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Outline for Lecture #19:

Outline for Lecture #19:. Name of game in strengthening metals … Slow down the dislocations !! Strengthening mechanisms Lattice friction depends on crystal structure Solid solution strengthening t y a √ X b Precipitation strengthening t y = Gb / L Strain hardening t y = G b √ r

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Outline for Lecture #19:

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  1. Outline for Lecture #19: • Name of game in strengthening metals … • Slow down the dislocations !! • Strengthening mechanisms • Lattice friction • depends on crystal structure • Solid solution strengthening • tya √ Xb • Precipitation strengthening • ty= Gb / L • Strain hardening • ty = G b √r • Grain boundary strengthening • sy = si + ky d-1/2

  2. 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

  3. 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

  4. 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)

  5. 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

  6. 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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