Date of Award
Doctor of Philosophy (PhD)
Abdel-Hamid Ismail Mourad
Low crude oil prices have impacted the economy of the Gulf Cooperation Council (GCC) member countries especially the United Arab Emirates (UAE). Hence it is vital to accelerate the diversification of the economy. Among the many potential diversification avenues, manufacturing is a promising area that could add to the GDP. This work brings out a sustainable and cost-effective method for manufacturing AMCs and expanding their applications.
This work deals with the processing and characterization of recycled AMCs manufactured using a novel approach. With the emphasis on sustainable manufacturing, this work aims to use Scrap Aluminum Alloy Wheels (SAAW) of cars as the matrix. SAAW was easily obtained from the scrap wheels of cars. The reinforcement material, Spent Alumina Catalyst (SAC), was sourced from the local oil refineries which is a waste material from crude oil refining. To achieve the objectives of this work, the following steps were followed.
Firstly, four AMCs were developed using stir-gravity casting. Four composites were made with different combinations such as LM25+Al₂O₃, SAAW+Al₂O₃, LM25+SAC, and SAAW+SAC. The microstructure analysis showed a nonhomogeneous distribution of reinforcements with a high amount of porosity. Therefore, this method was not used for the optimization and casting of AMCs.
Secondly, AMCs were produced using the stir-squeeze casting method. Similar to the previous casts, four composites of LM25+Al₂O₃, SAAW+Al₂O₃, LM25+SAC, and SAAW+SAC were made. The samples from this method exhibited better strength when compared to gravity cast samples. SAAW+Al₂O₃ exhibited an almost uniform distribution of reinforcement particles and superior mechanical properties with the lowest porosity (7.3%), highest hardness (69 VHN), and minimum abrasive wear loss (0.001g), second highest tensile (129 MPa) and compressive (320 MPa) strengths among the four composites. The results also revealed that optimizing the stir squeeze casting process parameters can further contribute to the performance of the recycled AMCs.
Thirdly, optimization of casting parameters using the Taguchi method was carried out. Taguchi-Grey Relational Analysis (GRA) was successfully utilized to handle the multi-response objective system for optimizing process parameters in the squeeze casting of AMCs. This method was used to determine the optimized condition with a minimal set of experiments, which is relevant in the stir–squeeze casting process. Taguchi method developed 9 samples (L1-L9) and out of that L5 and L6 exhibited the best mechanical properties. Thus, the optimum levels of process parameters are squeeze pressure of 100MPa, squeeze time of 30 s, die preheat temperature of 250°C and stirrer speed of 525 rpm.
Fourthly, the optimized sample (M2) was produced. Taguchi’s confirmation test was run based on the obtained mechanical properties and the L6 method showed an improvement in the GRG value by 12.5%. Based on the confirmation test, the optimized sample M2 was produced using a squeeze pressure of 100 MPa, a squeezed time of 45s, a die preheating temperature of 250°C, and a stirrer speed of 525 rpm. The M2 sample showed the lowest porosity (5.29%) and significantly higher ultimate compression strength (433 MPa) although it exhibited slightly lower hardness and ultimate tensile strength when compared with the L6 and L5 samples, respectively.
Fifthly, a hybrid AMC was produced to further enhance the performance. Five casts (1% graphite+ Al₂O₃, 3% graphite+ Al₂O₃, 4% graphite+ Al₂O₃, 3% SiC+Al₂O₃, 6% SiC+ Al₂O₃) were prepared with SAAW as matrix and alumina, graphite and SiC as fillers with different percentage. AMC with 4% graphite along with alumina showed the highest tensile and compressive strength of 250 MPa and 508 MPa respectively, followed by a sample with 3% SiC and alumina.
Lastly, Friction Stir Welding (FSW) was carried out to check the weldability. L5, L6, M2, and hybrid AMC samples were successfully welded using a cylindrical tool pin with 4 mm pin depth, tool rotation of 1100 rpm and feed rate of 50 mm/min. Tensile results from the welded zone showed that sample M2 and AMC with 4% graphite exhibited high strength of 185 and 210 MPa respectively. From these results, it can be seen that this approach can easily be scaled up for production in large volumes as well as open avenues for developing AMCs reinforced with other waste materials.
Christy, John Victor, "DEVELOPMENT AND CHARACTERIZATION OF SUSTAINABLE NOVEL ALUMINUM METAL MATRIX COMPOSITES" (2021). Dissertations. 164.