Tribological characterization of Al 6061 surface composites manufactured using Friction Stir Processing

Abstract

Surface composites are one of the leading class of materials in the modern day industry owing to the higher degree control in mechanical properties offered by them. In the current investigation, surface composites have been fabricated using Friction Stir Processing (FSP). FSP being a solid-state process, doesn’t involve the pressing challenge of heat management like the conventional fusion-based techniques. In the current study, Al-6061-T6 aluminum alloy has been chosen as the base material and a ceramic Boron Carbide (B4C) has been chosen as the reinforcement media. The Surface Composites are expected to show enhanced wear properties as compared to the base metal. The effect of FSP alone, i.e. without the addition of reinforcement media, on the wear behavior clearly needs to be studied at the onset. Using FSP, the specimen can be processed using an increasing number of processing passes, as well as a reversal of direction of processing passes. The primary aim of the study is to investigate the wear behavior of processed specimens with respect to the number and direction of processing passes. Another aim is to study the wear behavior of Surface Composites which are fabricated using the Hole and Slot method of powder (reinforcement) application. A small study on the effect of solvent for powder application on the wear behavior is also made. There is a significant enhancement of wear in the processed specimens as compared to the base metal. The enhancement is much more prominent in the specimens processed with the reinforcement media. With the increase in the number of processing passes, the wear of specimens increase, owing to the dissolution of the Mg2Si precipitates in the base metal. With the reversal of processing passes, the wear enhances owing to refinement and uniform distribution of the precipitates. Hole method gives little more enhanced wear resistance as compared to the Slot method, owing to better refinement and uniform distribution of the precipitates as well as the reinforcement media. Acetone as the solvent is marginally better as compared to methanol as the solvent for the wear resistance of the specimen. During application, surface composites are subjected to varying tribological parameters of normal load and sliding speed. A small study has thus been conducted to study the effect of tribological parameters like the xi normal load and sliding speed on the wear behavior of the surface composites. The surface composites resist well under a given threshold of normal load and sliding speed, but beyond the threshold, there is a sudden failure of the specimen. FSP clearly is one interesting and effective method of fabricating surface composites as it results in significant enhancement of wear in processed specimens.