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Production and characterization of high performance al – fe – v – si alloys for elevated temperature applications

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2009
Sayılgan, Seda
In the present study, the powder metallurgy was evaluated as a technique to produce high performance Al – 8Fe – 1.7V – 7.9Si (wt%) alloys for elevated temperature applications and the role of powder particle size range and extrusion ratio in the microstructural and mechanical properties of the extruded alloys was investigated. For this purpose, an air atomization method was employed to produce powders of the high temperature alloy and after that the produced powders were sieved and cold compacted. The compacted billets were subsequently hot extruded at 450 – 480 °C. Five selected ranges of powders which were different in particle size (−2000+212 μm, −212+150 μm, −150+106 μm, −106+90 μm, and −90 μm) and three different extrusion ratios (144:1, 81:1, and 26:1) were used in this study. In the first part of the thesis, microstructure and thermal stability of as – air atomized powders were described. α – Al matrix and α – Al13(Fe, V)3Si phases were characterized in all rapidly solidified powders by XRD. The fraction of the intermetallic phases was reduced as the powder particle size increased. DTA analysis revealed an exothermic reaction at 581 °C in all alloy powders of different size fractions. In the second part of the study, the effect of powder particle size and extrusion ratio on microstructural and mechanical properties (at different temperatures) of the extruded alloys was investigated. The results showed that decrease in powder particle size and increase in extrusion ratio refined the microstructure and improved the mechanical properties. It was revealed that the effect of powder size was more evident than that of extrusion ratio. Remarkable increases in mechanical properties (e.g. 60.7% increase in ultimate tensile strength at 250 °C) were observed as a result of rapid solidification process (atomization) and hot extrusion.