不同鍛造製程對Al-8Zn-2.5Mg-1.5Cu-xZr (x = 0.02, 0.2 wt. %)合金機械性質的影響

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Title:	不同鍛造製程對Al-8Zn-2.5Mg-1.5Cu-xZr (x = 0.02, 0.2 wt. %)合金機械性質的影響
Authors:	官鈺庭;Guan, Yu-Ting
Contributors:	機械工程學系
Keywords:	Al-Zn-Mg-Cu-Zr合金;鍛造製程;晶界角度;機械性質;Al-Zn-Mg-Cu-Zr Alloy;forging process;grain boundary angle;mechanical property
Date:	2018-08-06
Issue Date:	2018-08-31 15:03:30 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究探討不同鍛造製程對Al-8Zn-2.5Mg-1.5Cu-xZr (x = 0.02, 0.2 wt. %)合金機械性質的影響。實驗中利用高週波溶解爐，以AA7075為母合金，透過添加Al-10 % Zr錠材與99.9%純Zn錠的方式調整至目標成份，熔煉後澆鑄於Y型金屬模中。切除冒口後的試塊，將進行不同的均質化熱處理、鍛造條件(包括鍛造溫度與模具型態)，隨後再進行固溶、焠火與T73過時效處理。處理完成之試棒，按照ASTM-E8規範，利用CNC數控機床加工成公稱直徑9 mm的拉伸試棒並進行機械性質量測。拉伸測試後的試棒會進行以下實驗以檢測其性質，研磨、拋光，並透過光學顯微鏡(OM)，觀察試棒縱剖面之金相與顯微結構。利用影像分析軟體ImageJ，計算所觀測到的試片基地二次相顆粒尺寸與大小，並著重探討二次相、介金屬化合物(Intermetallic compounds, IMCs)等顆粒對機械性質之影響。利用FIB技術製備試片以進行掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)觀察。利用高解析場發掃描電鏡(FE-SEM)的電子背向散射繞射分析儀(EBSD)，分析材料縱剖面方向的晶界角度差異，並統計其高低角度晶界分布。研究成果表明，大變形量引致的高差排密度，會降低材料的再結晶溫度，但由於受剪力細化、散佈均勻的析出顆粒會阻礙晶界遷移，因此EBSD的解析結果顯示，經熱處理後的試片，其晶粒尺寸下降並且有少部分屬於高角度晶界。經由三段式均質化、開模式冷鍛的試片得到最優良的機械性質；最大抗拉強度506.11 MPa、降伏強度439 MPa以及延伸率約 12.2 %。;This study aims to investigate the effects of different forge and heat treatment conditions on the mechanical properties of Cast/Forge Al-8Zn-2.5Mg-1.5Cu-xZr (x= 0.02, 0.2 wt. %) alloy. High quality of Al-5.7%Zn-2.4%Mg-1.5%Cu alloy billets were used as base metal and melted in an induction furnace. For producing desired alloy samples, pure zinc ingot, and Al-10%Zr master alloys were added into the molten metal, then poured into Y-block mold. After solidification, the top risers of Y-block castings were removed to get block casting, and underwent different homogenization treatments and forged conditions. Then, the experiment samples were carried out solution treatment, water-quenched and T73 over-ageing treatment. After the above steps, refer to the ASTM-E8 specification, the experiment samples were machined to tensile test bar through CNC lathe. After tensile test, the sample were prepared for the following experiments. Grinded and polished to observed the microstructure through the optic microscope (OM). Then analyzed the photo by image processing software ImageJ and calculate the 2nd phase particle sizes and quantities. Discussion would be addressed on its effects to mechanical properties. Samples were also prepared for transmission electron microscope (TEM) and scanning electron microscope (SEM) observation. In this study, electron backscatter diffraction analyses (EBSD) were conducted to get the grain boundary misorientation angles of different sample. Deformation on samples produced high amounts of dislocation. Cold working retained high degree of dislocation density leading to reduce the recrystallization temperature. As a result, the sample obtained ultra-fine grains with high-angle grain boundary in matrix during solution/aging treatment. After subjecting to proper homogenization and sub-zero temperature forging, the optimum properties could be reached to have ultimate tensile strength (UTS) of 506.11 MPa, yield strength (YS) of 439 MPa and an elongation of 12.2 %.
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