What Is 7075-T651 Aluminum
7075-T651 is a high-strength aluminum alloy primarily alloyed with zinc, with smaller additions of magnesium, copper, and chromium. It is among the strongest aluminum alloys commercially available and is widely used where a high strength-to-weight ratio is critical. The T651 designation describes the temper condition, which combines solution heat treatment and artificial aging with stress relief by controlled stretching, giving the plate both high strength and excellent dimensional stability.
Understanding the T651 Temper
In the T651 designation, T6 indicates that the material has been solution heat treated and artificially aged to achieve high strength. The additional 51 indicates that the product has been stress relieved by a controlled stretching operation applied after heat treatment or cooling. This stretching removes a portion of the internal residual stress, so the plate resists distortion when material is removed during machining. The result is a product that holds its shape through precision sawing, milling, and thin-section cutting, which is particularly valuable for components that must meet tight tolerances.
Key Properties and Advantages
7075-T651 aluminum is recognized for exceptional strength-to-weight ratio and outstanding fatigue resistance, allowing it to maintain performance under high and repeated stress. It provides very high tensile and yield strength compared with most other aluminum alloys, making it suitable for load-bearing and weight-critical applications. Because of these properties, the alloy is extensively used in aerospace and aviation, and in demanding products such as rock-climbing equipment, bicycle components, and precision mechanical parts where strength and reliability are essential.
Precision Part Manufacturing
When supplied as plate, 7075-T651 can be cut with high-speed precision sawing while maintaining tight tolerances, often as close as ±0.005 inch in controlled conditions. The stress-relieved condition means that subsequent machining operations such as milling, drilling, and wire cutting do not cause the plate to bow or twist, which reduces scrap and rework. The material also machines well when sharp tools and appropriate cutting parameters are used, producing smooth surfaces and good edge quality for finished components.
High-Stress and Heavy-Load Applications
7075-T651 performs exceptionally well in high-stress and heavy-load environments. Its excellent fatigue strength and strong resistance to deformation make it suitable for applications that require a lightweight material capable of withstanding significant mechanical loads, such as aircraft fittings, structural brackets, molds, and tooling plates. Where a component must carry high loads over long service life without weight penalty, 7075-T651 is often the preferred choice.
Limitations and Selection Considerations
Two limitations should be considered during material selection. First, 7075-T651 has relatively poor corrosion resistance compared with many other aluminum alloys and usually requires protective surface treatment in outdoor or humid service. Second, the alloy is not well suited for welding; fusion welding is generally avoided because of cracking risk, and mechanical fastening or adhesive bonding is preferred. For applications that require welding or high corrosion resistance, alloys such as 6061-T6 or 5083 should be evaluated instead.
FAQ
Q1: What does the 51 in T651 mean?
The 51 indicates that the product has been stress relieved by controlled stretching after solution heat treatment and aging. This reduces residual stress and improves dimensional stability during machining compared with a basic T6 temper.
Q2: Is 7075-T651 weldable?
Welding of 7075 is difficult and prone to cracking because of the alloy's composition, so it is generally avoided. Mechanical fastening, riveting, or adhesive bonding is recommended for joining 7075-T651 components.
Q3: Does 7075-T651 require surface protection?
In most outdoor or humid environments, yes. Anodizing, chromate conversion coating, painting, or powder coating is recommended because 7075 has lower corrosion resistance than 6xxx series alloys.
Q4: What is the typical strength of 7075-T651 plate?
7075-T651 plate typically provides tensile strength in the range of 510-570 MPa depending on thickness, with yield strength around 430-500 MPa. Exact values should be confirmed against the applicable standard and mill certificate.
Q5: Can 7075-T651 be machined to tight tolerances?
Yes. The stress-relieved condition is specifically designed for precision machining, and the plate can be sawed and milled with minimal distortion when proper fixturing and sharp tooling are used.