The 7000 series grades of aluminum are referred to as the zinc grades with zinc as the largest alloying element use in the group. These alloys are the strongest and hardest commercial grades of aluminum. The strongest in this series is Alloy 7068, but 7075 is more commonly used at the present time.
Aluminum Alloy 7075
The most common of the 7000 series grades is grade 7075. It is an exceptionally high strength alloy. Actually, grade 7075 aluminum possesses greater strength than some types of mild steel.
Aluminum alloy 7075 possesses the highest level of strength among all of the common screw machine alloys. This alloy is an ideal replacement for 2014, 2017, and 2024 in many critical applications due to the exceptional stress corrosion resistance obtained in the T173 and T7351 tempers. The aircraft and ordnance industries also utilize Aluminum Alloy 7075 Plate due to its exceptional strength.
Aluminum Alloy 7068 – Ultra-Strength Aluminum
At about the turn of the century, the ordnance industry was asking for the development of a lightweight, ultra-high strength aluminum alloy that possessed corrosion resistance equal to or greater than that offered by 7075. As a result, an ultra-strength alloy referred to as 7068-T6511 was developed. This alloy possesses a yield strength of 99 KSI (683 MPa), which gives it the highest mechanical strength of all aluminum alloys commercially available. Its mechanical strength is 35% stronger than 7075 and 2.5 times stronger than 6061.
In fact, aluminum alloy 7068 possesses a mechanical strength greater than many steels. It has a yield strength close to that of pre-hardened stainless steels (HRC 26-32) in the 41XX and 400 series, but at only one-third of the weight. In terms of its strength-to-weight ratio and performance, it exceeds almost all existing engineering alloys. It delivers a 28% better strength-to-weight performance than 6Al-4V Grade 5 titanium and a 33% better performance than 7075.
Its limited availability and higher cost (which is as much as three to four times the cost 6061) has resulted in its limited use for the commercial applications.
Although 7068 was developed for ordinance purposes, it is currently being used or considered for use in other markets such as automotive, aerospace, recreational products, and medical devices – for instance, prosthetic limbs.
