Heat treatable aluminium alloy AA2219 is widely used for aerospace applications, welded through gas tungsten and gas metal arc welding processes. Welds of AA2219 fabricated using a fusion welding process suffers from poor joint properties or welding defects due to melting and re-solidification. Friction stir welding (FSW) is a solid-state welding process and hence free from any solidification related defects. However, FSW also results in defects which are not related to solidification but due to improper process parameter selection. One of the important process parameters, i.e., tool tilt angle plays a critical role in material flow during FSW, controlling the size and location of the defects. Effect of tool tilt angle on material flow and defects in FSW is ambiguous. A study is therefore taken to understand the role of tool tilt angle on FSW defects. Variation in temperature, forces, and torque generated during FSW as a result of different tool tilt angles was found to be responsible for material flow in the weld, controlling the weld defects. An intermediate tool tilt angle (1o-2o) gives weld without microscopic defect in 7 mm thick AA2219 for a given set of other process parameters. At this tool tilt angle, x-force, and Z- force is balanced with viscosity and the material flow strain rate sufficient for the material to flow and fill internal voids or surface defects in the weld.
This study examines the phase stability of perovskite SrTiO3 in Na2SO4 + 50 wt.% V2O5 and Na2SO4 + 10 wt.% NaCl environments at 900°C. Hot corrosion results show the formation of Sr2VO4, SrV2O6, and SrTiV5O11 phases in Na2SO4 + 50 wt.% V2O5 environment and Sr3Ti2O7, Na4TiO4, and TiO2 phases in Na2SO4 + 10 wt.% NaCl environment. Morphological observations revealed the austerity of hot corrosion attack on SrTiO3. The Sr2+ ions leached out from SrTiO3 and reacted with corrosive environments. These observations clearly indicate the destabilization of SrTiO3 in both environments.
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