N. GANGIL et al.: SURFACE NANOCOMPOSITE FABRICATION ON AA6063 ALUMINIUM ALLOY ... 77–82 SURFACE NANOCOMPOSITE FABRICATION ON AA6063 ALUMINIUM ALLOY USING FRICTION STIR PROCESSING: AN INVESTIGATION INTO THE EFFECT OF THE TOOL-SHOULDER DIAMETER ON THE COMPOSITE MICROSTRUCTURE IZDELAVA NANOKOMPOZITA NA POVR[INI ALUMINIJEVE ZLITINE AA6063 Z UPORABO VRTILNO-TRENJSKEGA PROCESA: RAZISKAVE VPLIVA PREMERA DR@ALA ORODJA NA MIKROSTRUKTURO KOMPOZITA Namrata Gangil 1 , Sachin Maheshwari 1 , Arshad Noor Siddiquee 2 1 Netaji Subhas Institute of Technology, Department of Manufacturing Processes and Automation Engineering, New Delhi 110078, India 2 Jamia Millia Islamia, Department of Mechanical Engineering, New Delhi 110025, India namrata.gangil@gmail.com Prejem rokopisa – received: 2017-10-09; sprejem za objavo – accepted for publication: 2017-11-14 doi:10.17222/mit.2017.172 In this work, surface metal matrix composites (SMMCs) were fabricated on AA6063 base metal through friction stir processing (FSP). In all the samples for surface composites, grooves of 2 mm × 2 mm were made along the centreline of plates and TiB2 powder (~80 nm) was filled and compacted in these grooves. A pinless tool was employed to initially cover and compact the grooves filled with TiB2 particles to prevent it from sputtering during FSP. Tools of different shoulder diameters (16, 18, and 20) mm with anti-clockwise scrolls on the shoulder surface were used for the FSP with constant pin diameter and pin length. The tool rotational speed of 900 min –1 , traversing speed of 40 mm/min and tilt 2°, respectively, kept constant for all the experiments. Macro, optical micro images and micro hardness tests were used to evaluate the particle distribution. Powder agglomeration was observed in the retreating side of samples processed with 16 mm and 18 mm shoulder diameter tools. On the other hand, significant improvement in particle distribution and excellent bonding with the substrate were observed for the sample processed with 20 mm shoulder diameter tool. The findings of this investigation are important and provide knowledge for better tool design and effective tool selection to bring out better distribution in a single pass. Keywords: friction stir processing, aluminium alloy, shoulder diameter, microstructure V tem prispevku avtorji opisujejo izdelavo in raziskavo izdelanega nanokompozita s kovinsko osnovo (angl.: SMMCs; Surface Metal Matrics Composites) na povr{ini aluminijeve zlitine vrste AA6063, izdelanega s pomo~jo vrtilno (rotacijsko) trenjskega procesa (angl.: FSP; Friction Stir Processing). Vsi vzorci povr{inskega kompozita {irine 2 mm in globine 2 mm so bili izdelani vzdol` sredi{~ne linije kovinske plo{~e. Pri tem so bili med FSP dodajani pribli`no 80 nm delci TiB2 prahu v nastajajo~e brazde. Za za~etno prekrivanje in kompaktiranje brazd napolnjenih s TiB2 so uporabili orodje brez trna in s tem prepre~ili razpr{evanje delcev med FSP. Za izdelavo SMMCs so uporabili dr`ala razli~nih premerov (16, 18, in 20) mm z valj~ki, name{~enimi na povr{ini dr`al, ki so se vrteli v nasprotni smeri urnega kazalca. Pri tem so za FSP uporabili trn s konstantnim premerom in dol`ino. Pri vseh preizkusih so za izbrani FSP uporabili hitrost vrtenja 900 min –1 , vzdol`no hitrost potovanja orodja 40 mm/min, in nagib 2°. Da bi ugotovili porazdelitev delcev TiB2 v izdelanih SMMCs so izvedli metalografske preiskave in dolo~ili mikrotrdoto kompozitov. Opazili so aglomeracijo pra{nih delcev na vzorcih izdelanih s 16 mm in 18 mm premerom dr`ala orodja. Po drugi strani pa so dosegli pomembno izbolj{anje porazdelitve pra{nih delcev in njihovo odli~no vezavo s kovinsko osnovo pri vzorcih, ki so bili izdelani z 20 mm premerom dr`ala orodja. Ugotovitve te raziskave omogo~ajo bolj{e oblikovanje in u~inkovito izbiro orodja za doseganje optimalne porazdelitve nanodelcev v kovinski osnovi pri FSP z enim samim prehodom F. Klju~ne besede: proces rotacijskega trenja, zlitina na osnovi aluminija, premer dr`ala, mikrostruktura 1 INTRODUCTION FSP is based on the principles of Friction Stir Weld- ing (FSW) developed at "The Welding Institute (TWI), UK" in 1991. 1 In FSP a cylindrical shouldered tool with a profiled probe or pin is rotated and plunged into base metal (BM) and traversed on the workpiece surface in the processing direction (Figure 1). The rubbing action of the tool shoulder generates frictional heat and softens the material under the shoulder, which also undergoes severe plastic deformation at high strain rate by the ro- tating pin (called stirring). 2,3 During FSW/FSP, material is subjected to a combination of metal working pro- cesses, e.g., friction, extrusion and forging. 3–5 FSP is evolving as a promising surface modification technology for surface composite fabrication mainly because it is a solid-state process and a green process by virtue of being free from use of consumables and evolution of effluent. One of the major challenges of the process, however, is the inhomogeneous distribution of reinforcement part- icles. A large number of research works have been focused on achieving a homogeneous distribution of particles, elimination of agglomeration of particles, over- coming of tunnel-like defects and achieving a wide Materiali in tehnologije / Materials and technology 52 (2018) 1, 77–82 77 UDK 669.715:621.9:621.9.041 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(1)77(2018)