The Influence of Ni and V Trace Elements on High-Temperature Tensile Properties and Aging of A356 Aluminum Foundry Alloy
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IN the last decades, aluminum alloys have been re-focused in terms of lightweight material for vehicles. Replacing cast iron with aluminum alloys can result in a significant weight reduction and consequently better fuel efficiency.[1,2] High-temperature performance is a critical characteristic affecting an alloy’s suitability for various automotive power-train applications. Contemporary automotive engines operate at the highest temperatures reaching up to 523 K (250 C).[3] This creates demanding operating requirements for the existing Al-Si-Cu and Al-Si-Mg alloys that typically lose strength above 423 K (150 C).[4–7] Industries have also shown a growing interest in the effect of increased Ni and V levels on the mechanical properties of aluminum alloy products. In fact, the deterioration in the coke quality and, as a result, in the quality of the anodes used in the Hall–He´roult process has led to an increase in the amount of these metal MARIA TERESA DI GIOVANNI, Assistant Researcher, and EMANUELA CERRI, Professor, are with Dip. Ingegneria Industriale, Universita´ di Parma, v.le G. Usberti 18/A, 43124-Parma, Italy. Contact e-mail: [email protected]. DANIELE CASARI, Postdoctoral Fellow, is with the Dept. of Physics, NTNU, Høgskoleringen 5, N-7491 Trondheim, Norway. MATTIA MERLIN and GIAN LUCA GARAGNANI, Professors, are with the Dip. Ingegneria, Universita´ di Ferrara, v. Saragat 1, 44122-Ferrara, Italy. LARS ARNBERG, Professor, is with the Dept. of Materials Science and Engineering, NTNU, A. Getz vei 2, N-7491 Trondheim, Norway. Manuscript submitted July 21, 2015. Article published online February 17, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
impurities in the downstream products. In the next years, the levels of Ni and V are expected to rise to 420 and 1080 ppm,[8] respectively. At present, there is no cost efficient method available for the removal of these impurities, and the response to the problem is mainly monitoring the Ni and V levels and checking for any negative influence.[9] Therefore, considering the new trends, it might be interesting to understand which role is played by Ni and V additions on the high-temperature mechanical behavior. A previous study investigated the room temperature tensile properties of sand cast and permanent mold cast unmodified A356 alloy containing 600 and 1000 ppm of Ni and V, respectively.[10] It was found that Ni and V strongly affect both the yield strength (Rp0.2) and ultimate tensile strength (UTS) of the sand cast alloy in the as-cast condition. In particular, Ni reduces Rp0.2 and UTS by 87 and 37 pct, respectively, whereas V increases Rp0.2 and UTS by 42 and 25 pct. Hence, the objective of this work is to evaluate the influence of Ni and V trace elements on the high-temperature tensile properties of the unmodified A356 foundry alloy in the as-cast and T6 heat-treated condition, solidified by means of both sand and permanent mold casting processes. High-temperature tensile tests and hardness measurements were performed to assess the mechanical properties. Observ
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