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Correlating Rapid Solidification Microstructure Morphology and Mechanical Properties in Hypo-eutectic Al-Cu Alloy

Alamoudi, Mohammed T (2022) Correlating Rapid Solidification Microstructure Morphology and Mechanical Properties in Hypo-eutectic Al-Cu Alloy. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Scanned laser melting (SLM) and subsequent re-solidification results in the formation of solidification microstructures that form under continuously changing conditions.
This study aims to advance our understanding of the mechanical properties and plastic deformation behavior for the non-equilibrium multiphase microstructures that can be accessed by Al-10at.%Cu hypo-eutectic alloy during rapid solidification (RS) after SLM. We combined nanoindentation with microstructural analyses by SEM and TEM to study processing- microstructure-property relationships. At low scan laser velocity (VL=3mm/s), a microstructure gradient develops as the solidification rate (VSL) increases from initially VSL=0mm/s at the bottom to a maximum of VSL≈VL=3mm/s at the top of the melt pool. The cellular α-Al(Cu), located centrally in the melt pool, consistently showed Cu-solute supersaturation by 20% relative to the equilibrium solid solubility limit of ~2.5at% and exhibited 36% hardness increase relative to the α-Al(Cu) in the as-cast state. The experimentally observed solute trapping in the α-Al(Cu) cells of the RS microstructure was found to be consistent with predictions from solidification theory using a cellular/dendritic growth model.
By increasing VL to higher scan velocities, i.e., 1m/s≤VL≤4ms, the maximum solidification rates achieved during RS of the alloy melt pools increase accordingly to the m/s range. At these large solidification rates different microstructure morphologies are revealed. They included columnar grain morphologies with continuous θ-Al2Cu, columnar grains with discontinuous θ/θ’-
Al2Cu and banded morphology region. The nanoindentation of these characteristic RS microstructure morphologies revealed hardness increases relative to α-Al in the as-cast state (1.1GPa) and the supersaturated cellular primary α-Al(Cu) (1.5GPa) observed for RS microstructures after scanned laser melting at low scan speed (VL=3mm/s). Hardness values of up to 3.32GPa and 2.98GPa have been determined for the columnar grains with continuous θ-Al2Cu and discontinuous θ’-Al2Cu, respectively. The banded region showed hardness values between 2.95 to 3.35GPa.
Isothermal annealing of the RS microstructures obtained after scanned laser surface melting at scan speeds of 2m/s and 4m/s at temperatures of 180 ̊C, 230 ̊C and 280 ̊C showed transformations with rapid kinetics establishing unusual populations of second phase Al2Cu related particles with fine scale and high density. The mechanical property evolution for morphologically distinct regions in the alloy microstructure during annealing has been determined.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Alamoudi, Mohammed Tmta23@pitt.edumta23
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWiezorek, Jörg M.K.wiezorek@pitt.eduwiezorek
Committee MemberShankar, M. Raviravishm@pitt.eduravishm
Committee MemberWang, Guofengguw8@pitt.eduguw8
Committee MemberJacobs, Tevis DBtjacobs@pitt.edutjacobs
Date: 6 September 2022
Date Type: Publication
Defense Date: 25 May 2022
Approval Date: 6 September 2022
Submission Date: 7 July 2022
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 164
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Rapid solidification, non-equilibrium microstructural analyses, Al-Cu alloy, hypo-eutectic alloy, mechanical properties, nanoindentation hardness.
Date Deposited: 06 Sep 2022 16:21
Last Modified: 06 Sep 2022 16:21


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