In A 356, alloy Elements - wt% are:
Cu - 0.02
Si - 6.99
Mg - 0.48
Mn - 0.02
Fe - 0.22
Ti - 0.18
Ni - 0.01
Zn - 0.04
Pb -
Si is BCC.
Refinement of eutectic silicon phase of aluminum A356 alloy using high-intensity ultrasonic vibration
X Jian, TT Meek, Q Han - Scripta Materialia, 2006 - Elsevier
In this alloy there are many metastable phases, it is therefore necessary to define the heat treatment.
One can relatively easy make a calculation with some CALPHAD type of database, e.g. TCAL1 and Thermo-Calc. One will then get the liquidus and solidus temperatures as well as the fraction of phases as a function of temperature.
This shows that first FCC starts forming at ca 616C and forms until the eutectic reaction L--> fcc + Si starts at 572 C. A couple of degress lower also the phase Al9Fe2Si2 starts forming. At ca 530C the phase Al18Fe2Mg7Si10 starts forming etc.
However, the major phases are fcc (mainly Al) and Si with the diamond structure. The phase Al18Fe2Mg7Si10 reaches as most almost 2% at around 400C and then disappears. All this is equilibrium of course. It is also easy to make a calculation assuming the Scheil mode which accounts for microsegregation but neglects diffusion in the solid state.
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