Structural study of electrodeposited aluminum-manganese alloys |
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Authors: | Benjamin Grushko Gery R Stafford |
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Affiliation: | (1) Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa, Israel;(2) Metallurgy Division, National Institute of Standards and Technology, 20899 Gaithersburg, MD |
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Abstract: | Aluminum-manganese alloys with compositions ranging between 0 and 27 wt pct Mn were electrodeposited at 150°C onto copper
substrates from a chloroaluminate molten salt electrolyte with a controlled addition of MnCl2. The specimens were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive
spectroscopy (EDS), and X-ray diffraction. The addition of small amounts of Mn results in the formation of a supersaturated
fcc solid solution of Mn in Al. At the higher Mn content, an amorphous phase is established. The highly faceted crystalline
surface of pure Al and Al−Mn solid solution becomes smooth and nearly specular when the amorphous phase is present. The amorphous
phase appears in the form of rounded grains and has a lower limit of Mn concentration close to the Al6Mn composition. There is a concentration discontinuity between the above limit and the higher Mn concentration limit of the
fcc phase (about 9 wt pct). Appearance of the amorphous phase in the alloy results in a decrease in the Mn concentration in
solid solution to about 2 wt pct. Crystallization of the amorphous phase starts at the fcc-amorphous phase interface at 230°C.
As a result of treatment at 230 °C to 340 °C, the amorphous phase completely transforms into Al6Mn, while the fcc phase is unaffected. Prior to crystallization, the amorphous phase shows a modification that could be interpreted
as the formation of a fine-grained icosahedral phase. The formation and distribution of phases by electrodeposition and rapid
solidification are discussed. |
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