Analyzing the microstructural evolution and hardening response of an Al-Si-Mg casting alloy with Cr addition

Journal Article · Wed Aug 15 04:00:00 UTC 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.06.026· OSTI ID:22805110

Zhan, Hongyi; Hu, Bin ^[1]

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1. General Motors Global Research & Development, China Science Lab, 56 Jinwan Road, Shanghai (China)

Highlights: • The formation of β-Al{sub 5}FeSi intermetallics was suppressed since impurity Fe has been consumed by Al{sub 13}Cr{sub 4}Si{sub 4} intermetallics; • A large number of Al{sub 13}Cr{sub 4}Si{sub 4} dispersoids were observed in Al dendrites in the as-quenched and aged alloy; • The precipitation of Cr-bearing dispersoids harden the as-quenched alloy by over 10HV; • The current thermodynamic database underestimate the solubility of Fe in Al{sub 13}Cr{sub 4}Si{sub 4} intermetallics during solidification simulation. - Abstract: Chromium is added to Al-Si based casting alloys for the mitigation of die soldering. In the present work, EBSD, EDS and TEM characterizations are combined with thermodynamic simulations to study the microstructural evolution and hardening response of an Al-Si-Mg-Cr casting alloy during heat treatments. It is shown that the Fe-containing intermetallic compounds formed in the inter-dendritic region were acicular π-Al{sub 8}(Fe, Cr)Mg{sub 3}Si{sub 6} phase and polyhedral Al-(Cr, Fe)-Si phase which is structurally similar to face-centered cubic Al{sub 13}Cr{sub 4}Si{sub 4}. The polyhedral Al-(Cr, Fe)-Si intermetallics that crystallized prior to β-Al{sub 5}FeSi consumed impurity Fe, suppressing the formation of β phase during gravity die casting process. Also, Cr-addition enables the precipitation of nano-scale Cr-bearing dispersoids in Al dendrite during solution treatment at 813 K. Hardness increment of over 10 HV can be induced by the Cr-bearing dispersoids for as-quenched alloy. Though the dispersoids have a moderate hardening effect on the as-quenched alloy, they may impair the ageing hardening response by acting as heterogeneous nucleation sites for coarse Mg-Si rods and Si particles when quenching into water at 338 K.

• OSTI ID: 22805110
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 142; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM COMPOUNDS
BACKSCATTERING
CHROMIUM ADDITIONS
COMPUTERIZED SIMULATION
ELECTRON DIFFRACTION
FCC LATTICES
HARDNESS
HEAT TREATMENTS
INTERMETALLIC COMPOUNDS
MAGNESIUM COMPOUNDS
MICROSTRUCTURE
PARTICLES
SILICON COMPOUNDS
SOLIDIFICATION
THERMODYNAMICS
TRANSMISSION ELECTRON MICROSCOPY