T4 designates a heat treatment (Al alloys only)

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

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

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

18. Yield strength Tensile strength Low-strength 30 ksi 60 ksi steel Pure aluminum 5 ksi 13 ksi Al alloy 2024-T4 47 ksi 68 ksi Changing structure changes properties!