1. Behold, O Man, you can create life. You can destroy life
Behold, O Man, you can create life. You can destroy life. But, lo, you have no choice but to experience life. And therein lies both your greatest strength and your greatest weakness
-Orange Catholic Bible

2. T4 designates a heat treatment (Al alloys only)
"solution heat-treated, quenched, and naturally aged to a substantially stable condition"
How do we know this works?…….& why does it make the material stronger?

3. How do we know it works?
We consult a road map for the material system
A portion of the Al-Cu
"phase diagram"

4. We have a nomenclature problem

5. A new concept - the solid solution

6. A new concept - the solid solution

7. A new concept - the solid solution

8. A new concept - the solid solution

9. A new concept - the solid solution

10. A new concept - the solid solution

11. A new concept - the solid solution

12. A new concept - the solid solution

13. A new concept - the solid solution
A single phase Cu-Zn alloy is formed
Then, where are the Zn atoms??

14. Note "close-packing"
rCu = 1.28 Å rZn = 1.37 Å
Substitutional solid solutions like this
are common in material systems

15. This is a single phase solid solution
Note: since Zn atom slightly larger, some distortion of structure.

16. Now, back to the road map
Soln ht treat
Purpose:
make single phase

17. Now, back to the road map
Age
Quench
Purpose:
start formation of 2nd phase
(pptn)
Purpose:
maintain single phase

18. Changing structure changes properties!
Yield strength Tensile strength
Low-strength ksi ksi
steel
Pure aluminum ksi ksi
Al alloy 2024-T ksi ksi

19. Assignments for next class:
1. review today's classnotes; know
what a phase is, solid solution, close-packing,
procedure for age hardening
2. check syllabus materials at: