6061 is a precipitation hardening aluminum alloy, containing magnesium and silicon as its major alloying elements. It has good mechanical properties and exhibits good weldability. It is one of the most common alloys of aluminum for general purpose use.
It is commonly available in pre-tempered grades such as, 6061-O (solutionized), 6061-T6 (solutionized and artificially aged), 6061-T651 (solutionized, stress-relieved stretched and artificially aged).
6061 has a density of 2.70 g/cm³ (0.0975 lb/in³).
The alloy composition of 6061 is:
Annealed 6061 (6061-O temper) has maximum tensile strength no more than 18,000 psi (125 MPa), and maximum yield strength no more than 8,000 psi (55 MPa). The material has elongation (stretch before ultimate failure) of 25-30 %.
T4 temper 6061 has an ultimate tensile strength of at least 30,000 psi (207 MPa) and yield strength of at least 16,000 psi (110 MPa). It has elongation of 16%.
T6 temper 6061 has an ultimate tensile strength of at least 42,000 psi (290 MPa) and yield strength of at least 35,000 psi (241 MPa). More typical values are 45,000 psi (310 MPa) and 40,000 psi (275 MPa),
In thicknesses of 0.250 inch (6.35 mm) or less, it has elongation of 8%
or more; in thicker sections, it has elongation of 10%. T651 temper has
similar mechanical properties. The famous Pioneer plaque was made of this particular alloy. A material data sheet  defines the fatigue limit under cyclic load as 14,000 psi.
6061 is highly weldable, for example using tungsten inert gas welding (TIG) or metal inert gas welding (MIG). Typically, after welding, the properties near the weld are those of 6061-0, a loss of strength of around 80%. The material can be
re-heat-treated to restore -T4 or -T6 temper for the whole piece. After
welding the material can naturally age and restore some of its strength
6061 is an alloy that is suitable for hot forging. The billet is heated through an induction furnace and forged using a closed die process. Automotive parts, ATV parts, and industrial parts
are just some of the uses as a forging.
Hydroforming (or hydramolding)
Is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which
makes use of the complex shapes possible by hydroforming to produce
stronger, lighter, and more rigid unibody structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminium tubes for bicycle frames.
Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die. To hydroform aluminum into a vehicle's frame rail, a hollow tube of aluminum is
placed inside a negative mold that has the shape of the desired end
result. High pressure hydraulic pistons then inject a fluid at very high
pressure inside the aluminum which causes it to expand until it matches
the mold. The hydroformed aluminum is then removed from the mold.
Hydroforming allows complex shapes with concavities to be formed, which would be difficult or impossible with standard solid die stamping. Hydroformed parts can often be made with a higher stiffness to weight
ratio and at a lower per unit cost than traditional stamped or stamped
and welded parts.
This process is based on the 1950s patent for hydramolding by Fred Leuthesser, Jr. and John Fox of the Schaible Company of Cincinnati, OH. It was originally used in producing kitchen spouts. This was done because in addition to the strengthening of the metal, hydramolding also
produced less "grainy" parts, allowing for easier metal finishing.
In sheet hydroforming there is Bladder forming (where there is a bladder that contains the liquid, no liquid contacts the sheet) and hydroforming where the fluid contacts the sheet (no bladder). A work
piece is placed on a draw ring (blank holder) over a male punch then a
hydraulic chamber surrounds the work piece and a relatively low initial
pressure seats the work piece against the punch. The punch then is
raised into the hydraulic chamber and pressure is increased to as high
as 15000 psi which forms the part around the punch. Then the pressure is
released and punch retracted and hydraulic chamber lifted and the
process is complete.
In tube hydroforming (THF) there are two major practices: high pressure and low pressure. With the high pressure process the tube is fully enclosed in a die prior to pressurization of the tube. In low
pressure the tube is slightly pressurized to a fixed volume during the
closing of the die (this used to be called the Variform process). In
tube hydroforming pressure is applied to the inside of a tube that is
held by dies with the desired cross sections and forms. When the dies
are closed, the tube ends are sealed by axial punches and the tube is
filled with hydraulic fluid. The internal pressure can go up to a few
thousands of bars and it causes the tube to calibrate against the dies.
The fluid is injected into the tube through one of the two axial
punches. Axial punches are movable and their action is required to
provide axial compression and to feed material towards the center of the
bulging tube. Transverse counterpunches may also be incorporated in the
forming die in order to form protrusions with small diameter/length
ratio. Transverse counterpunches may also be used to punch holes in the
work piece at the end of the forming process. Many industrial
applications of the process can be found, especially in the automotive
For large parts, explosive hydroforming can generate the forming pressure by simply exploding a charge above the part (complete with evacuated mold) which is immersed in a pool of water. The tooling can be
much cheaper than what would be required for any press-type process.
The hydroforming-into-a-mold process also works using only a shock wave
in air as the pressuring medium. Particularly when the explosives are
close to the workpiece, inertia effects make the result more complicated than forming by hydrostatic pressure alone.
Tools and punches can be interchanged for different part requirements.
One advantage of hydroforming is the savings on tools. For sheet metal only a draw ring and punch (metalworking) or male die is required. The bladder of the hydroform itself acts as the female die eliminating the need to fabricate a matching female die.
This allows for changes in material thickness to be made with usually no
necessary changes to the tool. However, dies must be highly polished
and in tube hydroforming a two-piece die is required to allow opening
Another advantage of hydroforming is that complex shapes can be made in one step. In sheet hydroforming (SHF) with the bladder acting as the female die almost limitless geometries can be produced. However, process
is limited by the very high closing force required in order to seal the
dies, especially for large panels and thick hard materials. Small
concave corner radii are difficult to be completely calibrated, i.e.
filled, because too large a pressure would be required. Limits of the
SHF process are due to risks of excessive thinning, fracture, wrinkling
and are strictly related to the material formability and to a proper
selection of process parameters (e.g. hydraulic pressure vs. time
curve). Tube hydroforming (THF) can produce many geometric options as
well, reducing the need for tube welding operations. Similar limitations
and risks can be listed as in SHF; however, the maximum closing force
is seldom a limiting factor in THF.
Hydroforming is capable of producing parts within tight tolerances including aircraft tolerances where a common tolerance for sheet metal parts is within thirty thousandths of an inch. Sheet metal hydroforming
also allows for a smoother finish as draw marks produced by the
traditional method of pressing a male and female die together are
When a blank is hydroformed the metal flows around the die rather than stretching, which produces less material thinning, and also reduces the rate of work hardening which helps eliminate the need for an
annealing process on some parts that might otherwise require further
Notable examples include: