• Dimensional Stability - Exceptional in the stress relieved (T2) condition
• Strength & Ductility- Ultimate strength 35 kpsi min., elongation 9% min.
• Shock Resistance - Charpy impact rating 10 to 12 foot pounds
• Fatigue Strength - 10 kpsi in any heat treat condition
• Corrosion Resistance - Far superior to any other casting alloy
• Machinability - Machines 4 times faster than other aluminum alloys
• Appearance - Can be polished to a mirror like finish

The dimensional stability of aluminum castings is adversely affected by internal stresses. These stresses are due to differential cooling within a casting after pouring or during the quench after solution heat treatment. Generally, the faster the cooling rate the higher the stresses. Because these stresses are concentrated at the surface of a casting, when a surface is machined they become unbalanced and the casting distorts. However, since 535.0 alloy develops few stresses during cooling, the majority of castings in this alloy can be successfully machined in the as cast (F) condition.

For increased stability, 535.0 can be stress relieved (T2 condition) by heating to 775°F for 5 hours and cooled in still air. This removes all internal stresses without affecting other mechanical properties.

All aluminum alloys can be stress relieved in this manner. However, all aluminum silicon alloys such as 356.0 not only become stress free with this heat treatment but annealed and useless.

Strength and Ductility

The maximum mechanical properties are available in 535.0 immediately after casting (F condition). These properties are not affected by stress relieving (T2 condition) and remain the same for the life of the casting as this alloy is non aging.

Most alloy specifications require minimum tensile properties from standard .505Ø separately cast test bars and state that in the casting the average ultimate and yield values shall not be less than 75% and the average elongation value not less than 25% of these minimums. However, the results from 535.0-F separately cast test bars are much more representative of actual properties in the casting as shown in the chart below. (Chart is based on tests by Morris Bean & Company, Yellow Springs, Ohio, using 12" x 6" x 3/4" cast plates chilled at one end and risered at the opposite end.)

Shock Resistance

With a Charpy Impact Rating of 10 to 12 foot pounds, 535.0 is ideally suited for applications encountering high shock loads. It is often used in naval vessels (where bombs and torpedoes create high shock loads), aircraft landing gear, rocket launchers and light weight armored vehicles.

Fatigue Strength

The fatigue endurance limit of most aluminum casting alloys, including 535.0, is 10 kpsi. However, since most aluminum casting alloys have internal stresses, this value must be reduced (by the value of the internal stresses) when designing fatigue critical parts. Since 535.0-T2 has no internal stresses, the full value of 10 kpsi can be used for design purposes.

Corrosion Resistance

The corrosion resistance of 535.0 is the highest of any aluminum casting alloy. This is due to the almost complete absence of heavy metal contaminants, the primary cause of electrolytic corrosion. Also, the fairly high content of magnesium gives it protection from mild alkalis, salt spray, sea water and mild acids such as fruit juices. Even when exposed to these corrosive elements, 535.0 retains its original color and appearance.

For these reasons, 535.0 is an excellent choice for marine applications as well as exposed architectural applications. In fact, 535.0 castings anodized with the sulfuric acid process have better sea water corrosion resistance than chrome plated brass.

Machinability

Because 535.0 contains no silicon, cutting tool life is much greater than with the more common 300 series of aluminum casting alloys such as 356.0-T6. Cutting speeds are also much higher: up to 18 times faster than gray iron and 4 times faster than the 300 series alloys.

Also, the lack of internal stresses in 535.0 eliminates the need for intermediate stress relieving operations that is commonly required for other aluminum casting alloys when close tolerances must be held.

Appearance

535.0 maintains its appearance when exposed to weather or other corrosive conditions. It can be polished to a mirror like chrome white finish without the blue tint of aluminum alloys containing silicon or copper. Machining at high speed with carbide tools produces an excellent finish.

Clear anodizing produces a satin white finish suitable for dyeing even with pastel colors or optical black. For color anodizing, the T2 condition is recommended to eliminate white spots due to concentrations of magnesium.

Other Advantages

Not subject to stress rupture or stress corrosion failure, 535.0 is an excellent choice where castings are subjected to continuous loads at or near the yield strength.

535.0 castings may be welded by any of the inert gas, shielded arc methods using 5356 rod or 535.0.

Some Disadvantages

535.0 is slightly (about 10%) more expensive and slightly more difficult to cast than the more common aluminum casting alloys. However, these cost disadvantages are often offset by the elimination of heat treatment, easier straightening (when necessary) and easier finishing operations.

Because it contains no silicon, molten 535.0 is less fluid than the more common aluminum casting alloys. Large, extremely thin sections are thus more difficult to cast. Generally, wall thicknesses as low as .16" can be cast but it is best to consult with the foundry on designs with wall thicknesses in this range.