Key Engineering Materials Vol. 794

Abstract: 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.

Abstract: In the present study, we investigate the effect of the sample size and layer direction on mechanical properties of the specimen fabricated by the FDM-type 3D printer under 4-point bending test. Acrylonitrile-butadiene-styrene (ABS) was employed as a source material. Bending tests were performed under several experimental conditions of layer direction, dimension of the specimens and supporting distance. The relationship between bending load and displacement depended strongly on the layer direction. Young’s modulus increased with increasing supporting distance, particularly, when the filaments were parallel to the loading direction. The strain distribution during the bending test was evaluated by DIC. When the supporting distance was short, strain distribution obtained from DIC became different from the theoretical distribution. This result indicated that the prominent shear deformation occurs in the bending of the printed material when the supporting distance is short. Subsequently, FEM analysis was performed to remove the error in the estimation of Young’s modulus due to the shear deformation, and the correcting equation was proposed.

Abstract: The mechanism of galling generation is studied with finish blanking using TiCN coated punch. A high-tensile-strength-steel plate with a thickness of 6mm is used in the present paper. The edge shapes of punch are two types, a punch with 1.0 mm chamfered edge (C1.0 punch) and a punch with right angle edge (RA punch). The clearance is kept to 0.5%t, and lubrication is not used in this experiment. Galling is observed at the first shearing operation except for RA punch, and galling can’t be found clearly even when the shearing number reaches 20 in the case of the RA punch. In order to clarify these differences of RA punch and C1.0 punch, the oxygen on burnished depth is observed by electron probe micro analyzer (EPMA). The oxygen is not detected on the burnished depth sheared by RA punch. On the other hand, the oxygen is detected on the burnished depth sheared by C1.0 punch. In the case of C1.0 punch, the oxide scale on the plate surface flow into the burnished depth because of the low surface expansion ratio of the burnish depth. Thermochemical simulation is carried out using a commercial code MALT and gem which solves chemical equilibrium problems by minimizing the gibbs energy of the system. TiCN reacts with oxide scale to form Fe and Fe₄N. As result of analyzing galling part of C1.0 punch from the cross section direction, Fe, Fe₄N, FeTiO₃ and Fe₂TiO₄ are detected and those detected elements coincides well with the Thermochemical simulation.