Experimental Damage Criterion for Static and Fatigue Life Assessment of Commercial Aluminum Alloy Die Castings
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TRODUCTION
CASTING is a process by which almost all kinds of products can be manufactured. This explains why there are many different application areas for castings; furthermore, 100 pct of castings can be recycled. Among the casting materials, particular importance is put on non-ferrous metals, and specifically, on aluminum alloys. Among all aluminum casting technologies, high-pressure die casting (HPDC) is one of the most versatile and highly productive process: currently about half of the world production of light metal castings is obtained by this kind of process.[1] For 2020, a global Aluminum foundry production close to 17 million tons is expected.[2] HPDC allows the production of large numbers of near-to-shape components of complex geometry, thin wall thicknesses and very good surface finish, and it is very economical for large scale production.[3] Nevertheless, the high number of sequential actions involved in the process may affect the casting quality and compromise its integrity.[4–6] As stated by Campbell,[7] the directness of the process from the liquid metal to the finished product involves the greatest difficulty as many aspects must be controlled simultaneously. A critical disadvantage of HPDC is the almost inevitable presence, in the produced castings, of surface and internal defects which are often hard to detect:
ELEONORA BATTAGLIA, FRANCO BONOLLO, and PAOLO FERRO are with the Department of Management and Engineering, University of Padova, Stradella S. Nicola, 3, 36100, Vicenza, Italy. Contact e-mail: [email protected] Manuscript submitted November 11, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
oxide bifilms and confluence welds,[8] porosity, primary intermetallic particles, and many others.[9–11] Defect classification for HPDC components, introduced in Reference 8 has been recently published as CEN/TR 16749:2014.[12] According to this classification and to a recent survey carried out by the European foundry industry, some of the most common defects and imperfections normally found in high-pressure die cast Aluminum alloys are porosity (due to gas entrapment and shrinkage) and filling-related defects (i.e., oxides) as illustrated in Figure 1.[8,13] In industry, different methods are used to detect casting defects and assess their quality. Visual inspection, magnetic particle and dye penetrant testing, radiographic analysis, ultrasonic and eddy current testing are the major six non-destructive investigation methods. Among them, the X-ray investigation is the main non-destructive testing (NDT) used within the HPDC foundries. The influence of defects on both static and fatigue behavior of high-pressure die cast aluminum alloys has been studied by several researchers.[14–16] In literature, many approaches for static and dynamic strength prediction of HPDC magnesium and aluminum alloys components have been proposed.[3,17–22] Gokhale et al.[17] and Timelli et al.[18] demonstrated that the mechanical properties decrease monotonically increasing the area fraction of defects revealed on the fracture surface
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