STUDY OF SURFACE MODIFICATION OF AL ALLOY USING SOLID STATE PLASTIC DEFORMATION

Abstract

Surface modification or surface composites are considered to have a potential for generation of new materials for numerous engineering applications due to their enhanced mechanical and physical properties. Fabrication of surface composites by Friction Stir Processing (FSP) with enhanced surface properties is attracting by researchers owing to improved life of the component. Friction Stir Processing (FSP) is a solid-state technique, which has been used for fabrication of Al-B4C surface composite. FSP is a relatively new solid-state technique that has been widely utilized for surface modification of Al alloy. The various methods are used for the fabrication of surface composite using different reinforcement applying methods but no research has been carried out on minimizing the reinforcement particles. Surface modification of Aluminium alloy has a wide range of applications in aerospace industries, where high strength to weight ratio is required. In this research work, the main focus has been made to fabricate Al-B4C surface composites with minimizing the B4C nanoparticle reinforcement through the processing and formation of Self-Assembled Monolayer (SAM) over the surface of substrate (base) metal followed by Friction stir processing (FSP) method. Al 7075-T6 alloy was used as a matrix material and B4C nanoparticles size (<30nm) was used as reinforcement through Self-Assembled Monolayer (SAM). It is very difficult to control the uniform or homogeneous distribution of nanoparticle reinforcement on the substrate (base) metal by other surface modifying technique. So, in the current method, we have modified the surface using B4C nanoparticles, which is processed through the Self-Assembled Monolayer on the surface of Al-alloy. SAM is

widely being used as a linking process on various surfaces. The major advantage of the Self- Assembled Monolayer technique is that it minimizes the quantity of B4C nanoparticles used in

the preparation of surface composite. Al-B4C surface composite with reinforced B4C nanoparticle through single-pass was performed using different tool rotation speed, traverse speed, and tool tilt angle 2o were constant during Al-B4C surface composite experimentation. This research investigated the process parameters of FSP such as tool rotational speed, tool traverse speed in accordance with Taguchi’s orthogonal array L9 for obtaining better surface properties of Al-B4C surface composites.

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In physical characteristic microstructure, Scanning Electron Microscope, Field Emission Scanning-Electron Microscope (FESEM) and X-Ray Diffraction (XRD) were examined to analyze the fabricated Al-B4C surface composite. Fractographs analysis was also done to know the fracture nature of the fabricated Al-B4C nano surface composite. In mechanical properties microhardness (HV) and ultimate tensile strength (UTS) of the fabricated Al-B4C surface composites was studied using ANOVA it was observed that in case of both UTS and HV, tool traverse speed had a more significant role than tool rotational speed. The Al-B4C surface composite sample has obtained higher hardness as compared to the base metal hardness. Compressive residual stresses are induced during the friction stir processing due to severe plastic deformation of metal. The wear behavior of the substrate (base) metal and surface composites were studied through a pin on disc tribometer. The maximum wear has been observed in the substrate (base) metal followed by the Al-B4C surface composites sample processed at tool speeds of 1000 rpm, 1400 rpm and 1200 rpm. Wear resistance has improved by up to 42.6%, the maximum wear resistance improvement in terms of percentage has been seen in the Al-B4C surface composites sample processed at 1200 rpm and subjected to 20N load. This follows the same pattern as the values from microhardness, which explains this phenomenon. Frictional and wear analysis highlights the mechanical durability and surface wear of substrate (base) metal and surface composites. Experimental data suggests that Al-B4C nano surface composite has the least wearing and frictional coefficient due to the effective application and processing of B4C nanoparticles Self-Assembled Monolayer technique. Substrate (base) metal has been reported to have least durability and highest frictional coefficient. The worn out surfaces of the Al-B4C surface composites and wear debris were analyzed through SEM studies to understand the wear mechanisms.