Shear Deformation Properties of Extruded AlZnMg Alloys

Abstract

INPG, Ge´nie Physique et Me´canique des Mate´riaux, Grenoble, France(Received November 25, 1997)(Accepted November 25, 1997)1. IntroductionMechanical characterization together with detailed studies of the microstructure and deformationmechanisms in various modes of loading are of vital importance to material modeling. In a simpletensile test of a polycrystalline metal, the force applied to the specimen acts on numerous crystallo-graphic planes, i.e. the applied stress is effectively decomposed into shear stresses on the actual slipplanes. The measured macroscopic deformation is the sum of the microscopic shear displacementswithin each grain. From this point of view, the shear stress vs. strain behavior of the material seems tobe of fundamental importance. Further, on the macro scale one can say that most metal formingoperations involve shear deformation of some sort.There are numerous ways to do shear testing. The most widely used is probably the torsion test [1].However, this method can not be applied directly to thin extrusions and rolled sheets. Among the otheroptions are specially designed tensile specimens [2], the Miyauchi shear test [3] and the Iosipescu sheartest [4]. The shear test used in the present work, however, was originally developed for testing solidpolymers [5] and later adapted for testing sheet metal samples [6,7,8]. This test offers severaladvantages. It employs rectangular test specimens that are easy to produce and which can be sampledout at different locations in the plate or sheet. Detailed information on the shear anisotropy, sheardeformation rates and microstructural gradients are easily obtained. Further it is possible to reach veryhigh strains without fracture or necking and to carry out stress reversal tests, strain path changes, strainrate changes etc.In earlier work on the present high strength AlZnMg alloys, both tensile testing and texturemeasurements have been employed [9]. These investigations revealed a strong directional dependencein the mechanical properties caused by crystallographic texture.2. Experimental ProcedureThe MaterialThe present investigations were carried out on flat extrusions (5mm 3 150mm) of the alloys AA7108and AA7030 with chemical compositions shown in Table 1. The plates were received from the RaufossHydro Automotive Research Centre AS in the as extruded condition.