| 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.(Received November 19, 2015; Accepted April 5, 2016) |
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| Key Words |
| alloys, casting, fatigue, hardness test, dynamic mechanical analysis |
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