Aluminum 7075 Microstructure and Current Research through the use of In-situ X-ray Diffraction

1. Aluminum 7075Microstructure and Current Research through the use of In-situ X-ray Diffraction By: Jay Schuren

2. Outline • Why Al 7075? • General Aluminum Overview • Microstructure of 7075 • Current Diffraction Research on Al 7075

3. Why Al 7075? • Aluminum is an abundant resource • Relatively cheap • High stiffness/density and strength/density ratios • Damage tolerant • Corrosion resistant compared with conventional alloys

4. Uses of Al 7075 • Gears and shafts • Aircraft • Other Aerospace and defense applications

5. General Aluminum Alloy Overview

6. Principal Aluminum Alloys Wrought alloys are divided into seven major classes Classes set by their principal alloy elements • Strengthened by work hardening • 1XXX, 3XXX, 4XXX, 5XXX • Strengthened by heat treatment (precipitation hardening) • 2XXX, 6XXX, and 7XXX The seven classes can be subdivided:

7. 1XXX -Commercially Pure Al. 3XXX - Al. Manganese Alloys 4XXX - Al. Silicon Alloys Overview Work Hardened Precipitate Hardened • 2XXX - Al. Copper Alloys • 6XXX - Al. Mg. Si. Alloys • 7XXX - Al. Zinc Alloys

9. 7075 Microstructure

11. 7075 Microstructure • Ingot can form (Fe,Cr)3SiAl12, Mg2Si and/or a pseudobinary eutectic made up of Al and Mg(Zn,Cu,Al)2. • Heating causes iron rich phases to transform to Al7CuMg precipitates. Chromium is precipitated from supersaturated solution as Cr2Mg3Al18 dispersoids, concentrated heavily in the primary dendrite region. • Recrystallized grains are extremely elongated or flattened because of dispersoid banding, and unrecrystallized regions are made up of very fine subgrains in which boundaries are decorated by hardening precipitates

12. Aging at elevated-temperature can provide: • Stable properties • Higher strengths • Improved corrosion resistance • Lower rate of growth of fatigue cracks are.

13. Diffraction Applied to 7075 • Approach • Measure the changes in lattice spacing of the aggregate as the specimen is under load • Use X-ray diffraction (XRD)

15. Experimental Setup

17. Actual Al 7075 T6 Data Strain Pole Figures

18. Stress-Strain Curve for 7075 T6

19. What In-situ X-ray Diffraction gives us • In-situ X-ray diffraction provides a “snap shot” of the aggregate lattice strain • Can invert lattice strain to find full strain tensor • Validates micromechanical models

20. References • Aluminum: Properties and Physical Metallurgy by John Hatch • Experimental measurement of lattice strain pole figures using synchrotron x rays by M. P. Miller • Measuring crystal lattice strains and their evolution in cyclic loading by J-S. Park • On the mechanical behaviour of AA 7075-T6 during cyclic loading by Turkmen • Influence of modelling variables on the distribution of lattice strains in a deformed polycrystal, with reference to neutron diffraction experiments by Loge • Elements of X-ray Diffraction by Cullity • http://www.sintef.no/static/mt/norlight/ProjectPortfolio/HeatTreatmentFundamentals/dispersoids.htm • http://www.alcoa.com • http://www.msm.cam.ac.uk/phasetrans/2002/robson/img4.htm • Electrochemical Characterization of 7075 Aluminum Alloys Using The Microcell by Barbara N. Padgett