7075 aluminium billet is direct-chill (DC) cast, homogenised round stock that forging shops and extruders convert into high-strength 7075 parts and profiles. Its value lies in what you cannot see: melt cleanliness, low hydrogen, a fine and uniform grain and an even chemistry from surface to centre. This guide explains how 7075 billet is made, the diameters available, which quality checks matter and how to specify it.
A billet is upstream feedstock: a cylindrical casting that has not yet been hot-worked into its final product. A 7075 bar, by contrast, has already been extruded or forged, heat-treated to a temper such as T651 and is ready for machining. Buyers of billet are usually forging plants, extrusion plants and makers of large machined blanks who control their own hot working and heat treatment.
Because the billet has a cast structure, its quality decides how the final product behaves. Oxide films, porosity and coarse intermetallic particles in the billet end up inside the forging or profile, where they lower fatigue life and can cause ultrasonic rejections. A good 7075 billet is therefore judged on internal soundness and consistency, not just diameter and chemistry.
| 7075 billet | 7075 bar / rod | |
|---|---|---|
| Structure | As-cast and homogenised | Wrought (extruded, drawn or forged) |
| Temper | Homogenised; no T temper | Usually T6, T651, T6511 or T73 |
| Typical buyer | Forging and extrusion plants | Machine shops, fabricators |
| Key quality checks | Ultrasonic soundness, grain size, hydrogen, chemistry | Mechanical properties, tolerances, ultrasonic |
| Strength as delivered | Low; not intended for direct service | Full temper strength |
7075 billet follows the same registered limits as wrought 7075 products. Some aerospace programmes ask for tighter iron and silicon (for example Fe ≤ 0.25 %, Si ≤ 0.15 %) to improve toughness and fatigue life; state these on the order if your end customer requires them.
| Element | Minimum | Maximum | Role in the alloy |
|---|---|---|---|
| Silicon (Si) | — | 0.40 | Impurity; kept low for toughness |
| Iron (Fe) | — | 0.50 | Impurity; forms coarse constituents that cut fatigue life |
| Copper (Cu) | 1.2 | 2.0 | Adds strength and improves stress-corrosion behaviour |
| Manganese (Mn) | — | 0.30 | Minor grain control |
| Magnesium (Mg) | 2.1 | 2.9 | Combines with Zn to form the MgZn2 strengthening phase |
| Chromium (Cr) | 0.18 | 0.28 | Controls recrystallisation and stress-corrosion cracking |
| Zinc (Zn) | 5.1 | 6.1 | Main alloying element |
| Titanium (Ti) | — | 0.20 | Grain refiner |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | About 87 – 91 % |
Weight of a round billet is π/4 × D² × L × 2.81 g/cm³. The table shows weight per metre for common diameters.
| Diameter (mm) | kg per metre | Typical use |
|---|---|---|
| 78 | 13 | Small extrusion presses, forging slugs |
| 102 | 23 | Extrusion of small profiles and rod |
| 127 | 36 | Extrusion of bar and tube |
| 178 | 70 | Medium presses, open-die forgings |
| 254 | 142 | Large extrusions, closed-die forgings |
| 305 | 205 | Heavy forgings, large rod |
| 406 | 364 | Large forgings and blocks |
| 508 | 570 | Rolled rings, very large forgings |
| 610 | 821 | Heavy-press forgings |
Immersion or contact ultrasonic testing finds porosity, cracks and inclusion clusters. Agree the acceptance class (for example by flat-bottom-hole size) before ordering, since forgings for aircraft parts are later tested to AMS-STD-2154 or equivalent.
Low dissolved hydrogen, measured on the melt or on samples, prevents porosity that would show up as blisters after heat treatment.
A transverse slice etched to reveal the grain should show fine, uniform equiaxed grains with no feathery crystals, cold shuts or centre cracking.
Filtration and clean handling reduce oxide films. Some buyers specify a PoDFA or similar melt-cleanliness test.
Analysis from several positions or casts confirms there is no strong segregation of zinc or copper across the diameter.
Each billet should carry its cast number so that any later defect can be traced back to the melt and homogenising batch.
Extrusion. 7075 is one of the hardest common alloys to extrude. Billets are preheated to roughly 380 – 440 °C and pushed at low ram speeds, giving exit speeds of only a few metres per minute, to avoid surface tearing and incipient melting. Containers and dies must be designed for high pressures. The profiles are then solution treated, quenched, stretched and aged, normally to T6511 or T73511.
Forging. For open-die and closed-die forgings, billets are heated in a narrow window, typically around 380 – 440 °C, because 7075 becomes crack-prone if forged too cold and risks incipient melting if overheated. Forged parts are heat-treated to T6, T652, T73 or T7352, with the stress-relieved "52" tempers produced by cold compression after quenching.
Direct machining. Billet is occasionally machined into parts without hot working, but cast-and-homogenised material has lower ductility, fatigue strength and toughness than wrought 7075. For structural parts, use plate, bar or forgings instead.
7075 billet is cast and homogenised feedstock for hot working; it has no heat-treated temper and is not meant for direct service. 7075 bar has been extruded, drawn or forged and heat-treated (usually to T6 or T651), so it is ready to machine into parts.
Round billet is commonly cast from about 73 mm up to around 630 mm diameter, in logs of about 3 or 6 m or sawn to press length. The right diameter depends on the extrusion container or the forging reduction you need.
Homogenisation dissolves low-melting eutectic phases, reduces segregation and forms the dispersoids that control grain structure. Without it, 7075 extrudes poorly, cracks more easily during forging and responds less evenly to heat treatment.
It can, but the cast structure gives lower ductility, toughness and fatigue strength than wrought 7075. For load-bearing parts, use 7075 plate, bar or a forging instead.
At minimum, chemistry by cast and an ultrasonic soundness test to an agreed acceptance level. For aerospace forging stock, add macro-etch grain checks, hydrogen measurement and full traceability, documented on an EN 10204 3.1 certificate.
Tell us the diameter, length, quantity, inspection level and destination port. We will confirm availability and documentation.
