Release Time:2019-03-09  Hits:

Indexed by: Journal Papers

Date of Publication: 2015-11-25

Journal: JOURNAL OF ALLOYS AND COMPOUNDS

Included Journals: Scopus、EI、SCIE

Volume: 650

Page Number: 896-906

ISSN: 0925-8388

Key Words: Eutectic silicon; Eu modification; A356; Mechanical properties

Abstract: The effect of Eu additions (0, 0.02, 0.04, 0.06, 0.08 and 0.1 wt.%) and T6 heat treatment on the microstructures and mechanical properties of A356 alloy have been investigated in the present work. Microstructures of the as-cast and T6 heat treated samples were examined by optical microscopy (OM) and scanning electron microscopy (SEM). It was found that 0.1% Eu modified the eutectic Si from a coarse plate-like form to a fully modified and fine fibrous one with a better uniform distribution. T6 treatment encouraged the spheroidization of eutectic Si particles. Correlating with the as-cast samples, the 0.1% Eu modified A356 alloy achieved likewise full modification of eutectic Si particles with lowest mean area and aspect ratio. In addition, the coarse and small Eu-rich intermetallics were both found in the 0.1% Eu modified A356 alloy. The cooling curves of A356 alloys showed that increasing Eu addition resulted in increasing nucleation undercooling and increasing growth undercooling. However, the recalescence (T-G - T-Min) increased by the initial addition of Eu, while it remained relatively stable for increasing additions (above 0.06%). The quenching experiment indicated that a large number of eutectic grains were located at or close to the tips of the aluminum dendrites with a jagged solid-liquid interface in unmodified alloy, while very few eutectic grains were formed in the interdendritic region with a smooth solid-liquid interface in 0.1% Eu modified alloy. An optimal combination of UTS (265 MPa) and EI (14.7%) of A356 alloy was achieved by the 0.1% Eu addition combined with T6 heat treatment. (C) 2015 Elsevier B.V. All rights reserved.