1. Dispersion and Solution Hardening

2. 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.

3. Solid Solution Hardening
Solid solution hardening in brass

4. Solid Solution Hardening
There is an interaction between the strain fields about a solute atom and the strain fields about the dislocations.

5. Solid Solution Hardening Example – Al Alloys
1.8%

6. 5000 series Aluminum Alloys (Al-Mg)
Hold at 450C (Solution Heat Treatment)
Cool moderately quickly to room temperature

7. Solid Solution Hardening – Al Alloys

8. 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

9. 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.

10. 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

11. Precipitate or Dispersion Hardening - Big Particles
Dislocation Bypass by the Orowan Bowing Mechanism:

12. 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

13. Precipitate or Dispersion Hardening - Big Particles
Strengthening
Particle Radius
f – volume fraction of particles
r – particle radius

14. Precipitate or Dispersion Hardening - Particle Size Effect

15. Age (Precipitation) Hardening

16. Age (Precipitation) Hardening
Room temperature microstructures in Al-4%Cu alloy.
(a) slow cooling; (b) moderately fast cooling

17. Age (Precipitation) Hardening

18. Aluminum Alloys
Wrought Alloy

19. Commercially Pure Aluminum – 1000 series

20. Commercially Pure Aluminum – 1000 series
Microstructure
sheet, cold-rolled and annealed. FeAl3 (black) particles.

21. Commercially Pure Aluminum – 1000 series

22. Al-Cu-Mg Alloys – 2000 series

23. Al-Cu-Mg Alloys – 2000 series
Microstructure
2024-T6 after solution, quenching and aging 12h at 190C.
GP Zones + S’(Al2CuMg)

24. Al-Cu-Mg Alloys – 2000 series

25. Al-Mn Alloys – 3000 series

26. Al-Mn Alloys – 3000 series Structures
3003 (1.2% Mn) annealed sheet; fine dispersion of (Mn, Fe)Al6 and (Al-Fe-Mn-Si) Precipitates.

27. Al-Mn Alloys – 3000 series
3003 (1.2% Mn) annealed sheet; fine dispersion of (Mn, Fe)Al6 and (Al-Fe-Mn-Si) Precipitates.

28. Al-Zn-Mg-Cu Alloys – 7000 Series

29. 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, ’

30. Al-Zn-Mg-Cu Alloys – 7000 Series