The Effects of Defects on Tensile Properties of Cast ADC12 Aluminum Alloy

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ndustry, aluminum alloys are the optimum choice for the manufacture of parts, because of their low weight and for environmental reasons, especially lower fuel consumption[1] and lower CO2 emission.[2] In fact, automotive parts made of cast irons (c = 7.8 g/cm3) have been replaced with lighter aluminum alloys (c = 2.7 g/cm3), and the production of cast aluminum alloy for automotive parts has increased in recent years.[2] The advantages of cast Al alloys include not only their light weight, with a density of approximately one third that of cast iron, but also their attractive appearance, excellent fabricability, and high resistance to corrosion.[3] In particular, the use of aluminum-silicon-copper (Al-Si-Cu) cast alloys is widespread in different fields of application because of their good castability. However, cast Al-Si-Cu components possess complicated

MITSUHIRO OKAYASU, Professor, is with Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama, 700-8530, Japan. Contact e-mails: mitsuhiro. [email protected], [email protected] HIKOYUKI SAKAI, Master Student, is with the Department of Materials Science and Engineering, Graduate School of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan. Manuscript submitted January 19, 2015. Article published online September 8, 2015 5418—VOLUME 46A, NOVEMBER 2015

microstructures and exhibit various defects, so the use of cast Al alloys to replace cast iron in the manufacture of safety-critical parts in automobiles is significantly restricted because of their low mechanical properties or low reliability. The mechanical properties of cast Al alloys have been investigated, and it was found that failure (or crack initiation) occurred, originating from the cast defects. One of the significant defects was associated with porosity (i.e., blow holes),[4,5] because related defects could involve the cast sample, especially caused by pressure casting, e.g., the cold-chamber die casting process. Jana et al.[6] reported that fatigue cracks emanated from the edges of porosities as a result of high stress concentration. There was a strong correlation between the porosity and mechanical properties of the cast Al alloys, in which the parameter of global volumetric porosity was used.[7] In the study by Zhao et al.,[8] the tensile properties of Al-Si-Cu cast plate samples were found to be directly affected by porosity. The effects of porosity on mechanical properties have been investigated by several researchers (e.g.,[9]). Irfan et al.[1] reported that there was a linear correlation between the pore area and ultimate tensile strength, but their data appeared to be slightly scattered. They stated that ‘‘due to the scatter in data it is hard to make any meaningful conclusions based on this data.’’ In their approach, the pore area was determined on one particular section of the tensile test sample, which may not be representative of the whole METALLURGICAL AND MATERIALS TRANSACTIONS A

volume of the tensile