand moulds. Unmodified, sodium-modified and strontium-modified castings have been tested. In this paper, the effects of eutectic modification and of the cooling rate on the impact properties of A356 aluminum-silicon alloys have been studied. When the value of the cooling rate is the same, unmodified samples show lower impact energies than modified ones: the effect of eutectic modification is emphasized in strontium modified samples. Moreover, a finer microstructure always corresponds to higher impact strength and an inverse correlation between impact energy and secondary dendrite arm spacing (SDAS) has been found. The fracture profile and surface of cracked samples have been analyzed by means of Optical and Scanning Electron Microscopes, in order to investigate the effect of eutectic silicon and intermetallic particles. Numerical simulations have been carried out to study the filling and the solidification behavior of the sand cast plates under different cooling conditions, in order to predict the final microstructure and shrinkage formation. A good correspondence between SDAS values, calculated by means of numerical simulations and measured with the linear intercept method, has been found.
Effect of eutectic modification and solidification rate on impact strength of A356 aluminum-silicon alloys
MERLIN, Mattia;GARAGNANI, Gian Luca
2008
Abstract
The impact energies of A356 aluminum-silicon alloys have been measured using a Charpy impact tester. The Charpy specimens have been machined from cast plates with the same geometry and produced in sand moulds. Unmodified, sodium-modified and strontium-modified castings have been tested. In this paper, the effects of eutectic modification and of the cooling rate on the impact properties of A356 aluminum-silicon alloys have been studied. When the value of the cooling rate is the same, unmodified samples show lower impact energies than modified ones: the effect of eutectic modification is emphasized in strontium modified samples. Moreover, a finer microstructure always corresponds to higher impact strength and an inverse correlation between impact energy and secondary dendrite arm spacing (SDAS) has been found. The fracture profile and surface of cracked samples have been analyzed by means of Optical and Scanning Electron Microscopes, in order to investigate the effect of eutectic silicon and intermetallic particles. Numerical simulations have been carried out to study the filling and the solidification behavior of the sand cast plates under different cooling conditions, in order to predict the final microstructure and shrinkage formation. A good correspondence between SDAS values, calculated by means of numerical simulations and measured with the linear intercept method, has been found.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
