STUDIES ON MECHANICAL PROPERTIES OF FRICTION STIR PROCESSED ALUMINIUM POWDER COMPOSITE

Abstract

Friction stir processing (FSP) has fast emerged as a technique for microstructural changes in aluminium and magnesium alloys which involves grain refinement, porosity removal and homogenisation. in the present study, the effect of FSP on Al synthesised from powder metallurgy route on its microstructure and mechanical properties has been investigated. During compaction and sintering, four different compaction pressures were used which were 220 MPa, 300 MPa, 400 MPa, and 500 MPa. The hot working nature and the stirring action of the rotating tool during FSP caused reduction of porosity in the powder product sample which resulted in a significant improvement in density. The densification was found to increase by over 5.2% in the Al- 1 wt% Mg powder sample compacted at 300 MPa and FSPed under the parameters 1025 rpm rotating speed and 2 mm/min traverse speed of the tool. Moreover, due to intense plastic deformation, grain refinement in the stir zone occurs. Initial grain size was an average of 74.3 jim and from electron backscatter diffraction, it was found that after FSP, it reduced to about 2.19jim. As a result the processed zone had shown better hardness then the unprocessed zone. The increase in hardness values was found to be most prominent in the sample compacted at 300 MPa under the FSP parameters 1025 rpm rotating speed and 2 mm/min traverse speed. An improvement of over 112%± 8% was found in this case. Furthermore, the ratio of tool rotating and traverse speed ratio, which is a direct measure of the heat input to the sample, was varied. Its effect on the sample compacted at 300 MPa was investigated. The ultimate tensile strength was found to enhance by 2 16.79% after being FSPed under 1025 rpm rotating speed and 2 mm/rn in traverse speed. At the same time, the hardness and tensile strength of the sample decreased with the increase in the ratio of tool rotating and traverse speed. Finally, FSP was carried out at 1525 rpm and 1 mm/mm processing combination on Al- Mg composites. The weight content of Mg in the composites was varied from 0% to 5%. The mechanical properties were improved remarkably after FSP in each case. Fractography revealed that the as- sintered samples which have a very poor strength showed a lot of inhomogeneous uneven pull-out structure in their fracture surfaces. After FSP, however, the fracture surface showed predominant dimple morphology to aid to its ductile property.