Aluminium Spar Welding (Again)

savageseadog

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Given that I will be doing some, anyone know what grade of (TIG) rod to use. There's hundreds if not thousands of alloys.
 

cliff

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Depends on the mast material - there are many different alloys and nearly as many filler metals.

You really need to find out which alloy your spar is made from - perhaps the original manufacturer can advise you. Once you know the base material alloy, selection of a suitable filler is straight forward.

Aluminium alloys fall into 8 catagories each with numerous alloys

1XXX Aluminium of 99% minimum purity
2XXX Aluminium-copper alloys
3XXX Aluminium-manganese alloys
4XXX Aluminium-silicon alloys
5XXX Aluminium-magnesium alloys
6XXX Aluminium-magnesium-silicon alloys
7XXX Aluminium-zinc-magnesium alloys
8XXX Miscellaneous alloys, e.g. aluminium-lithium alloys

I would suspect the spar is one of the 5XXX or 6XXX series. These are weldable with care. I assume you intend to use AC GTAW (TIG) and not DC.

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cliff

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Yep - had a wee chuckle to myself - anyway to answer "SSD"'s query, there are really only 4 common fillers used commercially, these are:

“Type” 1070 is highly resistant to chemical attack and weathering. It is a relatively soft alloy that is very formable and it is used extensively in thin-gauge and foil products. It has good welding characteristics. One characteristic feature of the alloy is the bright finish obtained by anodising. Non-heat treatable.

“Type” 4043 is one of the most widely used welding alloys. It is used for welding AlMgSi types and AlSi alloys with up to 7% silicon. Not recommended for anodising. Non-heat treatable.

“Type” 5356 is possibly the most widely used welding alloy and can be classified as a general-purpose type filler alloy. “Type” 5356 is typically chosen because of its relatively high shear strength. WARNING - A 5XXX alloy base material, welded with “type” 5356, with a weld pool chemistry greater than 3% Mg and service temperatures in excess of 65°C, will be susceptible to stress corrosion cracking. The alloy is non-heat treatable.

“Type” 5556 is a bare welding rod suitable for welding aluminium alloys with up to approx. 5% Mg that are not age hardenable and alloys where a higher tensile strength is required. The corrosion resistance in a marine atmosphere is very good.

There are a "few" others but not so commonly used.

Without knowing the base material it is not really possible to select the most appropriate filler although "type" 4043 or 5556 might do the business however the "quality" of the weld would be more by luck than by design.
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savageseadog

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That's great thanks. If I find out any more myself I'll let everyone know. I did call a couple of sparmakers who didn't really want to play ball.
 

cliff

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Atomic Emission Spectrophotometery or "classical" wet methods - none of which are DIY nor cheap.
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