Effect of shoulder diameter to pin diameter (D/d) ratio on tensile strength and ductility of friction stir processed LM25AA-5% SiCp metal matrix composites

• Application of LM25AA-5% SiC metal matrix composite is limited due to low ductility and toughness.
• Due to the uneven distribution of reinforcement particle, the quality of composite was affected.
• FSP can overcome the above said problem and capable of result processed zone of better properties.
• D/d ratio is one of vital parameter which will influence the processing efficiency predominantly.
• Effect of D/d ratio in the SiC particle breakup and distribution of particles were investigated.

Stir casted LM25AA-5% SiC Metal Matrix Composites (MMCs) consists of cast product dendrites and large agglomerated reinforced particle. The agglomeration of SiC creates difference in properties along the composite system. During loading it creates different stress field which causes failures in the composite material. Friction Stir Processing (FSP) is a novel processing technique facilitate by the frictional heat generation between the tool and the workpiece. FSP can triumph over the poor properties due to large sized and unevenly distributed SiC particle in the Al matrix. In this investigation, five different shoulder diameters to pin diameter (D/d) ratio is used for processing the composite material. Tensile properties and hardness of the friction stir processed material were evaluated and correlated with the macro and microstructure signatures. The characterization of processed composite material is carried out using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and X-ray diffraction technique (XRD). The effect of different D/d ratio (2, 2.5, 3, 3.5, 4) on microstructural formation, particle size and distribution in the matrix were analysed and found that the D/d ratio of 3 yielded higher tensile and hardness properties.