Reliability Analysis on the Fatigue Lift of ADC12 Die-Cast Alloy Under Resonant Vibration

• Main Authors: Yu Sheng Chen, 陳右昇
• Other Authors: 呂傳盛
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/47924316692397734047

碩士 === 國立成功大學 === 材料科學及工程學系 === 88 === The microstructure of a die-cast aluminum alloy, which is affected by casting temperature, has significant influence on the data fluctuation behavior of its mechanical properties. In this study, JIS-ADC12 Al-Si-Cu die-cast alloy prepared under different casting temperatures(650℃,680℃,700℃,720℃ and 750℃) was tested to collect resonant fatigue life data. The Weibull distribution function was adopted to analyze the types of data distribution and the failure modes. The purpose was to explore the factors affecting the reliability under resonant vibration environment. Besides, the tensile data were also analyzed to see whether the results can be referred to predict the reliability under resonant fatigue condition. For each casting temperature, 20 data points were collected for each of the resonant fatigue and tensile analyses mentioned above. According to the Weibull analysis, the Weibull modulus, m is below 1 for the two casting temperatures 650℃(m=0.86) and 680℃(m=0.94), indicating the infant failure mode. The Weibull modulus is larger then 1 when casting at 700℃(m=1.19), 720℃(m=1.65)and 750℃(m=1.37), which belong to left-leaning-wear failure mode. In other words, the failure mode of the resonant vibration fatigue life changes from the infant failure mode to wear failure mode as the casting temperature increases. From the OM and SEM observations, there are abnormal coarse a phase appear when casting temperatures at 650℃and 680℃. The cracks across and branch in the coarse a phase. But, the distribution of the coarse a phase is non-uniform and uncontrollable, hence, the data fluctuation of resonant vibration fatigue life is large. When casting at 700℃and 720℃ the morphology are refined and uniform, hence, the data fluctuation is smaller. Casting at 750℃ there are coarse needle like Al-Fe-Si intermetallic precipitate, which reduce the resistance of crack propagation, hence, the data fluctuation is larger. According to the reliability analysis of the resonant vibration fatigue life, increasing the casting temperature will improve the reliability of the ADC12. According to the tensile test results, the Weibull modulus of the ultimate tensile stress are 7.7～10.3 and the yield stress are 8.8～11.1, both belong to the right-leaning-wear failure mode. The resonant vibration samples failed from the surface where near the notch, while the tensile samples fail from inner cast defects. Besides, it is different in forced conditions. Therefore, it cannot use tensile property data from Weibull analysis and reliability analysis to predict the properties of resonant vibration fatigue life.