On Mon, 10 Feb 2014 20:11:37 -0600, Richard
wrote:

On 2/10/2014 7:40 PM, John B. wrote:


My guess is strength after welding and extrudability. 6061 will
naturally reharden after welding, though not to its pre-welded T6
condition. 5052 will remain more or less annealed near any welds.

Extrudability:
http://www.substech.com/dokuwiki/dok... uminum_alloys


Perhaps. There is usually a certain amount of welding on masts and
spars, if only to attach the end fittings, and I suspect that it is
unlikely that every shop has a forty or fifty foot heat treating oven
;-)

None of my spars have ever been welded.
The spreader fittings, mast head crane. etc were always bolted.

Although there are some specialty masts that are tapered and thus welded.


Not really "specialty". Quite a few masts on, say 40+ foot boats are
tapered by cutting and welding. My last boat, for example. 42 ft. deck
stepped with about 25% of the top tapered. Partially I think to make
more room for the jib furler. The spreader brackets were also welded
to the mast, as was a bracket for the steaming light.

No, I suspect the reason for 6061-T6 is because the spars are almost
always extruded.

And the stable temper of T6...

And the difference in tensile strength!
5052 yields at 28k
6061 yields at 40k



GENERAL ALUMINUM INFORMATION
1100
This grade is commercially pure aluminum. It is soft and ductile and has
excellent workability. It is ideal for applications involving intricate
forming because it work hardens more slowly than other alloys. It is the
most weldable of aluminum alloys, by any method. It is non
heat-treatable. It has excellent resistance to corrosion and is widely
used in the chemical and food processing industries. It responds well to
decorative finishes which make it suitable for giftware.

2011
This is the most free-machining of the common aluminum alloys. It also
has excellent mechanical properties. Thus, it is widely used for
automatic screw machine products in parts requiring extensive machining.

2014 & 2017
The 2017 alloy combines excellent machinability and high strength with
the result that it is one of the most widely used alloys for automatic
screw machine work. It is a tough, ductile alloy suitable for heavy-duty
structural parts. Its strength is slightly less than that of 2014.

2024
This is one of the best known of the high strength aluminum alloys. With
its high strength and excellent fatigue resistance, it is used to
advantage on structures and parts where good strength-to-weight ratio is
desired. It is readily machined to a high finish. It is readily formed
in the annealed condition and may be subsequently heat treated. Arc or
gas welding is generally not recommended, although this alloy may be
spot, seam or flash welded. Since corrosion resistance is relatively
low, 2024 is commonly used with an anodized finish or in clad form
(“Alclad”) with a thin surface layer of high purity aluminum.
Applications: aircraft structural components, aircraft fittings,
hardware, truck wheels and parts for the transportation industry.

3003
This is the most widely used of all aluminum alloys. It is essentially
commercially pure aluminum with the addition of manganese which
increases the strength some 20% over the 1100 grade. Thus, it has all
the excellent characteristics of 1100 with higher strength. It has
excellent corrosion resistance. It has excellent workability and it may
be deep drawn or spun, welded or brazed. It is non heat treatable.
Applications: cooking utensils, decorative trim, awnings, siding,
storage tanks, chemical equipment.

5005
This alloy is generally considered to be an improved version of 3003. It
has the same general mechanical properties as 3003 but appears to stand
up better in actual service. It is readily workable. It can be deep
drawn or spun, welded or brazed. It has excellent corrosion resistance.
It is non heat-treatable. It is well suited for anodizing and has less
tendency to streak or discolor. Applications same as 3003.

5052
This is the highest strength alloy of the more common non heat-treatable
grades. Fatigue strength is higher than most aluminum alloys.In addition
this grade has particularly good resistance to marine atmosphere and
salt water corrosion. It has excellent workability. It may be drawn or
formed into intricate shapes and its slightly greater strength in the
annealed condition minimizes tearing that occurs in 1100 and 3003.
Applications: Used in a wide variety of applications from aircraft
components to home appliances, marine and transportation industry parts,
heavy duty cooking utensils and equipment for bulk processing of food.

5083 & 5086
For many years there has been a need for aluminum sheet and plate alloys
that would offer, for high strength welded applications, several
distinct benefits over such alloys as 5052 and 6061. Some of the
benefits fabricators have been seeking are greater design efficiency,
better welding characteristics, good forming properties, excellent
resistance to corrosion and the same economy as in other non
heat-treatable alloys. Metallurgical research has developed 5083 and
5086 as superior weldable alloys which fill these needs. Both alloys
have virtually the same characteristics with 5083 having slightly higher
mechanical properties due to the increased manganese content over 5086.
Applications: unfired pressure vessels, missile containers, heavy-duty
truck and trailer assemblies, boat hulls and superstructures.

6061
This is the least expensive and most versatile of the heat-treatable
aluminum alloys. It has most of the good qualities of aluminum. It
offers a range of good mechanical properties and good corrosion
resistance. It can be fabricated by most of the commonly used
techniques. In the annealed condition it has good workability. In the T4
condition fairly severe forming operations may be accomplished. The full
T6 properties may be obtained by artificial aging. It is welded by all
methods and can be furnace brazed. It is available in the clad form
(“Alclad”) with a thin surface layer of high purity aluminum to improve
both appearance and corrosion resistance. Applications: This grade is
used for a wide variety of products and applications from truck bodies
and frames to screw machine parts and structural components. 6061 is
used where appearance and better corrosion resistance with good strength
are required.

6063
This grade is commonly referred to as the architectural alloy. It was
developed as an extrusion alloy with relatively high tensile properties,
excellent finishing characteristics and a high degree of resistance to
corrosion. This alloy is most often found in various interior and
exterior architectural applications, such as windows, doors, store
fronts and assorted trim items. It is the alloy best suited for
anodizing applications - either plain or in a variety of colors.

7075
This is one of the highest strength aluminum alloys available. Its
strength-to weight ratio is excellent and it is ideally used for highly
stressed parts. It may be formed in the annealed condition and
subsequently heat treated. Spot or flash welding can be used, although
arc and gas welding are not recommended. It is available in the clad
(“Alclad”) form to improve the corrosion resistance with the over-all
high strength being only moderately affected. Applications: Used where
highest strength is needed.

And

ALUMINUM TEMPER DESIGNATIONS
Temper designations of wrought aluminum alloys consist of suffixes to
the numeric alloy designations. For example, in 3003-H14, 3003 denotes
the alloy and “H14” denotes the temper, or degree of hardness. The
temper designation also reveals the method by which the hardness was
obtained. Temper designations differ between non heat-treatable alloys
and heat-treatable alloys. and their meanings are given below:

Non Heat-Treatable Alloys

The letter “H” is always followed by 2 or 3 digits. The first digit
indicates the particular method used to obtain the temper. as follows:

— Hl means strain hardened only.

— H2 means strain hardened, then partially annealed.

— H3 means strain hardened, then stabilized.

The temper is indicated by the second digit as follows:

2 1/4 hard

4 I/2 hard

6 3/4 hard

8 full hard

9 extra hard

Added digits indicate modification of standard practice.

Heat-Treatable Alloys

-F As fabricated

-O Annealed

-T Heat treated

The letter “T” is always followed by one or more digits. These digits
indicate the method used to produce the stable tempers, as follows:

-T3 Solution heat treated, then cold worked.

-T351 Solution heat treated, stress-relieved stretched, then cold
worked.

-T36 Solution heat treated, then cold worked (controlled).

-T4 Solution heat treated, then naturally aged.

-T451 Solution heat treated, then stress relieved stretched.

-T5 Artificially aged only.

-T6 Solution heat treated, then artificially aged.

-T61 Solution heat treated (boiling water quench), then
artificially aged.

-T651 Solution heat treated, stress-relieved stretched, then
artificially aged (precipitation heat treatment).

-T652 Solution heat treated, stress relieved by compression. then
artificially aged.

-T7 Solution heat treated, then stabilized.

-T8 Solution heat treated, cold worked, then artificially aged.

-T81 Solution heat treated, cold worked (controlled), then
artificially aged.

-T851 Solution heat treated, cold worked, stress-relieved
stretched, then artificially aged.

-T9 Solution heat treated, artificially aged, then cold worked.

-T10 Artificially aged, then cold worked.

Added digits indicate modification of standard practice.
--
Cheers,

John B.