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Dispersion and Solution Hardening
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Solid Solution Hardening
- Impurity atoms go into either substitutional or interstitial solid solution. Lattice strain field interacts between dislocations and these impurity atoms result, and consequently, dislocation movement is restricted. - The strain (or stress) field “roughen” the lattice structure and hinder the dislocation movement.
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Solid Solution Hardening
Solid solution hardening in brass
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Solid Solution Hardening
There is an interaction between the strain fields about a solute atom and the strain fields about the dislocations.
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Solid Solution Hardening Example – Al Alloys
1.8%
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5000 series Aluminum Alloys (Al-Mg)
Hold at 450C (Solution Heat Treatment) Cool moderately quickly to room temperature
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Solid Solution Hardening – Al Alloys
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Precipitate or Dispersion Hardening
Dispersion Strengthening - Strengthening by the introduction of a second phase. Precipitation Strengthening - Through the formation of extremely small uniformly dispersed particles of a second phase within the matrix
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Precipitate or Dispersion Hardening -Small particles
Particle Cutting Particles should be small enough to be cut. Large size particles offer more resistance to dislocation motion.
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Precipitate or Dispersion Hardening -Small particles
Strengthening effect can be estimated as: G – Shear Modulus r – Particle radius b – Burgers vector f – volume fraction of particles - strain field factor Strengthening Particle Radius
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Precipitate or Dispersion Hardening - Big Particles
Dislocation Bypass by the Orowan Bowing Mechanism:
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Precipitate or Dispersion Hardening - Big Particles
The stress required to bypass in this manner is given by the line tension when the dislocation is bowing at the maximum curvature – Depends then on the distance between particles (L): - Shear strength increase G – Shear Modulus b – Burgers vector L – Particle spacing
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Precipitate or Dispersion Hardening - Big Particles
Strengthening Particle Radius f – volume fraction of particles r – particle radius
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Precipitate or Dispersion Hardening - Particle Size Effect
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Age (Precipitation) Hardening
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Age (Precipitation) Hardening
Room temperature microstructures in Al-4%Cu alloy. (a) slow cooling; (b) moderately fast cooling
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Age (Precipitation) Hardening
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Aluminum Alloys Wrought Alloy
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Commercially Pure Aluminum – 1000 series
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Commercially Pure Aluminum – 1000 series
Microstructure sheet, cold-rolled and annealed. FeAl3 (black) particles.
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Commercially Pure Aluminum – 1000 series
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Al-Cu-Mg Alloys – 2000 series
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Al-Cu-Mg Alloys – 2000 series
Microstructure 2024-T6 after solution, quenching and aging 12h at 190C. GP Zones + S’(Al2CuMg)
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Al-Cu-Mg Alloys – 2000 series
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Al-Mn Alloys – 3000 series
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Al-Mn Alloys – 3000 series Structures
3003 (1.2% Mn) annealed sheet; fine dispersion of (Mn, Fe)Al6 and (Al-Fe-Mn-Si) Precipitates.
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Al-Mn Alloys – 3000 series 3003 (1.2% Mn) annealed sheet; fine dispersion of (Mn, Fe)Al6 and (Al-Fe-Mn-Si) Precipitates.
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Al-Zn-Mg-Cu Alloys – 7000 Series
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Al-Zn-Mg-Cu Alloys – 7000 Series
Microstructure Al-5Zn-2Mg alloy (a) 5d/20C+48h/120C, GP Zone only (b) 16h/80C + 24h/150C, GP + ’ (c) 24h/150C, ’
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Al-Zn-Mg-Cu Alloys – 7000 Series
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