Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The thesis includes the fabrication and characterization of metal/metal composites by (AccumEx) Accumulated Extrusion. AccumEx is a novel SPD technique which is derived from the concept of Accumulative Roll Bonding (ARB) and applied to a conventional extrusion process. The fabrication is carried out on two different metals namely aluminium and IF steel. with reduction of 66.67% per pass. The samples are deformed up to an effective strain of 5.08 using 4 passes. The characterization of the samples includes the observation of interfaces, hardness, tensile strength, fracture analysis, microstructure analysis and texture analysis. The results of fabrication and characterization are presented separately for two types of composites: a) The Al-Al composite The fabrication of Al-Al composite is carried out using three stacked layers of aluminium plates with dimensions of 50mm*20mm*6.67mm. The extruded single solid sample shows the interface cracking in pass 1 itself, indicating that the produced sample can never be a single solid sample, unless heat treated. The hardness is found to be improved up to pass 2 followed by saturation or reduction. The tensile properties show improvement in Yield Strength (YS) and Ultimate Tensile Strength (UTS) while reduction in % Elongation to Fracture (%EB) as straining of sample is increased. The fracture analysis shows the transformation from ductile to quasi- ductile fracture for pass 1 to pass 4 samples. The microstructure analysis shows the formation of submicron substructure having low angle misorientation however, the formation of a stable microstructure with high fraction of high angle grain boundaries is not realized completely. The texture analysis shows the formation of only fiber components indicating the applied deformation is pure plane strain. b) The Al-IF steel composite The fabrication is carried out for two dissimilar metals i.e. aluminium and IF steel. The samples possess the same width and length as that of the Al-Al composite but a different thickness as mentioned with stacking sequence. The composite employs a stack of five layers in sequence of Al(5mm)/IF steel(1.5mm)/Al(7mm)/IF steel(1.5mm)/Al(5mm). The sample is extruded similar to the Al-Al composite system. The OLM and SEM shows that the sample possess severe cracking between Al-Al and Al-IF steel layers beyond pass 2. The hardness is improved up to pass 1 followed by saturation or reduction. The tensile properties show a consistent drop in the YS, UTS and %EB with increase in deformation. The poor performance of the composite is due to non-uniform bonding of the Al-Al and the Al-IF steel layers at higher strain. The microstructure of aluminium shows achievement of submicron size substructure for aluminium with relatively high fraction HAGBs compared to the aluminium in the Al-Al composite. However, the IF steel does not yield a submicron size substructure. The OLM observations showed that the IF steel is less/not deformed in pass 2 and pass 4 samples. The texture analysis shows fiber components for pass 1 however, a shear component – rotated cube is observed beyond pass 2, indicating the applied deformation is no more a plane strain. Key words: AccumEx, SPD, Extrusion, Nano-grains, Metal-metal composites