Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Dissertations, Master's Theses and Master's Reports - Open Reports 2008 High cycle fatigue of AA6082 and AA6063 aluminum extrusions Nicholas E. Nanninga Michigan Technological University Follow this and additional works at: https://digitalcommons.mtu.edu/etds Part of the Engineering Science and Materials Commons Copyright 2008 Nicholas E. Nanninga Recommended Citation Nanninga, Nicholas E., "High cycle fatigue of AA6082 and AA6063 aluminum extrusions ", Dissertation, Michigan Technological University, 2008. https://doi.org/10.37099/mtu.dc.etds/18 Follow this and additional works at: https://digitalcommons.mtu.edu/etds Part of the Engineering Science and Materials Commons HIGH CYCLE FATIGUE OF AA6082 AND AA6063 ALUMINUM EXTRUSIONS By Nicholas E. Nanninga A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY (Materials Science and Engineering) MICHIGAN TECHNOLOGICAL UNIVERSITY 2008 Copyright©Nicholas E. Nanninga 2008 This dissertation, "High cycle fatigue behavior of AA6082 and AA6063 aluminum extrusions," is hereby approved in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in the field of Materials Science and Engineering. DEPARTMENT: Materials Science and Engineering Signatures: Dissertation Advisor Typewritten Name Calvin L. White Department Chair Typewritten Name Mark R. Plichta. Date Abstract The high cycle fatigue behavior of hollow extruded AA6082 and AA6063 aluminum extrusions has been studied. Hollow extruded aluminum profiles can be processed into intricate shapes, and may be suitable replacements for fatigue critical automotive applications requiring reduced weight. There are several features inherent in hollow aluminum extrusions, such as seam welds, charge welds, microstructural variations and die lines. The effects of such extrusion variables on high cycle fatigue properties were studied by taking specimens from an actual car bumper extrusion. It appears that extrusion die lines create large anisotropy differences in fatigue properties, while welds themselves have little effect on fatigue lives. Removal of die lines greatly increased fatigue properties of AA6082 specimens taken transverse to the extrusion direction. Without die lines, anisotropy in fatigue properties between AA6082 specimens taken longitudinal and transverse to the extrusion direction, was significantly reduced, and properties associated with the orientation of the microstructure appears to be isotropic. A fibrous microstructure for AA6082 specimens showed great improvements in fatigue behavior. The effects of elevated temperatures and exposure of specimens to NaCl solutions was also studied. Exposure to the salt solution greatly reduced the fatigue lives of specimens, while elevated temperatures showed more moderate reductions in fatigue lives. iii Acknowledgements The funding of this research project by Hydro Aluminium was greatly appreciated. I would like to thank my advisor, Dr. Calvin White, for his continual encouragement, support and knowledge. I want to thank my family for their support of me through graduate school. The assistance of MTU faculty and staff members was greatly valued, specifically, John Lukowski, Mike LaCourt and Owen Mills. I would also like to recognize Trond Furu, Richard Dickson, Ola Anderson and Helen Wykamp of Hydro Aluminum for materials and support. iv TABLE OF CONTENTS 1 INTRODUCTION ........................................................................... 1 2 BACKGROUND ............................................................................ 4 2.1 Fatigue.................................................................................................................. 4 2.2 AA6082 Alloy .................................................................................................... 13 2.3 AA6063 Alloy .................................................................................................... 22 2.4 Extrusion features .............................................................................................. 25 2.5 Experimental program outline ........................................................................... 37 3 EXPERIMENTAL PROCEDURE ................................................ 38 3.1 Materials ............................................................................................................ 38 3.2 Microstructural characterization ........................................................................ 42 3.3 Hardness testing ................................................................................................. 44 3.4 Tensile testing .................................................................................................... 45 3.5 Fatigue testing .................................................................................................... 45 3.6 FEM modeling ................................................................................................... 48 4 AA6082 RESULTS AND DISCUSSION ..................................... 51 4.1 Heat treatment .................................................................................................... 51 4.2 Heat treated microstructure ................................................................................ 53 4.3 Surface roughness .............................................................................................. 56 4.4 Baseline fatigue (L-NW specimens) .................................................................. 58 4.5 Effect of orientation/die lines on fatigue ........................................................... 60 4.6 Effect of seam welds .......................................................................................... 68 4.7 Effect of charge welds (position along extrusion length) .................................. 75 4.8 Effect of fibrous core ......................................................................................... 86 4.9 Heat treatment variations ................................................................................... 97 4.10 Effect of NaCl solution .................................................................................... 100 4.11 Effect of elevated temperature ......................................................................... 108 5 AA6063 RESULTS AND DISCUSSION ................................... 115 5.1 Heat treatment .................................................................................................. 115 5.2 Heat treated microstructure .............................................................................. 116 5.3 Surface roughness ............................................................................................ 117 5.4 Baseline fatigue (L-NW specimens) ................................................................ 118 5.5 Effect of orientation/die lines on fatigue ......................................................... 120 5.6 Effect of seam welds ........................................................................................ 122 5.7 Effect of charge welds ..................................................................................... 127 5.8 Effect of NaCl solution .................................................................................... 128 6 EFFECT OF ROUGHNESS ON RUN-OUT STRESS ............... 133 6.1 FEM Modeling ................................................................................................. 134 7 CONCLUSIONS ........................................................................ 141 8 FUTURE WORK ....................................................................... 144 9 REFERENCES .......................................................................... 146 v LIST OF FIGURES Figure 2-1. Schematic illustration of stages in fatigue failure ............................. 5 Figure 2-2. Association between in-service and laboratory stress cycles that lead to fatigue failure and nomenclature used in characterizing fatigue behavior of materials (after [6]) ............................................ 8 Figure 2-3. Illustration of a stress-life curve (after [6]) ..................................... 10 Figure 2-4. Illustration of competing roles of particle cutting and dislocation bowing in age hardening (after [6]) ................................................ 17 Figure 2-5. Illustration of PFZ .......................................................................... 20 Figure 2-6. Schematic of seam weld origin in extrusion process ..................... 28 Figure 2-7. a. Illustration of the origin of charge weld interfaces b. relationship between charge and seam welds .................................................. 29 Figure 2-8. The four stages or zones that can occur during continuous billet extruding of hollow profiles ............................................................ 32 Figure 2-9. Schematic of die line origins .......................................................... 33 Figure 2-10. Schematic S-N curve for smooth and notched fatigue specimens 36 Figure 3-1. Schematic illustration of profile and specimen locations obtained from A, B and C faces of extrusion profile ..................................... 39 Figure 3-2. Specimen geometry (in mm). Specimen thickness varies from 2.5 to 3.5 mm depending on extrusion wall ......................................... 41 Figure 3-3. Alignment specimen in grips