WELDING OF ALUMINUM ALLOYSINTRODUCTION TO ALUMINUM.CLASSIFICATION OF ALUMINUM ALLOYSWELDING PROCESSES USED FOR ALUMINUMSMAWGTAWGMAWWELDING DEFECTS

ALUMINUM Light in weight. Good corrosion resistance. Good thermal and electrical conductivity. Highly reflective. Non-magnetic (no arc blow). Pure metal is very ductile. Strengthened by alloying,cold working, heat treatment.

PROPERTIES OF ALUMINUMProperties Aluminum SteelMelting point, 0C 660 1536Specific heat, J/g.0C 900 460Density, g/cm3 2.7 7.87Thermal conductivity, 0.53 0.18cal/ cm3 .0C.s

Electrical resistivity,.cm 2.65 9.71

Wrought Aluminum alloysAlloys series principal alloying element

1XXX 99.0% min. ALUMINUM 2XXX COPPER

3XXX MANGANESE / (Si+Cu)

4XXX SILICON

5XXX MAGNESIUM

6XXX MAGNESIUM+SILICON

7XXX ZINC

8XXX OTHER ELIMENTS

Classification of Al-alloysNon heat treatable alloys: 1xxx, 3xxx, 5xxx series.Optimum mechanical properties- Strain hardening (cold working)

Heat treatable alloys: 2xxx, 6xxx, 7xxx series.Optimum mechanical properties- Thermal treatments (solution H.T+ aging)

4xxx series consists of both Heat treatable & non- heat treatable alloys.

It is pure aluminum series, non-heat treatable..U.T.S: 10-27 ksi.Good corrosion resistance, electrical properties.Welded with matching /4xxx filler material.Applications:Specialized chemical tanks manufacture.Piping, Bus bars, General structural applications1xxx series

2xxx seriesIt is Al-Cu (0.7-6.8% Cu ), heat treatable alloys.U.T.S: 27-62 Ksi.High strength and high performance alloys.Welded with 2xxx/4xxx series fillers.Some of these alloys are not Weldable (Susceptibility to Hot cracking and SCC)Applications:Aerospace and air craft applications.

3xxx seriesIt is Al-Mn(0.05-1.8 Mn), non heat treatable alloys.U.T.S: 16-41 Ksi.Moderate strength, good corrosion resistance and formability.Welded with 1xxx, 4xxx and 5xxx.

Applications:Heat exchangers in vehicles and power plants.Structural applications.

4XXX SERIES . It is Al-Si (0.6-21.5% Si), both H.T & Non H.T alloys.U.T.S: 25-55 ksi.These fillers are low M.P & improve its fluidity. (Predominantly used for Fusion welding & brazing)Addition of Mg (or) Cu to these alloys, improves respond to H.T.

5XXX SERIESIt is Al-Mg (0.2-6.2%), Non H.T alloys.U.T.S: 18-51 Ksi (Highest strength of Non H.T alloys).Readily weldable alloys.Base alloy < 2.5 % Mg welded with 4xxx/5xxx filler metals.Base alloy >2.5% Mg more susceptible to S.C.C.

ApplicationsShip buildingTransportationPressure vessels, Bridges

6XXX SERIESIt is Al-Mg-Si (Mg &Si additions of around 1%). U.T.S: 18-58 ksi,Heat treatable alloys. It should not be arc welded autogenously. (Solidification crack sensitive)They are welded both 4xxx & 5xxx series.Widely used in welded fabrication.

7XXX SERIESIt is Al-Zn (0.8-12%Zn), heat treatable alloy.U.T.S: 32-88 Ksi.(highest strength of Al-alloys).Some alloys regarded as unsuitable for arc welding.Welded alloys are welded with 5xxx series filler metals.ApplicationsUsed for high performance applications. (Aircraft & Aerospace applications)Used for competitive sporting equipment.

Joining of Al-alloys by fusion welding SMAWGTAWGMAW

SMAWWelding is done with a DCEP.Used for Non critical applications & repair work.Welding speed is slower.Important factors:Moisture content of the electrode covering.Cleanliness of the electrode and base metal.Preheating of base metal.Proper slag removal between passes and after welding.

GTAWTYPES OF WELDING CURRENTACDCEPDECNDC-PULSED.

AC CURRENTAlternate current, equal arc heat concentration at work/at electrode.Medium penetration (>DCEP &

DCENCurrent flows from electrode to work (-ve to +ve).Arc heat concentrated- 70% at work, 30% at electrode.Narrow & deep penetration.Size of the Tungsten electrode-small.Applications:Automatic welding.Maximum work thickness- 1/4 -3/4 inch.

DCEPCurrent flows from work to electrode +ve to -ve).Arc heat concentrated- 30% at work, 70% at electrode.Wide & shallow penetration.It has best cleaning action of the three but poor penetration.Size of the Tungsten electrode-big.Applications:Thin sheet welding also root pass on pipe.Maximum work thickness- very low (below 0.05inch).

DC- PULSED To provide good control of the molten weld pool, particularly welding in other than the flat position.Precaution in TIG welding: when TIG welding of Al-alloys, a band of white deposit appear alongside the weld bead. When deposit band is of hair line width, it indicates that the shielding gas is just adequate. If the band is wider, it means the gas flow is too much and gas is being wasted.

Preheat temperaturesFor welding Upto 6.3 mm thickness- no preheatFor welding 6.3 -9.5 mm thickness in flat position- 2000C.For welding 9.5 mm thickness in other positions -3150C. For welding 12.7 mm & more thickness in all position- 3150C.

GMAWWelding speeds are higher (continuous filler wire).

Higher deposition rate.

Heat effected zones are narrower & less distortion.

It gives greater weld strength at low welding costs.Problems:Porosity.Crater cracks.

Methods of removing various contaminantsDirt: By washing & scrubbing with a detergent solution.Mechanical cleaning/heavy oxide layer removal: By using with S.S. wire brush, steel wool, grinder, mill file/scraper.Chemical cleaning/grease and oil removal: Swabbing with an Organic solvent like acetone, carbon tetrachloride (or) trichlorethylene. Total oxide removal: Immersion in butylachohol-phosphoric acid type solution followed by washing with water and drying with hot air.

Shielding gasesArgon: It gives lower arc heat, smoother and steadier arc. It gives less penetration than He & less spatter. .It is prefer for thinner sections- Upto 19 mm thick.Helium: It gives higher arc heat, deeper penetration.weld profile which is wider and less convex.The spatter is slightly more than with Argon.

Weld defectsPorosity:Causes:Hydrogen is main cause (high solubility in molten Al).Moisture content, oil, greases on the work surface.Excessive moisture pickup in electrode covering.By maintaining the long arc length.By excessive current, higher travel speed.Remedies:Clean the joint area free from oil, grease, dirt etc.Store electrodes properly and Bake the electrodes just before welding. By change in weld parameters and technique.

Crater cracksRemedies:Reverse the direction of welding at the end of each tack/intermittent weld.Use run on and run-off tabs.Break the arc and restrike to fill the crater.Use special circuitry and power source control to produce a special rate of arc decay.

Thank Q