Soutenance mémoire
PHASE CHACTERIZATION IN AN AA5657 DC CAST INGOT
Deep-etching of metallographic sample
In order to reveal the original morphology of Fe intermetallic particles, deep-etching and SEM technique are used. This technique can also be useful for the study of nucleation and growth behaviour of the Fe intermetallic phases. There were two different etchants used in the present study. One is 10% NaOH solution at 60-70 °C, the other is 20% HC1 at room temperature. The former is mainly used for AA5657 alloy ingots, while the latter was used in the study of lxxx-series ingot. Put the surface of a finely grounded metallographic specimen in the etchant solution. The etching time varies from 5—10 minutes, after that the aluminum matrix on the surface layer of the specimen was dissolved while leave the intermetallic particles unaffected. The etched sample is studied by using Scanning Electron Microscope (SEM) system under the secondary electron imaging mode. The SEM system is JEOM JSM-6480LV (Figure 3.6). The energy dispersive spectroscopy is also used to give a chemical composition analysis.
Electron Backscatter Diffraction (EBSD)
After the metallurgical study, EBSD technique was used to further the identification study of Fe intermetallic phases. In the present research, EBSD was used as the principal technique for the phase identification. In order to identify the Fe intermetallic phases, EBSD technique was employed in present study. Using EBSD technique, the four types of Fe intermetallic phases appearing in the cast ingot were identified. It was found that the crystal structure of the intermetallic compound with a feathery like morphology was similar to AlmFe; The crystal structure of the intermetallic phase with chinese script morphology was agree well with Al7Fe2Si; The crystal structure of the intermetallic phase with curved plates morphology was agree well with AlôFe and the crystal structure of the intermetallic phase the needle like morphology can match well with A^Fe.
Fe intermetallic phases database creation
The EDS spectra show that every intermetallic particle contain Al and Fe, so all the compound listed in Pearson’s Handbook of Crystallographic Data for Intermetallic phases28 containing Al and Fe were selected as possible phases for identification (See appendices A). The crystallographic data were entered into HKL Channel 5 Twist diffraction database creator. For the identification of each intermetallic particle, the HKL software automatically suggests solutions for a given EBSD pattern ranked by lowest MAD (Mean Angular Deviation) as an index of ‘goodness of fit’. For acceptable identification solutions, the MAD number should be less than 0.7 in the present study.
EBSD sample preparation
The use of EBSD has quite high requirement of the sample quality. In the present study, a procedure for EBSD sample preparation was developed (Table 3.3).
As illustrated in Figure 3.7, the dashed line on the EBSD sample is parallel to the casting surface/chill end, which stands for a position to be studied. Six fields with dimensions about 150/on x 150/mi were chosen along the line under a magnification of 500X. On the corner of each field, four marks were made using Micro hardness in order to find the field easily under SEM:
The particles size smaller than 0.5fim x 0.5/an in dimension cannot be identified due to the poor quality of diffraction patterns, which take up about 5% of the total particles. Generally, there are totally 8 0 – 1 0 0 particles analyzed in the six fields of a sample.
|
Table des matières
ABSTRACT
RÉSUMÉ
ACKNOWLEDGMENTS
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
CHAPTER 1 DEFINITION OF THE PROBLEM
1.1 INTRODUCTION
1.1.1 DC casting AA5657 alloy
1.2 OBJECTIVE AND METHODOLOGY OF PRESENT WORK
CHAPTER 2 REVIEW OF THE LITERATURE
2.1 FINDINGS FOUND IN PREVIOUS RESEARCHES
2 . 2 FTZS AND FE INTERMETALLIC PHASES IN DC CAST AL ALLOYS
2.2.1 Iron intermetallic phases in the Al-Fe-Si system 13
2.2.1.1 AI3Fe phase
2.2.1.2 AI6Fe phase
2.2.1.3 AlmFe phase
2.2.1.4 AlxFe phase
2.2.1.5 a-AIFeSi
2.2.1.6 p-AIFeSi
2.2.2 Factors that affect Fe phases selection in AI alloys
2.2.2.1 Cooling rates
2.2.2.2 Fe/Si ratio
2.2.2.3 Grain refinement
2.2.2.4 Trace elements effects
2.3 DC CASTING SIMULATOR TECHNIQUES
2.4 EBSD TECHNIQUE
CHAPTER 3 EXPERIMENTAL PROCEDURES
3.1 ALLOY PREPARATION
3.2 MELTING AND CASTING
3.3 SAMPLE ANALYSIS AND CHARACTERIZATION
3.3.1 Chemical analysis
3. 3.2 Optical Microscopy
3.3.3 Deep-etching of metallographic sample
3. 3.4 Electron Backscatter Diffraction (EBSD)
3. 3.4.1 Fe intermetallic phases database creation
3. 3.4.2 EBSD sample preparation
3. 3.4.3 Fe intermetallic Phases quantitafication
CHAPTER 4 RESULTS AND DISCUSSION
4.1 PHASE CHACTERIZATION IN AN AA5657 DC CAST INGOT
4.1.1 Ingot microstructure
4.1.2 Fe intermetallic phases morphology and EDS results
4.1.3 Phase identification using EBSD technique
4.1.4 Phase quantitafication
4.2 PHASE CHARACTERIZATION IN AN AA1050 DC CAST INGOT ACROSS THE FTZS
4.2.1 Ingot microstructure
4.2.2 EDS and Deep-etching morphology
4.2.3 Fe Phase characterization using EBSD technique
4.2.4 Phase quantitafication
4.3 DC SIMULATOR AND FE INTERMETALLIC PHASES IN DC SIMULATOR CAST AA5657 INGOTS
4.3.1 DC simulator
4.3.2 Fe intermetallic phases in the base material of DC simulator cast AA5657 ingots (A01 alloy in Table 3.2)
4.3.2.1 Ingot microstructure
4.3.2.2 EBSD diffraction patterns
4.3.2.3 Image analysis results
4.4 EFFECT OF N I ON FE INTERMETALLIC PHASES IN DC SIMULATOR CAST AA5657 INGOTS
4.4.1 Ingots Microstructure
4.4.2 EBSD patterns
4.4.3 Image analysis results
4.5 EFFECT OF V O N FE INTERMETALLIC PHASES IN DC SIMULATOR CAST AA5657 INGOTS
4.4. IIngots structure
4.5.2 EBSD patterns
4.5.3 Image analysis results
4.6 EFFECT OF THE COMBINED ADDITION OF V AND N I ON FE INTERMETALLIC PHASES IN DC SIMULATOR CAST AA5657 INGOTS
4.6.1 Ingots Microstructure
4.2.2 EBSD patterns
4.6.3 Image analysis results
CHAPTER 5 CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK
5.1 CONCLUSIONS
5.2 SUGGESTIONS FOR FURTHER WORK APPENDICES
REFERENCES
Télécharger le rapport complet
