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The Effect of Solidification Dynamics on the Formation of the Skin in Die Cast Mg–Al and Mg–RE Alloys
Author(s) -
Yang Kun Vanna,
Easton Mark A.,
Cáceres Carlos H.
Publication year - 2013
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201200188
Subject(s) - materials science , alloy , microstructure , metallurgy , drop (telecommunication) , grain size , die (integrated circuit) , mass fraction , rheology , composite material , nanotechnology , telecommunications , computer science
The grain microstructures and hardness of the surface layers of a Mg–RE alloy (3.44 mass % La) and two Mg–Al alloys, (8.77 and 11.6 mass % Al), are compared. All three alloys exhibit a harder surface layer, or skin, with fine primary α (Mg) grains, and a softer core with a larger grain size due to the prevalence of externally solidified grains (ESGs), but the skin of the RE alloy is more continuous and uniform due to the relative absence of ESGs. The distribution of ESGs can be related to the rheology of the liquid–solid mixtures inside the die: the solid fraction in the RE alloy, for given drop in temperature, is much larger than for the Mg–Al alloys. Being more viscous, the liquid in the RE alloy prevents the migration of ESGs towards the surface, hence the more uniform and tightly packed grain microstructure and better defined skin.