75% Helium 25% Argon mix?

[ALCOA035]

Argon/Air mix

I've been welding aluminum for over 28 years and the mix usually sets at 80/20 for some items. 92/8 for more critical jobs.

[mdhimes]

Gas Mix info from Praxair

I have used this guide while at work in the past. Its a bit of a plug for Praxair but there is good information in it. I have bolded the information that pertains closely to this topic.

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Argon
Argon, an inert gas, is the most widely used (in its pure form) as a shielding gas for Gas Tungsten Arc Welding (GTAW). Its mild thermal conductivity produces a narrow, constricted arc column which allows greater variations in arc length with minimal influence on arc power and weld bead shape. This characteristic makes it the preferred choice for manual welding. In addition, argon provides good arc starting due to its low ionization potential. This property allows argon to carry electric current well when compared to other shielding gases.

For AC welding applications, argon is preferred over helium because of its superior cleaning action, arc stability, and weld appearance. When welding thicker aluminum alloys (> 1/4"), argon is mixed with helium to enhance the thermal conductivity of the shielding gas.

While pure argon may be used for mechanized applications, depending on the base material, thickness and composition, argon-helium or argon-hydrogen blends promote higher welding travel speeds. The hotter arc characteristics of argon-helium blends also make them more suitable for welding metals with high thermal conductivity, such as copper.

Helium
Helium, also an inert gas, has high thermal conductivity and high ionization potential, which produces higher arc voltages when compared to argon for a given current setting and arc length. This produces a "hotter" arc. The increased heat input affects depth of penetration and its wider, less constricted arc column increases weld bead width.

The use of helium is generally favored over argon at the higher current levels which are used for the welding of the thicker materials, especially those having high thermal conductivity or relatively high melting temperatures. It is often used for high-speed mechanized applications.

Although argon is widely used for AC welding of aluminum, pure helium has been successfully used for DCEN mechanized welding of this material. It produces greater penetration at higher travel speeds. However, surface oxides must be cleaned from the weld joint to obtain acceptable results, since the cleaning action of the AC arc is not present. Argon-helium mixtures are widely used with AC current when welding with aluminum alloys.

The physical properties of helium definitely offer advantages in some applications. However, due to it high ionization potential, it also produces a less stable arc and a less desirable arc starting characteristic than argon. Its higher cost and higher flow rates are also factors to be considered. In some cases, an argon mixture is used for igniting the arc and pure helium is used for welding. This technique is used for DC GTAW welding of heavy aluminum.

Argon-Helium Mixtures -- Praxair's HeliStar® Blends
Each of these gases (argon and helium), as explained above, has specific advantages. Praxair's Helistar blends (argon-helium blends) are basically used to increase the heat input to the base metal while maintaining the favorable characteristics of argon, such as arc stability and superior arc starting.

HeliStar A-75 Gas Blend
This blend is sometimes used for DC welding when it is desirable to obtain higher heat input while maintaining the good arc starting behavior of argon.

HeliStar A-50 Gas Blend
This blend is used primarily for high-speed mechanized and manual welding of nonferrous material (aluminum and copper) under 3/4 inch thick.

HeliStar A-25 Gas Blend
The speed and quality of AC welding on aluminum can be improved with this blend. It is sometimes used for manual welding of aluminum pipe and mechanized welding of butt joints in aluminum sheet and plate. The HeliStar A-25 Gas Blend is also used for many of the GTAW hot wire applications to increase the energy input while accommodating the high filler metal deposition rates of the process.

Argon-Hydrogen Mixtures -- Praxair's Hydrostar® Gas Blends

Hydrogen is often added to argon to enhance the thermal properties of argon. Its reducing effect improves weld surface color match with 300 series stainless alloys due to reduced surface oxidation.

The higher arc voltage associated with hydrogen increases the difficulty of starting the arc. For this reason, the lowest amount of hydrogen consistent with the desired result is recommended. Additions up to 5% for manual welding and up to 10% for mechanized welding are typical.

Argon-hydrogen blends are primarily used on austenitic stainless steel (300 series), nickel, and nickel alloys. Hydrogen enhanced mixtures are not recommended to weld carbon or low-alloy steel, or any of the copper, aluminum, or titanium alloys since cracking or porosity will occur due to the absorption of hydrogen.

Argon-hydrogen blends utilized as a purge gas are successfully applied to improve root appearance when TIG welding 300 series stainless pipe.

Warning
Special safety precautions are required when mixing argon and hydrogen. Do NOT attempt to mix argon and hydrogen from separate cylinders.

Praxair's HydroStar is a hydrogen-enhanced argon-based blend which is ideally suited for general purpose GTAW of most commercially available carbon, low alloy, and stainless steels. It may be substituted for pure argon in many applications.

HydroStar H-2 and H-5 Gas Blends
These blends are used for manual welding applications. Hydrostar H-5 is preferred on material thicknesses above 1/16 inch. These blends are also suitable for use with GTAW when welding 300 series austenitic stainless steels and as a back purge gas on stainless steel materials.

HydroStar H-10 Gas Blend
This blend is preferred for high-speed GTAW mechanized applications on austenitic stainless steel.

HydroStar H-15 Gas Blend
This blend, which contains 15% hydrogen, is used most often for welding butt joints in stainless steel at speeds comparable to helium, and 50 percent faster than argon. Hydrostar H-15 is also used to increase the speed of welding 300 series stainless steel. It can be used on all thicknesses of stainless steel. Concentrations greater than 15% may cause weld metal porosity, with multi-pass applications.

HydroStar H-35 Gas Blend
It is recommended as the plasma gas with plasma arc gauging, when cutting aluminum and stainless steel and when cut quality and face appearance are critical.

Note: Oxygen and carbon dioxide are chemically reactive and should not be used with GTAW. Their oxidation potential can cause severe erosion and degradation of the tungsten electrode at arc temperatures.

[SignWave]

I dont think it is advisable to use a mix gas for welding Aluminum unless its Helium and Argon. .

Oops I had a brain fart there. I thought you had said that you were using CO2/Argon mix to weld AL... Sorry'bout that.

[SignWave]

Ive got a 251 as well and I find that welding 0.1875" 5086 or thicker has proven a bit finicky. Im using 100% Argon for this. I dont think it is advisable to use a mix gas for welding Aluminum unless its Helium and Argon. If I wasnt so cheap, I'd go get a bottle of helium mix just to see and feel the difference. Maybe one day, but not tommorrow..

[Heavy D]

I,ve been takeing classes on tig for a while and asked my teacher his reply was helium is needed for thicker applications. as for me I've been welding eigth inch with 100 percent argon with no problems on a tig and belive this is the right way to go

[PLUMMER]

I am having trouble getting a mix from the LWS. No mixers are available anymore from what I was told. Only option was a Tank 3 times the size of what I use now. 300+ cu/ft for 363.00 and change. 75 Ar/25He. From what i have been reading anything more is usually for automated machines to speed up the weld, since it has soo much more heat from the He. And yes I can confirm from MIG or TIG the 75/25He does make the beads better and it makes the Auto balance work even better IMO. I can say from the 1/4" plate I was doin the machine was maxed out , but when I ran out and switched to straight Ar I couldn't do it at all without preheating alot. I started out with the penetration turned up and ended up back on the auto balance setting for tig

[welder_one]

i have never used any helium mix at all for aluminum. what are the advantages? mostly, i deal with 1/4 or better up to 2 inch thick. i havent had problems with fusion or penetration before. i use 100% argon, .035 wire and 5356 alloy filler. mostly 6061 t651, sometimes 5052 h38 and rarely 3003. most of my work gets x-rayed before it ships to the customer. i am curious about this mix.

[paulrbrown]

saf, I pretty much only use 50/50 He/Ar, that extra heat of the He seems to help me. I do both TIG and MIG, at .125 you should not need preheat, I also noticed my beads with TIG look at lot better. Hope this makes sense and helps, Paul, make sure you turn up the volume,as the He is so much lighter and will float up instead of down like Ar. But that makes it great for overhead...oh yeah!!!

[SAF]

I have mig welded aluminum with spoolguns and with the new 350p for quite some time. I haven't seen good penetration using straight Argon with the heavier aluminum as in .125". My welding partner told me he had worked a government job specked out for 75% Helium 25% Argon mix and they had good penetration although it was a little difucult to use. I just bid on a job that had some .125" aluminum that would be exposed to some vibration. I'll be using a 251 Millermatic with a 30A spoolgun. Any thoughts or suggestions?
Thanks,
SAF