Deformation Behavior of Al-Al and Al-Cu Laminated Materials Produced by Accumulated Extrusion

Accumulated Extrusion (AccumEx) is a novel SPD technique that has been introduced for the first time in this thesis. The processing technique was evaluated using experiments on commercially pure Al and Cu. The first study was done on Al-Al laminates. Stacks of Al were deformed up to 8 deformation passes. An UFG microstructure with an average equivalent grain size of 0.9 µm with high angle grain boundaries (HAGB) fraction of 70 % and a texture with combination of plane strain compression and shear components were obtained. The shear texture components began to increase in intensity from 4 passes onwards. The mechanical properties were good only till 4 passes with a yield strength of near 200 MPa and elongation to failure of 6 %. Both the grain size and the hardness saturated after 4 passes. The process induced severe strain inhomogeneities within the material and they increased as the number of deformation passes was increased. The effect of process induced shear on Al laminates was studied using the embedded-pin technique combined with continuum mechanics. True shear strains were derived to be a function of sample thickness after 1 pass and they accumulated after every deformation pass. They had a significant effect on the texture and microstructure of the material after 1 deformation pass, which were characterized using the EBSD technique. Grain size saturation was studied with the help of ex-situ plane strain compression tests coupled with spatial EBSD characterization. Grain size saturation was found to be a microstructure accommodative phenomenon driven by mechanisms such as grain splitting/pinching and triple junction motion. The two mechanisms were found to be a resultant of flow heterogeneities. AccumEx was applied as a co-deformation technique for the production of Al-Cu laminated materials. The composite was fabricated in two configurations and deformed up to 4 AccumEx passes. Irrespective of the configuration type, the interfaces had a detrimental effect on the material's mechanical properties above 2 passes. The process produced an UFG microstructure in the Al part of the composite but a relatively coarser microstructure in the Cu part of the composite, due to strain inhomogeneities. The strain inhomogeneities developed due to the difference in the hardening properties between Al and Cu. It instigated complex interactions between the materials and thereby influenced the microstructure, texture and the hardening properties of Al. AccumEx was compared with Equal Channel Angular Pressing (ECAP) and it was it found that AccumEx could produce an UFG microstructure in a comparatively rapid manner. The final properties were also comparable with each other, except for that AccumEx was successful only up to 4 passes in Al-Al laminates and up to 2 passes in Al-Cu laminates.

Jaar van publicatie:2018

Toegankelijkheid:Open