In the present study, composites have been synthesized by infiltration of 0.15 wt% carbon steel wool by molten magnesium and AZ91 alloy, which solidifies by cooling under vacuum. The microstructure of the composites observed on a plane normal to the direction of flow shows the transverse section of steel wool strands mostly and clustering of these strands due to pushing by stream of melt during infiltration. The composite based on AZ91 alloy shows network of precipitates of Mg 17 Al 12 along the boundaries of dendrite cells in the matrix, which are significantly finer compared to that in the cast AZ91 alloy. The microhardness of the steel wool in the composite increases with increasing steel wool content, which has been attributed to increased restraining influence of steel wool at higher steel wool content on the plastic flow of the surrounding matrix. The ultimate tensile strength (UTS) is higher in the AZ91 alloy-based composite compared to those observed in the composites based on commercial magnesium, at comparable steel wool content, and the strength increases with increasing steel wool content although densities of the composites increases as well.

The surfaces of coir fiber (CF) and coconut shell powder (CSP) were modified by alkali and silane treatment respectively to investigate the consequent effects on reinforcement of vinyl ester (VE) composites. Mono‐composites of VE with surface treated CFs and CSP as well as their hybrid composites with as‐received aramid fibers (AFs) have been prepared by hand layup followed by compression molding methods. The effectiveness of surface treated reinforcements in improving the mechanical properties of the composites was demonstrated. Significant differences between VE mono‐composites and their hybrid reinforcements on hardness and tensile properties of VE were observed, while no improvement in the above‐mentioned properties except for Young's modulus was observed for hybrid composite with AFs. It was also observed that surface treated CFs and CSP reinforced VE composites exhibited better hardness and tensile properties. SEM imaging confirmed decreased fiber pull‐out for VE reinforced with alkali treated CFs because of the enhanced adhesion between the CFs and the VE matrix. Flexural properties of all the composites decreased. This study has proved that the mechanical properties of hybrid VE composites can be enhanced by modifying the reinforcements by alkali and silane into their formulations. These results have been explained on the basis of structure and morphology in terms of fractography of VE composites. Furthermore, this study demonstrates that alkali treatment is a promising technique for improving the mechanical properties such as hardness and tensile properties of CF reinforced hybrid polymer matrix composites. POLYM. COMPOS., 39:4542–4550, 2018. © 2017 Society of Plastics Engineers

An attempt has been made to explore the effect of hybrid reinforcement on mechanical properties and dry sliding wear behavior of vinyl ester (VE) composites. Vinyl ester reinforced with alkali treated coir fibers (CF-VE), silanated aramid fibers (AFs) leading to fibridization and inclusion of coconut shell powder (CSP) with various weight proportions has been prepared resulting in hybridization. Effectiveness of treated fibers and CSP on mechanical and wear behavior of VE and their hybrids was evaluated. The density and hardness values of CF-VE composite increased steadily with inclusion of AFs and CSP. The tensile strength increased from 52 MPa at 0 wt.% AFs inclusion to a maximum of 76 MPa at 15 and 5 wt.% of AFs and CSP content. Further, it increased to a maximum of 78 MPa at 5 and 10 wt.% of AFs and CSP in CF-VE composite. The specific wear rate decreased more rapidly with the CSP content. Hence, it is deduced that hybrid VE (15CFs+5AFs) composite with 10 wt.% CSP is more effective against sliding wear. The type, geometry and dispersion of reinforcements contribute to the increased wear resistance. These results are important for the development of new composites incorporated with surface treated reinforcing materials such as CF and CSP, which will have significant application in automotive sliding or bearing components.