Fw: [MW:20949] Porosity in Al weld with Ar

 Porosity in Aluminum Welding— 

 All weld porosity results from the absorption of hydrogen during melting and the expulsion of

 hydrogen during solidification of the weld pool. The solubility of hydrogen in aluminum

 increases dramatically after the material reaches its liquid stage. When the aluminum is taken

 to temperatures above its melting point it becomes very susceptible to hydrogen absorption.

 The hydrogen can then form bubbles in the molten aluminum as it solidifies and these bubbles

 are then trapped in the metal causing porosity. The cause of porosity in aluminum is hydrogen.

 The sources of hydrogen that create porosity are:

• Hydrocarbons – In the form of paint, oil, grease, other lubricants and contaminants

• Hydrated aluminum oxide – Aluminum oxide can absorb moisture and become hydrated - the

   hydrated oxide will release hydrogen when subjected to heat during welding

• Moisture (H2O) – Moisture within the atmosphere can be a serious cause of porosity under   

   certain  circumstances - Moisture from other external sources such as compressed air,

   contaminated  shielding gas or from pre-cleaning operations must also be considered.

 

Some Methods that can be used to Help Meet Low Porosity Standards.

When experiencing porosity problems the first course of action is to identify the source of hydrogen that

is responsible for producing the porosity.

• Clean base metals by solvent cleaning or etching and then stainless steel wire brushing prior to assembling

    the weld  joint. The solvent must completely evaporate before welding.

• Use shielding gas flow rates and purge cycles recommended for the welding procedure and position being used.

• Monitor torch angle to ensure air is not being aspirated into the protective inert gas shield. The standard forehand

    angle is 10° to 15° from perpendicular.

• Ensure that the base metal and electrode are not wet with condensation.  Allow the welding material to reach

    room temperature prior to welding. Do not attempt to dry metal with an oxy-fuel torch since it will only add moisture

    to the metal surface and further hydrate the surface oxide already present.

• Do not weld in drafty conditions.

• Avoid excessive spatter buildup inside gas nozzle ( in 4G position).

• Use the correct contact tip to work distance.

• Avoid exhaust contamination from compressed air tools.

• Do not use anti-spatter compounds.

• Check for water leaks in case you use water-cooled welding systems.

•  Check for inadequately pure shielding gas (as supplied).

    Argon should be 99.997% pure (-76°F or lower) dew point. Use ultra High pure Argon gas (UHP  99.999 %) if required.

    Helium should be 99.995% pure (-71°F or lower) dew point.

•  Check for imperfections within the gas delivery line such as leaks.

•  Prevent hydrated aluminum oxide.

   Hope above tips should help u to avoid pores in the weld.

 

 C Sridhar.
 Mobile nos: 0 94449 71097

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On Wed, May 28, 2014 at 11:38 PM, Maulik <mlkthakkar2@gmail.com> wrote:

Dear experts,

Please guide me regarding following query:

We are leading fabricator of Al light weight vessels utilizing GMAW-P process. However, we found extensive porosity problems in most of times during 2G and 4G positional welding only when utilizing 99.995% Ar as a shielding gas. In 3G and 1G position seam is getting clear with no indication. We are also using He+Ar as a shielding gas & level of porosity drastically decrease due very known technical reason " getting hot arc welding".

However due to some constraints for short span of time, we are not able to utilize He+Ar for all seams & have to use Ar as shielding gas.

In view if above please suggest how to effectively utilize Ar shielding gas without RT failure, particular to welding in 2G and 4G positions.

Base Metal: AA5083
Filler Wire: ER5183
Thickness: 4 mm
Process: GMAW-P
Shielding Gas: 99.995% Ar with moisture content <2 ppm.

WPS parameters
I-90-120 AMP (2G position)
V-18-19 V
Travel Speed-350-450 mm/min

Regards,
Maulik H. Thakkar
Welding Engg & Metallurgist
L&T, Hazira, Surat
09924732922

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