Research Papers

An Investigation on Duplex Nucleation in AZ91 Magnesium Alloy and Its Influence on High Temperature Mechanical Properties

[+] Author and Article Information
A. Saber

Department of Materials Engineering,
Science and Research Branch,
Islamic Azad University,
Tehran, Iran
e-mail: alisaber2005@yahoo.com

R. Haghayeghi

Department of Materials Engineering,
Science and Research Branch,
Islamic Azad University,
Tehran, Iran
e-mail: rhaghayeghi@srbiau.ac.ir

H. Najafi

Department of Materials Engineering,
Science and Research Branch,
Islamic Azad University,
Tehran, Iran
e-mail: hnajafi@srbiau.ac.ir

Peiman Shahbeigi-Roodposhti

Institute of Materials Science,
University of Connecticut,
Storrs, CT 06269

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 13, 2017; final manuscript received March 19, 2018; published online April 18, 2018. Assoc. Editor: Antonios Kontsos.

J. Eng. Mater. Technol 140(4), 041002 (Apr 18, 2018) (6 pages) Paper No: MATS-17-1286; doi: 10.1115/1.4039791 History: Received October 13, 2017; Revised March 19, 2018

The grain refinement of Mg–Al alloy AZ91 via carbon inoculation, including the significant role of Mn in advanced nucleation, was analyzed, and the corresponding mechanical properties and aging behavior were investigated. To this end, various amounts of C were added into the liquid at the desired temperatures. Al8Mn5 particles, which are suitable nucleation sites for α-Mg, were identified as the primary grain refiners. In situ particle formation, along with appropriate wetting and a suitable orientation relationship (OR), facilitated the grain refinement mechanism. Al4C3 particles contributed to heterogeneous nucleation by providing suitable Al8Mn5 nucleation sites. Mn removal resulted in poor grain refinement in the Mg–Al alloy. The Hall–Petch relationship, high-temperature tensile behavior, and aging mechanism of the samples refined by 1 wt % C addition (as the best grain refiner) are discussed and compared with industrial practice.

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Fig. 1

The grain size variation versus carbon addition at 750 °C and 780 °C

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Fig. 2

Microstructure of the samples at: (a) 750 °C with 1% C addition, (b) 780 °C with 0.6% C addition, and (c) Mg-9 wt % Al (without Mn) at 750 °C and after 1% C addition

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Fig. 3

(a) SEM microstructure, (b) XRD analysis of identified particles in the microstructure, and (c) EDS analysis of the particle

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Fig. 4

Simulated SAED results on: (a) Al8Mn5, (b) α-Mg, and (c) overlaying α-Mg on Al8Mn5 representing complete match

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Fig. 5

The influence of: (a) 0.7 wt % C2Cl6 and (b) 1 wt % carbon additions on tensile strength of AZ91 alloy

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Fig. 6

The hardness versus aging time at 1 wt % C addition

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Fig. 7

Precipitates formation after 10 h of aging at: (a) 100 °C and (b) 200 °C

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Fig. 8

Vickers hardness versus grain size variation, Hall–Petch relation



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