Aluminium ENAW-7075 Bars & Rods (7075-O, 7075-T6, T651)

Product Description

EN AW-7075 (AlZnMgCu1.5) aluminum bars, rods, and round bars exhibit highly divergent mechanical profiles depending on their specific heat-treatment condition. Selecting between 7075-O, 7075-T6, and 7075-T651 dictates the material's formability, internal stress levels, and ultimate structural strength.

Understanding the Tempers

The core distinction between these three conditions lies in the state of their zinc-magnesium precipitate structures:

1. 7075-O (Annealed)

• The State: Fully annealed. The metal is heated to a high temperature and cooled slowly to achieve its softest, most ductile state.

• Best For: Severe cold-forming, bending, or deep drawing.

• The Catch: It has the lowest mechanical strength of all three states. If a strong finished part is needed, it must undergo post-forming solution heat treatment and artificial aging to reach T6 properties.

2. 7075-T6 (Solution Heat Treated & Artificially Aged)

• The State: Heated to dissolve alloying elements, quenched rapidly, and then baked at a lower temperature to force the uniform precipitation of hardening phases ($\eta'$ fine precipitates).

• Best For: High-stress applications requiring maximum tensile and yield strength.

• The Catch: High residual stresses from the rapid quench stage can cause the bar to warp, twist, or distort during aggressive machining operations (like deep slotting or asymmetric milling).

3. 7075-T651 (Stress-Relieved by Stretching)

• The State: Follows the exact same thermal cycle as T6, but includes a critical mechanical stretching step immediately after quenching (typically 1.5% to 3% permanent set stretch) before artificial aging.

• Best For: Precision CNC machining, aerospace bulkheads, and complex tooling plates.

• The Catch: Mechanical stretching limits this process primarily to simple, uniform cross-sections like extruded or rolled bars, rods, and plates.

Mechanical Property Comparison

The mechanical performance changes dramatically depending on the selected temper variant (values based on standard bar diameters up to 100 mm per EN 755-2):

Manufacturing Standards for Bars & Rods

When specifying EN AW-7075 bars and rods in engineering designs, cross-referencing European manufacturing standards ensures accurate dimensional tolerances:

• EN 755-1 to 9: Governs extruded aluminum round, square, hexagonal, and rectangular bars. It defines technical conditions for inspection, mechanical properties, and dimensional tolerances.

• EN 754-1 to 8: Governs cold-drawn aluminum bars. Cold drawing offers superior surface finish, tighter dimensional tolerances, and slightly higher mechanical values compared to raw extrusions.

Machining Tip: Always default to 7075-T651 for intricate or highly toleranced machined components. The mechanical stretching relieves the locked-in thermal stresses from quenching, meaning the material will remain flat and true as you cut away metal layers.