| Summary: | 碩士 === 大葉大學 === 機械與自動化工程學系 === 103 === The purpose of this study is aimed at the promotion in the ductility and toughness of A356 aluminum EPC castings. With the two solidification modes of atmospheric pressure and high-pressure, the castings produced to be investigated via tensile test and impact test. The process parameters used to experiment include the casting temperature, the coating thickness and the casting thickness. The casting shape is step-type plate form.
The experimental results show that at atmospheric pressure, the ductility and toughness of A356 aluminum EPC castings at 730℃ casting temperature is superior to those at 710℃ and 750 ℃ casting temperatures. The impact toughness value for 730℃ is 0.1~ 0.9 kg-m /cm2 higher than those for 710℃ and 750 ℃. The yield strength and tensile strength are 3~8 N /mm2 and the elongation rate is 1~2% for 730℃ higher than those for 710℃ and 750 ℃ at atmospheric pressure. The tendency and value differences for high-pressure is similar to that at atmospheric pressure. Under the same casting temperature, the yield strength, tensile strength and the elongation rate for 0.3mm coating thickness are 5~10 N /mm2 and 1~2% higher than those for 0.6mm coating thickness. In addition, the test values for A356 aluminum alloy EPC castings reveal that the maximum mechanical properties belonged to 5mm casting thickness and the minimum mechanical properties belonged to 25mm casting thickness. The differences of their yield strength and tensile strength are 25~35 N/mm2, and elongation difference is 1~ 2%.
The observation of A356 aluminum alloy tensile test specimen by optical microscope and was scanning electron microscope show that the cleavage planes and dimples variation for the different experimental conditions. The primary aluminum dendrites of high-pressure solidified castings are smaller and closer than those of atmospheric pressure, and the porosities are also similar. This result promotes the the mechanical properties of high-pressure solidified castings. From the observation of SEM, the cleavage planes become less and the dimples become more for high-pressure solidified castings, thus improve the ductility and toughness of A356 aluminum alloy EPC castings dramatically.
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