What filler rod

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Ok im making a shock mount for my motorcyle and i need the strongest weld i can get.  Im using 1 5/8 " 6061 T6 aluminum tubing with 5/16" thick walls and the ends of the tubing are going into 3/8" plate on each end of the tube, all 6061 T6 aluminum.  Im going to use TIG.So my questions is to weld the tube into the 3/8 plate what filler rod is going to give me the strongest weld ? 4043 ? 5356 ? i do plan on heat treating after the shock mount is made ? thanks guys.I keep getting people telling me different things, so im looking for somebody who knows his stuff ?Last edited by Califmike33; 01-05-2011 at 11:40 PM.
Reply:Originally Posted by Califmike33Ok im making a shock mount for my motorcyle and i need the strongest weld i can get.  Im using 1 5/8 " 6061 T6 aluminum tubing with 5/16" thick walls and the ends of the tubing are going into 3/8" plate on each end of the tube, all 6061 T6 aluminum.  Im going to use TIG.So my questions is to weld the tube into the 3/8 plate what filler rod is going to give me the strongest weld ? 4043 ? 5356 ? i do plan on heat treating after the shock mount is made ? thanks guys.I keep getting people telling me different things, so im looking for somebody who knows his stuff ?
Reply:For 6061 aluminum, 4043 is the correct choice if the weldment will be heat treated.  5356 is a good choice to provide higher strength than 4043 if the weldment is not heat treated.  6061 is very susceptable to cracking if welded without filler.
Reply:+1 on what was said by pulser and Donald.Further info.  4043 or 5356 filler are both common and 'valid' fillers for welding on 6061 aluminum parent material.  They both have certain trade-offs though.If the final product will be anodized, then 5356 is usually specified, because 4043 will anodize to a soot gray and thus stand out like a sore thumb unless you were anodizing the entire piece to a soot gray color.    5356 will anodize to the same color as the 6061 (pretty much).5356 is a little bit 'stronger', but strength of aluminum weldments is almost always trickier than steel weldments.There are other trade-offs as well.Also keep in mind that the 'margin' between OK and FAIL is much-much-much narrower with aluminum than with steel.  On workmanship and design and real-world life.  The best laid schemes ... Gang oft agley ...
Reply:Exactly what pulser said.  4043 is more ductile, and will offer the strongest joint if it will be heat treated after welding.  5356 will anodize bright, and is a LITTLE stronger without heat treatment, BUT it is also more brittle.  With 6061 being a very tough alloy, the joints need a little give or you can get cracks, so I'd suggest 4043 as well.  However, 4043 will look like crap if it is anodized.Post weld heat treatment is a good idea.  6061 loses its heat treated strength around weld joints (7000 series alloys fare better from this).Oh, and contrary to what was said before, anodizing REDUCES the strength of aluminum.The anodized layer offers no additional strength (it is extremely brittle and porous), offers sites for crack formation, and reduces the underlying metal thickness (reducing its strength).
Reply:4043 it is guys, and it will be heat treated after completion.  What i did is cut a piece about 10" of the 1 5/8 dia 6061 pipe, i then had my 3/8" plates that go on the ends, milled out 3/16" deep, by 1 5/8" dia so the pipe will fit in the cutouts then they were heated to 500 degrees then Tig welded with 4043, thats where it stands right now.  So its not a complete butt joint, its resting in the 3/16" holes. See if i can post a pic.
Reply:Here is some photos of it.  The holes is where it bolts to the main motorcycle frame, i still need to make brackets and weld them in the center of the pipe so the shock can bolt on, and feedback is welcome. Attached Images
Reply:Originally Posted by Donald BranscomThe way you mount that tube is part of the equation.Since we cannot see what you are doing it is hard to help you.Remember those aluminum motorcycle frames are very thin and weak.They are light weight and saves the asian companies on shipping costs but those frames make it difficult to work on the motorcycle because they have to be so massive. It is good for racing but not for the average guy to work on.When you buy a $20,000+ dollar  Ducati you get a tubular steel frame. Think about that.
Reply:The original shock mount was steel, with 1/8 plates on the ends, so im using 3/8" so yeah i know you have to use thicker aluminum than the same part in steel, i think it should be fine.
Reply:According to Aloca's aluminum filler rod selection chart, 4643 would be the recommended filler alloy for post weld heat treating 6061:  "note: (1) 4643 is a heat-treatable filler alloy and gives higher strength in thick 6xxx series weldments after postweld solution heat treatment and aging."But 4643 is also not commonly stocked at most welding supplies.
Reply:I did read about 4643, cant find a welding shop anywhere that stocks it.
Reply:Don't get too exotic.  The motorcycle manufacturers have been making motorcycle frames out of aluminum for years.  They don't use any exotic alloys.  Most welds are probably done with 5356 because most frames are anodized after welding.
Reply:Your 500F preheat temp is WAAAAAAY too high for aluminum.  Generally accepted preheat temp before welding for aluminum is 200F MAX ,with a 250F MAX interpass temp.You will pretty much need to redo the complete heat treatment of your welded part, solution heat treat then quench then natural (T4) or artificial (T6) aging, as right now you have some aluminum that is no longer 'strong' at all.6061-T4 has a tensile stress yield limit of ~ 21 ksi and a shear strength of ~24 ksi, 6061-T6 has a tensile stress yield limit of ~40 ksi and a shear strength of ~30 ksi, while 6061-O (annealed 'soft' 6061) has a tensile stress yield limit of ~8 ksi and a shear strength of ~12 ksi.The 4043 filler is supposed to meet ~18 ksi tensile yield, but 4043-O drops down to ~10 ksi tensile yield.Yeah, you'll have to heat treat that to get some strength back.  The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by MoonRiseYour 500F preheat temp is WAAAAAAY too high for aluminum.  Generally accepted preheat temp before welding for aluminum is 200F MAX ,with a 250F MAX interpass temp.You will pretty much need to redo the complete heat treatment of your welded part, solution heat treat then quench then natural (T4) or artificial (T6) aging, as right now you have some aluminum that is no longer 'strong' at all.6061-T4 has a tensile stress yield limit of ~ 21 ksi and a shear strength of ~24 ksi, 6061-T6 has a tensile stress yield limit of ~40 ksi and a shear strength of ~30 ksi, while 6061-O (annealed 'soft' 6061) has a tensile stress yield limit of ~8 ksi and a shear strength of ~12 ksi.The 4043 filler is supposed to meet ~18 ksi tensile yield, but 4043-O drops down to ~10 ksi tensile yield.Yeah, you'll have to heat treat that to get some strength back.
Reply:Acually your way off with 200 f, if you go and read on lincon electrics site, or call there technical support line you will find out up to 400 f is acceptable.  So yeah it was a little over heated but not WAYYYYYY over, and it dont matter if your going to post heat treat.