Investigation on effects of reciprocating extrusion process on microstructure of AA 6061 based composites

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Abstract
The reciprocating extrusion (RE) method was developed to fabricate the fine grain AA 6061 and AA 6063 alloys and to obtain their optimum mechanical properties. While 6061/72 μm aluminium alloy powder and AA 6063 bar material were used as a matrix material separately, SiC/20 μm ceramic particles were used as reinforcement. Billets were produced from AA 6061 powders and AA 6063 materials mixed with SiC ceramic particles by sintering and stir casting method respectively. Using the RE process, which was performed at 573 K for one, five and nine passes, the billets were extruded again to investigate the microcharacterisation of the products. The hardness, microstructure, grain size and distribution of the extruded samples were examined and analysed using an SEM. High resolution electron backscatter diffraction and TEM methods were also applied for grain analysis. The manufacturing method of the billets to be extruded reciprocatively affects the hardness that occurs after the deformation. The hardnesses of all samples increase first and then decrease with pass number. After extrusion passes, the longer or larger silicon particles were broken into finer particles and microstructures were changed from the initial to a new structure. A homogeneous distribution of SiCp and refined grain structure of the test materials were obtained by RE. However, the process temperature applied during the process has a greater effect on the change in grain size than that of the occurring deformation.

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