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530.352 Materials Selection

530.352 Materials Selection. Lecture #18 Strengthening - II Tuesday October 25 th , 2005.  H. Cu. Zn. Zn. Not as easy. Solid Solution Strengthening:.  y  √ C. L. + L. b+ L. T. . b. +b. A. B. Phase diagrams :. Cu-Al. Cu-Al. Cu-Ni. Fe-C. Lever rule :. .

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530.352 Materials Selection

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  1. 530.352 Materials Selection Lecture #18 Strengthening - IITuesday October 25th, 2005

  2. H Cu Zn Zn Not as easy Solid Solution Strengthening: y√C

  3. L +L b+L T  b +b A B Phase diagrams : Cu-Al Cu-Al Cu-Ni Fe-C

  4. Lever rule :  %  is d c + d %  is c c + d x c d T  x1 x x2 A B

  5. Precipitation strengthening: Solution,Quench,Heat treat: - forms  precipitates in the  matrix L 700 600 500 400 300 1.   Temperature  3. 2. Al % Cu

  6. cutting bowing precipitates get too big,i.e. spacing (L) too large. no precipitates precipitates form and grow The mechanical properties: 50 40 30 y (ksi) Heat Treating Time

  7. Cutting precipitates: When too small - dislocations can cut them:

  8. Surface Energy drives growth: For a fixed volume fraction: L ? L L Most surface area -> Least surface area Higher energy-> Lower energy

  9. Bowing: dislocations bow past precipitates precipitates slow dislocations ymb L

  10. Taylor relation: t = m b √r where Lbetween dislocations = 1 / √r L Work hardening See explanation by Alu MATTER: http://aluminium.matter.org.uk/content/html/eng/default.asp?CATID=62&PAGEID=1000900548 -> dislocation interaction slow down dislocations and strengthen metals and alloys L

  11. Yielding: • Single crystalsy b = Ffriction + Fsol’n + Fprec + Fwork hardening • Polycrystals • Yielding starts in some grains before others • General yielding occurs aty = 3y • Grain boundaries add strength

  12. Grain Boundary Strengthening: • dislocations pile up at boundary. • stress builds up. • dislocation motion initiated in neighboring grain. Hall - Petch relation: y = i + ky d -1/2

  13. Heat treating metals : • Annealing cold worked metals and alloys • removes strain hardening (dislocation tangles) • softens the metal • aides warm or hot working • Precipitation Hardening • solutionize, quench, nucleate and grow precipitates • used to precipitation strengthen

  14. Aluminum nomenclature : Wrought alloys: Pure Al (>99.00%) 1xxx Alloyed with: Cu 2xxx Mn 3xxx Si 4xxx Mg 5xxx Mg + Si 6xxx Zn 7xxx Others 8xxx x: alloy modification xx: 0.xx% Al min x: alloy modification- 0 is the original alloy - 1-9 are modification #’s xx: no special significance they identify different Al alloys in a group. E.g. 6061: Al-Mg,Si,Cu is (Al-.4-.8Si, .7Fe, .15-.4Cu, .15Mn, .8-1.2Mg, .25Zn, .15Ti)

  15. Aluminum Nomenclature : Cast alloys: Pure Al (>99.00%) 1xx.x Alloyed with: Cu 2xx.x Si (+Cu / Mg) 3xx.x Si 4xx.x Mg 5xx.x Zn 7xx.x Tin 8xx.x xx: 99.xx% Al min x: casting (0) -or- ingot (1) xx: no special significance they identify different Al alloys in a group. x: casting (0) -or- ingot (1) See: http://httd.njuct.edu.cn/MatWeb/material/m_al.htm http://shopswarf.orcon.net.nz/alalloy.html

  16. Al Heat treatments : • Temper designations • F : as fabricated • O : annealed • H : strain hardened • W : solution heat-treatments • T : temper heatments • T1 - high T shaping, cooled, nat. aged (NA) • T2 - high T shaping, cooled, cold worked (CW), NA • T3 - solution HT, CW, NA • T4 - sol’n HT, NA • T5 - high T shaping, coolded, aged • T6 - sol’n HT, artificially aged <- a common temper • T7 - sol’n HT, over aged • T8 - sol’n HT, CW, artificially aged • T9 - sol’n HT, artificially aged, CW • T10 - high T shaped, cooled, CW, aged

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