Abstract
The solidification of AlCuSi alloys with Mn and Fe was studied by rotating a magnetic field to understand the effect of melt flow. The specimens solidified with a forced convection, low cooling rate and low temperature gradient. Electromagnetic stirring generated by an electric coil around the specimens caused a transformation from equiaxed dendritic to rosette morphology, occasionally with spheroids and minor dendrites. The transformation was quantitatively observed with a specific surface Sv, that decreased for almost all alloys and marked the flow effect on α-Al. The computer coupling of phase diagrams and thermochemistry (CALPHAD) technique was applied for the calculation of phase diagrams and property diagrams. Forced convection decreased secondary dendrite arm spacing λ2 in almost all alloys, while it increased slightly in one studied alloy. The length of detrimental β-Al5FeSi phases decreased in the alloy, where β starts to precipitate in the presence of α-Al, while increasing in alloys where β starts as first and grows in the fully liquid melt. The average overall dimension of the Mn-rich phases increased in almost all alloys, and the number density decreased under flow. The modification of spacing for AlSi-eutectics and Al2Cu was analyzed. It was found that the occurrence of Al2Cu does not influence the fluid flow and vice versa.
Highlights
The cylindrical specimens (65 mm in height and 38 mm in diameter) were heated, melted and solidified in a graphite crucible. Both the alloy and the crucible were heated to a temperature of 800–805 ◦ C and moved from the electric resistance furnace into the solidification facility provided with thermal insulation (Sibral Fiberfrax, Unifrax, Tonawanda, NY, USA) and electric coils
The microstructure on the cross- and long-sections of specimens was investigated on micrographs using a light optical microscope (LOM), and all assumed, measured and calculated parameters were collected in a table
The property diagrams, Scheil solidification and the ternary phase diagram for the investigated alloys were calculated in the ThermoCalc [26]
Summary
The unique combination of properties provided by aluminum alloys make it one of the most economical and universal, and attractive, metallic materials for a broad range of uses, from soft foil to the most advanced engineering applications [1]. Flemings [4] discovered a non-dendritic structure in the semi-solid state of metallic alloys with special rheological properties. Non-dendritic structures exhibit rheological properties [6] improving the mechanical properties of alloys [7] and composites [8], making semisolid metal processing (SSM) [9], thixoforming [10], rheocasting [11] and thixowelding [12] unique for the production of advanced engineering parts [13].
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