Abstract
Ultrasonic welding (USW) is a promising technique of solid state joining of similar and dissimilar materials, including aluminum and titanium alloys. Differences in the physical and mechanical properties of the materials to be joined make it difficult to adjust the welding conditions to form high-quality joints. The development of natural aging in aluminum alloys may cause a change in the fracture mode and strength of Al / Ti ultrasonically welded joints. In present study, cryorolled and naturally aged AA2024 alloy sheet and annealed commercially pure titanium sheets were subjected to USW. The pre-treatment provided similar values of the hardness of the initial sheets. To avoid the adhesion of aluminum to the welding tool during welding, the AA2024 alloy sheet was sandwiched between the titanium sheets. Microstructure and properties of the welded joints after natural aging were examined. No cracks, discontinuities, pores were observed near the contact surfaces at magnifications of the microscope up to 1000 times. No diffusional or intermetallic reaction layers were revealed in the welded joints. The microstructure and microhardness of titanium sheets did not change after ultrasonic welding. Recovery / recrystallization development led to a decrease in microhardness of AA2024 alloy sheet. All welded samples fractured along the interface between the AA2024 alloy sheet and the bottom titanium sheet adjacent to the anvil. The average lap shear failure load of the welds was 1612 ± 278 N (shear strength of approximately 57 ±10 MPa).
Highlights
Welding of dissimilar materials is gaining more and more importance, as it allows one to obtain structures with a required balance of properties reducing the cost of their production
According to [7], the thickness of the TiAl3 intermetallic layer significantly affects the mechanical properties of Al / Ti joints obtained by friction welding, and the intermetallic compounds (IMCs) layer thickness cannot exceed the critical value of 5 μm
Cards of AA2024 alloy were placed between commercially pure titanium (CP Ti) sheets as shown in Fig. 1a to prevent the adhesion of aluminum to the surface of the anvil and welding tip during ultrasonic welding (USW)
Summary
Welding of dissimilar materials is gaining more and more importance, as it allows one to obtain structures with a required balance of properties reducing the cost of their production. Differences in the properties of titanium and aluminum (in the melting point, heat conductivity, coefficient of linear expansion, mutual solubility, etc.) make it difficult to obtain high-quality weld joints. Hard and brittle intermetallic compounds (IMCs) of the Al-Ti system are readily formed at the interface [2 – 4] In this regard, solid state welding techniques are developed such as diffusion bonding and various types of friction welding. One of promising techniques of solid state joining of similar and dissimilar materials, including aluminum and titanium alloys, is ultrasonic welding (USW) [8]. As with other welding techniques, it is difficult to adjust the USW conditions for welding dissimilar materials due to differences in their physical and mechanical properties (thermal conductivity, heat capacity, strength, wear resistance, etc.). In contrast to the cited studies, the materials to be joined had a similar strength before USW due to a preliminary thermal and deformation treatment
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