Effects of varying volume fractions of SiC nanoparticle (SiCNP) reinforcement on microstructure and mechanical properties of dissimilar AA2024-T351 and AA7075-T651 joints by friction stir welding (FSW) have been investigated experimentally. A rectangular section edge groove was prepared at the adjoining surfaces of the two plates with the butt configuration before FSW. Initially, four fractional volumes with 0, 5, 8, and 13% of SiCNP are reinforced into the grooves of width, 0, 0.2, 0.3, and 0.5 mm and the FSW was performed with the first and second pass to obtain metal matrix nanocomposite (MMNC) at the weld nugget zone (WNZ). The characterization of microstructure specimens was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction technique (XRD). The FSW joint specimen produced with 5 vol% fraction of SiCNP for second pass processing observes a defect-free, homogeneous distribution of SiCNP with a mean grain size of about 2–3 µm at the WNZ and weld joints higher in tensile strength, 411 MPa, yield strength, 252 MPa, and percentage elongation, 14.3. The result shows that varying volume fractions (5, 8, 13%) of the SiCNP after the FSW second pass led to significant grain refinement at the WNZ and higher mechanical properties compared with FSW specimens prepared without SiCNP. Higher hardness of 150 Hv was observed in the WNZ for specimen produced with 13 vol% fraction SiCNP.

An investigation was carried out to quantify and characterize the corrosion behavior ofAZ61A magnesium alloy joints. Extruded 6-mm-thick Mg alloy plates of AZ61A grade werebutt-welded using a solid-state, environmentally cleaner welding process, the frictionstir welding process. The weld specimens underwent immersion, salt spray, pitting andgalvanic corrosion tests in order to quantify and characterize the corrosion rates of thewelds with the influence of different pH values, chloride ion concentrations and thecorrosion time. The corrosion rates, microstructure, scanning electron microscopy andX-ray diffraction analysis concluded the optimum parameters for the usage of the magnesiumalloy welds for the best service applications.

In an effort to enhance safety for long time disposal of waste nuclear fuel, friction stir welding has been developed as one alternative to seal copper canisters. To avoid the formation of voids and cracks during the welding process, an understanding of the heat and material flow andthereby the evolution of the microstructure, is of great importance. Finite element modelling has been used to simulate the heat and material flow as well as thermal expansion during the friction stir welding process. A model involving heat transfer, material flow, and continuum mechanics has been developed. The steady state solutions have been compared with experimental temperature observations as well as analytical solutions, showing good agreement. Temperature distribution is affected by the welding speed. For a given reference pointperpendicular to the welding direction, a lower welding speed corresponds to a higher peak temperature. The plunging position of welding tool influences the temperature distribution and therefore the displacement distribution of the weldment.