The 7xxx or 7000 wrought aluminum series features Zinc (Zn) as the primary alloying element. And this series has higher mechanical strength than all groups in the Aluminum Association Inc designation. Most of the 7000 series members are the toughest commercial-grade aluminum alloys.

Figure 1 – Aluminum Grade 7xxx Series Alloys

Aluminum 7xxx Alloy Characteristics

Being sensitive to the alloying contents, crafting alloys of this group is complex. Solution treatment, aging, and heat treatment are directly involved in its manufacturing.

Some of the key features of the grade 7000 aluminum alloys are –

• Very high mechanical strength
• Ultimate tensile strength of 32ksi to 88ksi
• Heat treatable for strengthening
• Sufficient fracture toughness
• Mostly non-weldable
• Excellent fatigue properties
• Considerably high weight-to-strength ratio
• Satisfying corrosion resistance
• High ductility and formability

Yield strength can be increased by 3-5 times using solution treatment followed by natural/artificial aging. Moreover, Keeping the total alloying content below 8% ensures good formability and weldability. However, the ductility of these high-strength alloys declines with the heat treatment process. Minor impurities in compositions control the hardening and corrosiveness during the treatment.

Common Aluminum Grade 7xxx Alloys

The aluminum-zinc system also requires Magnesium (Mg) for specific properties. So, the functioning system is more like Al-Zn-Mg for the 7000 series. Mechanical properties tend to change considerably with slight variations in the alloying elements.

Widely used aluminum grade 7000 series alloys in the industry are –

• Grade 7001 (6.8% – 8.0% Zn, 2.6% – 3.4% Mg)
• Grade 7005 (4.0% – 5.0% Zn, 1.0% – 1.8% Mg)
• Grade 7039 (3.5% – 4.5% Zn, 2.3% – 3.3% Mg)
• Grade 7072 (0.8% – 1.3% Zn, Max 0.10% Mg)
• Grade 7075 (5.1% – 6.1% Zn, 2.1% – 2.9% Mg)
• Grade 7178 (6.7% – 7.3% Zn, 2.4% – 3.1% Mg)

Zinc addition can range between 0.8% and 12.0% for the alloys. And the Mg content should remain within 3.5%. But having more than 8% alloys in the composition may alter some desired properties.

Additional minor impurities are also important for finely-grained structures during treatment. Copper (Cu), Chromium (Cr), Manganese (Mn), and Zirconium (Zr) are minor impurities for grade 7xxx alloys.

Applications for Aluminum 7xxx Series Alloys

Superior mechanical strength makes 7xxx alloys suitable for heavy commercial applications. Extrusions, plates, sheets, and forging are this series’s most commonly used forms. Additional forms include bar, coil, pipe, strip, foil, tube, ring, and wire.

For more complex parts, die casting Aluminum metals could be a good alternative.

Aerospace

The 7000 series is the most advantageous commercial aluminum for aircraft. Lightweight yet high strength is one of the prerequisites of the aerospace industry. And the majority of widely used alloys from the group fit the requirements.

Welding

The weldability exclusively depends on the total alloying contents in the composition. Still, these alloys are spot weldable with filler materials but not fusion weldable. However, they can be welded using the Friction Stir Welding process. Alloys like 7005 deliver suitable welding with predominant 5xxx filler alloys.

Hydraulics

High-performance applications also use some high-strength alloys. Extremely stressing equipment like hydraulic press and similar parts often feature the series. Many competitive sports gears are also manufactured using these alloys.

Mobiles

The smartphone industry is the latest addition to the 7000 alloys applicability. The exterior made of Al-Zn-Cu can provide further ruggedness and longevity to smartphones. Even Apple introduced the metal alloys to its iPhone 6S, released in 2015.

Which Aluminum Alloy is Best for Your Project?

Not sure which aluminum alloys would be best for your project? Feel free to contact us for assistance. We are experts in aluminum die casting and CNC machining manufacturing. Moreover, we can also help you with friction stir welding of wrought alloys like the 7xxx series which is difficult to weld under normal conditions.