A Study on the High-Strain-Rate Superplasticity and Injection Molding of Zn-22 % Al Alloys Produced by Reciprocating Extrusion

• Main Authors: Y. C. Huang, 黃元璋
• Other Authors: J. W. Yeh
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/09229367437928304329

碩士 === 國立清華大學 === 材料科學工程學系 === 87 === Reciprocating extrusion was applied to processed super-plastic Zn-22 % Al alloys. In order to discuss the effect of extrusion times on microstructure and grain size, reciprocating processes were performed on the billets with 1, 5 and 10 times at 200℃, respectively. Increasing extrusion times can refine the grain of alloys to 0.3 m and obtain high angle grain structure. Furthermore, increasing extrusion times can effectively promote superplastic elongation. The optimum superplastic condition is the extrusion at 200℃ for 10 times combining with testing at 200℃ and strain rate at 2×10-2 s-1. The elongation can attain to 2510%, is almost the same with the best result in the memorials. Secondly, the high temperature fracture surfaces at low m values are dimple structure, and those at high m values are grain boundary sliding structure. It reveals that the behavior of grain boundary sliding is more active at high m values. In addition, the component of strain induced grain growth at high strain rate is more than that at low strain rate. At last, the injection molding processes were performed at 8×10-2 s-1 to form a disk with two raised ring. There were no cracks in these products. The results reveal that the Zn-22 % Al alloys pro-duced by reciprocating extrusion have the ability of near net shape forming.