7075 Aluminum

7075 is a zinc-copper-magnesium alloy developed specifically to push the strength ceiling of commercial aluminum. At 73,000 psi tensile in T651, it outperforms 6061 by more than 70 percent. It is the standard material for aerospace structural components where weight is a design constraint. Machinability is good — better than many people expect from a high-strength alloy — but it is not weldable in structural applications using conventional arc processes.

T651 is the primary plate form for aerospace and defense machining. The stress-relief stretch is particularly important in 7075 because the alloy develops higher residual stresses during quenching than lower-strength alloys, which would cause significant warping during material removal. T7351 is the overaged alternative, offering improved stress corrosion cracking resistance at a 10 to 15 percent strength reduction. T7351 is specified in applications where the part will see sustained tensile stress in a corrosive environment, particularly saltwater or humid conditions.

7075 is not a forgiving alloy. The strength advantage comes with tradeoffs: it is susceptible to SCC in T6 temper when stressed in the short-transverse grain direction, it is not weldable by conventional means, and it has lower fatigue strength than some lower-strength alloys under certain cyclic loading conditions. For parts that need weldability or very high fatigue life under variable loading, 6061 or 2024 may be more appropriate. For maximum static strength-to-weight, 7075-T651 has been the answer for 80 years.