Repair welding of HOKOTOL - Clinton Aluminum...Aluminium Walzprodukte GmbH Koblenz. The high-strength alloy HOKOTOL This high-strength alloy which was developed for the aeroplane industry,

Repair welding

of

HOKOTOL

• The high-strength alloy: HOKOTOL• Filler alloys• Preparation for welding• Welding• Welding parameter

Aluminium Walzprodukte GmbH Koblenz

The high-strength alloy HOKOTOL

This high-strength alloy which was developed for the aeroplane industry, was still further optimised for the tooling industry.The result is an alloy for tooling plates, called HOKOTOL, with highest strengthand wear-resistance as well as high regularity of strength.Adapted to the EN-Standards for HOKOTOL the name is AlZnMgCu2,0.These characteristics produces excellent machinability, also at large plate thickness,and remains constant throughout the entire plate thickness.A remarkable feature of HOKOTOL is a high form stability during machining. Due to the very high strength of HOKOTOL the advantages could also be used for other application ranges which normally used medium- or high-strength steels.High-strength aluminium alloys of type AlZnMgCu are in principle difficult to weld without any cracks.Repair welding with suitable welding processes, like TIG and MIG, are possiblefor conditions which are listed in the following.

Hardness profile of a 300 mm (11.8 inch) thick plate

2


Typical values of Yield strength

Welding Conditions

General

• In comparison to steel the welding temperature is not visible since aluminium meltsdo not turn the color to red.

• High energy (heat input) should be quickly applied.• Oxide film (melting temp.: 2020 °C) on the material surface is harmful to welding.

It should be removed before welding.

Welding method

• MIG and TIG are generally used. For thick plates, MIG is the better method to apply.

3


Filler alloys

• Filler material (rod and wire)The order is the recommendable ranking for usage.

• 1) AA 2319 (AlCu6Mn(A))• 2) AA 5183 (AlMg4,5Mn0,7)• 3) AA 5556 (AlMg5Mn0,7)• 4) AA 4043(A) (AlSi5)

Chemical composition of filler ( weight %)

Alloy Si Fe Cu Mn Mg Ti Zr

AA 2319 max. max. 5,8 - 0,20 max. 0,10 - 0,10 -AlCu6Mn(A) 0,20 0,30 6,8 0,40 0,02 0,20 0,25

AA 5183 max. max. max. 0,40 - 4,00 - max. -AlMg4,5Mn0,7 0,40 0,40 0,10 1,00 4,90 0,05

AA 5556 max. max. max. 0,50- 4,7- 0,05- -AlMg5Mn0,7 0,25 0,40 0,10 1,00 5,5 0,20

AA 4043A 4,5 - max. max. max. max. max. -AlSi5 6,0 0,6 0,30 0,15 0,20 0,15

• Filler must be put in an appropriate container and kept dry.• Bare hands or contaminated gloves should not be used when handling a filler wire.

Preparation for welding• Oil contamination and oxide film must be removed before welding.• Mechanical method: - Wire - brushing. Brush of stainless steel wire should be used.

- Filing- Machining etc.

• Chemical method: - Using organic solvent (Aceton)• Weld preparation: Examples of weld preparation are given in the following tables.

4


Weld preparation

• Preparing and welding of edges

Bad Good

45° R >10

Second pass

First pass

Welding direction

Welding direction

Second pass

First pass

5


Hardeness profile of welded HOKOTOL

• Welding process: TIG Filler alloy : AA 5556

Heat -affected

zone

Weldseam

50

100

150

200

Har

dene

ssH

V 10

6



• Welding process: TIG Filler alloy : AA 2319

Heat -affected

zone

Weldseam

60

80

100

120

140

160

180

200

Har

dene

ss(H

V10)

7


• Preparing and welding of areas.

Bad Good

R >10 > 10

R > 6 >10R > 10 >10

>10°

Crack

Bad Good

8


• Welding sequence for welded areas.

Crack

Welding sequenceBad Good

9



• Welding process: TIG Filler alloy: AA 2319

Picture: 2

A B

A B

Heat -affected

zone

Heat -affected

zone

Basematerial

60

80

100

120

140

160

180

200

Har

dene

ss(H

V 10

)

Basematerial

Weldseam

Heat -affected

zone

Basematerial

Weldseam

10



• Welding process: TIG Filler alloy: AA 5556

60

80

100

120

140

160

180

200

Har

dene

ssH

V 10

Picture: 7

Heat -affected

zone

Heat -affected

zone

Basematerial

11


Bad Good

> 30°

R > 6

R > 6

Crack

Wel

ding

dir

ectio

n

Wel

ding

dir

ectio

n

12


• Influence of filler alloy

Bad Good

Crack

Filler alloy:AA 2319first pass

Crack

Filler alloyAA 4043Afirst passno crack

Goodweld preparing welding

Filler alloyAA 2319

Filler alloyAA 4043A

R > 6

13



• Welding process: TIG Filler alloy: AA 2319and: AA 4043A

40

60

80

100

120

140

Har

dene

ss(H

V 10

)

Base material

Heat affected zone

Weld seam AA 4043A

Weld seam AA 2319

AA 4043A

AA 2319


14

Weld parameter

• Welding conditions are determined on size, thickness and welding position of material to be welded.• Starting and ending points should be carefully observed in order to avoid welding defects and

incomplete fusion which could often occur. Return welding is recommended.• The ending point is prone to crack, end crater control is definitely recommended. Return

welding is also recommended.• Pre-heating and temperature between passes should not be more than 175 °C.• Welding parameters for TIG - welding are shown in the next pictures.

Thickness (mm)

Wel

d cu

rren

t (A

)

0

100

200

300

400

500

600

2 6 10 18 22 26

0,50,25 1Thickness (inches)

0,75

AC - TIG - WeldingShielding gas: Argon ( 20 - 40 l/min)Weld type: butt weld


15

• Welding should be done in a downward direction• The best possible welding conditions would be:

Torch assembly

Influence of Shielding gas

• ArgonThe arc with argon is more stable than the arc with helium.

• HeliumThe helium shielded arc has a higher voltage than the argon arc and therefore thewelding speed for the helium shild arc is higher.

• Argon - helium - mixtures• With increasing helium( up to 75 %), arc voltage would increase the penetration.

Cross-sections of weld beads made with Argon and a mixture of 50 % argon +50 % helium are illustrated in the following picture.

ARGON (100 %) Mixture: ARGON + HELIUM50 % + 50 %

~ 3 - 5 mm

~ 10 - 15 °

~ 10 - 12 mm

Welding direction


16

Repair welding of HOKOTOL - Clinton Aluminum...Aluminium Walzprodukte GmbH Koblenz. The high-strength alloy HOKOTOL This high-strength alloy which was developed for the aeroplane industry,

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