Microstructure and mechanical properties evaluation after annealing heat treatment of 7475-T7351 alluminum alloy

Abstract

The mechanical strength of the 7XXX series aluminum alloys can be improved through cold rolling due to the hardening, however, there is a reduction on ductility, thus requiring a later stage of annealing heat treatment. The present work is aimed on the evaluation of the effects of an annealing heat treatment at 500 °C for 15 minutes, on the microstructure and mechanical properties of a cold rolled 7475-T7351 aluminum alloy with 3 mm thickness. For this purpose, it was used microstructural characterization by scanning electron microscopy / X-ray Dispersive Energy Spectrometry, and uniaxial tensile tests. It was concluded that the annealing heat treatment, promoted the matrix recrystallization, providing a decrease of the tensile strength and yield strength, and increase of the ductility. The coarse precipitates evidenced are similar and possibly Al7Cu2Fe and Al2CuMg.

Temperature and annealing time influences on cross-rolled 7475-T7351 aluminum alloy

“…There is the formation of "second phase" micro-constituents with the alloy casting and heat treatments on 7XXX series aluminum alloys. They can be divided into three different groups: [3,4,7,[10][11][12] (i) the primary particles (commonly Al 7 Cr, Al 3 Ti e/ou Al 3 Zr) are the first to solidify even before aluminum; (ii) the constituent particles (commonly Al 7 Cu 2 Fe, Al 12 (Fe,Mn) 3 Si, Al 6 (Fe,Mn), Mg 2 Si, SiO 2 , Al 2 CuMg and Al 23 CuFe 4 ), that are usually coherent with the matrix, have a coarse size and can be insoluble or partially soluble; and (iii) the dispersoids (commonly Al 12 Mg 2 Cr and MgZn 2 ) which are commonly smaller than 1 μm.…”

“…[13,14] Similarly, the 7xxx series alloys mechanical strength decreases, for temperatures above 150 ºC, may be associated with the solubilization of the η' dispersoids leading to the formation of MgZn 2 dispersoids, or the coalescing of the η' dispersoid. [13,14] In addition to the T7351 treatment, cold forming processes, such as rolling, can also be used to increase the tensile strength of the 7XXX series aluminum alloys [7,10]. During cold forming processes, important events occur that change the mechanical properties, such as: increase in dislocations density (hardening) and vacancy, change in grain shape which become elongated in the mechanical work direction, and developing crystallographic texture [15][16][17][18][19].…”