A357鋁矽鑄造合金是國防武器系統的重要材料之一，本研究利用低成本亥姆霍茲線圈(Helmholtz coil)在砂模鑄造之A357鋁合金鑄件固化的過程中提供交流磁場，利用外加磁場攪拌方式以達鑄件晶粒細化的效果，並在鑄件固化完成後進行T6熱處理，改善合金的顯微結構與機械性質，本實驗在鑄件固化的過程中分別外加不同強度的磁場(0、3.1、6.3、10.7 mT)，分析不同磁場強度對於鑄件的影響並找出最佳實驗參數改良砂模鑄件之品質。

通過光學顯微鏡(Optical microscope, OM)觀察砂模鑄造A357鋁合金在不同磁場強度下的顯微結構，再以維克氏硬度計(Vicker's Hardness test)以及拉伸試驗機(Tensile testing machine)進行機械性質的量測。拉伸試驗結束後，使用掃描式電子顯微鏡(Scanning electron microscope, SEM)觀察不同磁場強度下砂模鑄造之A357鋁合金的破裂形貌。透過X光繞射分析儀(X-Ray diffraction, XRD)鑑定鑄件的結構以及磁場強度對於結晶方向的影響和晶格常數的變化。藉由分析結果進一步探討外加磁場對A357鋁合金鑄件的作用機制。

由實驗結果得知，外加磁場強度的提升，除了使砂模鑄造之A357鋁合金產生晶粒細化效應外，且熱處理後的共晶矽組織更為均勻，使得A357鋁合金機械性質包含硬度與拉伸強度獲得改善，進一步提升鋁合金砂模鑄件之良率。

A357 aluminum-silicon cast alloy is one of important engineering materials with very high demand in military weapon systems. In the report, the enhancement of the mechanical properties and microstructure for sand-casting A357 aluminum alloy were performed via an AC magnetic field supplied by low-cost Helmholtz coils. The experimental parameter was designed as different magnetic fields intensity such as 0, 3.1, 6.3 and 10.7 mT, respectively. Found out the best experimental parameters to enhance the quality of sand-castings A357 alloy.

The observation of microstructure for sand-casting A357 casting in different magnetic field intensity was performed by an optical microscope. The mechanical properties were measured by Vicker's Hardness test and tensile testing machine. The fracture surfaces of those tensile samples after the tensile test were analyzed by scanning electron microscope. X-ray diffraction measurement (XRD) was applied for identifying the crystallograghic orientation, and the strain of the lattice constant of A357 alloy.

The experimental results show that the stirring effect of magnetic field during the solidification process of sand casting can make the grain refinement of α-Al phase and the modification of eutectic silicon for A357 alloy. After T6 heat treatment process, the mechanical properties such as hardness, tensile strength and ductility were improved.

致謝 i
摘要 iii
Abstract iv
目錄 v
圖目錄 viii
表目錄 xii
第一章 緒論 1
1.1 前言 1
1.2 研究動機 3
第二章 文獻回顧 5
2.1 鋁合金簡介 5
2.2 鋁合金命名 6
2.2.1 鍛造系鋁合金 7
2.2.2 鑄造系鋁合金 7
2.3 鋁矽鑄造合金介紹 8
2.4 鑄造方式 9
2.5 砂模鑄造 12
2.6 鋁合金的強化方式 14
2.6.1 晶粒細化 14
2.6.2 固溶強化 16
2.6.3 析出強化 18
2.6.4 加工硬化 20
2.7 晶粒細化的方法 21
2.7.1 溫度控制法 22
2.7.2 添加晶粒細化劑和微量元素 23
2.7.3 外力振動及攪拌 25
2.8 結晶優選方向與織構現象 31
2.9 磁場對結晶優選方向的影響 32
第三章 實驗流程與分析 37
3.1 材料製備 38
3.2 T6熱處理製程 41
3.3 顯微結構觀察 43
3.3.1 光學顯微鏡分析 43
3.3.2 晶粒尺寸測量 45
3.3.3 二次枝晶臂間距測量 46
3.3.4 掃描式電子顯微鏡分析 47
3.4 機械性質分析 48
3.4.1 維克氏硬度測量 48
3.4.2 拉伸試驗 49
3.4.3 品質參數分析 51
3.5 結構分析 52
3.5.1 X光繞射分析 52
第四章 實驗結果與討論 53
4.1 A357鑄件外加磁場後之結果與討論 53
4.1.1 A357鑄件之顯微結構觀察和分析 53
4.1.2 A357鑄件之晶粒尺寸及二次枝晶臂間距量測 57
4.1.3 A357鑄件之硬度分析 63
4.1.4 A357鑄件之拉伸強度分析 64
4.1.5 A357鑄件之破裂面分析 67
4.1.6 A357鑄件之X光繞射分析 68
4.1.7 晶格常數的變化和磁場關係 72
4.2 A357鑄件之T6熱處理後分析 75
4.2.1 A357鑄件之熱處理後微觀結構觀察 75
4.2.2 A357鑄件熱處理後硬度分析 80
4.2.3 A357鑄件熱處理後拉伸強度分析 80
4.2.4 A357鑄件熱處理破裂面分析 85
第五章 結論 87
參考資料 89

[1]機械材料，黃振賢，新文京開發出版
[2]structure and properties of Engineering alloys, William F. Smith, second edition, McGraw-Hill
[3]Materials Science and Engineering, 9th Edition SI Version, William D. Callister, David G. Rethwisch
[4]Foundations of Materials Science and Engineering, Willaim Smith, Javed Hashemi
[5]Mohamed et al, A Review on the Heat Treatment of Al-Si-Cu/Mg Casting Alloys. Heat Treatment - Conventional and Novel Applications
[6]Evolution of Metal Casting Technologies, Muhammad Azhar Ali Khan
[7]Pacz, US Patent 1387900, 1921
[8]Shahrooz Nafisi et al, Effects of modification during conventional and semi-solid metal processing of A356 Al-Si alloy, Materials Science and Engineering A 415 (2006) 273–285
[9]Physical Metallurgy Principles, Robert E.Reed-Hill, third edition, PWS
[10]Niels Hansen et al, Hall-Petch relation and boundary strengthening, Svripta Meterialia 51, p.801-806, 2004
[11]Balasubramanian N et al, The Strength–Grain Size Relationship in Ultrafine-Grained Metals. Metallurgical and Materials Transactions A, 47(12), 5827–5838
[12]Kalsar R. et al, Effect of Mg content on microstructure, texture and strength of severely equal channel angular pressed aluminium-magnesium alloys. Materials Science and Engineering: A, 140088.
[13]Poole W. J. et al, Work hardening in aluminium alloys. Fundamentals of Aluminium Metallurgy, 307–344.
[14]Khyati Tamta1 et al, GRAIN REFINEMENT OF CAST ALLOYS: A REVIEW, Int. J. Mech. Eng. & Rob. Res. 2014
[15]Ren-Guo Guan1 et al, A Review on Grain Refinement of Aluminum Alloys: Progresses, Challenges and Prospects, Acta Metall. Sin. (Engl. Lett.) 30 , 2014 , 409-432
[16]Liotti et al. Crystal nucleation in metallic alloys using x-ray radiography and machine learning, Sci. Adv. 2018;4: eaar4004
[17]L Wang et al, Effects of melt cooling rate on the microstructure and mechanical properties of Al-Cu alloy, Mater. Res. Express 6 (2019) 116507
[18]Sigworth G. K. et al, Grain Refinement of Aluminum Casting Alloys, International Journal of Metalcasting,2007 1,31–40
[19]ZHILIN LIU, Review of Grain Refinement of Cast Metals Through Inoculation: Theories and Developments , METALLURGICAL AND MATERIALS TRANSACTIONS A VOLUME 48A, OCTOBER 2017—4755
[20]S.S. Sreeja Kumari et al, Structure and properties of calcium and strontium treated Al–7Si–0.3Mg alloy: A comparison, Journal of Alloys and Compounds 460 (2008) 472–477
[21]S. H. Wu et al , Grain size-dependent Sc microalloying effect on the yield strength-pitting corrosion correlation in Al-Cu alloys, Materials Science & Engineering A 721 (2018) 200–214
[22]Y. B. Zuo et al, G.M. Scamans, Z.Y. Fan, Grain refinement of DC cast AZ91D Mg alloy by intensive melt shearing, Mater. Sci. Technol. 27 (2011) 101–107.
[23]Z. Bian et al, Extremely fine and uniform microstructure of magnesium AZ91D alloy sheets produced by melt conditioned twin roll casting, Mater. Sci. Technol. 25 (2009) 599–606.
[24]S. Ji et al, Semisolid processing characteristics of AM series Mg alloys by rheo-diecasting, Metall. Mater. Trans. A 37A (2006) 779–787.
[25]S. Ji et al, Effects of rheo-die casting process on the microstructure and mechanical properties of AM50 magnesium alloy, Mater. Sci. Technol.2005 21 1019–1024.
[26]Koulis Pericleous et al, Contactless Ultrasonic Cavitation in Alloy Melts, Materials 2019, 12, 3610
[27]Fuyue Wang et al, Micro-Structure and Mechanical Properties of 2A97 Al-Li Alloy Cast by Low-Frequency Electromagnetic Casting, Metals 2019, 9, 822
[28]Zhihao Zhao et al, Effect of low-frequency magnetic field on microstructures of horizontal direct chill casting 2024 aluminum alloy, Journal of Alloys and Compounds 2005 396 164–168
[29]Yubo Zuo et al, Effect of low frequency electromagnetic field on the constituents of a new super high strength aluminum alloy, Journal of Alloys and Compounds 2005 402 149–155
[30]Qingwei Bai1 et al, Crystal orientation and crystal structure of paramagnetic α‑Al under a pulsed electromagnetic field, Scientific Reports ,(2020) 10:10603
[31]Li Mingjun; Tamura Takuya, Crystalline orientation control of the platelet Nd2Fe14B phase to produce magnetic anisotropy via electromagnetic vibration processing, Scientific Reports 9(1), 2019
[32]Y. Rezaei et al, Phase-field modeling of magnetic field-induced grain growth in polycrystalline metals. Computational Materials Science, 2021
[33]Gong, Yuan-yuan et al, Textured, dense and giant magnetostrictive alloy from fissile polycrystal. Acta Materialia, 2015
[34]D. A. Molodov, Grain boundary dynamics and selective grain growth in non-ferromagnetic metals in high magnetic fields. Zeitschrift für Metallkunde, 96(10), 2005
[35]Z. Sun et al, Strong static magnetic field processing of metallic materials: A review , Current Opinion in Solid State and Materials Science. 16 (2012) 254-267
[36]Zheng, Tianxiang et al, Compression properties enhancement of Al-Cu alloy solidified under a 29T high static magnetic field. Materials Science and Engineering, 2018
[37]Wang, Yachao et al, Texture control of Inconel 718 superalloy in laser additive manufacturing by an external magnetic field, Journal of Materials Science
[38]亥姆霍茲線圈磁場(Magnetic fields of Helmholtz coil),戴明鳳，施宙聰, 2014
[39]C. S. Wang et al, “Effects of Helmholtz coil magnetic fields on microstructure and mechanical properties for sand-cast A201 Al-Cu alloy,” Materials Research Express, Vol.7, No.126504, pp.1-8, 2020.
[40]Vandersluis, E. et al, Comparison of Measurement Methods for Secondary Dendrite Arm Spacing. Metallography, Microstructure, and Analysis
[41]M. Drouzy et al, Interpretation of tensile results by means of quality index and probable yield strength-application to Al-Si-Mg foundry alloys-France,Int. Cast Metal. J. 5 (2) (1980) 43–50.
[42]C.H. Cáceres et al, A rationale for the quality index of Al-Si-Mg casting alloys, Int. J. CastMetals Res. 10 (5) (1998) 293–299.
[43]M. Tiryakioğlu et al, Evaluating structural integrity of cast Al–7%Si–Mg alloys via work hardening characteristics: II. A new quality index, Mater.Sci. Eng. A 368 (1) (2004) 231–238.
[44]E. Czekaj et al, Quality index of the AlSi7Mg0. 3 aluminiumcasting alloy depending on the heat treatment parameters, Arch. Foundry Eng. 16 (3) (2016) 25–28.
[45]N. Alexopoulos et al, A new quality index for characterizing aluminum cast alloys with regard to aircraft structure design requirements, Metall. Mater. Trans. A 35 (1) (2004) 301–308.
[46]Hao H et al, Twin-strand technology and microstructure analysis for the electromagnetic near net-shape casting of aluminum alloy , J Mater Process Technol 2005 142(2):526
[47]X.T. Li et al, Continuous Casting of Copper Tube Billets Under Rotating-Electromagnetic Field , Mater Sci Eng A (2007) 460–461:64
[48]Yan Z et al, Grain refinement of horizontal continuous casting of the CuNi10Fe1Mn alloy hollow billets by rotating magnetic field (RMF) , Mater Lett 2008 62(28):4389
[49]Eckert.S. et al, . Electromagnetic melt flow control during solidification of metallic alloys, The European Physical Journal Special Topics, 220(1), 123–137
[50]GRIFFITHS W. D. et al. The effect of electromagnetic stirring on macrostructure and macrosegregation in the aluminium alloy 7150, J. Mater Sci Eng A, 1997, 222: 140-148.
[51]K. Zhang et al., Influence of the low voltage pulsed magnetic field on the columnar-to-equiaxed transition during directional solidification of superalloy K4169, Journal of Materials Science & Technology 48 (2020) 9–17
[52]Yubo Zuo et al, Mechanism of grain refinement of an Al–Zn–Mg–Cu alloy prepared by low-frequency electromagnetic casting, J Mater Sci (2012) 47:5501–5508
[53]K. Zhang et al., Influence of the low voltage pulsed magnetic field on the columnar-to-equiaxed transition during directional solidification of superalloy K4169, Journal of Materials Science & Technology 48 (2020) 9–17
[54]S. He et al., Evolution of microsegregation in directionally solidified Al-Cu alloys under steady magnetic field. Journal of Alloys and Compounds 800 (2019) 41-49
[55]J. Wang et al. Microstructural evolution caused by electromagnetic stirring in superheated AlSi7Mg alloys, Journal of Materials Processing Technology 210 (2010) 1652–1659
[56]C. Li et al. Application of differential thermal analysis to investitation of magnetic field effect on solidification of Al–Cu hypereutectic alloy ,Journal of Alloys and Compounds 505 (2010) 108–112
[57]O. Uzun et al, Hardness and microstructural characteristics of rapidly solidified Al–8–16 wt.%Si alloys, Journal of Alloys and Compounds 376 (2004) 149–157
[58]Z. Chen et al.: In-situ Observation of Tensile Fracture in A357 Casting Alloys, J. Mater. Sci. Technol., 2014, 30(2), 139-145
[59]X. Shen et al, Effect of Ti/Sc atom ratio on heterogeneous nuclei, microstructure and mechanical properties of A357-0.033Sr alloys. Materials Science and Engineering: A, 671, 275–287.
[60]Q. G. Wang et al, Damage by eutectic particle cracking in aluminum casting alloys A356/357, Mater. Sci. Eng. A, 241(1998) 72-82.
[61]L. Zeng et al, Role of eutectic silicon particles in fatigue crack initiation and propagation and fatigue strength characteristics of cast aluminum alloy A356, Eng. Fract. Mech. 115(2014) 1-12.
[62]D. LADOS et al, Fatigue crack growth mechanisms at the microstructure scale in Al–Si–Mg cast alloys: Mechanisms in the near-threshold regime, Acta Mater. 54(2006) 1475-1486.