Aluminum Alloy 7075 belongs to the 7xxx series of metals, establishing it as one of the highest-strength aluminum materials available commercially. This alloy is primarily composed of aluminum, zinc, magnesium, and copper. Because of its outstanding mechanical performance and strength-to-weight ratio, 7075 earned the enduring nickname “aircraft aluminum.” Its remarkable strength is engineered through its unique chemical makeup and a precise thermal process.
Specific Mechanical Properties of 7075
The strength of 7075 aluminum is most commonly measured in its heat-treated condition, referred to as the T6 temper, which provides maximum static strength. This temper yields an Ultimate Tensile Strength (UTS) that typically reaches 572 megapascals (MPa), or 83,000 pounds per square inch (psi). This metric represents the maximum stress the material can endure before it fails completely.
Equally important is the Yield Strength (YS), which defines the point at which the material begins to deform permanently. For 7075-T6, the typical yield strength is around 503 MPa, or 73,000 psi.
The stiffness of the material is characterized by its modulus of elasticity, also known as Young’s Modulus, which is approximately 71.7 GPa (10,400 ksi). This measurement indicates the material’s resistance to elastic deformation under stress. The alloy also exhibits a high degree of surface hardness, with a typical Brinell hardness rating of 150 HB for the T6 temper.
The Influence of Temper and Alloying Elements
The extraordinary strength of 7075 is directly attributable to its alloying elements and the subsequent heat treatment process known as precipitation hardening. Zinc, present at approximately 5.6–6.1% by weight, is the primary strengthening agent, working in concert with magnesium and copper. The combination of zinc and magnesium forms minute precipitates that lock up the aluminum’s crystal structure.
During the precipitation hardening process, the alloy is subjected to a solution heat treatment, followed by quenching and an artificial aging cycle. This aging process encourages the formation of extremely fine particles, most notably the eta prime phase, a compound of magnesium and zinc (MgZn2). These precipitates impede the movement of dislocations within the metal’s grain structure, which is the mechanism that causes material deformation, dramatically increasing the alloy’s strength and hardness.
Different heat treatments, or tempers, are employed to tailor the final mechanical properties for specific needs. The T6 temper uses a single-stage aging process to achieve the peak of this precipitation hardening, resulting in maximum strength. A different temper, such as T73, uses a two-step “over-aging” process where the material is aged beyond its peak strength.
This intentional reduction in strength allows the precipitates to grow larger and redistribute, which significantly improves the material’s resistance to stress corrosion cracking (SCC). Engineers must select the temper that best balances the need for ultimate strength (T6) against the requirement for resistance to environmental degradation (T73).
Comparative Strength and Practical Limitations
The strength of 7075-T6 is best understood when compared to the common structural workhorse, 6061-T6 aluminum. In terms of ultimate tensile strength, 7075-T6 (up to 572 MPa) is nearly double the typical 310 MPa found in 6061-T6. Similarly, the yield strength of 7075-T6 is also roughly double, making it a distinctly superior choice for high-load applications.
Despite its high strength, 7075 has practical limitations that prevent its universal use. The high alloying content, particularly copper, makes the alloy highly susceptible to a loss of strength when welded. Fusion welding typically results in a weak, brittle joint, meaning that 7075 components must almost always be joined mechanically with fasteners.
The alloy also presents a higher susceptibility to stress corrosion cracking, particularly in the maximum-strength T6 temper. This vulnerability requires the use of protective coatings or the selection of the slightly weaker T73 temper when the material will be exposed to corrosive environments. Furthermore, the material’s higher cost compared to alloys like 6061 limits its use to applications where its strength-to-weight ratio is indispensable.
Key Applications Requiring High Strength
The superior strength-to-weight properties of 7075 aluminum make it the preferred material for performance-driven industries. Its primary use remains in aerospace, where it is utilized for highly stressed airframe components, including wing spars, fuselage bulkheads, and landing gear parts. The ability to withstand extreme forces while keeping aircraft weight low is paramount in this sector.
Beyond aviation, 7075 is frequently specified for military and defense equipment, such as missile components and structural parts in armored vehicles. In the sporting goods market, its strength is leveraged for high-performance cycling components, high-end rock climbing equipment, and ATV sprockets. The alloy is also used in the creation of durable tooling, molds, and machine parts that require high resistance to wear and deformation.