Age hardening in aluminium alloys: State whether the following is correct: “Adding copper to aluminium enables significant strengthening after solution heat treatment and age hardening.”

Introduction / Context:
Precipitation hardening (age hardening) is the dominant strengthening mechanism in many aluminium alloy families. The Al–Cu system (e.g., duralumin) is a classic case, historically foundational in aerospace because of its excellent strength-to-weight ratio after proper heat treatment.

Given Data / Assumptions:

• Alloy family considered: Al–Cu with possible minor Mg/Mn.
• Heat-treatment route: solution treatment → quench → natural or artificial ageing.
• Strengthening phase: fine precipitates formed during ageing.

Concept / Approach:
Solution treatment dissolves copper into a supersaturated solid solution. Upon quenching and subsequent ageing, fine coherent or semi-coherent precipitates (e.g., GP zones, thetaʺ, thetaʹ) form, impeding dislocation motion and dramatically increasing strength. This principle applies broadly to wrought Al–Cu alloys and many cast Al–Cu alloys, though exact parameters differ.

Step-by-Step Solution:
Start: dissolve Cu in Al matrix by solution heat treatment.Quench: retain supersaturated solid solution.Age: form fine precipitates that hinder dislocations, raising yield and tensile strength.Conclusion: the statement is correct.

Verification / Alternative check:
Property charts show large increases in yield strength from T4/T6 tempers relative to annealed O temper in Al–Cu alloys.

Why Other Options Are Wrong:
Limiting to cast alloys or to very low temperatures ignores widespread practice; claiming suppression of age hardening is contrary to the Al–Cu phase behaviour.

Common Pitfalls:
Confusing natural ageing with artificial ageing; overlooking that over-ageing at excessive temperature/time reduces strength.

Final Answer:
Correct