Texture and formability studies on AA7020 Al alloy sheets R. Shabadi a,b,n , S. Suwas b , S. Kumar b , H.J. Roven c , E.S. Dwarkadasa b a Physical Metallurgy and Materials Engineering, Unit of Materials and Transformations, University of Science and Technology of Lille, Villeneuve d’Ascq 59655, France b Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India c Department of Materials Science and Engineering, NTNU, Trondheim, Norway article info Article history: Received 21 May 2012 Received in revised form 7 August 2012 Accepted 8 August 2012 Available online 24 August 2012 Keywords: Texture 7020 Forming r-value Deformation bands Marciniak testing abstract This paper deals with the influence of crystallographic texture on room temperature mechanical behavior of the sheets of the aluminum alloy AA7020 processed to different thicknesses. Three different thicknesses of the alloy sheet, namely 1, 1.85, and 3.6 mm, corresponding to different textures were investigated. Tensile tests were carried out at 01, 451 and 901 with respect to sheet rolling direction and the resulting in-plane anisotropy in 0.2 proof stress, work hardening and plastic strain ratio (r-value) were determined. Texture derived r-values are also calculated and discussed vis-  a-vis the experimen- tally obtained r-values. Finally the formability of the optimal alloy was studied using forming limit diagrams. Effect of natural aging, with a simulated heat treatment of 70 1C for 2 h on FLD was studied and compared with the as solutionized samples. It was observed that, the strain levels in the bi-axial region of the FLD were not much affected by the heat treatment. & 2012 Elsevier B.V. All rights reserved. 1. Introduction The heat treatable 7xxx alloys are preferred for applications in aerospace and the automotive body panels, where both the surface quality and formability are important issues. A detailed processing of various Al alloys applied in automotive industry has been extensively discussed by Furu et al. [1], including the raw material processing till the production of the end product. It is well known that formability depends on work hardening, strain rate sensitivity, anisotropy due to crystallographic texture and the tempering state. For example, when a sheet is probed in different directions, the yield strength and subsequent work hardening as well as plastic strain ratio (r-value) varies as a function of angle from the rolling direction. With sheet metals, efforts have been made to control anisotropy by developing processing routes, which produce desirable textures. Many Al alloys are formed in the solid solutionized condition as the material the material is relatively soft and hence the easiness in forming the shapes. However, in the as solutionized condition, Mg in solid solution in these alloys is known to be efficient diffusing to the dislocation segments thereby temporarily pinning them down. This behavior exhibit the Portevin–Le Chatelier (PLC) effect [2–4], which is caused by the dynamic strain aging and characteristically leads to the serrated yielding and associated with the propagating deformation bands [5]. Shabadi [6] has shown that the negative strain rate sensitivity associated with the dynamic strain aging in Al–Zn–Mg alloys promote the localization of the strain and formation of the shear bands that limits the formability of these materials. In sheet products, crystallographic texture plays an important role to tailor the desirable mechanical properties: recent studies [7–9] have shown that ideal cube texture decreases the form- ability, intensity and the sharpness of the cube texture plays an important role in the localization of strain. In an earlier study by Wu et al. [10] using simulations have shown that ideal cube texture decreases formability while as spread about cube texture delays the localized necking in a material subjected to bi-axial stretching. A detailed testing of 7108 and 7030 alloys by Lademo et al. [9], have shown that the materials with nearly random texture exhibit superior formability. This was mainly attributed to the enhanced work hardening of these materials. For the material with strong-fiber texture (AA7108), lower formability was found in equibiaxial stretching than in plane strain, while this char- acteristic was not observed for the material with strong cube texture (AA7030). The reduced formability was caused by the formation of shear bands prior to necking. Shabadi [6], have showed that in solutionized Al–Zn–Mg alloys with recrystallized pancake grain structure, the strain localization caused PLC effect subsequently leads to the formation of a shear band. Lademo et al. [9] have also experienced that the strain localization in Al–Zn–Mg alloys has a detrimental effect of the formability of the materials. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A 0921-5093/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2012.08.024 n Corresponding author at: Physical Metallurgy and Materials Engineering, Unit of Materials and Transformations, University of Science and Technology of Lille, Villeneuve d’Ascq 59655, France. Tel.: þ33 699212594; fax: þ33 320434040. E-mail address: rajashekhara.shabadi@univ-lille1.fr (R. Shabadi). Materials Science & Engineering A 558 (2012) 439–445