359 Corrosion Behaviour of Multiaxial Compressed AlMgSi Alloy Abir Roy and Abhishek Kumar * Department of Applied Mechanics, Motilal Nehru National Institute of Technology Allahabad, Prayagraj - 211 004, India * E-mail: abhishek@mnnit.ac.in ABSTRACT In the present study, AlMgSi alloy was processed through multi-axial compression (MAC) to produce ultrafne-grained microstructure at room temperature. The AlMgSi alloys are widely used in automobile industries for making cylinder heads and brake disks etc. MAC was performed up to three cycles and showed improvement in mechanical properties. The impact of diferent strain levels upon microstructure changes is investigated using electron backscatter difraction (EBSD). The average grain size reduced from an initial average grain size of ~ 124 to ~ 3 μm after completion of three cycles of MAC processing. Samples were tested for mechanical properties using uniaxial tensile test, hardness measurements, and corrosion. Tensile test results show a considerable increase in yield strength from ~90 MPa to ~249 MPa after 3 cycles of MAC. The average hardness value increased from 52 VHN to 90 VHN after 3 cycles of MAC. The corrosion resistance of MAC processed samples was found to decrease in comparison to solution-treated samples. Keywords: Multiaxial compression; Potentiodynamic polarisation; Mechanical behaviour; AlMgSi alloy Defence Science Journal, Vol. 71, No. 3, May 2021, pp. 359-364, DOI : 10.14429/dsj.71.16723 © 2021, DESIDOC 1. INTRODUCTION The severe plastic deformation (SPD) technique is a top-down approach to produce ultrafne-grained (UFG) materials from their bulk state and have improved mechanical characteristics such as ultimate tensile strength and hardness, which makes them more applicable for structural applications. Several SPD processes have been used to develop UFG materials, such as multi-axial compression (MAC) 1 , accumulative roll bonding (ARB) 2 , equal channel angular pressing (ECAP) 3 , high-pressure torsion (HPT) 4 and constrained groove pressing (CGP) 5 . MAC is a repeated compression technique that develops large strains with relatively less loss of ductility in comparison to conventional deformation techniques. The moderate ductility in ultrafne-grained material processed by MAC is attributed to grain orientation randomisation 6,7 . MAC and multi-axial forging (MAF) are similar terms in use found in the literature 8 . MAC term is used to refer to the processing method employed in the present work. In the MAC processing, the same amount of strain is introduced in all the pressing directions, sequentially to a cuboidal- shaped sample kept in a constrained channel die set-up 9 . AlMgSi alloys are used in marine applications, therefore there is always a need for a material having higher strength with excellent corrosion resistance. Studies of corrosion behaviour of material processed by SPD methods are not yet well defned. Few corrosion studies on Al alloys indicated improvement in corrosion resistance after SPD, while some studies reported decreased corrosion resistance after SPD 10-12 . The irregularities of the corrosion behaviour primarily depend on the corrosive solvents, the chemical composition of materials, and the type of deformation processes. According to literature MAC technique is less explored to produce ultrafne-grained materials; therefore, in the present work, an efort has been made to process AlMgSi alloy using MAC for the diferent magnitude of strain to understand the efect of MAC processing on the mechanical and corrosion behaviour. 2. RESEARCH METHODOLOGY 2.1 Materials AlMgSi alloy was procured in square bars of cross- section 20 mm × 20 mm from the local market. The chemical composition of the procured alloy is given in Table 1. Table 1. The chemical composition of procured AlMgSi alloy Element Mg Si Fe Mn Cu Al Composition (wt. %) 0.66 0.57 0.48 0.05 0.05 Bal. The specimen of dimensions 40 mm × 20 mm × 20 mm were precisely cut for further processing. All samples were solution-treated at 530 °C for 2 h to acquire a homogenised microstructure 13 . The samples after solution-treatment have been stated as ‘as-received’. 2.2 Material Processing The as-received samples of AlMgSi alloy were processed as shown in Fig. 1 for multiple cycles of MAC. The lubricant Molybdenum disulfde (MoS 2 ) was used to reduce friction between the die and sample surface. Received : 27 January 2021, Revised : 02 February 2021 Accepted : 09 February 2021, Online published : 17 May 2021