Aluminium is the third most common element on Earth. It is mined as stuff called bauxite. Australia produces 33% of the world’s supply of the pure metal. Pure aluminium (called Aluminum in the US) is very soft and has little strength. It is used for pots and pans, as an outer skin for bitter fizzy drinks and lots of other things that are extruded. It is far too weak for use as a mast.
The metal we use for a mast is an alloy. An alloy is a mixture of two or more elements, eg. Brass is a mixture of copper and zinc, bronze is copper and tin. Steel alloys are very complex, eg, High Speed Steel (lathe tools, drills and cutters) contain iron, carbon, chromium, cobalt, tungsten, vanadium and a few other special elements. The aluminium for “Mast” alloys for our use may contain: silicon, magnesium, copper, iron, zinc and or a few other special elements to produce specific physical properties. Most aluminium alloys are known by an Alfa Numerical name, i.e. a number that may also include one or more letters. This number is a code that designates the alloy, the method of producing it and how hard it is. Hardness in aluminium alloys relates closely to strength and is known as Temper.
Basic temper is designated by the letters and subdivisions of letters and numbers. Eg:
-O Annealed, recrystallized
-H , H is always followed by two or more digits. The first indicates the specific combination of basic operations, eg.
-H1 Strain-hardened only
-H2 Strain-hardened and then partially annealed
-H3 Strain-hardened and them stabilized
The second number following (H1, H2, and H3) indicates the final degree of strain-hardening. The numeral “8” indicates a final degree of strain-hardening equivalent to that resulting from aprox. 75% reduction of area. Tempers range from “0” to “8”. The softest is 0, the hardest is 8. If the ultimate strength is halfway between these numbers (4), it is known as “half hard”. Some tempers are given a three digit number. The third digit indicates a variation of the two digit number. The minimum ultimate strength of a three digit type is close to that of a two digit type of alloy.
The letter “T” denotes that the alloy has been heat-treated to produce stable tempers with or without strain-hardening.
Alloys designated “T5” are artificially aged only: Applies to products which are artificially aged after an elevated-temperature rapid-cool fabrication process, such as casting or extrusion, to improve mechanical properties or dimensional stability, or both.

T6 alloys are solution heat-treated and then artificially aged : Applies to products which are not cold worked after solution heat-treatment, or in which the effect of cold work in flattening or straightening may not be recognized in applicable specifications.

T8 alloys are solution heat-treated, cold worked and then artificially aged: Applies to products which are cold worked to improve strength, or in which the effect of cold work in flattening or straightening is recognized in applicable specifications. (ref. “Machinery’s Handbook” edition 24, page 529)
The table at the bottom of the post may explain it clearer for you. (Ref, “Machinery’s Handbook” edition 24, page 538)

The specific characteristics of the alloys are arranged into numerical groups.eg.
1000 series have high corrosion resistance
2000 series contain Copper and require heat-treatment for optimum properties
3000 series contain Manganese and are generally non heat-treatable
4000 series contain silicon, lowers the melting point.
5000 series contain Magnesium, increases the strength of the alloy
6000 series contains silicon and magnesium. These added elements form magnesium silicide which makes the alloy able to be heat-treated. The major alloy in this series is 6061 being one of the most versatile of the heat-treatable alloys.
7000 series contains zinc and other elements. A notable member of this group is 7075 which is among the highest strength aluminium alloys available and is used for air-frame structures and highly stressed parts.

The following table is from Machinery’s Handbook edition 24, page 538

Alloy and Temper ..Ultimate Strength.............Yield Point
6063-0...................... 13 .............................. 7
6063-T1 ................... 22 .............................. 13
6063-T4 ................... 25 .............................. 13
6063-T5 ................... 27 .............................. 21
6063-T6 .................. 35 .............................. 31
6063-T83 ..................37 .............................. 35
6063-T831 ................ 30 .............................. 27
6063-T832 ................ 42 .............................. 39

The Ultimate Strength and Yield Point are given in "KPS".
I am not sure what “KPS” means. I think it is the old (?) unit used in the USA and means Kips Per Square Inch. A Kip is 1000 pounds (454.5kg)
Note: For all calculations, it is far better to use the Yield Point as the actual strength of the material. Yield Point is the point reached when deformation occurs, i.e., it bends or stretches beyond the point where it will no longer return to the original shape (or size) if the stress (load) is removed.

Kody

Thank you Paul, thats one of the greatest compliments I have ever had.
Kody

Hi All and particularly gizmo,
Just been perusing my "Smart Aluminium Product Catalogue" and have discovered something really neat. Scaffold tube is not the only tube they make that is Alloy/Temper 6061 T6.
Scaffold Tube has an O.D. of 48.41mm, wall thickness of 4.47mm and a Mass of 1.67kg/m.
They also list an extruded tube with Alloy/Temper 6061 T6 that has an O.D. of 63.5mm O.D., wall thickness 6.00mm, mass 2.93kg/m and therefore I.D. 51.5mm, therefore spacer sleeve thickness (nylon, abs plastic, kevlar??) 1.545mm between tubes.

This means that in Australia without importing material, we can produce a 5m mast in two sections with a 500mm overlap half way in high grade aluminium that will weigh approximately 12.4kg, given the bottom section is 2.5m long, which is a 4.05kg sacrifice for the convenience of a two piece mast.

Damn Cisco, you are a clever dicky for finding that out. You should get a medal for that. Stay tuned, more good stuff coming.

Adios Amigos, Cisco.

I was thinking that set up would be lighter stronger and simpler than the multi tube masts I have seen. I haven't weighed one but they seem to be very heavy.

If these T6 tubes were used for the bottom half of the mast and the lighter 1.5mm sections for the upper half, would we then be approaching the desired result?

The best aluminium mast I have seen is the system used on the Seagull yachts. Unfortunately that material is not available in Aus.

A buying collective to import a bulk amount of those tubes would be a good idea and something I would be in for. Any takers??

Cheers Cisco.

Thanks Phil, will do. I don't yet fully understand the grading specs ie T6 -T81 etc but will study and learn what I can.

Cheers Cisco

So does this mean we need some T9
As a quick guide for landyacht tubes this is the rules I work by.
T5 is what they BEND to make roobars , T6 is tough and usually in the 3-5mm wall thickness,and our beloved T8 range is in the 1.2-2mm range usually 1.5 or 1.6mm.
I get the sense that we are drifting slowly back into the dark age. you cant even buy a good axe these day and that would probably be the oldest tool of all

I came across a company in melb tht made composite tubes for acid and chemical pipes but they were only a good surface on the inside OR the outside. cost was around $20pm. Windrush in perth make tubes for yachts and dinghies but the last time I enquired was when I was building my schooner and had a budget of $0 it would be worth the email to see what they can make.
i have had the feeling for a year now that cl 5 will have to have a good think about the construction rules as some materials become unavailable.
Its not just in Australia.
The new FISLY PROMO rules specify an aluminium section that is only available from French manufacturers and requires all the manufacturers to get together to do a bulk order for the mill to make a run of the stuff.
. The brazilians get it from the Argentinians,who get it from the french , the Chileans( My favourite landyachting nation) has to virtually beg to get the drill cuttings from a mast.
Mabe we do have to have a big think about it

got a reply for windrush yet??

Windrush= 93141317 speak to Brett.

i guess my interest is i used to work for Windrush. Blowing my knee out windsurfing put a quick end to that. I used to do a lot of work with masts and booms etc, and generally working with prepreg.
And yes landsailing may be a distinct possibility in the future if my knee doesnt recover enough.
I nearly bought a blowkart some time back but the distance to travel to baldivis is a slight hurdle. would be nice if we had bigger tides and could run on the beach like i've seen down at sommers in victoria, coz i live just near sorrento beach.

Windrush pump out some of the best CF tube around. Their Moth masts are world renowned as the best. They do the highest performance composite work in the state to excellent standards. I'd have no probs sending my own money their way.