The E.O. Paton Welding Institute 1 NEW TECHNIQUE FOR EXPLOSION WELDING OF HIGH-STRENGTH ALUMINUM ALLOYS OF SERIES 7xxx S.Yu. Illarionov*, L.D. Dobrushin**, Yu.I. Fadeenko E.O. Paton Electric Welding Institute, Kiev, Ukraine

The E.O. Paton Welding Institute 2 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 Institute3 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 Institute4 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 Institute5 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 Institute6 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 Institute7 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 of Material UTS, MPa 0.2% YS, MPa Elongation, % Alloy 7017 Т Alloy 7018 Т Base material

The E.O. Paton Welding Institute8 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 Institute9 Appearance of Tensile Test Specimens before and after Tests Appearance of Shear Test Specimens before and after Tests

The E.O. Paton Welding Institute10 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 Institute11 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 Institute12 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 Heating + quenching + natural ageing during 32 days As-received State--

The E.O. Paton Welding Institute13 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 Institute14 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 state350* * 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 Heating + quenching + natural ageing during 29 days Heating + quenching + natural ageing during 70 days ≈350≈100 UTS in shear is 175…201 MPa

The E.O. Paton Welding Institute15 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 Institute16 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 Institute17 THANK YOU FOR YOUR ATTENTION