| Summary: | 碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 100 === In this study, mechanical properties of Al-Zn alloys were conducted, with various parameters including Zn contents, grain size, and tensile strain rate. Experimental samples were all manufactured with friction stir processing method. Samples of Al-Zn alloys with the grain size of 1.5μm, 1μm, or 0.5μm and five Zn concentration were pulled in tension at strain rate of 10-3s-1,10-4s-1 and 10-5s-1 .
The data set were then used to draw engineering and true tensile stress vs. strain curves , flowing stress vs. Zn contents curves, Hall-Petch equation curves, m vs. Zn contents curves and m vs. grain size curves. Quantitative analysis were conducted to discover that solid solute softening and inverse Hall-Petch relation were present in Al-Zn alloys, which were more prominent at slower tensile strain rate when grain size was less than 1μm and the Zn contents was higher than 10wt%.
Quantitative analysis of strain rate sensitivity (m) showed the trends of increasing value of m with higher Zn contents and smaller grain sizes when solid solute softening and inverse Hall-Petch relation were present. The high grain-boundary diffusion coefficient of Zn which accelerates the efficiency of dynamic recovery are considered the main reason. The effect gets more prominent with increasing Zn contents , smaller grain size , and slower tensile strain rate. For Zn concentration higher than 10wt%, dynamic recovery may drive inverse Hall-Petch relation to appear when grain size is about 1μm large.
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