Aluminium alloy 7075 is an aluminium alloy, with zinc as the primary alloying
element. It is strong, with a strength comparable to many steels, and has good
fatigue strength and average machinability, but has less resistance
to corrosion than many other Al alloys. Its relatively high cost limits its use
to applications where cheaper alloys are not suitable.
7075 aluminum alloy's composition roughly includes 5.6–6.1% zinc, 2.1–2.5%
magnesium, 1.2–1.6% copper, and less than half a percent of silicon, iron,
manganese, titanium, chromium, and other metals. It is produced in many tempers,
some of which are 7075-0, 7075-T6, 7075-T651.
Basic properties Aluminium 7075A has a density of 2.810
g/cm³. Mechanical properties
The mechanical properties of 7075 depend greatly on the temper of the material.
= 7075-0= Un-heat-treated 7075 has maximum tensile
strength no more than 40,000 psi, and maximum yield strength no more than
21,000 psi. The material has an elongation of 9–10%. It is very highly
corrosive and has good strength. = 7075-T6=
T6 temper 7075 has an ultimate tensile strength of 74,000–78,000 psi and yield
strength of at least 63,000–69,000 psi. It has a failure elongation of 5–11%.
The T6 temper is usually achieved by homogenizing the cast 7075 at 450 °C for
several hours, quenching, and then aging at 120 °C for 24 hours. This yields the
peak strength of the 7075 alloy. The strength is derived mainly from finely
dispersed eta and eta' precipitates both within grains and along grain
boundaries. = 7075-T651=
T651 temper 7075 has an ultimate tensile strength of at least 67,000–78,000 psi
and yield strength of 54,000–67,000 psi. It has a failure elongation of 3–9%.
The 51 suffix has no bearing on the heat treatment but denotes that the material
is stress relieved by controlled stretching.
= 7075-T7= T7 temper has an ultimate tensile
strength of 73,200 psi and a yield strength of 63,100 psi. It has a failure
elongation of 13%. T7 temper is achieved by overaging the material. This is often
accomplished by ageing at 100–120 °C for several hours and then at 160–180 °C for
24 hours or more. The T7 temper produces a micro-structure of mostly eta
precipitates. In contrast to the T6 temper, these eta particles are much
larger and prefer growth along the grain boundaries. This reduces the
susceptibility to stress corrosion cracking. T7 temper is equivalent to T73
temper. = 7075-RRA=
The retrogression and reage temper is a multistage heat treatment temper.
Starting with a sheet in the T6 temper, it involves overaging past peak hardness
to near the T7 temper. A subsequent reaging at 120 °C for 24 hours returns
the hardness and strength to or very nearly to T6 temper levels.
RRA treatments can be accomplished with many different procedures. The general
guidelines are retrogressing between 180–240 °C for 15 min 10 s.
Uses 7000 series alloys such as 7075 are
often used in transport applications, including marine, automotive and
aviation, due to their high strength-to-density ratio. Their
strength and light weight is also desirable in other fields. Rock climbing
equipment, bicycle components, inlineskating-frames and hang glider
airframes are commonly made from 7075 aluminium alloy. Hobby grade RC models
commonly use 7075 and 6061 for chassis plates. One interesting use for 7075 is
in the manufacture of M16 rifles for the American military. In particular high
quality M16 rifle lower and upper receivers as well as extension tubes are
typically made from 7075-T6 alloy. Desert Tactical Arms, SIG Sauer, and
French armament company PGM use it for their precision rifles. It is also
commonly used in shafts for lacrosse sticks, such as the STX sabre, and
camping knife and fork sets. Due to its high strength, low density,
thermal properties, and its ability to be highly polished, 7075 is widely used
in mold tool manufacture. This alloy has been further refined into other 7000
series alloys for this application, namely 7050 and 7020.
= History= The first 7075 was developed in secret
by a Japanese company, Sumitomo Metal, in 1936. 7075 was used for the
Mitsubishi A6M Zero fighter's air frame for the Imperial Japanese Navy starting
in 1940. = Trade names=
7075 has been sold under various trade names including Zicral, Ergal, and
Fortal Constructal. Some 7000 series alloys sold under brand
names for making molds include Alumec 79, Alumec 89, Contal, Certal, Alumould,
and Hokotol. References
Further reading "Properties of Wrought Aluminum and
Aluminum Alloys: 7075, Alclad 7075", Properties and Selection: Nonferrous
Alloys and Special-Purpose Materials, Vol. 2, ASM Handbook, ASM International,
1990, pp. 115–116.