Effects of thermo-mechanical treatment on the microstructures and mechanical / hydrogen storage properties of the ZK60 alloy

• Main Author: 彭瓊慧
• Other Authors: 林昆明
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/58727512518084798543

碩士 === 逢甲大學 === 材料科學與工程學系 === 103 === In this study the cast ZK60 alloy was strained by Hot Rolling 10%, 50% and Equal Channel Angular Pressing (ECAP) Route BA 1Pass, 4Passes, respectively. After 380oC/1 hr solid solution treatment followed by water quenching then aging or furnace cooling, the effects of various thermo-mechanical treatments on the microstructures and mechanical / hydrogen storage properties of the ZK60 alloy were investigated. The microstructures of the alloy ingots are composed of the dendrite of α phase and the interdendrite of eutectic / eutectoid mixtures. By FESEM observation under 100kX for various thermo-mechanical treatments, it shows a nanostructure with a three-dimensional network of intermetallic phases in the matrix of α phase. EPMA analysis shows that the second phase which contains Zr and is indentified possibly as Mg3Zn5Zr does not exist in the matrix of α phase but is mixed in the eutectic / eutectoid mixtures, and its volume fraction is far less than that of the eutectic / eutectoid mixtures. After 380oC/1 hr solid solution treatment followed by water quenching then aging at room temperature, the hardness of the alloys increases with increasing aging time, and it reaches a maximum at 32 hrs for Hot Rolling then decreases with aging time due to over aging. However, the hardness of the alloys for ECAP after 32 hrs still increases monotonically and approaches an upper value with increasing aging time, and is obviously higher than that for Hot Rolling. Under the same conditions, the tensile stress σUTS of the alloys for ECAP is slightly higher than that for Hot Rolling. However, the fracture strain εf for ECAP is obviously higher than that for Hot Rolling. It means that the tensile properties of the alloys for ECAP is superior to that for Hot Rolling. By various mechanical processes followed by 400oC/10 hrs activation treatment, the hydrogen capacity of the alloys increases with increasing hydrogenation temperature and / or plastic strain. The hydrogen capacity can reach 2.29wt% for the alloy by ECAP BA 4Passes at 400oC. However, the hydrogenation properties of the alloys is still not so good. After improvement by adding 5wt% activated carbon and 20 hrs ball-milling, the hydrogen capacity of the alloys increases obviously at hydrogenation temperature higher than 280oC, and it can reach the maximum 6.43wt% at 360oC, then decreases with hydrogenation temperature due to the increasing of the hydrogen absorption pressure. It shows the fact that the hydrogenation properties of the alloys can be improved significantly by the addtion of 5wt% activated carbon and the treatment of 20 hrs ball-milling rather than various thermo-mechanical treatments.