Iranian Journal of Materials Science and Engineering

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Abstract: The supersolidus liquid phase sintering characteristics of commercial 2024 pre-alloyed powder was studied at different sintering conditions. Pre-alloyed 2024 aluminum alloy powder was produced via air atomizing process with particle size of less than 100 µm. The solidus and liquidus temperatures of the produced alloy were determined using differential thermal analysis (DTA). The sintering process was performed at various temperatures ranging from the solidus to liquidus temperatures in dry N2 gas atmosphere for 30 min in a tube furnace. The maximum density of the 2024 aluminum alloy was obtained at 610ºC which yields parts with a relative density of 98.8% of the theoretical density. The density of the sintered samples increased to the maximum 99.3% of the theoretical density with the addition of 0.1 wt. %Sn powder to the 2024 pre-alloyed powder. The maximum density was obtained at 15% liquid volume fraction for both powder mixtures.

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Geometrical design of the spiral crystal selector can affect crystal orientation in the final single crystal structure. To achieve a better understanding of conditions associated with the onset of crystal orientation in a spiral crystal selector, temperature field was investigated using three-dimensional finite element method during the process. Different geometries of spiral crystal selector were used to produce Al- 3 wt. % Cu alloy single crystal using a Bridgman type furnace. The Crystal orientation of the samples was determined using electron backscattered diffraction (EBSD) and optical microscopy. Analysing the temperature field in the crystal selector revealed that, the orientation of growing dendrites against liquidus isotherm in the spiral selector was the reason for crystal misorientation which differs in various selector geometries. Increasing the take-off angle from 35° up to 45° increases the misorientation with respect to <001> direction. Further increase of take-off angle greater than 45° will decrease the crystal misorientation again and the efficiency of the selector to produce a single grain is decreased.