Hydrogen-based Pore Formation in Aluminum Alloy Castings

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The control of pore formation in near-net-shape aluminum alloy castings is critical from the standpoint of increasing their use in the automotive sector as the presence of pores can act to seriously undermine the performance of components subject to cyclic loading. Reduced productivity associated with pore-related defects and the need to over-design many components also adds cost, further eroding increased commercial adoption of cast aluminum products. The mechanism of microporosity formation in aluminum alloy castings is complex, owing to its dependence on the interaction of a number of phenomena occurring during solidification including the decrease in hydrogen solubility, volumetric shrinkage, the presence of suitable sites for pore nucleation and the development of the solidification microstructure. There is an on-going need for fundamental research to understand these various phenomena and their contribution to pore formation. The proposed research program described below will focus on two of these phenomena: 1) the role of the solidification microstructure as influenced by strontium-based modification; and 2) the role of surface oxide film entrainment in nucleating pores. Both subject areas continued the applicants overarching research interest for the past 21 years in understand and predicting defect formation in casting processes. The resulting knowledge and the tools to apply this knowledge in an industrial setting will be of significant benefit to both the primary metal producers and manufactures of near-net-shape aluminum products. The primary outcome of this work, if successfully applied commercially, will be a reduction in the cost-to-cast, near-net-shape, aluminum products stemming from a reduction in product yield loss associated with pore formation. A secondary outcome will be the ability to expand the use of cast, near-net-shape aluminum products in applications that demand good fatigue performance thus increasing market opportunities for the Canadian foundry industry.