[stefans]

Hi Everyone,

We are trying to weld a sand casting and an AL pipe but the strength of the weld is not that great. The weld keeps breaking.

Sand casting is A356.0
Al Tube 6061. 3mm thick

parts are welded, anodized then powder coated

Part will be used in low temp environment; salt water

The weld is breaking when we place 160lbs at 3ft out from the weld.

Question:

1-What is the best result we can expect from our weld? 600lbs or greater?
2- How does our weld look?

Solutions for improvement
We are going to change our filler to 4145, and pre heat the parts to see if we can improve the weld strength.

Any help or info would be great as we are not sure if the shop we are using really knows what we should expect from the weld strength.

Test Setup

TestSet-up.jpg (30.12 KiB) Viewed 1442 times

Break3

Break1.jpg (43.27 KiB) Viewed 1442 times

break4

Break5.jpg (72.65 KiB) Viewed 1442 times

[rake]

Here's a couple of thoughts.
1 preheat get that casting plenty hot
2 improve the fit up
3 gas purge to avoid defects from the back side
4 more reinforcement not just one pass and done
5 post heat/normalize it and slow the cooling rate

[stefans]

@rake,

Thanks for the suggestions. If Welded correctly, do you have Any idea what kind of load this weld should be able to withstand?

Thanks again.

Here are some more photos of the broken weld.

Break6.jpg (54.79 KiB) Viewed 1435 times

Break7.jpg (23.49 KiB) Viewed 1435 times

[VooDoo]

if there is room for testing, i might try 4047 filler, works great for casting repairs. And groove out the weld, then at least 2 passes over.

[noddybrian]

I admit I do not have a huge experience with aluminum due to the nature of my usual work - but I feel I weld enough for some general comments - I don't intend this to sound rude - but here goes.

The casting does not appear to have been cleaned up so your taking alot of surface contamination into the weld.
The casting does not really fit to the pipe except by the taper created by the draft of the pattern
The weld itself appears to be a somewhat irregular single pass showing porosity & other defects - if this is a hobbyist welding in his garage then OK - but it appears more of a shop where better could be expected ? also the very crystalline nature of the break would seem to be either the part was welded while cold & the resulting rapid cooling did this & / or the filler metal is not suited to both parent materials.
Lack of consistent full depth penetration.

Obvious points to improve the situation

Clean the casting if only with a flap disc to remove outer skin & possible sand inclusions.

Can the cast part be mounted in a mill & have a short parallel machined onto the spigot that will allow the pipe to slide onto it making a mechanical joint & a socket weld instead of a butt - this will improve strength - if not even a careful guy with the right size hole saw could produce a similar if not perfect result - an added benefit would be to create an internal backing for the weld - as you to a V prep on both sides & leave an open root allowing you to easily do a consistent root pass - then clean any defects ' porosity & weld a cover pass.

Try to pre-heat the casting part - the tube is less important being thinner & you don't want excessive heat on 6061

Possibly research best compatible filler rod - I'm sure there are experienced guys here - or on internet sites or local LWS if their good - possible this new Hobart filler people are talking about ?

Hope some of this helps - as to ultimate strength - I'm not sure I'd like to put a figure on it - but with the thin wall of that tube I would expect once the actual weld problem is solved that it's the yield point of the tube itself over that length rather than the connection to the cast part.

Good luck with your project

[Otto Nobedder]

I concur with everything noddybrian said.

For alloy choice, there are more qualified voices than mine where cast aluminum as concerned, but it appears the main problems are, lack of penetration (to be fixed with preheat, and prep), lack of fusion (same fixes, and hotter weld amperages), shrink-stress (pre-heat/post-heat), and it wouldn't hurt to have more reinforcement, meaning more passes.

The finished weld should actually be stronger than the 6061's heat-affected zone near the weld, meaning the tube should fail before the weld.

Another prep option would be to grind the area the weld will be plus 1/4" on each side, and "butter" the cast, meaning building up a layer of clean weld metal attached only to the cast, then grind and prep this, so the joining weld is on clean fresh metal on both parts.

Just some suggestions...

Steve S

[stefans]

Hi Everyone,

Thanks for all the feedback it's really appreciated.

We will do our best to have the shop take everyone's suggestions into action moving forward.

I'll post some more photos in the coming days.

here is a photo of our part joint.

CAD-Joint Design2.jpg (16.8 KiB) Viewed 1381 times

Joint design

CAD-Joint Design.jpg (26.15 KiB) Viewed 1381 times

[stefans]

Hi Everyone,
Thanks for everyone’s help on this!

Today we cleaned the part with a Stainless S. wire brush, heated up the casting, and used 5356 filler. Put a second pass on it and made sure we had good penetration.

Test result was the same 4.26ft with 160lbs, however, this time the pipe broke, actually it ripped slowly. Before when the weld was failing, it was snapping like a cold icicle.

The weld had great flex, about 1.5ft before it broke.

We also tested two pieces of 6061 welded together. It flexed more but this could have been because the part was held a bit differently. However it still broke with 160lbs at 4.26ft

The AL tube is rated a 200Mpa and this test result is about what it is supposed to break at. So all in all, a great day

Again, thanks for all your help on this.

XQ-12-27-13-0017.jpg (45.76 KiB) Viewed 1363 times

XQ-12-27-13-0010.jpg (52.84 KiB) Viewed 1363 times

XQ-12-27-13-0007.jpg (47.76 KiB) Viewed 1363 times

[noddybrian]

Glad to have been some help - I guess unless you are able to use a thicker wall tube you have reached the ultimate strength of this part as it is now the strength of the tube & not the weld which is the weakest link.

The weld itself while holding better still looks less than perfect - it maybe the welder is competent - but not in regular practice for smallish pipe joints on aluminum - the bead is still a bit irregular & the minimal cleaning action & mild peppering / black edges would suggest maybe you need more gas flow / larger cup / gas lens & take care to do a dry run as Jody often advises to ensure you can follow the joint round while maintaining a good torch angle - a flex head / flexloc torch obviously makes this easier - I imagine the size of the cast part would not allow you to rotate the joint leaving the torch in a relatively fixed position ( ie improvised welding lathe / rotator ) I don't consider this cheating & do it where I can as I go so long between Tig jobs my first few welds suffer !

[stefans]

@noddyBrian,

Thanks for the continued support. We will keep trying to improve the weld as we would like it to be cosmetic; still a long way to go but at least we understand the load and failure parameters now.

I like the idea of turning the part as we will be trying to do a lot of these as quickly as possible.

Thanks and I'll post some more photos

[TamJeff]

That joint is begging for a gusset. If a gusset is not possible, the joint/casting should be redesigned for a scarf instead of a butt for that type of stress testing as proof. In other words, the test is not fair for that type of joint.

[noddybrian]

I'm not familiar with what this part is used for so I don't know if it's possible to re-design it or if it's too late as the cast part is already made? - but as TamJeff said - adding a gusset would help - or if you could have the casting machined to allow the pipe to sleeve over the cast spigot - or bore the spigot & insert the tube - or bore & insert a short length of tube inside the main one doubling the wall thickness for a short distance - or weld it as you have been - then grind the weld down flush & drop a short length of tube that's a good fit over the join & weld round both ends acting as an external doubler - I would think there has to be a way round improving the strength ( unless it's not critical & / or not cost effective )

If you can improvise a rotator it will help speed / consistency / torch angle & make the welding much simpler especially if this is a repetitive job - even if it's hand turned by an assistant it will likely give enough benefit to justify his wages - it need'nt be elaborate - something as simple as holding an end of bar stock in a bench vise that the part will slide over & rotate on will help.

Good luck with your project - will be interested to see a finished picture & possibly what this piece does.

[TamJeff]

If there was enough of that boss to where an 1/8-3/16" gap could be afforded and still have a backer in the open butt, it would solve both the strength and the aesthetic quality of the joint. With a pinstripe weld nicely convexed and perfect edges. Those look like big pond aerators or something.