Nanoparticle reinforced lightweight metal composites: from microstructure to properties
File(s)
Author(s)
Xu, Zhuocheng
Type
Thesis
Abstract
Nanoparticles with superior mechanical properties are ideal reinforcements for Mg alloys as their ability to enhance the strength while preserving the lightweight characteristics of the Mg matrix. However, several challenges persist, including achieving uniform nanoparticle dispersion within the Mg matrix and establishing strong interfacial bonding between the NPs and the Mg matrix.
Ultrasonication treatment (UST) has been widely recognized as an effective method for enhancing nanoparticle dispersion during the melt processing. However, the mechanisms of nanoparticle deagglomeration (particularly for CNTs) and the optimal UST parameters for achieving uniform nanoparticle dispersion are not yet fully understood. In this thesis, the dynamic interactions between cavitation bubbles and CNT agglomerates during UST were directly observed for the first time using high-speed imaging. Furthermore, a numerical model built by collaborator aimed to find the optimize UST parameters was tested.
SiC has been identified as an effective coating to enhance the interfacial bonding between CNTs and the Mg-Al alloy matrix due to its excellent wettability with the Mg-Al melt. However, its interfacial reactions with Mg-Al melt during melt processing and the crystallographic orientations among SiC, interphases, and α-Mg grains remain insufficiently understood in previous studies. In this thesis, a detailed investigation using multiscale advanced characterisation techniques was conducted at the SiCwh-Mg AZ91 interface for the first time. The results revealed the formation of T2-Al₂MgC₂ during the interfacial reactions and the formation of this interfacial carbide played a crucial role in improving the interfacial bonding between the SiC and Mg matrix and promoting matrix grain refinement.
Lastly, a novel high-throughput method based on stationary shoulder friction stir channelling was developed for fabricating SiC-reinforced AZ91 matrix composites. Through microstructural and mechanical characterisation, a gradient structure with varying SiC concentrations and mechanical properties was identified, demonstrating the potential of using this method in the future composites’ prototyping.
Ultrasonication treatment (UST) has been widely recognized as an effective method for enhancing nanoparticle dispersion during the melt processing. However, the mechanisms of nanoparticle deagglomeration (particularly for CNTs) and the optimal UST parameters for achieving uniform nanoparticle dispersion are not yet fully understood. In this thesis, the dynamic interactions between cavitation bubbles and CNT agglomerates during UST were directly observed for the first time using high-speed imaging. Furthermore, a numerical model built by collaborator aimed to find the optimize UST parameters was tested.
SiC has been identified as an effective coating to enhance the interfacial bonding between CNTs and the Mg-Al alloy matrix due to its excellent wettability with the Mg-Al melt. However, its interfacial reactions with Mg-Al melt during melt processing and the crystallographic orientations among SiC, interphases, and α-Mg grains remain insufficiently understood in previous studies. In this thesis, a detailed investigation using multiscale advanced characterisation techniques was conducted at the SiCwh-Mg AZ91 interface for the first time. The results revealed the formation of T2-Al₂MgC₂ during the interfacial reactions and the formation of this interfacial carbide played a crucial role in improving the interfacial bonding between the SiC and Mg matrix and promoting matrix grain refinement.
Lastly, a novel high-throughput method based on stationary shoulder friction stir channelling was developed for fabricating SiC-reinforced AZ91 matrix composites. Through microstructural and mechanical characterisation, a gradient structure with varying SiC concentrations and mechanical properties was identified, demonstrating the potential of using this method in the future composites’ prototyping.
Version
Open Access
Date Issued
2024-10-03
Date Awarded
2025-02-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Li, Qianqian
Shaffer, Milo
Publisher Department
Aeronautics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)