This study investigates the effect of tool rotational speed (TRS) and welding speed (WS) on the interface evolution and mechanical behavior of friction stir-welded dissimilar joints between pure copper (Cu) and AZ31B magnesium (Mg) alloy. Welding trials were performed for TRS values of 765, 1070 and 1500 rpm and WS values of 31.5, 50 and 78 mm/min with a constant tool offset of 1 mm and tilt angle of 2°. The results show that the joint quality is strongly affected by the synergistic effects of heat input and material flow. The sound weld interface was obtained at 1070 rpm and 31.5 mm/min with the highest tensile strength of 118 MPa. Low TRS resulted in insufficient plasticization, while high TRS and higher WS resulted in brittle intermetallic formation (IMC), voids and incomplete weld consolidation due to undesirable heat input conditions.
A new fundamental model was presented in the previous work [1], which incorporated the chemical potential gradient of CaO along with the formation of the low melting ( CaO·FeO) layer. The same model is applied in this work to understand effects of slag viscosity (markedly affected by the SiO_2 and FeO contents of slag), turbulence (the effect of stirring on mass transfer caused by the top jet and bottom gas), changing activity of slag components, and the effect of morphology on dissolution rate of lime particle. Furthermore, the contradictions in some of the results reported in the literature are explained.
The DMR249A steel has been developed by the Defence Material Research Laboratory (DMRL) for the construction of Indian naval ships and submarines. A high-phosphorus electroless nickel-phosphorus (ENP) coating has been developed on substrate steel DMR249A for marine applications. The corrosion resistance by potentiodynamic polarisation tests and the electrochemical impedance spectroscopic method, as per ASTM-G 102 standards, as well as the salt spray test, as per ASTM B117 standards, indicates improvement in corrosion resistance, along with change from hydrophilic to hydrophobic behaviour. The coating morphology, analysed by AFM, exhibits a smoother surface in higher coating thicknesses. The surface functional groups and structure analysed by FTIR, XRD, FESEM, and EDAX techniques indicate the presence of a passive layer and an amorphous structure of the coating. The high-phosphorus electroless nickel-phosphorus (ENP) coating on DMR249A can therefore enhance the service life of naval ships and submarines.
Wastewater from copper, lead, and zinc smelting contains high concentrations of arsenic. Trivalent arsenic (As(III)) is unstable and highly toxic, and needs to be oxidized to pentavalent arsenic (As(V)) before arsenic removal treatment. This study developed a catalytic oxidation method for As(III) using ozone combined with activated carbon (AC) catalysis. AC was modified with hydrogen peroxide to improve its catalytic performance. XPS analysis showed that the content of oxygen functional groups in the modified AC (H2O2/AC) was significantly increased. Under H2O2/AC catalysis, the ozonation rate significantly increased. At pH = 1, with the addition of 5 g H2O2/AC, the conversion rate increased by 41.7
Red mud, a highly alkaline solid waste generated during the Bayer alumina process, poses substantial environmental hazards while offering considerable potential as a secondary resource. Effective valorization critically depends on a multiscale understanding of its complex physicochemical nature, defined as a cross-scale cognitive process spanning from microstructural states to macroscopic process behaviors. To operationalize this concept, this review consolidates existing analytical methodologies into a cohesive characterization framework tailored for metallurgical applications. Specifically, it examines key techniques, such as X-ray fluorescence and inductively coupled plasma mass spectrometry for bulk elemental analysis, X-ray diffraction and vibrational spectroscopy for mineral phase identification, and electron microscopy for microstructural investigation, and further discusses the integration of real-time macroscopic monitoring with predictive computational tools. By emphasizing the correlation between mineralogical speciation, amorphous phase behavior, and macroscopic process variables, the proposed framework directly informs optimal recovery strategies, including iron extraction, de-alkalization, and cementitious material production. Finally, the adoption of standardized, multimodal data protocols is advocated to mitigate heterogeneity-induced uncertainties in sustainable metallurgical valorization circuits.
