On the microstructure and mechanical properties of squeeze-cast Al-7 wt% Si alloy

Specimens of commercial Al-7 wt% Si alloy have been solidified under different pressures, varying from atmospheric to 70 MN/m 2, into rods 10 mm in diameter and 50 mm in length. Two types of porosity have been examined in these specimens, macro-porosity (observed at magnifications < 100 x and mic...

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Veröffentlicht in:Journal of materials processing technology 1994, Vol.40 (1), p.73-85
Hauptverfasser: El. Mahallawy, N.A., Taha, M.A., Lofti Zamzam, M.
Format: Artikel
Sprache:eng
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Zusammenfassung:Specimens of commercial Al-7 wt% Si alloy have been solidified under different pressures, varying from atmospheric to 70 MN/m 2, into rods 10 mm in diameter and 50 mm in length. Two types of porosity have been examined in these specimens, macro-porosity (observed at magnifications < 100 x and micro-porosity (observedf at magnifications > 100 x), and the pressure was found to have reduced the volume fraction and size of both. Critical pressures have been found for each type of porosity, above which the pores disappear. Different features of the microstructure have been examined. Whilst the type of structure does not change with variation of pressure, the volume fraction of primary dendrites increases and their secondary arm spacing decreases. A more homogeneous structure with more perfectly arrayed dendrites is obtained in squeeze-cast specimens. The improvements in soundness and microstructure in squeeze castings are reflected in their mechanical properties, which are found to be superior to those of gravity-cast castings. By increasing the pressure, the tensile fracture strain and strength and the impact toughness are increased. Correlation between the fracture tensile strength and the microstructure is established.
ISSN:0924-0136
DOI:10.1016/0924-0136(94)90478-2