The Characteristics of Aluminum/Magnesium Multi-layers Composite after Accumulative Roll Bonding

• Main Authors: Ming-Che Chen, 陳明哲
• Other Authors: 吳威德
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/66621013782497137009

博士 === 國立中興大學 === 材料科學與工程學系 === 96 === Metals were widely used in the world for their good characters of working property, forming property, and toughness. Metal materials can reach to ultra-perfect physics and mechanical properties by different treating processes. Sometimes the single metal can not offer the application that we need, so it leads the bi-metal or composite to become more expectative. The bi-metal means the material composed with two kinds of metals with different properties. This project will use the methods of solid state joining and hot working processes to get the purpose of accumulative layers, and it will obtain the advantage and eliminate the disadvantage properties of each other. The snap-stack working to reduplicate the Mg-Al metal is chosen and then thinner and longer by executing rolling and repeating the processes. Accumulative roll bonding (ARB) involves the severe plastic deformation of sheet metal without changing the original sheet dimensions, which can produce high strength metals with ultra-fine grained microstructure. Mechanical properties are significantly increased due to the altered ultra-fine grain microstructure. In this study, the ARB process is used with the snap-stack working to reduplicate Al (ASM-1100) / Mg (AZ31). The procedure entails repeated roll-bonding two sheets of metal, of equal dimensions. Alloy is chosen and then through repeated rolling and deformation made, thinner and longer. Samples underwent four rolling and stacking cycles four times, which produced a 24-layer structure. The ARB process creates a multilayer compound between Al/Mg layers with excellent bonding characteristics. The excellent bonding characteristics were due to atomic diffusion. The diffusion zone was obtained after four cycles of the ARB process. The layers of the intermetallic compounds Al3Mg2 and Al12Mg17 were observed in the diffusion zone. The composition-depth curves of the diffusion zone were determined by electron microprobe analyses of the IMCs. The three interfaces of Al(Mg)/Al3Mg2, Al3Mg2/Al12Mg17 and Al12Mg17/Mg(Al) were identified. Growth constants k of Al3Mg2 was higher than Al12Mg17. The pertaining activation enthalpies were 72 and 167 KJ mol-1. Interdiffusion coefficient Dβ and Dγ were increasing to 5.24 cm2/s and 0.7 cm2/s with the temperature increasing to 673 K. The grain sizes of Al and Mg alloys were reached to 926 nm and 1024 nm after fourth cycle. The hardness of the Al and Mg alloys were raised to Hv42 and Hv91 after fourth cycles. The third cycle had maximum ultimate tensile strength (UTS) with 117 MPa and the fourth cycle had minimum elongation. The grain refined and the Mg that was protect perfectly by Al, result in the 2 cycles specimen had the best corrosion resistance which Icorr, Ecorr, and Rp were 6.757 μA/cm2, -1.047V, and 0.378 MΩ, respectively. Pitting corrosion occurred in all cycle of ARB specimens. Galvanic corrosion was only appeared on 3 and 4 cycles, because the minority of Mg was exposed to the corrosive surface.