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In this study, the effects of pores on strength and ductility were examined for an Al-Si-Mg alloy produced by a high-pressure-die-cast method with and without secondary intensified pressure. Tensile t...ests were performed using 25 specimens and correlations between the characteristics of all the pores in each specimen and mechanical properties were analyzed utilizing tomographic observations. The results showed a strong correlation between ultimate tensile strength and maximum pore diameter, and those between uniform and local elongations and porosity. The existence of coarse pores larger than 240μm in diameter resulted in significant reduction in tensile strength, whereas more moderate dependency was also observed for smaller pores. There seemed to be no definite correlation between 0.2% proof stress and the characteristics of pores, probably because pre-existing pores do not grow under such low stress/strain levels. Although high porosity inevitably exerted effects on uniform and local elongations, almost constant uniform elongation of 3 to 4% was observed above the porosity of 0.08%. Incidence of local elongation was observed only when porosity was less than 0.004%, above which local elongation was truncated immediately after the maximum load was attained. Since these behaviors were more sensitive to local characteristics of pores than to average ones, a specimen with a porosity level less than average happened to show significant reduction in the properties due to the existence of local pore clustering. Overall, it can be concluded that ductile fracture is not strongly dominated by the existence of pores when pores are eliminated by intensifying pressure during high-pressure die-casting. On the other hand, it can be summarized that when pores are introduced to some extent, strength and ductility become sensitive to pores, especially to local porosity, regardless of whether there are coarse pores or not.続きを見る
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