Effects of strain rate and anisotropy on the tensile deformation properties of extruded AlZnMg alloys

Abstract

Two extruded AlZnMg alloys have been investigated in uniaxial tension, emphasizing the mechanical anisotropy and strain-rate effects. A strong mechanical anisotropy was found in the extruded profiles which had recrystallized and nonrecrystallized microstructures. The recrystallized alloy had a lower strength level and less variation in ductility and formability parameters than the nonrecrystallized alloy. Mg in solid solution causes dynamic strain aging (DSA) in both alloys. With increasing strain rate, the DSA became less effective and the strain localization caused by DSA vanished. Thus, the room-temperature formability, in the solution heat-treated and quenched condition, may be improved significantly by a sufficient increase of the strain rate. Additional tests on an as-cast sheet-ingot AlMg alloy were performed to isolate the effect of Mg from Zn in solid solution. These tests confirmed the effect of strain rate on the tensile behavior.

Temperature and strain rate dependence of the dynamic strain aging effect in an Al–Zn–Mg alloy

“…1). A texture analysis of extruded AA7030 with identical production as in the present case was performed by Fjeldly and Roven, 10 and it was shown to have a recrystallisation texture.…”

“…The present study is aimed at characterisation of DSA properties of AA7030 aluminium alloy with respect to heat treatment, temperature and strain rate. Fjeldly and coworkers [10][11][12][13][14][15] have earlier investigated the extruded AA7030 with respect to SRS, PLC effect and anisotropy, however only in the solution treated condition at room temperature. In the present study also the peak aged temper is included, because this is the condition in which the material is used industrially.…”

Precipitation, mechanical properties and early slant ductile fracture in cyclic and naturally aged Al-Zn-Mg(-Cu) alloys

“…Interestingly, higher work hardening, higher uniform elongation and higher uniform strength, as well as a yield strength similar to the artificially peak aged condition, was reported to be obtained by NA of an Al-Zn4.8-Mg1.4 alloy [13]. However, in some cases, an early shear fracture has been reported to occur, rather than ordinary necking in tensile tests of naturally aged alloys [14][15][16]. Chung et al [15] found for an as quenched 7075 alloy, that the shear fracture was replaced by ordinary necking instability at low temperature tests and suggested that the reason for shear fractures may be the dynamic strain ageing phenomenon, associated with the Portevin-Le Chatelier effect in this type of alloys [17].…”

Temperature and Strain Rate Effects on the Dynamic Strain Ageing of Aluminium Alloy AA7030

“…Owing to the low Zr content, the microstructure became recrystallized during extrusion with an average grain size of 110 µm (ASTM grain size number 3-4), and only a small elongation of the grains in the longitudinal direction was observed. In other investigations the material has been shown to have a recrystallization (cube) texture [7]. The material was tested in two different states, naturally aged (NA) and peak aged (PA).…”

“…This investigation concerns the combined effects of strain rate and temperature on the mechanical properties of AA7030, in relation to DSA, under tensile deformation. This alloy has earlier been shown by Fjeldly and Roven [5,7] to exhibit serrated flow and negative strain rate sensitivity (SRS) in the solution treated condition at room temperature and the aim here is to more extensively investigate the effect of heat treatment, strain rate and temperature.…”