Fracture behavior of thixoformed 357-T5 Al alloys |
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Authors: | Chul Park Sangshik Kim Yongnam Kwon Youngseon Lee Junghwan Lee |
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Affiliation: | (1) the Division of Materials Science and Engineering, Engineering Research Institute, Gyeongsang National University, 660-701 Chinju, Korea;(2) the Materials Engineering Department, Korea Institute of Machinery and Materials, 641-010 Changwon, Korea |
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Abstract: | The effects of microstructural features on the fracture behaviors, including impact, high-cycle fatigue, fatigue crack propagation,
and stress corrosion cracking, of thixoformed 357-T5 (Al-7 pct Si-0.6 pct Mg) alloy were examined. The resistance to impact
and high-cycle fatigue of thixoformed 357-T5 tended to improve greatly with increasing volume fraction of primary α. An almost threefold increase in impact energy value was, for example, observed with increasing volume fraction of primary
α from 59 to 70 pct. The improvement in both impact and fatigue properties of thixoformed 357-T5 with increasing volume fraction
of primary α in the present study appears to be related to the magnitude of stress concentration at the interface between primary α and eutectic phase, by which the fracture process is largely influenced. The higher volume fraction of primary α was also beneficial for improving the resistance to stress corrosion cracking (SCC) in 3.5 pct NaCl solution. The in-situ slow strain rate test results of thixoformed 357-T5 in air and 3.5 pct NaCl solution at various applied potential values
demonstrated that the percent change in tensile elongation with exposure decreased linearly with increasing volume fraction
of primary α within the range studied in the present study. Based on the fractographic and micrographic observations, the mechanism associated
with the beneficial effect of high volume fraction of primary α in thixoformed 357-T5 alloy was discussed. |
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