The Portevin–Le Châtelier (PLC) effect often results in serrated plastic flow during tensile testing of aluminum alloys. Its magnitude and characteristics are often sensitive to a material’s heat treatment condition and to the applied strain rate and deformation temperature. In this study, we analyze the plastic deformation behavior of an age-hardenable Al-Cu alloy (AA2017) and of a particle reinforced AA2017 alloy (10 vol. % SiC) in two different conditions: solid solution annealed (W) and naturally aged (T4). For the W-condition of both materials, pronounced serrated flow is observed, while both T4-conditions do not show distinct serrations. It is also found that a reduction of the testing temperature (−60 °C, −196 °C) shifts the onset of serrations to larger plastic strains and additionally reduces their amplitude. Furthermore, compressive jump tests (with alternating strain rates) at room temperature confirm a negative strain rate sensitivity for the W-condition. The occurring PLC effect, as well as the propagation of the corresponding PLC bands in the W-condition, is finally characterized by digital image correlation (DIC) and by acoustic emission measurements during tensile testing. The formation of PLC bands in the reinforced material is accompanied by distinct stress drops as well as by perceptible acoustic emission, and the experimental results clearly show that only type A PLC bands occur during testing at room temperature (RT).

An experimental analysis of the effect of in-plane strain path changes and Bauschinger effects during mechanical loading that involves compression is quite challenging for sheet materials because they are prone to buckling. In this paper, we present a newly developed method that allows to deform sheet metals in tension and in compression. Our experimental setup primarily consists of an anti-buckling clamping device that can be used in a universal mechanical testing machine. Surface strains are measured with a digital image correlation (DIC) system. To demonstrate the viability of our method, first tests are conducted on thin sheet specimens (1 mm thickness) of a DC06 steel. Several approaches to reduce friction between the clamping system and the specimen are investigated. The validity of the test results is established in monotonic tensile tests. Measurements with different amounts of maximum tensile strain and reversed strain values are also discussed, showing that the material exhibits a Bauschinger effect, which is further quantified using different Bauschinger parameters.

Equal-channel angular pressing (ECAP) is often used as effective tool for grain refinement for many different metallic materials. It is well known that grain size is an important microstructural feature influencing superplastic properties of fcc materials like aluminum alloys. The magnitude of introduced shear strain depends on geometrical parameters of the ECAP channel. In this contribution, the impact of different geometrical parameters of the ECAP channel on the resulting magnitude of introduced shear strain is analyzed. ECAP on AA5083 aluminum sheets with the dimensions of 200x200x1.8 mm3 is performed. Microhardness measurements reveal a considerable increase of hardness after ECAP and microstructural investigations by electron backscatter diffraction (EBSD) show the beginning formation of a deformation-induced substructure which is known to be a preliminary stage of the grain refinement process. It is assumed that this fine-grained microstructure results in an enhanced superplastic forming capability. Furthermore, a numerical model of the process based on the experimental results is established. The bending of the ECAP processed sheet metal as well as its microhardness are used for the validation of the model. The friction coefficient between the channel and the aluminum sheet significantly influences the results of the simulation. With the applied model different channel angles and inner corner radii are varied in order to determine a maximum magnitude of deformation resulting in sufficient grain refinement of the investigated material. With the help of the results gained in this study, suitable ECAP parameters for sheet metals can be derived that enable creating ultrafine-grained materials for superplastic forming operations.