What Is 6061-T651
6061-T651 aluminum is a high-strength, heat-treatable Al-Mg-Si alloy known for excellent corrosion resistance and outstanding dimensional stability. Compared with standard 6061-T6, the T651 temper offers superior machinability and reduced distortion, making it ideal for precision-critical aerospace, marine, and structural applications. The alloy contains approximately 1.0 percent magnesium and 0.6 percent silicon.
What T651 Means
The T651 designation indicates that the alloy has been solution heat treated, artificially aged, and then stress relieved by controlled stretching. The stretching operation, typically 1 to 3 percent permanent elongation for plate, minimizes internal residual stresses introduced by quenching, which are the main cause of warping and distortion during machining.
Key Characteristics
6061-T651 provides high tensile and yield strength, similar to T6, but with significantly better dimensional stability. Machinability is excellent, better than T6 because of reduced internal stress. Weldability is good, and corrosion resistance is very good, including in marine environments. The plate typically carries a mill finish and is intended for functional rather than decorative purposes.
T6 versus T651
6061-T6 is solution heat treated and artificially aged, offering strong mechanical properties. 6061-T651 adds the stress-relief stretching step, giving significantly better dimensional stability and reduced warping during machining, typically at a slightly higher cost. The mechanical properties are essentially identical, with tensile strength about 290 to 310 MPa and yield about 241 to 276 MPa.
Applications
6061-T651 is used for aerospace wing spars, fuselage components, and structural frameworks; boat fittings, hardware, and propeller components; automotive brake pistons and hydraulic parts; and general engineering precision parts, tooling plates, heat sinks, fixtures, bicycle components, and connectors.
Standards and Supply
6061-T651 plate conforms to AMS QQ-A-250/11, AMS 4027, and ASTM B209. Plates are supplied with mill finish, and shear or laser cutting is available for standard thicknesses. The combination of certified composition and controlled processing makes it the default choice for machined components requiring accuracy, consistency, and long-term reliability.
Frequently Asked Questions
Q: What does T651 mean?
A: Solution heat treated, artificially aged, and stress relieved by stretching.
Q: How does T651 differ from T6?
A: T651 adds stress relief, improving dimensional stability during machining.
Q: What is the tensile strength of 6061-T651?
A: About 290 to 310 MPa.
Q: What applications use 6061-T651?
A: Aerospace, marine, automotive, tooling plates, and precision fixtures.
Q: What standards cover 6061-T651 plate?
A: AMS QQ-A-250/11, AMS 4027, and ASTM B209.
Q: Is T651 more expensive than T6?
A: Yes, slightly, because of the additional stretching operation.
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