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Upward Unsteady-State Solidification of Dilute Al–Nb Alloys: Microstructure Characterization, Microhardness, Dynamic Modulus of Elasticity, Damping, and XRD Analyses

Department of Mechanical Engineering, University of Brasília-UNB, 70910-900 Brasília, Brazil
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Metals 2019, 9(6), 713; https://doi.org/10.3390/met9060713
Received: 30 April 2019 / Revised: 4 June 2019 / Accepted: 5 June 2019 / Published: 25 June 2019
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Abstract

Aluminium alloys form many important structural components, and the addition of alloying elements contributes to the improvement of properties and characteristics. The objective of this work is to study the influence of thermal variables on the microstructure, present phases, microhardness, dynamic modulus of elasticity, and damping frequency in unidirectional solidification experiments, which were performed in situ during the manufacturing of Al–0.8 Nb and Al–1.2 Nb (wt.%) alloys. Experimental laws for the primary (λ1) and secondary (λ2) dendritic spacings for each alloy were given as a function of thermal variables. For Al–0.8%wt Nb, λ1 = 600.1( T ˙ )−1.85 and λ2 = 186.1(VL)−3.62; and for Al–1.2%wt Nb, λ1 = 133.6( T ˙ )−1.85 and λ2 = 55.6(VL)−3.62. Moreover, experimental growth laws that correlate the dendritic spacings are proposed. An increase in dendritic spacing influences the solidification kinetics observed, indicating that metal/mold interface distance or an increase in Nb content lowers the liquidus isotherm velocity (VL) and the cooling rate (). There is also a small increase in the microhardness, dynamic modulus of elasticity, and damping frequency in relation to the composition of the alloy and the microstructure. View Full-Text
Keywords: Al–Nb alloys; microstructure characterization; dendritic spacing; unidirectional solidification Al–Nb alloys; microstructure characterization; dendritic spacing; unidirectional solidification
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Moreira Coutinho, M.; Saraiva Silva, J.I.; Primo Sousa, T.; Monteiro Rosa, D. Upward Unsteady-State Solidification of Dilute Al–Nb Alloys: Microstructure Characterization, Microhardness, Dynamic Modulus of Elasticity, Damping, and XRD Analyses. Metals 2019, 9, 713.

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