Cleaning prior to welding
To achieve low porosity levels for x-ray quality welds, it is important to understand the methods available for the effective removal of hydrocarbons and moisture from the weld area, and to incorporate the appropriate methods into the welding procedure. If these contaminants are present in the weld area during welding, they will produce hydrogen and significantly contribute to porosity problems.
When designing welding procedures intended to produce low levels of porosity, it is important to incorporate degreasing and oxide removal. Typically, you can achieve this through a combination of chemical cleaning and/or the use of solvents to remove hydrocarbons followed by stainless steel wire brushing to remove contaminated aluminum oxide.
--2018-05-08 9:11 GMT+03:00 'c sridhar' via Materials & Welding <materials-welding@googlegroups.com >:Your photos clearly shows endless amount pores in the weldThe main cause for porosity in aluminum is hydrogen, which has very high solubility in molten aluminum but very low solubility in solid. Hydrogen gas is therefore evolved as the weld pool solidifies. If the cooling rate is too high, the gas remains in the metal in the form of porosity. Thus, any compound containing hydrogen and contaminating the filler wire or work surface can cause porosity.
Oil, moisture or other contaminants may be present on the filler wire. In addition, the oxide layer of aluminum tends to get hydrated and improper cleaning of the oxide layer immediately preceding welding could be a cause for porosity. Ensuring that the plate is clean before welding and switching to clean, high quality electrodes will reduce the likelihood of forming porosity.
The amount of porosity depends on how fast the weld pool solidifies. Increasing the welding current and/or decreasing the travel speed will increase the heat input, and help retard the cooling rate allowing gases to escape from the weld pool and thereby reducing the risk of porosity.
Filler wires should ideally be kept in their packaging until needed; wire that is left out ion open workshop conditions will absorb moisture into its oxide layer. It is advisable when welding aluminum to wipe each wire prior to use with a clean cloth dipped in acetone.Sridhar.Pre heat the weld and HAZ area to mimnimum150 deg. C to eliminate hydrogen pores. Once you overcome it, the tests
will pass through.On Monday, 7 May, 2018, 4:16:16 PM IST, Hani Al Masry <hanyonalfy@gmail.com> wrote:Dear experts--regarding A/M Subject kindly advice why the PQR Test had been failed two times even this WPS/PQR Approved before and we just tried to copy itall welders 2 times failed in root bend / tension some times not reach 250 MPA as required (2 root bend + 2 root face + 2 tensile testing are required)the lab said first time there are porosity
and inclusions but even 2nd test was failed (attached photos for your reference)BASE METAL : AA 5083 H 321FILLER METAL : ER 5356Joint Preparation: - Single V CPJ
Weld Layer
WELDING PROCESS
WELDING POSITION / DIRECTION
ELECTRODE(S)
GAS SHIELD
GAS FLOW RATE
lit/min.
AMPS
VOLTS
WELDING SPEED mm./min.
FLUX
WFS
M/Min.
Mode of Metal transfer for MAW
SIZE
mm
TRADE NAME
POLARITY
1
GMAW
3G
1.2
AUTO ROD 5356
DCEP
ARGON 99.99%
15-25
120-180
18-26
12-20
NA
8.5
Pulse transfer
2
GMAW
3G
1.2
AUTO ROD 5356
DCEP
ARGON 99.99%
15-25
120-180
18-26
120 - 140
NA
8.5
Pulse transfer
Back weld
GMAW
3G
1.2
AUTO ROD 5356
DCEP
ARGON 99.99%
15-25
120-180
18-26
100 - 110
NA
8.5
Pulse transfer
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Dr. Georgios Dilintas,Dipl. Ing. In Aeronautic and Space EngineeringPh.D in Mechanics of Solids - Computational MechanicsA.I.S, A.N.I, IRCA Lead AuditorWelding, Stress Analysis, Corrosion, QA/QC, Failure Analysis, Risk Analysis--
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