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Vickers Microindentation Hardness Testing of Brazed Joints in Aluminum

Vickers Microindentation Hardness Testing of Brazed Joints in Aluminum. Patricia B. Roy, Fiona M. O’Connell, Thomas H. Callahan, Edward J. Armellino , and Wayne L. Elban Department of Engineering Loyola University Maryland Baltimore, Maryland 21210

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Vickers Microindentation Hardness Testing of Brazed Joints in Aluminum

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  1. Vickers Microindentation Hardness Testing of Brazed Joints in Aluminum Patricia B. Roy, Fiona M. O’Connell, Thomas H. Callahan, Edward J. Armellino, and Wayne L. Elban Department of Engineering Loyola University Maryland Baltimore, Maryland 21210 27th Annual National Educators' Workshop NEW: Update 2012 November 4 – 7, 2012, Fort Wayne, Indiana

  2. Joining Metals by Brazing • Brazing is the joining of two base metals via a filler metal. • Brazing operations apply heat broadly to the base metals. • The filler metal is then placed into contact with the base metals and melts. • The filler metal wicks into the joint via capillary action.

  3. Polished Cross-section of Vacuum-brazed Aluminum Alloy Sample fins extrusion extrusion 3003 Al core part of extrusion 5 4004 Al liner area where microhardness indentations are part of extrusion 1 extrusion 4 extrusion 3 extrusion 2 3.5 mm

  4. Learning Goals • To become familiar with: • Vickers microindentation hardness testing, a prominent technique for characterizing the mechanical response of materials • brazing technology • the process of creating a computer-based mechanical property correlation for various materials

  5. Experimental Goals • To measure the Vickers hardness profile across a set of brazed joints in an aluminum alloy; and • To obtain a computer-based mechanical property correlation

  6. Vickers Hardness Testing • Square-base diamond pyramid indenter • 10 gf applied load for 25 seconds dwell • Resulting indentation formed by plastic deformation • Diagonal length measured optically

  7. Vickers Hardness Number (VHN) VHN calculated using VHN = 1.8544 P/d2 where P= Applied load, kgf d= Indentation diagonal length, mm VHN [=] kgf/mm2

  8. Experimental • Calibrate using standard reference test block • Perform series of twenty hardness determinations using 10 gf applied load for 25 seconds dwell • Over 5.875 mm distance perpendicular to four brazed joints to obtain hardness profile

  9. Data Analysis • Compute VHN for each hardness impression • Plot tensile strength versus Knoop hardness number (KHN) using Wilson (Instron) Desk Chart 60 • Obtain tensile strength estimates for VHN determinations

  10. Photomicrograph of Left-hand Brazed Joint Assembly 8 5 2 7 3

  11. Hardness Profile of Two Brazed Joint Assemblies 3 7 16 11 12 1 9 18 14 5

  12. Tensile Strength - Knoop Hardness Number Correlation (from Wilson Desk Chart 60; 500 gf)

  13. Hardness Values with Corresponding Tensile Strength Estimates

  14. Hardness Insights • Highest hardness values found at impressions #3, 7, 12, and 16 in the actual brazed joints • Elevated hardness found in regions closest to brazed joints at impressions #4, 6, 13, and 15 • Lowest hardness found at nominal centers of 3003 core sheets at impressions #5 and 14 • High hardness values due to solid solution hardening and precipitation hardening of filler metal

  15. Tensile Strength Comparison

  16. Computer-based Mechanical Property Correlation • Cambridge Engineering Selector (CES) EduPack2012 software • Plot generated: tensile strength versus Vickers hardness • Labeled materials: • Alumina • Aluminum alloys • Bamboo • Cellulose polymers (CA) • CFRP, epoxy matrix (isotropic)* • Flexible polymer foam (MD) • Silica glass* • Stainless steel • Stone* • * Has estimated material property

  17. Tensile Strength vs. Vickers Hardness

  18. Mechanical Property Correlation Insights • Expected strong correlation: tensile strength increases with increasing hardness • Tensile strength = highest measured load divided by initial area and typically associated with plastic deformation • Vickers hardness gives measure of a material’s ease to deform plastically in accommodating the indenter

  19. Acknowledgements Dr. S.F. Baumann ALCOA Mill Products Heat Exchanger Products Technical Center 1480 Manheim Pike Lancaster, Pennsylvania 17601 Dr. M.R. Staker Department of Engineering Loyola University Maryland Baltimore, MD 21210

  20. Extra Slides to Follow (for possible discussion issues)

  21. Photomicrograph of Right-Hand Side Brazed Joint Assembly 10 12 14 16

  22. Indenter Load Effect

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