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Solidification microstructure selection and coupled eutectic growth in Al-Fe and Al-Fe-Mn alloys

Authors
  • Wang, Y.
Publication Date
Jan 01, 2000
Source
OpenGrey Repository
Keywords
Language
English
License
Unknown

Abstract

The effect on solidification microstructure of Al-3wt%Fe produced by addition of either 1.0wt% or 0.1wt% Cu, Mg, Si or 0.01 to 0.1wt% V has been determined by means of wedge chill casting, direct chill simulation casting and Bridgman growth over the range of solidification front velocity between 0.033 to 1.03mm/s during steady state growth with an temperature gradient of 8 to 18K/mm. Coupled eutectic growth has been investigated and the effect of the further additions on the eutectics and their transitions have been determined by constant velocity Bridgman growth (CBG) and by accelerating Bridgman growth (ABG) with accelerations 3.61 x 10"-"4, 1.11 x 10"-"3 and 1.86 x 10"-"3mm/s"2 over the velocity ranges 0.033 to 0.33mm/s, 0.33 to 0.67mm/s, and 0.67 to 1.0mm/s, respectively. Growth competition was found to be between primary #alpha#Al dendrites, primary Al_3Fe intermetallic and five eutectics, i.e. #alpha#Al-Al_3Fe (Eu1), #alpha#Al-Al_6Fe (Eu2), #alpha#Al-AI_mFe (Eu3), #alpha#Al-#alpha#AlFeSi (Eu4) and #alpha#Al-Al_xFe (Eu5), for the alloys and ranges of solidification front velocity and temperature gradient in the present work. With an acceleration of 3.61 x 10"-"4mm/s"2, ABG revealed that, for binary Al-3wt% Fe, Eu1 was suddenly replaced by Eu2 at V#>=#0.10mm/s. Cu addition favoured eutectic Al_6Fe over primary Al_3Fe whilst Mg promoted growth of both primary Al_3Fe and Eu1 to higher velocity, with 0.60 and 0.33 mm/s being required in Al-2.84Fe-1.11 Mg for suppression of primary Al_3Fe and replacement of Eu1 with Eu2, respectively. Crystallographic faceting of eutectic Al_6Fe crystals was observed in Al-2.84Fe-1.11Mg alloy with the facet planes being determined to be #left brace#110#right brace#. Si addition resulted in formation of cubic #alpha#AlFeSi phase in both DC simulation cast and Bridgman grown samples, with the critical velocity for the transition from Eu1 to Eu4 being determined to be 0.091mm/s (CBG) or 0.2mm/s (ABG). Vanadium addition, however, introduced Eu5 with fully Eu5 structure being obtained from 0.071 to 1.03mm/s, 0.34 to 1.03mm/s and 0.20 to 0.34mm/s in Al-2.5Fe-0.12V, Al-3.09Fe-0.044V and Al-3.15Fe-0.006V, respectively. Eu5 in the Al-2.85Fe-0.12V and Al-3.09Fe-0.044V alloys showed a morphological transition from lamellar to rod-like with increasing growth velocity. The dependence of Eu5 eutectic interphase spacing #lambda# on growth velocity V was found to follow the theoretically predicted relationship, #lambda##sq root#V=A, with A=22.4#+-#1.8 or 13.8#+-#2.1#mu#m"3"/"2s"-"1"/"2 for lamellar and rod-like growth, respectively. The observed ratio #lambda#_l_a_m/#lambda#_r_o_d =1.6 for fixed growth velocity V is close to the applicable value 1.55 predicted by the Magnin and Trivedi modification of the Jackson and Hunt model of eutectic growth. Growth temperature T_G of Eu5 at a temperature gradient G ranging from 8 to 18K/mm in the Al-2.85Fe-0.12V alloy conformed to the relationship, #DELTA#T_E_U = T_E_U - T_G = B#sq root#V, with eutectic temperature T_E_U = 649.0#+-#1.0 deg. C and constant B = 0.32#+-#0.04 Ks"1"/"2/#mu#m"1"/"2. (author) / SIGLE / Available from British Library Document Supply Centre-DSC:DXN037773 / BLDSC - British Library Document Supply Centre / GB / United Kingdom

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