The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 11

NEW TECHNIQUE FOR NEW TECHNIQUE FOR EXPLOSION WELDING OF EXPLOSION WELDING OF

HIGH-STRENGTH ALUMINUM HIGH-STRENGTH ALUMINUM ALLOYS OF SERIES 7xxxALLOYS OF SERIES 7xxx

S.Yu. Illarionov*, L.D. Dobrushin**, Yu.I. FadeenkoS.Yu. Illarionov*, L.D. Dobrushin**, Yu.I. Fadeenko

E.O. Paton Electric Welding Institute, Kiev, UkraineE.O. Paton Electric Welding Institute, Kiev, Ukraine

illarionov@optima.com.ua illarionov@optima.com.ua *dobrushin@voliacable.com*dobrushin@voliacable.com

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 22

Non-heat-treatable Aluminum Alloys

Heat-treatable Aluminum Alloys

1xxx

3xxx

4xxx

5xxx

2xxx

6xxx

7xxx

They have the highest strength (up to 700 MPa)owing to:

1) presence of zinc, magnesium and copper as alloying elements;

2) three step heat-treatment process:

solution heat-treatment → quenching → age hardening

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 33

The beginning of migration from riveted airframes

to welded ones in commercial aviary sets the

problem of production of reliable weldments in

7xxx series aluminum alloys

These type of aluminum alloys can be considered as “difficult to

weld”. Their mechanical and structural properties are significantly

assigned by heat-treatment cycle. Therefore, there can be loss of

strength or even “hot short” cracking in the heat-affected zone

So, finding techniques for improving high-

strength aluminum alloys weldability is a topical

problem of modern welding engineering

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 44

The main problem of explosion welding

(EW) of high-strength aluminum alloys is

a lack of plasticity

Elongation of wrought 7xxx series alloys is 3…16% depending

on the type of alloy and its heat-treatment condition

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 55

Conventional Two-step Method of Explosion

Welding of Low-ductility Aluminum Alloys

High-strength aluminum alloy (cladding)

High-strength aluminum alloy (base)

Technical pure aluminum thin layer

The scheme allows to use “soft” regime of EW that leads to surface

activation of the hardest metal up to level when strength of joint reaches

strength of technical pure aluminum.

But for some applications this is not acceptable

So, direct welding of Al alloy + Al alloy is an important issue

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 66

New technique proposed for EW of high-strength

aluminum alloys of series 7xxx is based on unique

feature of heat-treatable alloys – natural ageing

The Sequence of Procedures to Be Done

Cladding plate

is heated up to

465…480°C

during 1 hour to

dissolve of

soluble phases

Cladding plate

is quenched in

water to

develop of

supersaturation

EW during

incubation

period

Natural or artificial (if possible) aging to strengthen cladding plate material and bond zone respectively

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 77

The following materials were under investigation:

Cladding material:

- Alloy 7017 T651 plates (10 mm thickness);

- Alloy 7018 T7651 plates (15 and 10 mm thickness);

* these alloys are typically used for armour for protection

Base material is modern modification of 7010 and 7050 alloys

Type ofMaterial

UTS,MPa

0.2% YS,MPa

Elongation,%

Alloy 7017 Т651 468 425 13.0

Alloy 7018 Т7651 350 291 16.4

Base material 510 476 7

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 88

Test Methods of Cladding Material

and Mechanical Properties of Joint

1) Cladding plate hardness (HRB under a load of 600 N) measurement

for permanent control of strengthening during its natural aging

2) Tensile tests of the joints

Base Alloy

Cladding Alloy

3) Shear tests of the joints

Cladding Alloy

Base Alloy

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 99

Appearance of Tensile Test Specimens before and after Tests

Appearance of Shear Test Specimens before and after Tests Appearance of Shear Test Specimens before and after Tests

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1010

Appearance of the Sample after Explosion Cladding

It should be noted that to select optimal parameters for explosion welding of high-

strength aluminum alloys of series 7xxx, it is necessary to maximize the time of the

impact by the detonation products on the cladding plate. In practice it is required to tend

to minimize standoff distance and to maximize layer of explosive simultaneously.

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1111

Typical Microstructure of Interface

between Alloy 7017 (up) in As-received

State and Base Alloy (down), X100

Typical Microstructure of Interface

between Heat-Treated Alloy 7017 (up)

and Base Alloy (down), X100

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1212

The measurements showed that after 20 days of natural ageing of alloy

7017 its hardness (under a load of 600 N) became HRB 87…89, after 32

days - 90…92, whereas in the as-received condition it was 105…106

Heat-Treatment State of Cladding Plate

in 7017 alloy

UTS of Joint,MPa

UTS of Joint to UTS of Cladding Plate Material

Ratio, %

Heating + quenching + natural ageing

during 6 days

272 58

Heating + quenching + natural ageing during 32 days

420 89

As-received State - -

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1313

Typical Microstructure of Interface

between Alloy 7018 (up) in As-received

State and Base Alloy (down), X100

Typical Microstructure of Interface

between Heat-Treated Alloy 7018 (up)

and Base Alloy (down), X100

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1414

The measurements showed that after 20 days of natural ageing of alloy

7018 its hardness (under a load of 600 N) became HRB 80…82, after 32

days - 87…89, whereas in the as-received condition it was 101…102

Heat-Treatment State of Cladding Plate

in 7018 alloy

UTS of Joint,MPa

UTS of Joint to UTS of Cladding

Plate Material Ratio, %

As-received state 350* * it must be noted that interface line has

crests and eddies; this can adversely affect on fatigue and cyclic strength

100

Heating + quenching + natural ageing during 6 days

290 82

Heating + quenching + natural ageing during 29 days

340 97

Heating + quenching + natural ageing during 70 days

≈350 ≈100

UTS in shear is 175…201 MPa

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1515

Appearance of the Samples

Prepared for Electron Beam

Welding

Macrosection of full-scale combined

joint (EW + EBW)

The Example of Possible Foreseen Usage of the Presented Results

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1616

It can be concluded:

1) Receiving joints of high-strength heat-treatable aluminum alloys using

proposed technique seems to be possible (for the case when maximum

strength of cladding plate is 470 MPa in particular).

2) Application of natural ageing makes possible not to apply heat-treatment

of the joint after explosion welding. It is too important when it is not

allowed to heat base alloy.

3) Application of proposed technique is useful and effective in combination

with conventional butt welding methods in case it is impossible to weld

high-strength alloy.

The E.O. Paton Welding InstituteThe E.O. Paton Welding Institute 1717

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