TITLE:
Microstructural Evolution of Cast Hyper-Eutectic Al-18% Si Alloy during Cyclic Semi-Solid Heat Treatment
AUTHORS:
Mohamed Ramadan
KEYWORDS:
Microstructural, Cyclic, Semi-Solid Heat Treatment, Al-18% Si, Microstructure, Hyper-Eutectic, Cast
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.3 No.5,
August
24,
2015
ABSTRACT: The cyclic semi-solid heat treatment represents a promising technique for improving microstructure
and mechanical properties of a wide range of metallic alloys. In the current research the influence
of cyclic semi-solid heat treatment on microstructure of Al-18% Si alloy containing 0.8%
Fe has been studied. All specimens were heated in an electrically heated resistance furnace with
heating rate of 10°C·min-1 to 585°C. For a complete one cycle heat treatment (5 min heating time), samples after 5 min holding at 585°C were cooled to a temperature of 550°C in still air cooling and the samples were taken out immediately for water quenching. It was found that heat treatment cycles should be limited to 3 cycles or less in order to maintain fine grain size and globular structure without agglomeration and coalescence. Cyclic semi-solid heat treatment changes morphology
of iron-rich intermetallics phases to be plate-like and fine plate iron-rich intermetallics phases,
in stead of needle-like iron-rich intermetallics phases that are observed in as-cast samples. Cyclic
heating shows a relatively higher hardness for all heating cycles compared with as-cast one due to
its finer and globular structure. Cyclic semi-solid heat treatment technique results in lower coarsening rate constant compared with isothermal heat treatment one due to coarsening discontinuous
effect.