Enhanced Fatigue Crack Propagation Resistance of Friction Strir Welded Al-Cu-Li Alloys (similar and dissimilar)

Tuesday, May 8, 2018: 4:00 PM
Naples 2 (Gaylord Palms Resort )
Ms. Carla Isabel dos Santos Maciel , University of São Paulo, São Carlos, Brazil
Dr. Cassius Olivio Figueiredo Terra Ruchert , University of São Paulo, São Carlos, Brazil
Mr. Evandro Menassi Siqueira , University of São Paulo, São Carlos, Brazil
Mr. Victor Ferrinho Pereira , Brazilian Nanotechnology Laboratory, Campinas, Brazil
Dr. François Brisset , ICMMO University Paris-Sud, Orsay, France
Mr. Fernando Fernandez , Embraer, São José dos Campos, Brazil
Prof. Waldek Wladimir Bose Filho , University of São Paulo, São Carlos, Brazil
Recent development of Al alloys and joining technologies brought new opportunities to the aircraft industries for weigh reduction. The AA7050 alloy was developed to withstand stress corrosion through heat-treated microstructures to improve stress and corrosion resistance without compromising the mechanical properties, while AA2198 and AA 2050 alloys were developed with the purpose of having lower density and higher elasticity modulus by Li addition, as well as good fatigue resistance. Friction stir welding, FSW, process allows joins productions of similar and dissimilar metals with high mechanical strength, along with a defect free joint. This work seeks to explore the fatigue crack growth behaviour, FCG, in parent plate and local welded regions of advanced AA2198-T851 and AA2050-T84 Al-Cu-Li alloys (including dissimilar parent AA7050- T7451 welded to AA2050-T84) produced by FSW. Both intrinsic materials factors (microstructure) and extrinsic testing variables (air and 3.5 wt% aqueous saline environment) were addressed. Microstructure-properties relationships to explain the FCG behaviour were developed at different DK values near its threshold, 6 MPa.m0.5 and 15 MPa.m0.5 (stage II) were carried out in air and saline environment (3.5 % NaCl) in the parent plate of AA7050- T7451, AA2198-T851, AA2050-T84, AA2198-T851 (similar) and AA2050-T84/AA7050- T7451 - T7451 (dissimilar) FSW joins. The results has shown that the weld process affected the FCG behaviour of the similar AA2198-T851 FSW, but it did not affected the dissimilar FSW AA2050-T84/ AA7050- T7451. In both cases, the saline environment affected negatively the FCG rate. To explain the observed fatigue behaviour, detailed fractography and EBSD analysis were performed and it was observed that the recrystallized small grains at the nugget play an important role in determining the fatigue crack path. In addition, it was observed that there is no sensitive deviation during fatigue crack propagation under the effect of saline environment.
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