Abstract

Incipient melting of secondary phases during solution heat treatment of Al alloys is detrimental to their mechanical properties. In this research, incipient melting was analyzed in-situ using a high temperature Laser Scanning Confocal Microscope (LSCM) in a novel Al-Cu alloy. Thermal analysis and microstructural analysis were carried out on the alloy cast at fast and slow cooling rates to examine the resulting solidification and microstructural characteristics. The results showed that incipient melting was accompanied by a clustering liquid droplets followed by a complete melting of Al2Cu which occurred at approximately 548 ℃. Additionally, the use of LSCM enabled an understanding of the underlying mechanisms behind incipient melting. It was also found that incipient melting led to microstructure that consisted of a higher presence of ultra-fine eutectic clusters, needle-like Al2Cu and porosity along the grain boundaries. Lastly, the solution heat treatment temperature was optimized for the Al-Cu alloy using the data from LSCM, Differential Scanning Calorimetry and solution heat treatment experiments.

Highlights

  • Lightweight engineering materials are crucial in improving the fuel economy of automotive vehicles, while ensuring safety and performance are not compromised

  • The results showed that solution heat treatment (SHT) at temperatures of 550 and 560 °C resulted in incipient melting and oxidation

  • This study investigated the microstructural and solidification characteristics of a novel Al-Cu alloy, HT200

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Summary

Introduction

Lightweight engineering materials are crucial in improving the fuel economy of automotive vehicles, while ensuring safety and performance are not compromised. There is a need for extensive studies to gain a fundamental understanding of the high temperature behaviour during heat treatment processing This will be done using high temperature laser scanning confocal microscopy (LSCM) as a tool for in-situ observation of the microstructural evolution of the alloy at elevated temperature. A review on the solution heat treatment of aluminum alloys is discussed This includes details on past studies on the incipient melting of secondary phases and the experimental methods used for the analyses. This includes the melting and casting experiments, thermal analysis, sample preparation, characterization techniques, solution heat treatment experiments and mechanical property evaluation.

Chapter 2 Literature Review
Aluminum-copper Alloys
B206 Alloy
Solidification
Nucleation Theory
Homogeneous Nucleation
Heterogeneous Nucleation
Dendritic Solidification
Heat Treatment of Aluminum Alloys
Solution Heat Treatment
Incipient Melting
Quenching
Age Hardening
Ageing
Mechanisms of Hardening
Effect of Ageing on Mechanical Properties
Laser Scanning Confocal Microscopy
Instrument and Procedure
Alloy Melting and Casting
Control of Mould Temperature
Thermal Analysis
Sample preparation
Microscopy samples
Etching
Microstructural Analysis
Quantitative Image Analysis
Phase Microanalysis
Laser Scanning Confocal Microscopy (LSCM)
Differential Scanning Calorimetry (DSC)
Solution Heat Treatment of HT200 alloy
Hardness Measurements
Density Measurements
Results and Discussion
Differential Scanning Calorimetry (DSC) – Solidification Analysis
Section Summary
Grain Structure
Secondary Phases
In-situ Analysis of Incipient Melting
Analysis of Microstructure Post-LSCM
Mechanisms of Incipient Melting
Solution Heat Treatment (SHT) of HT200 Alloy
Effect of SHT Temperature on Density and Hardness
Post-Solution Heat Treatment Analysis
Conclusions
Future Work
Full Text
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