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The Characteristics of Aluminum/Magnesium Multi-layers Composite after Accumulative Roll Bonding
|關鍵字:||Accumulative roll bonding;累積軋延製程;intermetallic compounds;grain sizes;activation enthalpies;corrosion;介金屬化合物;晶粒尺寸;活化能;腐蝕||出版社:||材料科學與工程學系||摘要:||
累積軋延製程屬於一種將金屬板材做劇烈塑性變形的加工方式而不改變其金屬板材的原始厚度尺寸，此製程可以產製極細晶粒結構並具有高強度之金屬材料。晶粒細化的結果意味著著機械性質提高。本研究使用累積軋研製程製備Al (ASM-1100) / Mg (AZ31) 複合金屬塊材，將Al-Mg重疊加以輥軋的方式加工使變薄增長，再將其折疊，後施以軋延，如此反覆數次將可令其組織細化，達到強化的目的。
經過四次的循環軋延過程，24層之 Al / Mg 複合金屬塊材成功的製備。由於 Al 與 Mg 原子相互擴散，Al / Mg 層狀複合金屬之界面在經過多道次的軋延後具有優良的接合性質。經過四次的循環軋延後界面形成一擴散區域，此擴散區會形成Al3Mg2 與 Al12Mg17 之介金屬化合物，並利用EPMA做成份-深度曲線分析。Al(Mg)、 Mg(Al)、 Al3Mg2 與 Al12Mg17 之間存在 Al(Mg) / Al3Mg2、 Al3Mg2 / Al12Mg17 與 Al12Mg17/ Mg(Al) 等三個界面。Al3Mg2 與 Al12Mg17 兩相活化能分別為 72 與 167 kJ/mol，而擴散係數分別為 3.1×10-8 與 0.092 cm2/s。當退火溫度增加到 673 K時，相互擴散係數 Dβ 與 Dγ 個別增加到 5.24 cm2/s 與 0.7 cm2/s。
鋁與鎂晶粒尺寸隨著累積軋延製程分別因軋延次數增加至第四次循環而達到約926 nm與 1024 nm。鋁與鎂的硬度值隨著累積軋延次數增加至第四循環時硬度增加至Hv 42與Hv 91。在拉伸試驗中，第三次循環軋延有最高的抗拉強度117 MPa；在第四次循環軋延之延伸量最低。
腐蝕試驗結果，第二次循環軋延試片具有最佳之抗腐蝕能力，其腐蝕電流（Icorr ）、電位（Ecorr ）分別為 6.757 μA/cm2 與 -1.047V，腐蝕阻抗 (Rp)為 0.378 MΩ。第四次循環軋延試片在累積軋延製程中，其抗腐蝕性最差。腐蝕現象種類於第一次循環至第四次循環軋延試片具有孔蝕現象，而伽凡尼腐蝕僅在第三次循環與第四次循環試片中發現。
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.
|Appears in Collections:||材料科學與工程學系|
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