| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 91 === Several commercial Al alloy systems, including Al-Al3Ni, Al-Si (Al-4Si and AC8A), Al-Cu (2218), were chosen in this study to investigate the plastic deformation resistance at elevated temperatures and the softening feature. Pure Al (1070) was also examined for comparison. In addition, an Al-4Cu-4Ni-4Si-1Mg, designated as 4441, was also prepared for understanding the combined effect of Cu, Ni, and Si.
According to the results of tensile tests from room temperature to 300oC, the flow stress of all the samples descends slightly before a critical temperature for a drastic drop in the strength (softening temperature). Second phase particles, including Si, Al3Ni, and precipitates, are able to improve the high temperature strength and rise the softening temperature. It can be found that the increasing effect of the precipitates on the softening temperature and the deformation resistance is more significant than Si and Al3Ni particles. However, Al alloys with the addition of Si particles exhibit a higher softening temperature than those with Al3Ni. Interestingly, large amount of Si and Al3Ni additions seems to have no effect on the critical temperature for softening.
Comparing AC8A to Al-4Si, the results indicate that adding small amount of the precipitation hardening elements (Cu, Mg) increases high temperature strength but not softening temperature. On the other hand, adding Al3Ni and Si particles into the precipitation hardening Al-Cu alloys is not capable of improving both the high temperature deformation resistance and softening temperature.
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