7075 Aluminum – The Ultimate Aerospace Alloy
Originally introduced in 1943, 7075 aluminum alloy is still the “go to” alloy for the aerospace industry. Its main alloying ingredients are zinc (between 1% and 8%) and copper, making it one of the strongest aluminum alloys available. In fact, in the T6 temper, it displays typical strength higher than most mild steels.
It was the first successful Al-Zn-Mg-Cu, high-strength alloy to use chromium, which adds good stress-corrosion cracking resistance in aluminum sheet products.
Although there are other alloys in the 7XXX range with better specific qualities, 7075 aluminum remains the baseline alloy as it displays the best overall balance of properties.
Alloy 7075 is available in sheet and plate products in the annealed form and in T6, T73 and T76 tempers. It is precipitation hardened to very high strength levels, and displays high strength, moderate toughness and good corrosion resistance, making it ideal for use in aircraft and aerospace applications, as well as for other highly stressed components.
Forming and Machinability
7075 is comparatively strong for an aluminum alloy, producing greater spring-back during forming operations. Formability is best achieved by warming the material to between 200 and 250F, and is best done in the annealed condition. Machining capability is good, but should also be done in the annealed condition. Good oil lubricants should be used.
7075 aluminum should be annealed at 775 F for three hours, then controlled cooled at a 50F per hour reduction in temperature until it reached 500 F. It can then be air cooled.
You should only use resistance welding when working with 7075 aluminum alloy. Gas welding should be avoided, and use of arc welding may result in the overall corrosion resistance being compromised.
Hot and Cold Working
Formability is made much easier by first warming the material to 250F. When the alloy is in the soft, annealed conditioned, it can readily be cold worked. You can use standard forming methods, although spring-back is greater with this alloy than any of the others.
7075 can be solution annealed at 900 F for two hours followed by a water quench. It can then be subjected to precipitation hardening.
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