5% si or 5% mg, how to choose which one to use?

[Pete.]

So I've bought four boxes of rods for a great price, and I've been trying out both types just practicing run after run on flat plate and 2m treadplate.

I don't seem to find any dfference in how they perform, or that my learning-curve hasn't extended enough so I can actually tell. I read on the labels that either are good for the flat plate I'm using for practice, but when it comes to doing a real-world job how do I choose which rod is best?

 

[TechnicAl]

The 5356 should freeze a little quicker making positional welds easier

They are designed for welding different grades of Aluminium

 

[carbon]

I'm sure someone has a better explanation but I found this chart when looking myself a couple of months ago Filler Selection Chart regarding the choice of filler for different aluminium grades

 

[Pete.]

Thanks for that. What if I don't know the grade of the alloy I'm welding? for instance, I asked about work if there was something other than flat ally sheet I could weld and was given a cast aluminium sump off a hydraulic pump which had the four mounting lugs snapped off. I did manage to do the job but I couldn't decide which rod was best, so I went with 5% mag.

 

[carbon]

From the weldequip shop Tig Consumables. The last two fillers "5356 Not suitable for cast aluminium" and "4043 suitable for cast aluminium". Also stated on the No.15 packet "cast"

 

[chevy2]

I keep 4043 and 5356,
as a rule i generally use the 4043 on anything thats cast, apparently its lest likely to crack,

Use the 5356 on stuff that needs to be more structurally sound.

 

[toddy]

4043 can be used for nearly any alu.. but then it depends on what it is going to be used for
5356 is good for a few alloys.. but it smokes a little.. but i have been making items out of this wire for additive manufacturing (3D printing with a tig set)

 

[hotrodder]

Silicon is virtually always the primary alloying element in cast aluminium making a 4xxx series filler the best choice
Extrusions (tube, angle, tees etc) are virtually always a 6xxx series, usually 6063-t6 or 6082-t6. Other flavours of ally are extruded but are FAR less common
Loads of different flavours of sheet and plate... the 1.5 and 2mm sheet we were playing with last week was 1050-h14 which is 1/2 hard commercially pure Al. 3103 (Al + Mn) is less common and has similar ductility but is a bit stronger. The other common suspect for sheet which is noticable harder is 5251-h22 although several other 5 and 6xxx series are used for both sheet and plate. The 5 bar treadplate i left you is 5754, 3 bar/triple grip is 5052.
Aluminium tempers and a load of other useful stuff... http://aluminium.matter.org.uk/aluselect/

While any flavour of ally filler wire will often work some are far more prone to solidification (hot) cracking than others. It's to do with the different hardening phases in aluminium that become crack sensitive at certain concentrations... 6xxx series for example use both Si and Mg which together form magnesium silicide and make the alloy heat treatable. There is no 6xxx series filler wire because magnesium silicide has quite a wide range of crack sensitivity, particularly around 1 - 2%, which needs diluting with either some excess Mg or Si hence the two common filler wires are 4043 and 5356 which are 5% Si and Mg respectively.

On the flip side of the coin one of the softer flavours like 1050 or 3103 are best welded with a 1xxx series wire like 1050 or even with strips with sheared from the parent material. 4043 is often recomended for welding 1050, especially for 'strength' which is totally backwards as the whole point of these flavours is that they're soft and ductile. While 4043 is rich enough in silicon to usually keep the weld zone out of the crack sensitive region (0.8 - 1.5ish % Si) 4043 is very brittle relatively speaking which is the last property that's needed in a fuel tank (work hardening from fuel sloshing about) or coachwork where the welds are gonna be planished out

While it'll probably be a while before you can spot the differences in how they weld as Al said 5356 is a bit faster freezing... adding Si to ally lowers it's melting temp and gives a wider 'mushy' range which is why 4043 is typically described as 'wetting out' better and (and often wrongly depending on the job and flavours of ally at hand) being the most forgiving and crack resistant. As an aside 4047 at ~12% Si is the eutectic composition and as such has a lower and 'sharper' melting temp of 585C versus 660C for pure ally

ETA that Alcotec filler wire chart is probably one of the best out there as it looks at things from various different aspects but being American some of the designations are a little different... they have 1100 and 3003 for example while we use virtually identical 1050 and 3103, what they call 7005 we call 7020, 6061 vs 6082, 5052 vs 5251 etc

 

[Pete.]

From the weldequip shop Tig Consumables. The last two fillers "5356 Not suitable for cast aluminium" and "4043 suitable for cast aluminium". Also stated on the No.15 packet "cast"

Damn I read that label too and missed the 'cast' bit. Thanks guys for all the advice. I've done a few hours practice today and really improved my technique to the extent that I need to be thinking about filler instead of just laying down beads. Long way to go but with the quality help I'm getting from members here it'll be a lot easier than if I just went it alone.