What Is 6061-T651 Rolled Plate?
6061-T651 is a flat-rolled wrought aluminum product in the 6061 aluminum-magnesium-silicon alloy family. The T651 temper designation describes a specific processing route: solution heat treatment, stress relieving by controlled stretching, and artificial aging. The stretching step distinguishes T651 from the standard T6 temper; it removes residual stress so that the plate stays dimensionally stable when machined.
According to the Aluminum Association, flat-rolled aluminum products, including sheet and plate, represent the largest share of aluminum consumption in the United States, and rolled aluminum is more widely used than castings, extrusions, forgings, or bars. Rolled plate is produced on rolling mills that convert ingot into flat stock with uniform thickness and predictable mechanical properties.
Manufacturing Process
6061-T651 rolled plate is produced through a wrought rolling process followed by three controlled steps: solution heat treatment, stress relieving by stretching, and artificial aging. Solution heat treatment dissolves the alloying elements into a uniform solid solution; stretching relieves internal stress and improves flatness stability; artificial aging precipitates the Mg2Si phase that gives the alloy its strength. The result is a plate with higher strength and improved machinability compared with many other aluminum alloys.
Chemical Composition
As a 6061 alloy, the plate contains magnesium and silicon as the principal strengthening elements, with copper and chromium as controlled additions. Typical composition ranges include silicon about 0.4-0.8%, magnesium about 0.8-1.2%, copper about 0.15-0.4%, iron up to 0.7%, chromium 0.04-0.35%, zinc up to 0.25%, manganese up to 0.15%, and titanium up to 0.15%, with the balance aluminum. Exact limits follow the governing standard such as ASTM B209.
Physical and Mechanical Properties
The physical properties of 6061-T651 include a density of about 0.0975 lb/in3 (2.70 g/cm3), electrical conductivity of about 47% IACS, thermal conductivity around 1250 BTU-in/hr-ft2-F, and a melting range near 1140 F. These values make the plate attractive for weight-sensitive and heat-transfer applications.
Mechanical properties vary with thickness and test direction. Typical published ranges across tempers span a yield strength of roughly 8-39 ksi and a tensile strength of 16-45 ksi, with elongation of 12-25% and a Brinell hardness of 30-123. In the T6/T651 temper, typical yield strength is around 40 ksi and tensile strength around 45 ksi. Modulus of elasticity is approximately 10,000 ksi, and the machinability index is about 30%. Buyers should reference the governing standard edition for certified minimum values at the specific thickness.
6061-T651 Rolled Plate vs Cast Tool and Jig Plate
Cast tool and jig (CT and J) plate is made by a different route and excels in flatness and dimensional precision: typical thickness tolerance is plus or minus 0.005 in, and flatness deviation is very tight across the full range of thicknesses. Rolled 6061-T651 has looser flatness tolerances that vary with thickness, with deviations up to roughly 3/16 in for plate between 0.25 in and 3 in thick.
In mechanical terms, 6061-T651 offers significantly higher strength: typical yield strength of about 40 ksi versus about 18 ksi for cast tool and jig plate, with tensile strength around 45 ksi versus 41 ksi, and Brinell hardness around 95 versus 70. Cast tool and jig plate offers excellent machinability, superior anodizing quality, and minimal distortion during machining, while 6061-T651 rolled plate offers excellent welding performance and higher strength for structural applications.
Typical Applications
6061-T651 rolled plate is commonly used in marine applications such as boats and canoes, automotive bodies and structural components, scaffolding and transmission towers, furniture and architectural structures, and chemical equipment and industrial hardware. It is also a standard material for fixture tables, molds and machine bases where dimensional stability after stress relief is valuable.
Choosing Between the Two Materials
Select the 6061-T651 rolled plate when high strength, hardness, weldability, and structural performance are the priorities. Choose cast tool and jig plate when flatness, dimensional accuracy, and minimal machining distortion are critical, such as in precision jigs, fixtures and inspection tooling.
FAQ
Q: What does the T651 temper mean?
A: T651 means the plate was solution heat-treated, stress-relieved by controlled stretching, and artificially aged. The stretching step reduces residual stress for better dimensional stability during machining.
Q: What is the difference between T6 and T651?
A: Both are artificially aged to peak strength. T651 includes an additional stress-relieving stretch after solution heat treatment, which improves flatness stability and machined-part accuracy.
Q: Is 6061-T651 weldable?
A: Yes. 6061 welds reliably with standard TIG and MIG processes using 4043 or 5356 filler wire, and the joint can be re-aged toward T6 properties after welding when required.
Q: Can 6061-T651 be anodized?
A: Yes, the alloy anodizes well and produces an attractive, protective oxide finish, although cast tool and jig plate typically gives a superior anodized appearance for cosmetic parts.
Q: Which standard covers 6061 rolled plate?
A: ASTM B209 is the governing specification for aluminum sheet and plate in the US system; GB/T 3880 is the corresponding Chinese standard. Minimum mechanical values differ slightly between editions and thicknesses.
