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Materials (Basel). 2014 Feb 12;7(2):1165-1172. doi: 10.3390/ma7021165.

In situ Neutron Diffraction during Casting: Determination of Rigidity Point in Grain Refined Al-Cu Alloys.

Author information

1
Computational Materials Laboratory, Ecole Polytechnique Federale Lausanne, station 12, Lausanne CH-1015, Switzerland. jean-marie.drezet@epfl.ch.
2
Computational Materials Laboratory, Ecole Polytechnique Federale Lausanne, station 12, Lausanne CH-1015, Switzerland. bastien.mireux@epfl.ch.
3
Institut Laue Langevin, Salsa instrument, Grenoble F-38042, France. szaraz@ill.fr.
4
Institut Laue Langevin, Salsa instrument, Grenoble F-38042, France. pirling@ill.fr.

Abstract

The rigidity temperature of a solidifying alloy is the temperature at which the solid plus liquid phases are sufficiently coalesced to transmit long range tensile strains and stresses. It determines the point at which thermally induced deformations start to generate internal stresses in a casting. As such, it is a key parameter in numerical modelling of solidification processes and in studying casting defects such as solidification cracking. This temperature has been determined in Al-Cu alloys using in situ neutron diffraction during casting in a dog bone shaped mould. In such a setup, the thermal contraction of the solidifying material is constrained and stresses develop at a hot spot that is irradiated by neutrons. Diffraction peaks are recorded every 11 s using a large detector, and their evolution allows for the determination of the rigidity temperatures. We measured rigidity temperatures equal to 557 °C and 548 °C, depending on cooling rate, for a grain refined Al-13 wt% Cu alloy. At high cooling rate, rigidity is reached during the formation of the eutectic phase and the solid phase is not sufficiently coalesced, i.e., strong enough, to avoid hot tear formation.

KEYWORDS:

coalescence; hot tearing; rigidity temperature; solidification

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