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

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?

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

We have a nomenclature problem

A new concept - the solid solution

A new concept - the solid solution

A new concept - the solid solution

A new concept - the solid solution

A new concept - the solid solution

A new concept - the solid solution

A new concept - the solid solution

A new concept - the solid solution

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

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

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

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

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

Changing structure changes properties! 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