Effect of cryogenic treatment On mechanical and corrosion Behaviour of friction stir Welded aa5083 thick plates

Abstract

Aluminum alloy 5083 is a weldable, strain hardening structural material suitable for marine applications due its excellent formability, good strength and high corrosion resistance. Particularly, 8 mm and above is the typical thickness used in shipbuilding. The alloy 5083 also has very good low temperature mechanical properties which make the alloy suitable for newlinemanufacturing liquid natural gas (LNG) carriers, tanks and cryogenic containers. Friction stir welding, being a solid state process, offers several benefits over the traditional fusion welding processes. The benefits include ease of handling, little, or no, joint preparation, high levels of repeatability and high joint quality. In the recent past, there have been a few studies reporting beneficial effects of cryogenic treatment (CT) on different metallic newlinealloys, particularly, aluminium alloys. However, 5xxx series aluminum alloys have rarely been investigated for effects of cryogenic treatment. Specially, the friction stir welded AA5083, which is a candidate material for cryogenic applications, has hardly been studied for possible changes in mechanical properties and corrosion behaviour. In this investigation, the effect of cryogenic treatment (CT) on room temperature mechanical properties and corrosion behaviour was studied. Full-penetration, defect-free joints were produced on 10 mm thick AA5083- H321 plates using friction stir welding. Both base metals and friction stir welded joints were subjected to deep cryogenic treatment using liquid nitrogen at -180°C. The mechanical properties of the welds with and without cryogenic treatment were evaluated using micro Vickers hardness, tensile, impact and wear tests. Microstructural studies were also carried out using optical microscopy and scanning electron microscopy to understand structureproperty relations. Microhardness surveys carried out across the welded joints reveal higher hardness values in the weld nugget and lower hardness values in the newlineheat-affected zone. This is considered to be a usual hardness t