Browsing by Subject "CBS"

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    Correlation between homogenisation parameters and property evolution of AA3104 CBS after hot finish rolling
    (2025) Lebakeng, Khethisa; George, Sarah
    AA3104 can-body stock (CBS) is produced through a series of thermomechanical processing stages, including direct chill (DC) casting, homogenisation, hot rough rolling, hot finish rolling, and cold rolling. Homogenisation is an important phase that controls the growth of intermetallic particles (IMPs) and dispersoids, affecting mechanical performance and texture evolution in following rolling stages. This study investigates the impact of different homogenisation procedures on the microstructure and mechanical properties of AA3104 during lab-scale hot rough rolling and plane strain compression (PSC) testing, which simulates hot finish rolling. Industry supplied DC-cast AA3104 ingot material was exposed to various homogenisation procedures at temperatures ranging from 500°C to 610°C to produce differences in IMP morphology and dispersoid dispersion within the structures. The homogenised samples were subjected to lab-scale hot rough rolling to achieve strain and IMP breakdown in line with that of industrial rough rolling. PSC testing on a Gleeble 3800 was utilised to simulate industrial hot finish rolling conditions. The microstructural evolution was investigated using light microscopy, scanning electron microscopy (SEM) in conjunction with energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) for grain and texture characterisation. The findings show that homogenisation temperature has a significant influence on IMP fragmentation, dispersoid refinement, which then has a marked effect on recrystallisation behaviour and texture development. The findings show that the 600°C/520°C condition resulted in coarse dispersoids (127 nm) with low number density (8.93 particles/µm²), the 560°C/520°C condition produced intermediate sized dispersoids (104 nm, 19.85 particles/µm²), and the 520°C condition generated fine, closely spaced dispersoids (56 nm, 55.92 particles/µm²). The cube texture intensity was found to increase with dispersoid density, with the 520°C sample displaying the strongest cube texture (~9.04), followed by 560°C/520°C (~7.5) and 600°C/520°C (~4.8). the 560°C/520°C homogenisation resulted in the largest recrystallised grains. While the 520°C homogenisation contained the finest dispersoids, the EBSD maps showed a fully recrystallised structure with recrystallised grains being smaller than the 560°C/520°C homogenisation. This is attributed to a combination of insufficient pinning pressure to fully retard recrystallisation as well as IMP topology effects on PSN and the overall recrystallisation kinetics, resulting in a smaller grain size than anticipated. There was no recrystallisation in the as-cast protocol, demonstrating that the dispersoids play an essential role in recrystallisation. None of the high temperature homogenisation practices resulted in sufficiently fine dispersoids to retard recrystallisation. These findings emphasise the significance of adjusting homogenisation parameters to alter microstructural features, such as IMPs and dispersoids for better hot rolling performance and final property and microstructural development. The findings do illustrate the importance of a more detailed interrogation of the role of these critical features in the rolling process. This should be achieved on a laboratory scale initially. The experimental protocol for this work used a fully lab scale simulation approach, which showed successful alignment with initial partial industrial samples. The microstructures of the 560°C/520°C material were compared to samples where only the finish rolling was simulated (on industrially supplied transfer bar after industrial homogenisation and rough rolling). The grain size and cube texture intensity of the two approach showed similarities in grain size and cube texture intensities. This indicates an equivalent thermomechanical processing route to achieve these similar microstructures. This is a successful first step in the validation of a full through process simulation of processing on a laboratory scale.
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    Open Access
    Feasibility, validity and utility of HIV testing data as key components of HIV case-based surveillance
    (2025) Jacob, Nisha; Boulle, Andrew
    Background: HIV case-based surveillance (CBS) is recommended by the World Health Organization and other global agencies, for tracking progress towards achieving the 95-95-95 targets to end the HIV epidemic. CBS involves gathering individual-level data for each person diagnosed and linking these data from multiple data sources to other key data points along the HIV care cascade. Despite the high burden of HIV in sub-Saharan Africa and existing routine HIV program monitoring, opportunities to implement CBS have not been optimally used. The maturation of the health information system in the Western Cape province presents a unique opportunity to implement a version of case-based HIV surveillance that is integrated into a routine operation system within the antenatal services setting. This thesis seeks to explore the validity of HIV case ascertainment within a routine health information exchange, the feasibility of embedding HIV testing data into routine information systems and the utility of these routine data for enhanced HIV CBS. Methods: Routine pregnancy and HIV data consolidated within the Provincial Health Data Centre (PHDC) from January 2010 to December 2020 were analysed using retrospective cohort and cross-sectional methods. Routine data were linked using a unique patient identifier to ascertain sentinel events within the HIV and vertical transmission prevention cascades. Temporal trends in HIV prevalence, HIV testing, linkage to care, ART coverage and vertical transmission estimates were evaluated and where relevant, triangulated with other key data sources historically used as sources for these estimates. These included routine aggregate data from the District Health Information System, national and provincial sentinel antenatal seroprevalence surveys and mathematical model estimates. Risk factors for vertical transmission were further evaluated using multivariable analyses. A specific intervention implemented at a selected facility to enhance CBS through digitisation of routine point-of-care HIV tests was further evaluated for operational feasibility using both quantitative and qualitative research methods. Findings: PHDC antenatal HIV prevalence estimates from 2011-2013 were widely disparate from aggregate and survey data (due to incomplete electronic data), whereas from 2014 onwards,n estimates were within the 95% confidence interval of survey estimates, and closely correlated to aggregate data estimates (r=0.8; p=0.01). PHDC data show a slow but steady increase in provincial antenatal HIV prevalence from 16.7% in 2015 to 18.6% in 2020. ART coverage by the time of delivery in mothers of live births increased from 67.4% in 2011 to 94.7% by 2019. This pattern of increasing antenatal ART coverage was also seen in the DHIS data, and estimated by mathematical models, but was less consistent in the antenatal survey data. Ascertainment of HIV status among children exposed to HIV increased over time to 87.2% (16 908/19 382) in 2020. In recent years (2017 – 2020), 2.0% of children exposed to HIV (1 461/73 590) were diagnosed with HIV. Children born after implementation of lifelong ART in pregnant women, were less likely to have HIV than children born in the prior policy period (aOR 0.7; 95% CI 0.6 – 0.7), mediated through expanded ART access. Young maternal age, no antenatal ART, previous TB diagnosis and no records of antenatal visits were associated with vertical transmission. The intervention to enhance CBS through digitisation of HIV testing data, demonstrated that 51.3% (95% CI 48.4–54.1%) of patients testing HIV-positive at a selected health facility were retesting, supporting the utility of these data to enhance CBS. While the intervention is operationally feasible, various logistical, health system and cost-related challenges require careful consideration before scale-up. Conclusions:This study demonstrates that CBS embedded within a routine health information exchange may be reliably used for HIV prevalence, ART coverage and vertical transmission surveillance, providing more granular estimates, more efficiently than sentinel surveillance and aggregate programmatic data. This would enable more timely action in response to surveillance such as interventions targeting gaps in care or tailored for high-risk groups. However, these strategic gains may be strengthened by digitisation of HIV point-of-care data, implementation of which is operationally feasible but complex.