Browsing by Author "Lombardi, A"

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    Evolution of residual stress through the processing stages in manufacturing of bore-chilled sand-cast aluminum engine blocks with pressed-in iron liners
    (Research Square, 2021-11-30) Stroh, J; Sediako, D; Lombardi, A; Byczynski, G; Reid, M; Paradowska, AM
    The cumulative global emissions produced by the automotive industry over the last decade has put a tremendous strain on the environment. Consequently, automotive engineers and manufacturers have been forced to improve the efficiencies of their automobiles which is frequently accomplished by increasing the operating pressure, and therefore temperature, of the combustion engine. Unfortunately, in addition to the rise in operational pressures and temperatures, large tensile residual stresses often accumulate in the cylinder bridges during the casting process of aluminum engine blocks due to the use of cast-in iron cylinder liners, leading to combined stress magnitudes above the strength of the currently used aluminum alloys. Thus, the present study aims to characterize the evolution of residual stress, with application of neutron diffraction, at several critical stages of the manufacturing process of sand-cast aluminum engine blocks that have eliminated the iron cylinder liners from the casting process and replaced them with cylinder bore chills that are pressed-out after the thermal sand reclamation process. The replacement of the iron liners shifted the stress mode from purely tension to purely compression until the bore chills were removed. Following removal of the bore chills, the maximum tensile stress at the top of the cylinder bridge was ~70% lower than the engine’s predecessor which was produced with iron liners. Moreover, in the production-ready state (i.e., T7 heat treated, machined and press-fit liners inserted), the stress mode maintains the partially compressive nature with low magnitudes of tension, thereby lowering the material’s susceptibility to crack growth and propagation. This work is licensed under a Creative Commons Attribution 4.0 International License.
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    Stress characterization of bore-chilled sand cast aluminum engine blocks in as-cast and T7 condition with application of neutron diffraction
    (Springer Nature, 2020-01-28) Stroh, J; Sediako, D; Byczynski, G; Lombardi, A; Paradowska, AM
    In an effort to improve vehicle fuel efficiency, aluminum (Al) alloys have been gaining upward momentum for use in automotive powertrain components such as engine blocks. Al alloys are lightweight and have good mechanical strength at engine operating temperatures; making them a suitable choice for engine block production. However, during the manufacturing process factors such as inhomogeneous cooling rates and/or coefficients thermal expansion mismatches in multi-material castings can lead to the development of residual stress. This is of particular concern for the relatively thin cylinder bridges, which are exposed to large thermo-mechanical loading during engine operation. The casting process used at Nemak for I6 engine block production does not utilise cast-in liners and therefore may be also be suitable for future mass-produced linerless blocks. This paper utilizes neutron diffraction and SEM/EDS to determine how the elimination of cast-in liners as well as a T7 heat treatment effects the magnitude of residual stress in cast Al (A319 type alloy) engine blocks. It was observed that the T7 treatment resulted in a significant reduction of the strain/stress in the Al cylinder bridge (up to ~50% of the radial stress at the top of the bridge). In addition, the absence of the cast-in Fe liners allowed for unrestricted natural contraction of the Al bridge; leading to a combination of low tension and moderate compression as compared to the typically high tensile stress. © 2020 Springer Nature Switzerland AG
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    Stress characterization of bore-chilled sand cast aluminum engine blocks in as-cast and T7 condition with application of neutron diffraction
    (The Minerals, Metals & Materials Society, 2020-02-24) Stroh, J; Sediako, D; Byczynski, G; Lombardi, A; Paradowska, AM
    In an effort to improve vehicle fuel efficiency, aluminum (Al) alloys have been gaining upward momentum for use in automotive powertrain components such as engine blocks. Al alloys are lightweight and have good mechanical strength at engine operating temperatures; making them an suitable choice for engine block production. However, during the manufacturing process factors such as inhomogeneous cooling rates and/or coefficients of thermal expansion in multi-material castings can lead to the development of residual stress. This is of particular concern for the relatively thin cylinder bridges, which are exposed to large thermo-mechanical loading during engine operation. The casting process used at Nemak for I6 engine block production does not utilise cast-in liners and therefore may be also be suitable for future mass-produced linerless blocks. This paper utilizes neutron diffraction and SEM/EDS to determine how T7 heat treatment reduces the magnitude of residual stress in cast Al I6 engine blocks. © The Minerals, Metals & Materials Society