Investigation of the Phase Relations in the Al-Rich Alloys of the Al-Sc-Hf System in Solid State
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asic and Applied Research: Section I
Investigation of the Phase Relations in the Al-Rich Alloys of the Al-Sc-Hf System in Solid State L.L. Rokhlin, N.R. Bochvar, J. Boselli, and T.V. Dobatkina
(Submitted January 18, 2010; in revised form March 2, 2010) Using electrical resistivity measurements, optical microscopy, and scanning electron microscopy (SEM) with energy dispersive x-ray analysis (EDS), the combined solubility of Sc and Hf in solid Al and the phases in equilibrium with Al solid solution at 600, 500, and 400 °C were studied. The investigation indicated the progressive decrease of the total solubility of Sc and Hf in solid Al with increasing Sc/Hf ratio in the alloys and decreasing temperature. ScAl3 and HfAl3 were observed in equilibrium with Al without formation of a continuous solid solution between them. Based on the established extension of the Al solid solution and also extensions of the ScAl3 + (Al) and HfAl3 + (Al) phase fields, the partial isothermal section of the Al-Sc-Hf phase diagram at 600 °C was constructed.
Keywords
aluminum alloys, phase diagram, phase equilibria, solid solution, ternary phase diagram
the Al-Hf system was confirmed to be HfAl3.[5] Two allotropic forms have been reported for this compound, with crystal structures described by the Pearson symbols tI8 (prototype TiAl3) and tI16 (prototype ZrAl3).[4]
1. Introduction
2. Methods
There appears to be no information in the literature regarding the Al-rich part of the Al-Sc-Hf ternary phase diagram. This phase diagram is interesting because Sc and Hf interact similarly with Al in the binary systems. The most interesting part of the Al-Sc-Hf phase diagram is the Al-rich corner, because Sc is known to improve significantly the strength of aluminum alloys.[1-3] In this work, the Al-rich part of the Al-Sc-Hf phase diagram was studied.
2.1 Preparation of the Alloys
1.1 Adjoining Binary Systems The Al-rich side of the binary phase diagram Al-Sc has been studied extensively. According to Massalski et al.,[4] the main features are the invariant eutectic reaction at 655 °C near the melting point of Al (660.452 °C), the small solubility of Sc in solid Al, which decreases with decreasing temperature from 0.24 at.% at 655 °C to 0.03 at.% at 500 °C and the existence of the compound ScAl3 in equilibrium with solid Al. The crystal structure of the ScAl3 is cubic of the L12 type (Au3Cu prototype, Pearson symbol cP4). The Al-Hf phase diagram is characterized, according to our previous work,[5] by the peritectic invariant reaction at 661 °C and low solubility of Hf in solid Al, which decreases with decreasing temperature from 0.153 at.% at 661 °C to 0.05 at.% at 500 °C. The composition of the phase in equilibrium with Al solid solution in L.L. Rokhlin, N.R. Bochvar, and T.V. Dobatkina, Baikov Institute of Metallurgy and Materials Science RAS, Moscow, Russia; J. Boselli, Alcoa Technical Center, Alcoa Center, Pittsburgh PA, USA. Contact e-mail: [email protected].
The alloys for investigation of the combined solubility of Sc and Hf in soli
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