Whats Gone Wrong With This Welding?

[gasgas249uk]

Had the hub welded twice. The first weld lasted good but the 2nd weld is disintergrating into thin air . It was painted immediately after welding.

The weld took well and its only thin so preheating perhaps isnt really needed ?Ive read that preheating the mag to 200 degrees in only needed on thick material.

Ive never seen anything like this before and the welder who didnt seem ti understand it either .The weld is magnesium as ive done the vinegar test.

My guess is that perhaps the wrong mix of mag / alloy rod was used OR it been contaminated. I find the contamination theory strange as the hub was taken back to the brake liner , so all was there was the steel.

I dont want to keep having to get this welded so anyone have an answer as to why and a solution please.

Ta in advance

Edited April 11, 2012 by gasgas249uk

[copemech]

From what I can tell of the pics, it looks as though you may have more of a corrosion problem than a weld problem. Magnesium is highly corrosive and must be well protected. Simple painting don't always work, one needs a clean base(glass bead after welding if necc) and a corrosion inhibitive primer such as zinc chromate or epoxy that is non porus and seals the metal from oxidation and moisture and gives proper adhesion of the paint.. as just paint don't stick well , either.

[gasgas249uk]

From what I can tell of the pics, it looks as though you may have more of a corrosion problem than a weld problem. Magnesium is highly corrosive and must be well protected. Simple painting don't always work, one needs a clean base(glass bead after welding if necc) and a corrosion inhibitive primer such as zinc chromate or epoxy that is non porus and seals the metal from oxidation and moisture and gives proper adhesion of the paint.. as just paint don't stick well , either.

Thanks Copemech for the reply.Just thinking it through logically why it then that i have other mag casings with no paint on , that arent corroding?.

Any advice on the grade of rod i should be using. Local welding shops dont know. I read an old forum saying az101 is the best to use but this is american grade and the shops ive contacted dont know the uk equivilent.

Ive spoken with one coded welder locally and he doesnt deal with the stuff.

One shop said they only sell 5356 , but they dont know if its suitable.

Perhaps its just try again and paint in corrosion inhibitive primer and 2k top coat

[b40rt]

The hub is probably acting as a sacrificial anode for the steel liner, no easy answer.

[ham2]

The hub is probably acting as a sacrificial anode for the steel liner, no easy answer.

''..Check out the big brain awn Brad..!''

(Pulp Fiction)

[gasgas249uk]

The hub is probably acting as a sacrificial anode for the steel liner, no easy answer.

Anode - na - not buying that one at the mo.Thanks for the advice though. It all goes into the melting pot

The first load of welding is still perfect.

Trouble is none can remember the rods he used

any ideas on the rod code? It's more that 5 percent mag that's for sure

[craig10]

I'm with Ross on the anode theory, but not necessarily just to the steel. The first weld was probably done with the right rod, the second one with a material that will act as an anode to the surrounding metal, just like zinc does on galvanised metal

[copemech]

Thanks Copemech for the reply.Just thinking it through logically why it then that i have other mag casings with no paint on , that arent corroding?.

Any advice on the grade of rod i should be using. Local welding shops dont know. I read an old forum saying az101 is the best to use but this is american grade and the shops ive contacted dont know the uk equivilent.

Ive spoken with one coded welder locally and he doesnt deal with the stuff.

One shop said they only sell 5356 , but they dont know if its suitable.

Perhaps its just try again and paint in corrosion inhibitive primer and 2k top coat

I have never attempted to weld the Mag. A bit of research seems to suggest thet the ER AZ92A is the filler rod of choise for most cast mag products. It also seems to have gone off quite expensive at over $100 per pound.

Also, best I can tell, even though the 5356 rod does have a small MG content, it is basically used for 5000 series ali welding, and I found no compatability listings for use in the cast magnesium. This does bring in some compatability issues potentially if it were used previously, as far as corrosion goes. That is all I can find!

[toofasttim]

Take it to an aircraft fitter/welder and get his/her opinion.

[monty_jon]

If you are unsure of the material used cut it out and start again

[lowbrow]

Try Roper Welding Services. 01285 861031. This old boy has a lifetime of experience and there's not much he doesn't know or can't do. He's got a unit in Ashton Keynes between Cirencester and Swindon if that's anywhere near handy for you?

[gasgas249uk]

Mr Roper certainly does know his stuff and is confident. Says he's seen it before which is more than any other elder I've spoken with. He recons to much alloy in rod caused corrosion.Trouble is he's some way from me. He said it would be a 95 percent pure mag rod or thereabouts. So gives me some clue as to the rod to buy. I have confidence in my , he just needs right rods.

[charliechitlins]

Maybe an acidic flux used and not cleaned off.