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Microstructual Characteristics of Magnesium Metal Matrix Composites

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Microstructual Characteristics of Magnesium Metal Matrix Composites University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2012 Microstructual Characteristics Of Magnesium Metal Matrix Composites Dongho Shin University of Central Florida Part of the Materials Science and Engineering Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Masters Thesis (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Shin, Dongho, "Microstructual Characteristics Of Magnesium Metal Matrix Composites" (2012). Electronic Theses and Dissertations, 2004-2019. 2244. https://stars.library.ucf.edu/etd/2244 MICROSTRUCTUAL CHARACTERISTICS OF MAGNESIUM METAL MATRIX COMPOSITES by DONGHO SHIN B.S. Korea Military Academy, 2006 A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical, Materials and Aerospace Engineering in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Summer Term 2012 Major Professor: Yongho Sohn 1 © 2012 Dongho Shin ii ABSTRACT Magnesium (Mg) Metal matrix composites (MMCs) reinforced by ceramic reinforcements are being developed for a variety of applications in automotive and aerospace because of their strength-to-weight ratio. Reinforcement being considered includes SiC, Al2O3, Carbon fiber and B4C in order to improve the mechanical properties of MMCs. Microstructural and interfacial characteristics of MMCs can play a critical role in controlling the MMCs’ mechanical properties. This study was carried out to understand the microstructural and interfacial development between Mg-9wt.Al-1wt.Zn (AZ91) alloy matrix and several reinforcements including SiC, Al2O3, Carbon fibers and B4C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy was employed to investigate the microstructure and interfaces. Al increase in hardness due to the presence of reinforcements was also documented via Vicker’s hardness measurements. Thermodynamic consideration based on Gibbs free energy was employed along with experimental results to describe the interfacial characteristics of MMCs. Reaction products from AZ91-SiC and AZ91-Al2O3 interfaces were identified as MgO, since the surface of SiC particles is typically covered with SiO2 and the MgO is the most thermodynamically stable phase in these systems. The AZ91-Carbon fiber interface consist of Al4C3 and this carbide phase is considered detrimental to the mechanical toughness of MMCs. The AZ91-B4C interface was observed to contain MgB2 and MgB2C2. In general, Vicker’s hardness increased by 3X due to the presence of these reinforcements. iii I dedicate this work to my family, Korea Army and especially my advisor, Dr. Yongho Sohn. Thank you for your never-ending support, love and guidance. iv ACKNOWLEDGMENTS I would like to express my sincerest thanks to my advisor, Dr. Yongho Sohn for his continued patience, guidance, support and encouragement. I also wish to thank the students in research group under Dr. Sohn for their continuing support, critical discussions and encouragement. I want to thank my family and friends for their patience and support as well. I would also like to acknowledge the scholarship and stipend of the Korea Army for my study at the University of Central Florida. v TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES .......................................................................................................................... x LIST OF ABBREVIATIONS ........................................................................................................ xi CHAPTER 1: INTRODUCTION ................................................................................................... 1 CHAPTER 2: LITERATURE REVIEW ........................................................................................ 3 2.1. Metal Matrix Composites ..................................................................................................... 3 2.1.1. Metallic Matrices ........................................................................................................... 3 2.1.2. Reinforcements .............................................................................................................. 5 2.1.3. Interface ......................................................................................................................... 6 2.1.4. Applications of Metal Matrix Composites..................................................................... 7 2.1.4.1. Aerospace ................................................................................................................ 7 2.1.4.2. Automotive .............................................................................................................. 8 2.1.4.3. Military ................................................................................................................... 8 2.1.4.4. Energy ..................................................................................................................... 8 2.2. Magnesium Metal Matrix Composites ................................................................................. 9 2.2.1. Magnesium Matrix ........................................................................................................ 9 2.2.2. Ceramic Reinforcements ............................................................................................... 9 2.2.3. Interface Microstructures of Mg-Metal Matrix Composites ......................................... 9 2.2.3.1. Magnesium-SiC Particle Interface .......................................................................... 9 2.2.3.2. Magnesium-Al2O3 Whisker Interface ................................................................... 10 2.2.3.3. Magnesium-C Fiber Interface ............................................................................... 10 2.2.3.4. Magnesium-B4C Particle Interface ....................................................................... 11 2.3 Magnesium Metal Matrix Composite Processing: Squeeze Casting .................................. 11 CHAPTER 3: EXPERIMENTAL PROCEDURE ........................................................................ 15 3.1 Materials .............................................................................................................................. 15 3.2 Metallographic Preparation ................................................................................................. 16 vi 3.2.1 Preparation for X-ray Diffraction ................................................................................. 16 3.2.2 Preparation for Scanning Electron Microscopy............................................................ 16 3.3 Microstructure Analysis ...................................................................................................... 17 3.3.1 X-ray Diffraction .......................................................................................................... 17 3.3.2 Scanning Electron Microscopy ..................................................................................... 18 3.3.3 Transmission Electron Microscopy .............................................................................. 19 3.3.4 Hardness Test ................................................................................................................ 19 CHAPTER 4: RESULTS AND DISCUSSION ............................................................................ 20 4.1. Microstructure of Composites ............................................................................................ 20 4.1.1. AZ91 Metal Matrix Composite Reinforced by SiC Particles ...................................... 20 4.1.2. AZ91 Metal Matrix Composite Reinforced by Al2O3 Whiskers ................................. 24 4.1.3. AZ91 Metal Matrix Composite Reinforced by Carbon Fibers .................................... 28 4.1.4. AZ91 Metal Matrix Composite Reinforced by B4C Particles ..................................... 30 4.2. Interfacial Features of Composites ..................................................................................... 37 4.2.1 Characterization of AZ91-SiC Particle Interface.......................................................... 37 4.2.2 Characterization of AZ91-Al2O3 Whisker Interface ..................................................... 41 4.2.3 Characterization of AZ91-Carbon Fiber Interface........................................................ 41 4.2.4 Characterization of AZ91-B4C Particle Interface ......................................................... 43 4.3 Hardness Testing ................................................................................................................. 47 CHAPTER 5: CONCLUSIONS ................................................................................................... 48 LIST OF REFERENCES .............................................................................................................. 49 vii LIST OF FIGURES Figure 1. Schematics of crack growth for poor, medium, and good fiber-matrix adhesion. .......... 7 Figure 2. Example of XRD sample attached with clay. ...............................................................
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