Estudo do processo de soldagem a ponto por fricção de juntas dissimilares entre ligas de alumínio e titânio
Abstract
Multimaterial structures between aluminum and titanium alloys are a
technologically attractive field of research and their increasing use in the
transportation sector for weight and emission reduction is part of the motivation
of this study. The currently used techniques are either too expensive or limited
in performance, especially by excessive formation of undesirable intermetallic
compounds, opening opportunities for innovation in this area. Friction spot
welding (FSpW), a solid state joining process recently developed by Helmholtz
Zentrum Geesthacht, has proven to be one of the promising technologies for
joining dissimilar materials as it involves short steps and low thermal cycles,
also with the advantages of adding no weight to the structure and having
geometrical compatibility to replace rivets. The present work studies the
feasibility in welding AA5754-H22/Ti6Al4V and AA6181-T4/Ti6Al4V joints
through FSpW. In addition, it is intended to establish the microstructure/
properties / process relationships of the resultant joints, in order to understand
the formation and growth of the joining interface and its consequences on the
mechanical performance. The proposed joints are produced in overlap
configuration through different combinations of parameters, which were
established by statistical methods involving design of experiments, and later
submitted to mechanical and metallurgical characterization. The results reveal
that Al/Ti dissimilar joints with high strength and reproducibility can be produced
by using FSpW. The mechanical behavior of the joints presents a strong
dependence on the intermetallic thickness formed at the bounding interface,
identified as TiAl3. Tool rotational speed and dwell time are key process
parameters in controlling the resistance of welded joints. Moreover, the bending
load associated to differences in stiffness and/or thickness of the welded
specimen appears as an important variable influencing the crack propagation
path during shear and fatigue tests.