As aerospace structures grew larger and required thicker aluminum plate, engineers found that 7075 in T7351 temper — while strong — suffered from reduced toughness and stress corrosion cracking resistance as plate thickness increased beyond 3–4 inches. This is a fundamental metallurgical challenge with the zinc-magnesium-copper system: the quench rate from solution annealing slows in thick sections, leaving behind a less uniform microstructure.[1]
7050 addresses this by modifying the alloy chemistry — adding zirconium to refine grain structure and adjusting the zinc, magnesium, and copper ratios — to produce a more stable microstructure that maintains properties through greater thickness. The result is an alloy that can be produced in plate thicknesses up to 6 inches or more while still meeting the mechanical property and ultrasonic inspection requirements of aerospace procurement.[1][2]
| Property (typical) | 7075-T7351 (plate) | 7050-T7451 (plate) |
|---|---|---|
| Ultimate tensile strength | 73 ksi / 503 MPa | 76 ksi / 524 MPa |
| Yield strength (0.2%) | 63 ksi / 434 MPa | 68 ksi / 469 MPa |
| Elongation | 11% | 10% |
| Fracture toughness (KIc, L-T orientation; values vary with orientation) | ~24 ksi√in / 26 MPa√m | ~32 ksi√in / 35 MPa√m — better |
| SCC resistance (short transverse) | Fair in thick plate | Good — engineered for thick section |
| Standard plate temper | T7351 | T7451 |
| Governing plate specification | AMS 4078 | AMS 4050 |
| UT inspection required? | Yes — for thick plate per applicable spec | Yes — mandatory per AMS 4050 |
| Typical thickness range | Up to ~4 in / 100 mm effectively | Up to 6 in / 152 mm and beyond |
| Relative cost vs 6061 | 2–3× | 3–4× (less commonly stocked) |
Properties are typical mill values; AMS 4050 and AMS 4078 minimums are lower and decrease with plate thickness (see the AMS 4050 article).
7050 plate is almost always specified in the T7451 temper. Breaking down the designation: T74 is the aging designation, meaning solution heat treated and overaged to a level between T73 and T76 for SCC resistance; it is the 7050 counterpart of T73 on 7075 (a slightly lesser overage). The "51" suffix means the plate was stress relieved by stretching with no subsequent straightening ("511" would permit minor straightening). This makes T7451 the 7050 equivalent of 7075-T7351 — but engineered for better through-thickness consistency.[3]
The correct drawing callout for 7050 plate is: Aluminum Alloy 7050-T7451 per AMS 4050. This callout also invokes the mandatory ultrasonic testing requirement specified within AMS 4050.
AMS 4050 requires that 7050 plate be ultrasonically tested prior to shipment to verify internal soundness — free from porosity, inclusions, cracks, and other internal discontinuities that cannot be detected by surface inspection alone. This is not optional; it is a mandatory requirement of the specification that the mill or service center must certify on the material certification document.[2]
When you order 7050-T7451 per AMS 4050, you should receive a material test report (MTR) confirming that ultrasonic inspection was performed and the plate passed. If you are buying to this specification and do not receive UT certification on the MTR, the material does not comply — and should not be accepted for aerospace structural use.
We verify AMS 4050 certifications and UT inspection records as part of our material receiving process. Submit your RFQ and we'll confirm compliance before cutting begins.