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Korean Journal of Metals and Materials > Volume 54(9); 2016 > Article
Korean Journal of Metals and Materials 2016;54(9): 626-636. doi: https://doi.org/10.3365/KJMM.2016.54.9.626
승용디젤엔진 실린더 헤드용 Al-Si-Mg-(Cu) 합금의 저주기 피로 특성에 미치는 첨가원소 효과
진보라, 정창열
동국대학교 원자력 ・에너지시스템공학과
Effect of Alloying Elements on the Low-Cycle Fatigue Properties of Al-Si-Mg-(Cu) Alloys for the Cylinder Head of a Passenger Diesel Engine
Bo-Ra Jin, Chang-Yeol Jeong
Dept. of Nuclear and Energy System Engineering, Dongguk University, Gyeongju-si 38066, Republic of Korea
Correspondence  Chang-Yeol Jeong ,Tel: +82-54-770-2858, Email: jcy@dongguk.ac.kr
Received: 19 November 2015;  Accepted: 5 April 2016.  Published online: 5 September 2016.
ABSTRACT
To improve automobile fuel efficiency and reduce emissions, there has been a growing demand for more durable alloys for engine components with improved high temperature fatigue resistance. This study examined the effect of alloying elements on the high temperature mechanical behavior of Al-Si-Mg-(Cu) casting alloys for diesel cylinder heads. Depending on the effect of the alloying elements on the strength of the matrix, hardness at high temperatures increased with increasing Cu and Ti content with a concomitant increase in tensile strength. The LCF (low cycle fatigue) lives decreased with increasing alloy content according to the Coffin-Manson relation, due to smaller elongation. On the other hand, an analysis of fatigue lives with hysteresis loop energy, which consists of both strength and elongation, showed that the fatigue lives were normalized with an alloy of the same strengthening mechanisms, regardless of the test temperature. In the case of the alloy without Cu, an obvious cyclic softening behavior was observed, whereas the cyclic softening decreased significantly and the peak stress was maintained at 250 ℃ for the alloy with Cu. Dynamic mechanical analysis results showed that the mechanical properties of the Al2Cu precipitate hardened alloy were maintained at temperatures over 250 ℃, whereas the degradation of mechanical properties of the Mg containing alloy occurred at 170 ℃ due to coarsening of the Mg2Si precipitation phase.
Keywords: alloys, casting, fatigue, hardness test, dynamic mechanical analysis
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