Banca de QUALIFICAÇÃO: JULIANO AUGUSTO MEDEIROS DE MENEZES E OLIVEIRA

Study of the effect of electrical pulses on the mechanical and microstructural behavior of the AA7075 alloy (Al-Zn-Mg-Cu) for self-healing of pre-deformed alloys

Self-Healing; Al - Alloy;

Over the past few years, research into self-repairing materials has gained increasing scientific attention. In this 
class of bioinspired materials, engineers and scientists rely on biological mechanisms to design new materials 
with unique characteristics. Advances in this sense are widely noted in several classes of materials. Specifically 
for metallic materials, processing by electrical pulses, or EPT (Electropulsing Treatment), is a new approach to 
self-healling that is growing in importance in the technological field. The application of a controlled current of 
sufficiently high density, but with a low temperature rise, generates a flow of electrons with energy capable 
of modifying the microstructure, which may promote stress relief, the reduction of micro-sucks and micro-cracks 
or even the recrystallization. Given the importance of techniques that increase the useful life of aeronautical
 components, the purpose of this work is to establish a methodology with the development of appropriate 
parameters for the self-repair process via electrical pulses in the aluminum alloy AA 7075 (Al-Zn-Mg -Ass). 
Compositional and phase analysis was performed via X-ray fluorescence (FRX) and X-ray diffraction (XRD). 
The mechanical behavior and generation of crystalline defects was previously evaluated in specimens machined 
according to the ASTM e8 standard, under interrupted tensile tests at deformations of 60%, 70%, 80%, 90% 
and 95% relative to rupture, resulting in the increase of yield stresses and reduction of ductility. The hardest
 samples (90 and 95% deformed) were treated via EPT with peak current (Ip) of 300 A, 400 A and 500 A; 
base current 0 A (Ib), Peak time (Tp) and base time in 0.1 s (Tb) in a total treatment time of 5s totaling 
25 cycles. The deformed samples before and after the EPT were analyzed by tensile tests, the results of which 
showed a trend towards increased ductility and reduced yield stress with increasing applied current, indicating
 the effectiveness of the repair with the adopted parameters. Preliminary analyzes of the surfaces of the 
specimens, via scanning electron microscopy (SEM-EDS), were still not enough to prove the microstructural 
effect of self-repair, requiring more detailed analyzes of the internal microstructure of the materials, which 
are in progress.