How to prevent porosity in aluminium welding?(Reasons of porosity)

Remedies for weld porosity in aluminium.

Table of contents

  • what is porosity?
  • What causes porosity in welding?
  • Why porosity is more in aluminium?
  • Causes/reasons of porosity in welding?
  • Types of porosity in welding
  • How to prevent/avoid porosity in aluminium welding?

Dear engineers,

i am giving deep knowledge about porosity in welding.from what is aluminium,what are its properties to why porosity is major problem in al.
Today i am updating post about what is porosity,causes/reasons of porosity in aluminium welding,And preventive measures to aluminium porosity defect.
causes and prevention of porosity inweld.

If you want to know what is aluminium and its properties application.

Read it Aluminium,characteristics and applications

What is porosity in welding?

porosity is group of small voids.Whereas blow hole and porosity seems same.
but the difference is
porosity is group of small holes.
and blow hole is bigger in size also called cavity.

porosity in aluminium welds.

How porosity caused in welding?

The parent metal melted under the arc tends to absorb gases like hydrogen,carbon monoxide,,nitrogen and oxygen if thy are present around the molten metal pool.These gases may be produced due to some coating ingredients in the electrode or moisture,oil,rust,grease etc.existing on the base plate to be welded.These gases get spread throughout the molten pool by diffusion and convection.The solubility of gases in the molten metal reduces as it cools down and thus the dissolved gases liberated from liquid metal until it starts to freeze.
for porosity to occur the concentration of gases  in the molten weld metal must be above the standard solubility of gases in the solid metal at melting point.
The porosity formed at solid liquid interface.




porosity creating process

Tags
what is porosity,causes/reasons of porosity in aluminium welding,And preventive measures to aluminium porosity defect,how to avoid porosity in welding,how to prevent porosity in welding

Why porosity in aluminium is more than any other metal?

Because oxide layer is created on aluminium surface.This layer if cleaned by acids or mechanical cleaning thereafter quickly within a minute oxide layer starts building over aluminium surface.Due to which in aluminium welding porosity is more than any other metal.

causes of porosity in welding process

Cause/reasons of porosity in aluminium

  1. Oxide layer forms continuously over surface.
  2. Cleanliness is most important.
  3. Gas flow is not proper.
  4. Improper or expired filler wire or electrode used.
  5. Moisture on filler wire/electrode.
  6. Moisture on plate to be welded
  7. Elements like coatings on metal to be welded, moisture,oil,rust,grease,etc on weld surface.
  8. Unskilled welder
  9. Improper shielding causes due to improper nozzle to job gap and less or over gas flow rate.
  10. Longer arcs
  11. Faster Arc/welding speeds.
  12. Too low or too high currents weld parameters.
  13. Incorrect welding technique.
  14. electrode with damaged coating/flux.
  15. Improper base metal composition. generally sulfur and carbon contents tends to porsosity.
  16. Improper torch angle.
  17.  Improper weld equipment,like damaged o rings,contaminated,liners,hoses,

Types of porosity in welds.

  • uniformly distributed porosity.
  • Cluster porosity
  • Linear porosity
  • Worm-hole porosity.
types of weld porosity

Preventive measures to avoid porosity in aluminium Welding?

1-Proper cleaning

aluminium cleaning before welding

In aluminium cleaning is most important parameter to avoid welding defects.
because oxide layer is continuously formed on the surface of aluminium.
And also its thermal conductivity is high so its also absorbs moisture available in atmosphere.



Prevention/remedy 

So base metal cleaning to remove oxide layer, dust,oil,grease etc is important.
Cleaning done in two methods
  • Mechanical cleaning-its mostly used cleaning method because ease of handling and cost reduction and mainly safety.it consist of wire brushing,grinding,buffing etc.
  • Chemical cleaning - it also used in some cases the chemical agents like strong alkaline,Solvents.

2-Torch angle most important parameter.

Add captionwelding angles to avoid porosity

Torch angle is one of most important parameter for aluminium welding.for finish and defect free welding.



Prevention/remedy 

It hampers quality,finish and strength of welding.So choosing appropriate weld angle is important.
It depends upon Joint type.for groove joints 90 degree torch angle with 45 degree forehand angle is best.
for Fillet welds 45 degree torch angle and 15-20 degree forehand angle is best.
for TIG welding torch held at 60-70 degree to the work
and filler rod 20-30 degree to the work.
For all other types use same forehand angle.

3-Proper selection of chemical agents



aluminium chemical cleaning

Dont use antispatter oils and sprays.Because most of antispatter agents use silicon base for preventing spatter.
but in aluminium if silicon come in contact with welding it will react with welding create weld defects like pinholes,blow holes and porosity etc.

Prevention/remedy 
So select any antispatter and other cleaning agents properly because dont use silicon base antispatter sprays and oils.

antispatter for aluminium
4-Improper welding parameters


weld parameters also affects welding quality and finish.wrong parameters tends to weld defects like  cracks,porosity,undercut etc.
  • Too high currents and too low currents cause porosity so using proper current is important.
  • Too high and too low voltage also cause porosity,cracks and other problems.
Prevention/remedy 
setting parameters is depends upon joint type,thickness of material,composition of material,Thermal conductivity etc.

So i am not able to give perfect parameters.So i suggest You best way to setting parameter i.e. trial and error.
Take trials on scrap material with different currents,voltages and gas flow and test welds with NDT methods manual inspection.
In aluminium surface porosity acceptable so check by buffing weld upto 1mm.
and freeze parameters that gives best results.

5-Improper welding position

welding position is also important.Make joint to be in simple weld positions like 2g,2f,1g,1f etc.Avoid overhead positions.

Prevention/remedy 
Try to weld job in easy positions.
Maintain gap between nozzle of weld torch and joint between 10 mm to 15mm.

6-Shielding gas type flow and equipment's

  • Low gas flow and high gas flow also cause weld defects like blow holes,porosity,blackness.
  • Use of wrong gas composition.
  • Defected equipment's
  • Blocked gas nozzle blocks gas flow and creates porosity.
Prevention/Remedy
Use gas with proper composition according to type,grade and composition of material.
For example-
Mild steel 
Use CO2 gas
high strength steel(weldox,hardox etc) -
Use Argo-shield AR+CO2 (80%  and 20% co2)
Aluminium
Use pure argon You can also use helium it will give additional heat that will help to avoid porosity in aluminium.But helium gas cost is high so you can also use helium and Argo different mixtures.

  • Use gas flow according to welding process.
      • Automation welding use 20-25 LPM(high speed)
      • Manual use between 15-20 LPM.(low speed)
    • it also depends upon speed of welding.refer brackets above.
  • Check for faulty equipment's and do proper maintenance time to time.
    • Check for leakages in gas hose.
    • Check O rings,perforated rings.for any damages.
    • Impurities in gas hose.
  • Clean nozzle time to time for blockage due to spatters in nozzle it will block shielding gas flow and cause porosity in welding.so clean it time to time properly.


                                                                 
7-Proper Welding technique

Pull(drag) welding means backhand welding technique creates blackish appearance of weld and also inclusions and porosity problems.
Also don't use downhill welding it also cause defects and low strength to weld.

Prevention/remedy
Use push welding forehand welding technique  which is best and creates better finished welds and silvery white welds and reduced weld defects like porosity.
Use uphill welding instead downhill it will improve strength of weld and reduce defects.

8-Proper base metal-electrode selection

if you use wrong filler wire for welding it will also cause weld defects.
Prevention/remedy
Check base metal composition,grade and series.and then select proper filler wire that best suits you according to applications finish you want.and Importance of project.
for example
7xxx series of aluminium
commonly used filler wires are ER5356,ER5556,ER 4043 etc.

9-Proper weld equipment's.

It is also important factor to avoid porosity.because leakages in gas flows due to defected equipments like cuts in gas hose,loose tighten joints near regulator and end points.Faulty regulator.
using Proper liner is also required.Defected 'O' rings,perforated rings also cause leakages it will tends to porosity due to ineffective shielding.

Prevention/remedy

  • Check hoses and hose start point means regulator joint for any leakages.
  • Check for impurities in gas hose
  • Check for leakages in cylinder opening.
  • Check regulator is working properly or not by calibrating it.if not showing right pressure and gas flow then change it.
  • Check for perforates rings,O rings for any damage and change them  if damaged.
  • Use teflon/graphite liner for aluminium dont use steel spiral liner because aluminium reacts with it and create inclusions.due to sulphur and other contaminants.
  • check for proper earthing clamps
10-Check gas purity
If you following all things i shown in this post for avoiding porosity in aluminium welding.
and after following steps porosity is coming then its problem with your shielding gas provider.
You are getting impure gas from your provider then you absolutely get porosity when you are following all preventive methods also.

Prevention/remedy
Please contact your shielding gas provider and check for purity of gas and then use shielding gas after confirmation







Share on Google Plus

About Ketan Pujari

This is a short description in the author block about the author. You edit it by entering text in the "Biographical Info" field in the user admin panel.
    Blogger Comment
    Facebook Comment

2 comments:

  1. This is very Great..Aluminium stair nosing are an ideal way to ensure an anti-slip protection at the stairs. These nosings also resist wear and tear at the front edge of stair steps and thus help extending the life of stairway..Aluminium nosings are available in various sizesdepending on functional and architectural requirements of the Project and Client

    ReplyDelete
  2. MIG welding is a process that is done with metal inert gas. In MIG welding metal rod is used as electrode and workpiece used as another electrode. If you want to buy a NIG welder then you should choose Miller 211 is a very popular MIG welding machine. Miller 211 for sale

    ReplyDelete