Don't get it

admin

I don't get it.  How the heck are you supposed to figure out the type of metal you're working on.  I need to tig some aluminum and as I'm looking I'm trying to figure out if it's 6061 or something else.  What is the secret to this stuff?  Some magic black book I can only get at www.sendallyourmoneytofranz.com or something?
Reply:YUP, and as soon as you get that site set up let me know cause I sure don't figure Social Insecurity's gonna make me rich.Steel can be enough of a chalenge to figure out some days, and you want aluminum too.  Worse than that, you want the answers on the week OlPilot, our only metalurgist, is off duty.Yer in a heap of trouble son.Appreciation Gains You Recognition-
Reply:LOL, not only am I in trouble, but I'm even behind in reading the thread on the progress with the vise.
Reply:I'm back!  At the risk of oversimplifying things, most AL alloys are weldable.  The biggest exceptions are the high-strength aircraft grade alloys 2XXX and 7XXX, typically 2024 and 7075, which contain copper and zinc respectively.  The kindest thing AWS will say about them is that "joining is difficult" (Read "impossible" for the average welder.)   Yes, I've Tig welded scrap sections together just for grins, but they invariably crack afterwards.Electrical conductivity testers are the fastest way to determine an AL alloy.  They give a readout based upon the International Annealed Copper Scale (IACS).  Most good non-destructive inspection shops will have one if they deal with much aluminum.  The other way to test is chemical spot testing, but it's involved.   And you won't find much of the stuff needed in your medicine cabinet or local drugstore.The most accurate  spot test for copper requires an involved procedure using a witch's assortment of sodium hydroxide, nitric acid, citric acid, ammonium hydroxide and sodium diethyldithiocarbamate.  I won't go into it here.A less sensitive, but easier test for copper presence is to place one drop of 10M sodium hydroxide (80 g in 200 ml of water) on the surface for 5 min.  Wash off and dry.  The spot will be green or black if the AL alloy contains any appreciable amount of copper.  Similarly, to test for zinc, you'll need hydrochloric acid, cobaltus sulfate and ammonium mercuric thiocyanate. Again, I won't go into this involved procedure  unless someone requests it in a later posting.Similar to the less sensitive test for copper, the less sensitive test for zinc is to to place one drop of cadmium chloride solution (3 g cadmium chloride and 3 g sodium chloride dissolve in concentrated hydrochloric acid then diluted to 60 ml) for two minutes.  If a dark spot develops, it indicates zinc in the alloy, probably in excess of 2%.There are other chemical spot tests for the presence of silicon, manganese, magnesium, nickel and chromium in aluminum alloys, but I won't detail them here.   Copper and zinc are the worst show-stoppers in obtaining acceptable aluminium welds.I think the IACS conductivity checker is the best bet if you don't want to become a chemist.  Also, it will lead you quickly to the proper filler metal selection.
Reply:Originally posted by OlPilot At the risk of oversimplifying things...
Reply:So-How much jack for a  conductivity tester?  Hope it won't set me back as much as that hundred grand water laser...
Reply:bomberz1qr20, when I mentioned the risk of oversimplifying, I wasn't referring to the   chemical testing which is obviously quite involved, I was talking about lumping all 2XXX and 7XXX aluminum alloys into the non-weldable categories.  There are exceptions to many rules.  Accordingly, there are a few alloys in the 2XXX and 7XXX series that are quite weldable.  2219, which is used extensively for jet engine nose cowl lip skins due to good crack resistance from anti-ice air temperature cycling, Tig welds nicely with 2319 filler.   7005 and 7039 have less than .1% copper and can be Tig welded readily with high magnesium fillers such as 5180, 5183, 5356 and 5556.  While the 70 series contain zinc as the primary alloying element, they also contain copper.  It's not really a question of just heat-treating the 7XXX alloys to make good welds.  As the copper content increases, the weldability goes down.  You can weld 7075 or 7178 and heat treat it afterward and generally it will still crack due to the high copper levels.5180 is the best filler for 7005.  After heat treating, it provides high weld mechanical properties.  The other 5XXX fillers don't respond as well to heat treating.pjt, as far as conductivity testers go, they are basically eddy current testers.  I haven't bought one in years and the new ones have added lots of bells and whistles.  I think they are around $1000, maybe less.  Hocking makes some good ones.  Try their site below or do a  Google search for other manufacturers.http://www.hocking.com/as_3000.htm
Reply:Originally posted by OlPilot bomberz1qr20, when I mentioned the risk of oversimplifying, I wasn't referring to the   chemical testing which is obviously quite involved, I was talking about lumping all 2XXX and 7XXX aluminum alloys into the non-weldable categories.
Reply:With aluminum, if you assume it is 6061, you will be right about 85% of the time, and most of the times you are wrong it wont make much difference- it will either weld just like 6061, or it wont weld at all.But most aluminum has the alloy printed right on it. All new aluminum, that is.I am assuming you are trying to fix some oddball thing that is already built- most likely its 6061. AC, High Frequency continous, make a ball on the tungsten, and burn yourself- its pretty simple.
Reply:Ries, I doubt that 85% is 6061, simply because it is a heat treatable alloy, occasionally used on aircraft, and costs more.  I think most of what you find is in the 3XXX or 5XXX series, unless you are involved with aircraft.  But you are right about the weldability being about the same.  4043 filler generally works well on all three.
Reply:For everyone's edification, I'll attempt to attach two pages in .pdf format concerning the weldability of wrought and cast aluminum alloys.  These were extracted from the recent successor to Military Handbook 5, which is "Metallic Material and Properties Development and Standardization" published by the FAA for military and commercial aircraft design and repair.  The document is free to the public and I believe it can be downloaded, but it's 1728 pages, so you'll need Roadrunner, DSL or a month of spare time. Attached Imagespages from mmpds-01.pdf (86.7 KB, 42 views)