MaterialsAluminium and light alloys

7075 aluminium — EN AW-7075 / 3.4365

The high-strength Al-Zn-Mg-Cu alloy 7075: designations, EN 573-3 composition, T6, T651, T73 and T7351, plate and bar strength by thickness, physical properties, heat treatment, stress corrosion and the conductivity check, quench stresses and distortion, welding, and machining.

LiveUpdated 15 October 202613 min read

7075: composition limits and a rib machined from plate

Zinc, the main alloying element (EN 573-3): 5.1–6.1% Zn
Typical tensile strength in T6, nearly twice 6061-T6: 572MPa
Minimum Rm of T651 plate 120–150 mm, against 540 in thin plate: 360MPa
Conductivity of T73 (AMS 2658D); T6 reads 30.5–36.0: 40.0–43.0% IACS

7075 is a high-strength aluminium–zinc–magnesium–copper alloy of the 7xxx series. Its typical T6 tensile strength, 572 MPa, is nearly twice that of 6061-T6. It is made into aircraft structures, highly stressed parts, and moulds, jigs and fixtures. Three facts shape how it is bought and machined: it is not arc welded, T6 has low resistance to stress corrosion cracking, which the T73 temper was developed to overcome, and thick plate keeps quench stresses that can distort a machined part.

Designations

Designation	7075
EN numeric	EN AW-7075
EN chemical	EN AW-AlZn5,5MgCu
ISO	AlZn5.5MgCu
Material number	3.4365
Old DIN name	AlZnMgCu1,5
UNS	A97075
Old national	BS 2L95 (T651 plate), AFNOR A-Z5GU

US material specifications include AMS 4045 (T6 sheet and T651 plate), AMS 4078 (T7351 plate) and AMS-QQ-A-200/11 (extrusions) (Aircraft Materials, Referans Metal). The European standards are EN 573-3 for composition (2026), EN 485-2 for sheet and plate (2016+A1:2018), EN 755-2 for extrusions (2025) and EN 754-2 for drawn products (2024). The stockist tables below do not say which edition they reproduce; the bar values probably come from earlier editions, and changes in the current ones could not be checked.

Chemical composition

EN 573-3 limits, % by mass. Single values are maximums.

Element	Limit
Zn	5.1–6.1
Mg	2.1–2.9
Cu	1.2–2.0
Cr	0.18–0.28
Si	0.40
Fe	0.50
Mn	0.30
Ti	0.20
Others, each / total	0.05 / 0.15
Al	remainder

For extruded and forged products, a limit of Zr + Ti ≤ 0.25 % may be agreed between supplier and purchaser. The Aluminum Association’s nominal composition is Zn 5.6, Mg 2.5, Cu 1.6 and Cr 0.23 % (Kaufman). BIKAR, Wieland, Euralliage and MatWeb print the same limits.

Tempers

Temper	What it is
O	Annealed, the lowest-strength temper
T6	Solution heat-treated and artificially aged
T651	T6, stretched before ageing to relieve quench stresses
T73, T7351	Overaged for resistance to stress corrosion; T7351 is stretched
T76, T7651	Overaged; between T6 and T73 in strength (Euralliage), moderate stress-corrosion resistance (ECSS)

THeat treatedThermally treated to a stable temper other than F, O or H.

7OveragedSolution heat-treated, then aged beyond the point of maximum strength to improve a property such as corrosion resistance.

3Stress-corrosion variantFor 7075: specially aged to resist stress corrosion cracking.

51StretchedStress-relieved by stretching after solution treatment. Permanent set 1½–3 % for plate, 1–3 % for rod, bar and extruded shapes.

Solution treatmentQuenchStretchOverageing

Reading a 7075 temper code. T7 means aged beyond peak strength; the 3 of T73 marks the stress-corrosion variant; 51 means stretched. Pick a code.

For plate, the stretch is a permanent set of 1.5–3 % (Kaufman, MIL-H-6088G); Total Materia gives 0.5–3 %. Extrusions are stretched to 1–3 % and sold as T6510 or T6511, and as T73510 or T73511.

Mechanical properties

Sheet and plate

EN 485-2 minimums for T6 (sheet) and T651 (plate). HBW values are for information only.

Thickness (mm)	Rm (MPa)	Rp0.2 (MPa)	A (%)	HBW
0.4–0.8	525	460	6 (A50)	157
0.8–1.5	540	460	6 (A50)	160
1.5–3	540	470	7 (A50)	161
3–6	545	475	8 (A50)	163
6–12.5	540	460	8 (A50)	160
12.5–25	540	470	6	161
25–50	530	460	5	158
50–60	525	440	4	155
60–80	495	420	4	147
80–90	490	390	4	144
90–100	460	360	3	135
100–120	410	300	2	119
120–150	360	260	2	104
150–200	360	240	2	–
200–300	360	220 or 240	1	–

BIKAR and Euralliage give every row up to 150 mm, and Wieland (from 6 mm) and IBL (from 8 mm) agree; BIKAR and Wieland give 150–300 mm and differ on the proof strength above 200 mm (220 and 240 MPa). BIKAR and Wieland give A50 up to 12.5 mm and A above; IBL labels every row A50. GLEICH and Metall Service Menziken note that the core strength of thick plate drops above about 80 mm.

Minimum strength of plate against thickness: 7075-T6/T651 (orange) and 6082-T6/T651 (blue); solid lines Rp0.2, dashed lines Rm. Thick 7075 plate loses much of its advantage: at 120–150 mm its minimum proof strength is 260 MPa, against 240 MPa for 6082. Dark dashes on the 6082 line mark values from one source only (BIKAR). Hover a step to read it.

For T73 and T7351 plate only Euralliage’s table was found: Rm 460 and Rp0.2 385 MPa at 1.5–6 mm, 475 / 390 MPa from 6 to 50 mm, falling to 430 / 340 MPa at 80–100 mm. AMS 4078 asks for 468 / 385 MPa in T7351 plate from 6.35 to 50.8 mm (Referans Metal).

Bar and extrusions

EN 755-2 (extruded) and EN 754-2 (drawn) minimums, MPa.

Product, temper	Size (mm)	Rm	Rp0.2	A (%)
Extruded bar, T6/T6510/T6511	d ≤ 25	540	480	7
	25 < d ≤ 100	560	500	7
	100 < d ≤ 150	530	470	6
	150 < d ≤ 200	470	400	5
Extruded bar, T73/T73510/T73511	d ≤ 25	485	420	7
	25 < d ≤ 75	475	405	7
	75 < d ≤ 100	470	390	6
	100 < d ≤ 150	440	360	6
Drawn bar, T6	d ≤ 80	540	485	7
Drawn bar, T73	d ≤ 80	455	385	10

From BIKAR, Wieland and Euralliage. For drawn T6 bar Euralliage prints 520 / 460 MPa, and BIKAR’s round-bar table has 550 / 440 and 440 / 400 MPa for 100–150 and 150–200 mm, against its own square-bar rows and the other sources.

Typical values

Property	T6 / T651	T73 / T7351
Tensile strength Rm (MPa)	572	505
0.2 % proof strength (MPa)	503	435
Elongation (%)	11	13
Hardness (HB)	150	135
Shear strength (MPa)	331	300
Fatigue strength, 5 × 10⁸ cycles (MPa)	159	150

Aluminum Association typical values, through MatWeb; Continental Steel and voestalpine agree. Typical values are not guaranteed; design to the minimums.

Where 7075 sits: typical 0.2 % proof strength (bar) and tensile strength (outline) of 6061-T6, 2024-T351 and 7075 in T73 and T6. Aluminum Association typical values through MatWeb.

T73 costs strength. From the typical values, it gives up 12 % of the tensile strength and 14 % of the proof strength of T6; from the extruded-bar minimums up to 25 mm, 10 % and 12.5 %. These percentages are calculated here; Kaiser’s 1976 report for NASA speaks of the weight penalty that the lower strength brings.

Physical properties

Property	Value
Density (g/cm³)	2.80 (EN producers) / 2.81 (Aluminum Association)
Elastic modulus (GPa)	72 (Aluminum Association 71.7)
Shear modulus (GPa)	27
Thermal conductivity, T6 (W/(m·K))	130–134
Thermal conductivity, T73 (W/(m·K))	155
Thermal expansion 20–100 °C (10⁻⁶/K)	23.4–23.6
Electrical conductivity, T6 (% IACS)	33
Melting range (°C)	475–635
Long-term service temperature (°C)	about 90

MatWeb gives 130 W/(m·K) for T6, voestalpine and Euralliage 134; the T73 value is MatWeb’s. Specific heat is printed as 862 J/(kg·K) by the European sheets and 960 J/(kg·K) by MatWeb and Aircraft Materials (the latter at 100 °C). Aircraft Materials gives a solidus of 532 °C, against 475–477 °C elsewhere. BIKAR gives 110–125 °C and GLEICH 120 °C for short-term service.

Heat treatment

Step	Conditions
Solution treatment	460–499 °C for sheet, plate and rolled bar; 460–471 °C for extrusions (MIL-H-6088G). Stockists give 470–480 °C.
Quench	Water; the bath at no more than 38 °C at the end of the quench (MIL-H-6088G)
Ageing to T6	About 120 °C for 24 h
Ageing to T73	Two steps: 105–107 °C for 6–8 h, then 163–177 °C. Second step about 24–30 h at 165 °C for plate, 8–10 h at 175 °C for bar and forgings, 6–8 h at 175 °C for extrusions (Total Materia)
Ageing to T76	3–30 h at 121 °C, then 15–18 h at 163 °C (Total Materia)
Annealing to O	415 °C for 2–3 h, cool to 205 °C or below, then 4 h at 230 °C (Total Materia). BIKAR: 380–420 °C, cool at 30 °C/h or less to 230 °C, hold 3–5 h

The T6 practice is the same in Total Materia, Kaiser’s NASA report and two US patents. MIL-H-6088G warns that 7075 can begin to melt above 482 °C (900 °F) and recommends no more than 488 °C for plate and bar over 4 in (102 mm); Total Materia gives 490 °C to avoid eutectic melting. Ageing to T73 or T76 needs tighter control of time, temperature and heating rate than T6 (Total Materia).

Heat treatment to T73: solution treatment, water quench, then two ageing steps, the second hotter, which takes the alloy past peak strength. The second-step time depends on the product. Insets schematic; time not to scale.

Stress corrosion and the conductivity check

ECSS-Q-70-36A, the European space standard for stress-corrosion selection, rates 7075-T6 low, T76 moderate and T73 high, and asks for mechanically stress-relieved products (TX51 and similar) where possible. In its article on stress-corrosion cracking, Total Materia notes that 7079-T6, 7075-T6 and 2024-T3 account for more than 90 % of service failures among high-strength aluminium alloys, and that the limits of 7075-T6 led to the T73 and T76 tempers. US patents on 7xxx ageing agree that T73 lowers strength “significantly” against T6.

Why T73 exists. Ageing past the peak lowers strength but raises stress-corrosion resistance and electrical conductivity. Curve schematic, drawn through the typical tensile strengths; ratings from ECSS-Q-70-36A; conductivity ranges from AMS 2658D as MacKenzie reproduces them.

Because overageing raises electrical conductivity, conductivity is the routine check that a part really is T73. AMS 2658D gives typical ranges of 30.5–36.0 % IACS for T6 and 40.0–43.0 % IACS for T73; the two do not overlap. NASA’s process specification PRC-2002 requires conductivity tests to ASTM E1004 against the AMS 2658 values. One stockist page gives 33 % IACS for T7351, which is a T6 value.

Quench stresses and distortion

Quenching thick plate leaves compression at the surfaces and tension in the core. Stretching the plate by 1.5–3 % (T651, T7351) cuts these stresses by about a factor of ten, but what is left is still enough to distort aircraft parts machined from the plate; the rework and scrap cost the industry tens of millions of dollars a year. Those measurements were made by Prime and co-workers at Los Alamos on 7050, a related alloy; studies on pre-stretched 7075-T7351 plate measure the residual stress to predict machining distortion.

Stress through the thicknessAs quenched: compression at the surfaces, tension in the core. Stretching cuts it sharply but not to zero.

After machining from one sideRemoving material upsets the balance; the part bows under the stress that is left.

Schematic, no magnitudes. Left: residual stress through the thickness of quenched plate, and the much smaller stress after stretching. Right: a part pocketed from one side bows when the material that held the stresses in balance is cut away.

For machined parts, buy stretched material: T651 or T7351 plate, T6511 or T73511 extrusions. Producers disagree on how stable 7075 plate is in machining: BIKAR and GLEICH rate its dimensional stability poor, Metall Service Menziken good.

Welding

7075 is not arc welded. The producer sheets rate gas, TIG and MIG welding unsuitable (Metall Service Menziken alone says conditional), and ESAB calls it unweldable by arc welding. For electron-beam welding they disagree: Euralliage rates it good, GLEICH poor. Copper and magnesium together make the weld sensitive to cracking as it solidifies (ESAB, TWI), and The Fabricator notes that the heat-affected zone is prone to cracking and to stress corrosion in service. Resistance spot and seam welding are rated good, and friction stir welding joins 7xxx alloys with low distortion (TWI). Brazing and soldering are not suitable.

Corrosion and anodizing

General corrosion resistance is poor in the atmosphere and in seawater; MARKS advises protection outdoors. Protective and hard anodizing work; decorative anodizing does not, according to every producer sheet that rates it. Metall Service Menziken adds that hard chrome and electroless nickel plating are possible.

Machining

7075 belongs to ISO 513 group N. Seco uses AW-7075 as the reference material of its group N1 and recommends its uncoated H25 or coated F15M grades first. ISCAR files hardenable wrought aluminium under group 22 with kc1.1 = 800 N/mm² and mc = 0.25, without naming 7075; that gives about 1200 N/mm² at h = 0.2 mm. No other tool maker’s kc value was found.

Temper. Machine it aged. MARKS says chips break well only in the aged condition. The producers’ ratings disagree: GLEICH, Metall Service Menziken and voestalpine call 7075 very good or excellent to machine, Aircraft Materials and Smiths only fair; MatWeb puts T6 and T73 at 70 % on its aluminium scale. The scales differ, so the ratings are not comparable.

Speeds. Wieland gives 300–800 m/min. Haas lists 610 m/min for its HSAM2 carbide end mills in wrought aluminium (ISCAR groups 21–22), with fz 0.025–0.254 mm for diameters of 3–25 mm. Built-up edge and the remedies for it are the same as for 6061 and 6082.

Moulds and fixtures. BIKAR and GLEICH rate 7075 very good for EDM and polishing, which suits mould and model making.

Choosing a temper

T651 plate for strength: jigs, fixtures, moulds and parts not exposed to stress corrosion.
T7351 plate for parts under sustained stress in a corrosive environment (Online Metals, ECSS), accepting about 10–20 % less strength; the proof strength drops most.
Thick sections: check the minimum for the actual thickness. From 50 mm the minimum proof strength falls steadily, from 440 MPa at 50–60 mm to 260 MPa at 120–150 mm.
Arc-welded designs: not 7075.

Typical uses named in the sources: aircraft structures and fittings; gears and shafts; tool, mould and model making, jigs and fixtures; defence and missile parts; machine frames and robot arms; motorsport parts; bicycle and climbing equipment.

Sources (49)

Every value and quotation on this page comes from the documents below.