Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 620, Issue -, Pages 181-189Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2014.10.004
Keywords
Al-Si alloys; Mo addition; Creep resistance; High temperature mechanical properties; Dispersoid strengthening; TEM
Categories
Funding
- NSERC (Natural Sciences and Engineering Research Council of Canada)
- Rio Tinto Alcan (RTA)
- NSERC/Rio Tinto Alcan Research Chair at University of Quebec at Chicoutimi
- McGill University
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The influence of Mo addition on the microstructure and mechanical properties of an Al-7Si-0.5Cu-0.3Mg alloy (wt%) was investigated. The Mo-containing alloy exhibited significant improvement in creep resistance over the base alloy. At 300 degrees C and 30 MPa, the minimum creep rate decreased by 95% while creep time-to-fracture was increased by 2 orders of magnitude, from 50 min to 1500 min. The tensile yield strength at 300 degrees C was also increased by 25%. These effects were attributed to the formation of novel Al-(Fe,Mo)-Si dispersoids during solution treatment in the grain interiors (intradendritic regions). Unlike the age-hardening precipitates, which coarsened resulting in loss of strength, these dispersoids were thermally stable and retained their strengthening effect at 300 degrees C. TEM investigations showed that the dislocation motions were effectively hindered by these fine dispersoids, leading to the reduction in the minimum creep rate. The onset of the tertiary creep stage was delayed by postponing the dislocation pile-up at the interdendritic Si particles. It was found that Mo addition suppressed the formation of the brittle plate-like beta-Al5FeSi intermetallics and formed a blocky phase in the cast microstructure, which resulted in 34% increase in elongation at 300 degrees C. (C) 2014 Elsevier B.V. All rights reserved.
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