More fun tigging - Aluminium

[FranV8]

Hello all,

Halfway through a project to make what is, in effect, a bigger version of an axle stand. It's for my father in law - he's got a dinghy and where they're kept (on grass) people like to tilt the front of their boats up to avoid some of the weed growth.

It's 5mm ally plate, and it's the first bit of useful aluminium welding I've done (I did some practice runs and made some vice guards before).

I'm using a 160A AC welder, which is way underpowered for 5mm, but it'll still put a useful join down. The top piece is a piece of 20mm dia solid rod. Not the prettiest but I'm pleased with how it's secured on, and is a continuous beed.

The butt welds for the base triangular frame I did a top pass, with a very slight vee - put in using the jigsaw canted over. I then went along the bottom of each butt as well. On one I had interesting, and instant, cracking right down the middle of the weld fillet, from the end where I finished welding to. Interestingly, remelting it again made the crack instantly reappear, I filed it out in the end to get rid of it and then it was fine.

I've been using the jigsaw with a metal blade to do most of the cutting, it's done a really good job, and noticeably better when I apply oil (from an old trigger oil can, in fact I just use clean motor oil).

Any comments, and explanation of what happened on the cracking would be gratefully received! I think perhaps I should have put more of a vee in and left a gap too to weld into.

Welding current was mainly 120A, but I was on the pedal so varied it accordingly.

Sorry - last question - the start of each weld was iffy (I was on it for quite a while to get a bead to form) and also how do you finish off a butt without getting the edge to burn back?

Many thanks for reading!

 

[julieanncharters]

Hello all,

Halfway through a project to make what is, in effect, a bigger version of an axle stand. It's for my father in law - he's got a dinghy and where they're kept (on grass) people like to tilt the front of their boats up to avoid some of the weed growth.

It's 5mm ally plate, and it's the first bit of useful aluminium welding I've done (I did some practice runs and made some vice guards before).

I'm using a 160A AC welder, which is way underpowered for 5mm, but it'll still put a useful join down. The top piece is a piece of 20mm dia solid rod. Not the prettiest but I'm pleased with how it's secured on, and is a continuous beed.

The butt welds for the base triangular frame I did a top pass, with a very slight vee - put in using the jigsaw canted over. I then went along the bottom of each butt as well. On one I had interesting, and instant, cracking right down the middle of the weld fillet, from the end where I finished welding to. Interestingly, remelting it again made the crack instantly reappear, I filed it out in the end to get rid of it and then it was fine.

I've been using the jigsaw with a metal blade to do most of the cutting, it's done a really good job, and noticeably better when I apply oil (from an old trigger oil can, in fact I just use clean motor oil).

Any comments, and explanation of what happened on the cracking would be gratefully received! I think perhaps I should have put more of a vee in and left a gap too to weld into.

Welding current was mainly 120A, but I was on the pedal so varied it accordingly.

Sorry - last question - the start of each weld was iffy (I was on it for quite a while to get a bead to form) and also how do you finish off a butt without getting the edge to burn back?

Many thanks for reading!

id suggest using a 40grit flap disc in a grinder to prep angles on yer joint a lot quicker and no oil to contaminate weld that yer getting with ya jigsaw setup..
a 60 degree v down to the bottom will give ya a sporting chance,your photo looks a little tight.
after yer first pass turn it over and back chip/cut out all down the seam till ya get clean metal then do ya final weld.
this removes all dirty poo at the bottom of first weld which will upset the second weld.
i use a 4 inch tct blade in a grinder which requires a bit of caution.
sounds to me like ya second weld was done over a dirty root from first hence the crack.
doin well to weld 5mm with 160 amp ya must stand there for ages waiting for the puddle to form.
failing that could be ya filler wire is not suitable for parent metal.
backing off on the pedal at the end should cure ya burn off ,takes a bit of practice will prob be harder with an underpowered machine.

 

[RichardM]

Paraffin makes a better cutting lube than oil for alu.

 

[hotrodder]

The butt welds for the base triangular frame I did a top pass, with a very slight vee - put in using the jigsaw canted over. I then went along the bottom of each butt as well. On one I had interesting, and instant, cracking right down the middle of the weld fillet, from the end where I finished welding to. Interestingly, remelting it again made the crack instantly reappear, I filed it out in the end to get rid of it and then it was fine.

Solidification (hot) cracking, lots of things can cause this. When you 'went along the bottom of each butt' were you using filler wire?
It could be as simple as welding too cold/ not using enough wire i.e. not enough weld metal to resist the solidification shrinkage. Leaving a crater at the end of a weld is a favorite for initiating such cracks.

Some alloys are more prone to this than others. The 6xxx series for example need to be diluted with filler wire or they will almost certainly suffer hot cracking. Flavour of filler wire has an effect too, 4043 is more resistant to hot cracking than 5356 i.e. leaving a crater with 5356 (or 1050) is more likely to bite you than with 4043 wire

 

[Engineer]

Looks like not enough heat, and maybe the wrong filler wire. If the material you are welding seems too thick for good penetration, then prep the joint with 45 degree angle on each piece of material, and get some good tacks at the weld root before finishing rest of weld.

 

[Delgado]

Sorry - last question - the start of each weld was iffy (I was on it for quite a while to get a bead to form) and also how do you finish off a butt without getting the edge to burn back?

One way is to put a good tack on the end you're going to finish on, should reduce the chance of it melting away (at least not so quickly). If your machine is underpowered, pre heat with propane and weed burner torch.

 

[FranV8]

Thanks chaps - great advice. It was 4043 rods I was using, and I did rush the prep a bit.

With the filler wire - I didn't have to add that much - which I guess didn't help (it's the silicone in there that helps it resist cracking is it not?) - so for a chunk of the weld I was just doing it with the parent metal.

Well - it's all learning! This is thicker than I'll want to do normally on ally - but I'm pleased at least I've mostly managed to stitch some together at this thickness. I should have some more to post up once I've made the leg sections - I need to sit down with my trigonometry head on though for the cutting angles - as they're right angle sections that will go on with the external corner pointing outward.

 

[hotrodder]

Yep it's the silicon that lowers sensitivity to hot cracking. If the part was made from strip/flat bar then it'll be a 6xxx series alloy which needs to be diluted with filler (4043 or 5356) as it's chemistry makes it prone to hot cracking. If your welding from both sides can just leave a gap although veeing it will make the welding easier

 

[FranV8]

Thanks all, great advice. I'm just posting up my latest set of woes!