Quench factor analysis of wrought and cast aluminum alloys

130 Pages·2016·6.62 MB·English

by  Vishwanath Gandikota

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Masters Theses Student Theses and Dissertations
Spring 2009
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Vishwanath Gandikota
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QUENCH FACTOR ANALYSIS OF WROUGHT AND
CAST ALUMINUM ALLOYS
by
VISHW ANATH GANDIKOTA
A THESIS
Presented to the Faculty of the Graduate School of the
MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY
In Partial Fulfillment of the Requirements for the Degree
MASTER OF SCIENCE IN MATERIALS SCIENCE AND ENGINEERING
2009
Approved by
Joseph W. Newkirk, Advisor
Von L. Richards
Matthew J. 0' Keefe
© 2009
Vishwanath Gandikota
All Rights Reserved
Ill
ABSTRACT
Mechanical property variation across the cross section of heat treatable aluminum
alloys is a major concern. To minimize such variation, a proper understanding of kinetic
transformations and estimation of mechanical properties is required. The Jominy end
quench test has been used successfully to study the effect of quench rate on the final heat
treated properties of wrought and cast aluminum alloys. This test produces varying
cooling rates along the length of a cylindrical sample cooled with water at one end.
Jominy bars of wrought and cast aluminum alloys were solutionized, end
quenched, and aged to T6 temper condition after delays of 1 hour and 120 hours. The
hardness values were measured along the length of the Jominy bar. Previous studies have
shown that the hardness along the length of the bar follows an A vrami relationship. The
present work also measures hardness along the Jominy bar, and the data was used to
determine the A vrami parameters (k,n) for various delays and heat treatments of alloys.
The accuracy ofthe Avrami parameters was verified by plotting the calculated Avrami
against the hardness data as a function of distance from the quenched end.
Mini tensile samples were then taken from specific locations on the Jominy bar.
The experimental strength values and their Avrami fit were plotted as a function of
distance from the quenched end. Strength values estimated from the A vrami fit were 95%
accurate. This study allows prediction of strength at a given quench rate.
Finally, cooling curves were simulated at various points along the Jominy bar
using FLUENT. Quench factors were calculated along the length of the bar. Using the
cooling curves and the calculated quench factors, C-curves were generated for each alloy,
and a specific heat treatment applied.
IV
ACKNOWLEDGEMENTS
I wish to express my deepest gratitude to my advisor, Dr. Joseph W. Newkirk for
providing me with an opportunity to pursue a master's degree in Missouri University of
Science and Technology. His enthusiasm and constant support have motivated me to
successfully complete my research work. His suggestions, guidance and personal
attention have been constant source of encouragement.
I would like to thank my committee members, Dr.Von L. Richards and Dr.
Matthew J. O'Keefe for their time and effort. I would like to Dr. Rajiv Mishra for
providing me the required equipment.
I would like to thank Anand Jambunathan and Jen Hsien Hsu for their continuous
support. I would also like to thank the research group working for Dr. Rajiv Mishra in
helping with the mini tensile samples testing.
Finally, I would like to thank my parents, brother and friends for their continuous
support and care.
v
TABLE OF CONTENTS
Page
ABSTRACT ...................................................................................................................... .iii
ACKNOWLEDGEMENTS ........................................................................ iv
LIST OF ILLUSTRATIONS ........................................................................................... viii
LIST OF TABLES .............................................................................................................. xi
SECTION
1. INTRODUCTION .............................................................................................. 1
1.1.BACKGROUND ........................................................................................... 1
1.2. PROBLEM STATEMENT ........................................................................... I
1.3. METHODOLOGY ...................................................................................... 2
2. LITERATURE REVIEW .................................................................................... 4
2.1. Al-Zn-Mg-Cu ALLOY SYSTEM ................................................................. 6
2.1.1. Effects of Processing Parameters ................................................. 7
2.1.1.1. Solution Heat Treatment ................................................ 8
2.1.1.2. Quenching ............................................................................. 9
2.1.1.3. Aging .......................................................................... 9
2.2. Al-Mg-Si SYSTEM .................................................................................... II
2.2.1. Effects of Processing Parameters ........................................... 13
2.2.1.1. Solution Heat Treatment. .......................................... 13
2.2.1.2. Quenching ................................................................ 13
2.2.1.3. Aging .......................................................................... 13
2.3. CAST ALUMINUM ALLOYS .................................................................. 14
VI
2.3.1. Effects of Processing Parameters ............................................... 16
2.4. USE OF JOMINY END QUENCH TEST ..................................... 17
2.5. QUENCH FACTOR ANALYSIS ...................................................... 20
3. EXPERIMENTAL PROCEDURE ................................................................... 23
3.1. JOMINY END QUENCH TEST ............................................................... 23
3.2. AGING TREATMENT. ............................................................................ 25
3.3. HARDNESS STUDIES ............................................................................. 25
3.4. MINI TENSILE TESTING ............................................................... 29
3.5. SIMULATION OF COOLING CURVES ......................................... 32
4. RESULTS AND DISCUSSION ........................................................................ 37
4.1. HARDNESS VERSUS JOMINY DISTANCE PLOTS ............................. 37
4.2. MINI TENSILE TESTING ......................................................................... 45
4.3. QUENCH FACTOR ANALYSIS .............................................................. 56
5. CONCLUSIONS ............................................................................................... 59
6. FUTURE WORK. .............................................................................................. 60
APPENDICES
A. HARDNESS VALUES ........................................................................... 61
B. TENSILE DATA ............................................................................... 70
C. COOLING CURVES DATA ................................................................ 87
D. EXAMPLE OF MATLAB CODE ......................................................... 103
E. EXAMPLE OF STRESS STRAIN CURVE .............................................. lOS
F. THERMOCOUPLE COOLING DATA FOR A356 ..................................... 107
BIBLIOGRAPHY ............................................................................................................ IIS
Vll
VITA ............................................................................................................................... 118
Vlll
LIST OF ILLUSTRATIONS
Figure Page
3.1. Jominy end quench System with water umbrella indicating proper alignment.. ........ 25
3.2. First fixture used for hardness testing, with Jominy sample and indexing wheel
for position change. ..................................................................................................... 27
3.3. Second fixture used for hardness testing, with Jominy sample and indexing wheel
for position change ............................................................................... 28
3.4. Hardness as a function of distance from the quenched end with the first fixture ....... 28
3.5. Hardness as a function of distance from the quenched end with the second fixture .. 29
3.6. Mini tensile test sample used for tensile testing ......................................................... 31
3.7. Positioning of the mini tensile specimens on the slice of JEQ cylinder. .................... 31
3.8. Mini tensile test frame with the cross heads .............................................................. .32
3.9. 2-D view ofmeshed cylinder. ..................................................................................... 33
3.10. 3-D view ofmeshed cylinder .................................................................................... 34
3 .11. Cross section of cylinder showing meshed elements ................................................ 34
3.12. Simulated cooling curves at various locations on the Jominy Bar for 7075 .......... 35
3.13. Comparison between simulated and thermocouple cooling curves ................... .36
4.1. Rockwell 8 Hardness plots for A vrami and experimental values of 707 5,
with 1-hr delay ...................................................................................... 38
4.2. Rockwell 8 Hardness plots for Avrami and experimental values of7075,
with 120-hr delay ............................................................................... 38
4.3. Rockwell 8 Hardness plots for Avrami and experimental values of6061,
with 1-hr delay .................................................................................. 39
4.4. Rockwell B Hardness plots for A vrami and experimental values of 6061,
with 120-hr delay ................................................................................................... 39
4.5. Vickers micro hardness plots for A vrami and experimental values of 8319,
with 1-hr delay ......................................................................................... 40
IX
4.6. Vickers microhardness plots for Avrami and experimental values of8319,
with 120-hr delay ................................................................................. 40
4.7. Vickers microhardness plots for Avrami and experimental values of A356,
with 1-hr delay ................................................................................... 41
4.8. Vickers microhardness plots for Avrami and experimental values of A356,
with 120-hr delay .................................................................................. 41
4.9. Variation ofUTS with Jominy distance for 7075 with 1-hr delay ...................... .46
4.10. Variation ofYS with Jominy Distance for 7075 with 1-hr delay ..................... .46
4.11. Variation of UTS with Jominy distance for 7075 with 120-hr delay ................. .47
4.12. Variation ofYS with Jominy distance for 7075 with 120-hr delay ................... .47
4.13. Variation ofUTS with Jominy distance for 6061 with 1-hr delay .................... .48
4.14. Variation ofYS with Jominy Distance for 6061 with 1-hr delay .................... .48
4.15. Variation ofUTS with Jominy Distance for 6061 with 120-hr delay ................ .49
4.16. Variation ofYS with Jominy Distance for 6061 with 120-hr delay ................. .49
4.17. Variation ofUTS with Jominy distance for A356 with 1-hr delay .................... 52
4.18. Variation ofYS with Jominy distance for A356 with 1-hr delay ..................... 52
4.19. Variation of UTS with Jominy distance for A356 with 120-hr delay ................. 53
4.20. Variation ofYS with Jominy distance for A356 with 120-hr delay .................. 53
4.21. Variation of UTS with Jominy distance for with 8319 1-hr delay .................... 54
4.22. Variation ofYS with Jominy distance for 8319 with 1-hr delay ..................... 54
4.23. Variation ofUTS with Jominy distance for 8319 with 120-hr delay ................. 55
4.24. Variation ofYS with Jominy distance for 8319 with 120-hr delay .................. 55
4.25. C-curve for 7075 T6 temper. .............................................................. 56
4.26. C-curve for 6061 T6 temper. ............................................................... 57