http://hdl.handle.net/11189/1912 2026-09-02T04:52:58Z http://hdl.handle.net/11189/10774 Title: Optimization of FSP parameters in fabricating AA5083/Coal composites using Taguchi method Authors: Muribwathoho, Oritonda; Msomi, Velaphi; Mabuwa, Sipokazi Abstract: This study investigates the optimization of Friction Stir Processing parameters to fabricate AA5083/Coal composites using the Taguchi method. The influence of key process parameters—tool tilt angle, tool rotation speed, and traverse speed—on the mechanical properties of the composites was evaluated, specifically focusing on ultimate tensile strength, microhardness, and elongation. Taguchi’s L9 orthogonal array was employed to minimize the number of experiments and maximize the efficiency of parameter selection. A Hounsfield tensile test machine was used to evaluate ultimate tensile strength, and Innova Test Falcon 500 hardness testing machine was used to determine microhardness. The highest ultimate tensile strength, microhardness and percentage elongation achieved with the orthogonal arrays were 242 MPa, 96.27 HV, and 22.43%, respectively. The optimal parameters were identified as a tool tilt angle of 2°, a tool rotation speed of 900 rpm, and a traverse speed of 60 mm min−1 based on signal-to-noise ratio. Furthermore, an analysis of variance was conducted to evaluate the parameter contributions. Analysis of Variance revealed that rotational speed had the most significant impact on microhardness and percentage elongation, while tilt angle most strongly influenced ultimate tensile strength. This study demonstrates the viability of coal particles as a cost-effective reinforcement material for AA5083 composites and provides a robust framework for optimizing friction stir processing parameters using statistical methods. 2025-01-01T00:00:00Z http://hdl.handle.net/11189/10771 Title: Microstructure and mechanical properties of tungsten inert gas welded dissimilar aluminum alloys joint subjected to normal multi-pass friction stir process Authors: Msomi, Velaphi; Mabuwa, Sipokazi; Ngonda, Tiyamike; Mehdi, Husain; Saxena, Kuldeep Kumar Abstract: This work investigated the effect of multi-pass friction stir processing on the tungsten inert gas welded joints of AA6082/AA8011. The friction stir processing approach is broadly used in the marine, automotive, and aerospace engineering sectors. The flow of plasticized material seems to be significant in the mixed flow region, which causes an erratic intercalation pattern. By using a stirring tool action, deformation was induced in situ extrusions of dissimilar alloys. The plasticized material was moved layer by layer to generate a lamellae structure. Theparent materials AA6082 and AA8011 were seen to be penetrating and vigorously mixing in this zone. After the fourth pass friction stir processing, the tungsten inert gas weldment's ultimate tensile strength and % strain dramatically increased. The defects that had been present before friction stir processing were eliminated when the coarse grain structure of the tungsten inert gas weldments was changed into a refined grain structure from 18.09 to 8.92 µm. The microstructure study shows the linear relationship between friction stir processing passes and grain size. The increases in friction stir processing pass resulted in a decrease in grain size. The maximum ultimate tensile strength (89.60) was observed in tungsten inert gas + 4 pass friction stir processing compared to the other joints. 2025-01-01T00:00:00Z http://hdl.handle.net/11189/10765 Title: Diffusion coefficients of graphite foil carbon in Mo during spark plasma sintering process Authors: Mwaro, William Baya; Mphahlele, Mahlatse; Walker, Mark Abstract: This study investigated the influence of electric current on carbon diffusivity in molybdenum (Mo) during spark plasma sintering (SPS). The samples comprised 0.2-mm-thick graphite foils, 3-mm Mo discs annealed at 1000 °C for 1–8 h, and a Ti-Mo alloy annealed at 1200 °C for 4 h. Elemental concentration profiles were analyzed using electron probe microanalysis (EPMA), while microstructure evolution was examined via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) in various modes. Diffusion coefficients were determined using the Den Broeder method and compared with literature values to assess possible enhancement. Contrary to expectations, the results indicated no enhancement of diffusion coefficients under electric current; instead, they decreased with increasing carbon concentration. This reduction was attributed to the formation of a molybdenum carbide layer, which hinders further carbon diffusion into the Mo matrix. The study also observed that diffusion of carbon into the sample occurs predominantly via solid-state diffusion at the graphite-metal interface, rather than vapor-phase transport. 2025-01-01T00:00:00Z http://hdl.handle.net/11189/10757 Title: Implementation of a decoupled Model Reference Adaptive Control (MRAC) of a flotation process Authors: Samodien, M.T.; Tshemese-Mvandaba, Nomzamo; Mnguni, Mkhululi E. S. Abstract: The approach of applying the Massachusetts Institute of Technology, MIT rule as a decoupled Model Reference Adaptive Controller (MRAC) for a column flotation process is taken up in this article. The airflow rate and wash water flow rate can be adequately regulated with this control scheme. The air holdup and froth depth in the collection zone are used to determine the process performance. Furthermore, a Beckhoff PLC is utilized to evaluate the decoupled MRAC controller. Determining the performance requirements for the implemented controller based on the design simulations is the aim of this evaluation. Unlike the simulated results, the implemented MRAC controller exhibits stability depending on the magnitude of the set point change. This is evident in both the gas holdup and froth height responses. This study indicates the ability of the MRAC controller to be improved by tailoring the reference model accordingly. Improvements such as Overshoot, Peak, and Rise Time can be seen when comparing the response characteristics of Tables II and IV. However, there is not much improvement when it comes to the system’s Settling Time. 2025-01-01T00:00:00Z