Black soot in MIG

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Anthony Dalisay

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Mar 31, 2022, 3:34:08 AM3/31/22
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Dear experts,

We have been welding aluminized sheet using MIG welder with the following parameters:

Amps: 125
Volts: 29.5
TS: 50cm/min
Gas flow rate: 12L/min
Gas type : 18%CO2 and 82%Ar

However, I cant get rid of black soot (smoke) in the weld vicinity. What do you think, is the best way to do to achieve cleaner weld in aluminized sheet such as this? 

Refer to attached photo for reference.



Thanks in advance for your expert advice.

Regards,
Anthony
--
Anthony Dipasupil Dalisay
TWI AWeldI

james gerald

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Mar 31, 2022, 6:06:19 AM3/31/22
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Try AC current

Thanks & Regards

J.Gerald Jayakumar




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Prem Nautiyal

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Mar 31, 2022, 6:46:09 AM3/31/22
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Hi Anthony 

You may please try with 99.9995% Ultra Pure Argon gas. Use a gas cup size of 20#.

Use the forehand technique in MIG.
MIG always works with DC, for GTAW you should go with AC.

Use a better quality branded filler wire spool.

Regards 

Prem Nautiyal 
Welding & NDT Specialist 
Cell 9769316004

james gerald

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Mar 31, 2022, 6:53:50 AM3/31/22
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AC GTAW with water cooled torch & HF unit

Thanks & Regards may be suitable for sheet metal.

J.Gerald Jayakumar

0091-8838619635



Anthony Dalisay

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Mar 31, 2022, 7:23:02 AM3/31/22
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Thanks for this Prem, I must try the forehand technique and see how it goes. Regarding Ultra pure Argon I will first try the 97% Ar and 3%O2 and see how it goes too. Ultra pure must have been pricey, I hope by trying your recommendation I would be able to solve the problem. Anyway, I am using robotic Mig welding machine with .8 diameter filler wire and so torch manipulation and degree angle is programmed and recorded.

Regards,
Anthony

Kannayeram Gnanapandithan

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Mar 31, 2022, 11:45:57 PM3/31/22
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what is welding rod classification

THANKS & BEST REGARDS,
KG.PANDITHAN, BE, IWE,  CSWIP 3.1,
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CONSULTANT-WELDING & QUALITY
Mobile no: +919940739349


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Anthony Dalisay

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Mar 31, 2022, 11:56:54 PM3/31/22
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Filler wire is ER70-6S @0.8 diameter size. 

james gerald

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Apr 1, 2022, 6:24:27 AM4/1/22
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seems to be like Aluminium alloy with slight additions of Zn, Mg & Cu mostly in Aerospace industries,

Thanks & Regards

J.Gerald Jayakumar

Anthony Dalisay

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Apr 1, 2022, 6:55:28 AM4/1/22
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This is actually for motorcycle industry and the base material is not of any kind of pure aluminium series. It is an aluminized sheet welded by a robotic MIG using a normal carbon steel filler wire. With given parameters in the email thread.

Regards,
Anton

james gerald

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Apr 1, 2022, 7:10:44 AM4/1/22
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Sorry i mistook it to be aluminium alloy 7065. IN Aluminiumized sheets welded using carbon steel filler you can prevent black spots by removing aluminium  from the steel sheet in the area of welding  and avoid diffusion of Al into weld metal as Al as a naturally tendency to oxidize as Al2O3

Thanks & Regards

J.Gerald Jayakumar


james gerald

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Apr 1, 2022, 7:39:28 AM4/1/22
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Just to add avoid weaving and go for stringer bead so the Al comes in the slag.

Thanks & Regards

J.Gerald Jayakumar


Anthony Dalisay

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Apr 1, 2022, 7:41:22 AM4/1/22
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I thought of doing the same too, however, it will cost me down time to remove the surface aluminium of all the items (about 40k pieces). You are correct that it is natural tendency for aluminium to oxidize when diffused with the weld arc, although this seems to be illusive, would changing the gas flow rate(to higher), welding progression(from pull to push) and angle of torch and contact tip to work distance (CTWD) will help eliminate the black soot? I have not tried those I mentioned yet except adjusting the CTWD to much closer distance to base material but surely I will try and see if that would work. I you think I missed something out please feel free to mention it.

If this black soot still occurs, I might switch to High Purity Argon as my last resort and see if thats going to be a success. I let you guys know the result of this experiment shortly. I appreciate all your inputs.

Regards,
Anton

james gerald

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Apr 3, 2022, 11:40:18 PM4/3/22
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how many passes are you welding. If it is more than one try FCAW for the 2nd pass as it would provide an scavenging action and forms light density slag of Al2O3

Thanks & Regards

J.Gerald Jayakumar


Charles Jacob

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Apr 3, 2022, 11:42:14 PM4/3/22
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Dear Antony,

This black soot is coming due to the turbulence in the sheilding gas and air is getting mixed with the aluminum vapor during welding. Try to increase the sheilding area and reduce the flow of gas by 10%. If there is oxygen or carbon monoxide in the sheilding gas as impurities, same will happen.

Change these 2 variable and you will see better results.


Regards,
Charles.


pravin.n...@gmail.com

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Dec 19, 2025, 1:09:26 AM (yesterday) Dec 19
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Dear,

ER70S6 filler wire suitable but the problem is more about surface chemistry of aluminized steel and gas composition than filler wire choice.
My suggestion as below
1) Avoid pure Argon for MIG on steel—it can cause poor penetration and lack of fusion.
2) Change gas mix to 97% Ar / 3% O₂.This stabilizes the arc and reduces oxidation
3) Slightly increase gas flow i.e 14–16 L/min.
4) Use forehand (push) instead of pull to direct fumes away from the weld.

Regards,
Pravin Nimbalkar

sridhar cn

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11:13 AM (9 hours ago) 11:13 AM
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Dear Mr. Anthony,


Black soot on Aluminized Mild Steel (ALMS) during MIG welding is a very common issue, and it 

typically indicates that the Aluminium coating is burning off and oxidizing not necessarily a weld 

defect, but rather a process/parameter & shielding issue. The soot is due to the vaporization of the 

Aluminium-Silicon coating and oxidation promotion due to CO2. So, reduce the CO2 content. Try 

92% Ar/8% CO₂ (best balance) or 95% Ar/5% CO₂ (almost no soot & very clean arc). 98% Ar/2% 

CO₂ is the cleanest but may affect the weld bead finish.


Further, for your 125A selection, 29.50V is too high and increases the heat input, and the vaporization 

and tend to distort. The ideal Voltage is between 20 to 22V. It will also help to reduce the spatter level. 

Pulsed MIG (if your power source supports Pulse) with a lower average heat input gives cleaner results 

on ALMS. 12 LPM is on the borderline for a coated sheet, and increase it to 16 LPM. Maintain a stick out 

of 12-15 mm and avoid excessive stick out to reduce the overheating and spatters.


As Aluminium coating cannot be removed prior to welding, we apply the Aluminium paint (at the weld & 

HAZ zones) after cleaning the soot, and it restores surface reflectivity, improves corrosion resistance (partially), 

and provides cosmetic improvement.


rgds,

C Sridhar.


Virus-free.www.avg.com

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