Fracture energy evaluation on 7075-T651 aluminum alloy welds determined by instrumented impact pendulum
(1. Instituto Politécnico Nacional CIITEC-IPN, Cerrada de Cecati S/N Col. Sta. Catarina C.P 02250,
Azcapotzalco, DF, México;
2. Mechanical and Aerospace Engineering, Carleton University,
1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada;
3. Universidad Autónoma de Coahuila (UAdeC), Facultad de Metalurgia, Carr. 57, Km 5, Monclova, Coahuila, México)
Azcapotzalco, DF, México;
2. Mechanical and Aerospace Engineering, Carleton University,
1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada;
3. Universidad Autónoma de Coahuila (UAdeC), Facultad de Metalurgia, Carr. 57, Km 5, Monclova, Coahuila, México)
Abstract: By using an instrumented impact pendulum, the force versus time curves of 7075-T651 aluminum welds were obtained from standard Charpy-V samples. Considering the force-time curves and constant impact velocity, the fracture energies for different zones were quantified. A fracture energy improvement for the HAZ (33.6 J) was observed in comparison with the weld metal (7.88 J), and base metal (5.37 J and 7.37 J for longitudinal and transverse directions, respectively). This toughness increment was attributed to the microstructural transformation caused by the thermodynamic instability of η′ precipitates during the welding. Fracture energy for weld metal was higher than that for base metal, probably due to pores created during solidification. Regarding the dynamic yielding force obtained from the force-time curves, an approximation to the dynamic yield strength for weld, HAZ and base metal was determined. Fracture surfaces revealed an intergranular failure for base metal in longitudinal direction, whereas a predominately brittle failure (cleavage) with some insights of ductile characteristics was observed for the transverse direction. In contrast, a ductile failure was observed for weld metal and HAZ.
Key words: 7075-T651 welded joint; instrumented Charpy pendulum; force-time curve; fracture energy; dynamic yield strength