Browsing by Author "Abdulmumin, Adebisi Adetayo"

Stir casting (SC) process is a promising technique for aluminium silicon carbide particulate (Al-SiCp) composite. However, the processing of Al-SiCp composite with this technique has limited its commercial application on the industrial scale due to inconsistent distribution of the reinforced SiCp and interface reaction which in turn influences the composite properties. Moreover, over 70% of composite industries producing Al-SiCp have interest in adopting this technique due to its flexibility and cost effectiveness. This technique is influenced by several processing parameters which has the possibility to enhance and optimize the properties of the Al-SiCp composite. In order to achieve optimum properties, the SC process is used to develop Al-SiCp composite considering reinforcement fraction (RF), stirring speed (SS), processing temperature (PTemp) and processing time (PT) as the input factors for evaluating the wear rate (wr), coefficient of friction (µ), hardness (Hr) and surface roughness (Ra) as responses. In this study, an experimental plan is designed based on four factors - five level central composite design (CCD) in order to establish the model development and optimization analysis using analysis of variance (ANOVA) and multi-objective optimization (MOO). During Al-SiCp processing, the addition of oxidized SiCp and Mg created a reactive boundary which leads to the formation of MgO and MgAl2O4. These compounds improve the interface reaction, wettability and also suppress the formation of undesired phases. The characterization of Al-SiCp composite and constituent phases was performed using SEM/EDX and XRD analyzer. The examination of surface models describes the interactions among the significant parameters on responses. Validation of the models and optimal parameters revealed that prediction accuracy is within the limit of 1.2 to 5.5% error when compared to the confirmation test. Moreover, optimal response is achieved with 13 wt% RF, 500 rpm SS, 828 °C PTemp and 150 secs PT as optimum process parameters with lower wear rate. Process parameters beyond 828 °C PTemp and 500 rpm SS increase the wear rate and also influence other properties. This is because higher PTemp translates to higher energy gained by the reinforced SiCp which in turn facilitates faster settling of particles in the melt. In addition, higher SS promotes vortex formation which entraps inclusions such as gases resulting to porosity development in the composite. Due to these conditions, further increase of the RF beyond 13 wt% of SiCp does not bring a significant change in the wear properties. The wear rate of the optimized Al-SiCp recorded a significant decrease compared to conventional cast iron material in this study. This was achieved due to the sufficient formation of a stable tribo-layers or thin film interface which plays a significant role in the wear and friction performance. The surface roughness profile attained a smooth rubbing contact with an average of 0.14 µm under optimum parameter conditions. Furthermore, the SEM morphology of the worn surface of the optimized Al-SiCp composite showed shallow grooves and mild adhesive wear mechanisms with a protective thin layer. This layer acts as a coating shield and SiCp act as a solid lubricant resulting in improved wear resistance and better friction performance (0.32-0.45) which falls within the industrial range of brake system application.

Braking action is recognized as one of the challenges in automotive industries as a result of frictional heat generated on the interface between brake rotor and pad. This process results to high temperature which induces several undesirable conditions such as, thermal deformation and permanent distortion resulting in braking deficiency. The application of advanced materials with improved processing technique is required to tackle these challenges for brake rotor production. In this work, multiple particle size (MPS) reinforced silicon carbide particulate (SiCp) is incorporated into aluminium matrix as reinforcement phase in order to develop a light weight automotive composite brake rotor using the novel stir casting process. Finite element (FE) and actual braking analyses were performed by considering the influence of material type, particle size variation and volume fraction on mechanical and thermal performance stability. This study covers the effect of incorporating MPS-SiC in developing aluminium matrix composite (AMC) by evaluating the microstructural and mechanical properties when compared to 6061 aluminium alloy and commercial cast iron. Actual braking test was performed using a passenger car (Proton Wira 1.3) brake system rig set up and a high speed infrared (IR) camera to capture thermal distribution on the rotor surface. It was found that the microstructural and mechanical properties of MPS-SiCp AMC were influenced by varying the 20 wt% SiC particle size in the aluminium matrix. The microstructural analysis revealed a uniform distribution of the MPS-SiC reinforced particulate in the matrix which in turn improves density and tensile strength value. The tensile strength recorded an increment of 45.8 % and 10.2 % when compared to matrix alloy and cast iron material respectively. However, the ductility reduced due to particle reinforcement. The wear rate of cast MPS-SiC AMC is lower compared to the matrix alloy and cast iron used for various type of commercial brake rotor material as revealed from previous studies. Moreover, the friction coefficient is between 0.31 to 0.44, which is observed to be within the deviation band for automotive brake system application according to the industrial standard range. On the other hand, the actual braking test for 2 MPa pressure application on the rotor contact surface revealed an average temperature of 265.1 °C and 351.6 °C for the MPS-SiC AMC and cast iron rotors respectively indicating a significant thermal difference of ~25 %. It can be therefore concluded that AMC improved heat dissipation as a result of high thermal conductivity compared to cast iron thereby avoiding undesirable effects caused at high temperature. Moreover, a good agreement was achieved for thermal profile analysis between the simulation and actual braking results which did not exceed 5.5 % for the AMC brake rotor. Conclusively, the light weight MPS-SiC AMC has successfully improved the thermal and mechanical performance of the newly fabricated AMC brake rotor.