Table. 1. Chemical composition of 390 alloy (wt.%). Table. 2. Reactions during solidification of A390.1 alloy. Table. 3. Reactions during solidification of A390.1 alloy. Table. 4. Characteristics of phases observed by Micrography/SEM/EDX. Table. 5. Chemical composition of Al-Si alloy(a390) used. Table. 6. Experimental conditions for each of the processes. Table. 7. Experimental condition for the hot extrusion. Table. 8. Experimental condition for tribology test. Table. 9. Variation of size and aspect ratio of Si particles of the cast specimens before and after hot extrusion, and U.T.S and elongation of the extruded specimens.
Fig. 1. Schematic representation of spray-forming process. Fig. 2. Schematic illustration of Spray-deposition process and Spray-casting process involved in spray-forming process. Fig. 3. Flow chart depicting independent process parameters at each intermediate stage in Spray-casting. Fig. 4. Interrelationship between processing, microstructure and properties. Fig. 5. The tensile strength variation of unrefined and phosphorus refined Hyper-eutectic alloys. Fig. 6. Schematic illustration of the tribology tester. Fig. 7. (a)schematic diagram and (b)variation of Percent Linear Change of the thermal cycle test. Fig. 8. Microstructure of specimens before and after hot-extrusion. Fig. 9. Distribution of the Si particle measured by Image Analyzer before and extrusion. Fig. 10. Microstructure of specimens before hot-extrusion;(a)permanent Mold Casting, (b)squeeze Casting and (c)spray Casting 1. Fig. 11. Variation of density of specimens before and after hot extrusion measured by principle of the Archimedian. Fig. 12. Microstructure of specimens after hot extrusion and T6 treatment ; (a)permanent Mold Casting, (b)squeeze Casting, (c)spray casting1 and (d)spray Casting 2. Fig. 13. Ultimate tensile strength and elongation versus average size of the primary Si particles. Fig. 14. Microstructure of the fractured surface of extruded and T6 treated specimens after tensile test ; (a)permanent mold Casting, (b)squeeze Casting and (c),(d)spray Casting2. Fig. 15. Microstructure of extruded and T6 treated specimens by Spray Casting. Fig. 16. Ultimate tensile strength and elongation versus average size of Si particles. Fig. 17. Wear characteristics of extruded specimens at the applied loads
of 5N ; (a)wear volume and (b)specific wear rate and Friction coefficient. Fig. 18. Variation of wear volume versus (a)each of the process and (b)average Si particle size at the applied load 5,10,15N and sliding distance of 1,000m. Fig. 19. SEM micrographs of the worn surface (a)permanent mold Casting, (b) Squeeze Casting, (c)spray Casting1 and (d)spray Casting2 rubbed at the applied load of 5N and sliding distance of 1,000m. Fig. 20. High magnification image of the worn surface of (a)permanent mold casting and (b)spray Casting rubbed at the applied load of 5N and sliding distance of 1,000m. Fig. 21. SEM micrographs of the worn surface of (a)permanent mold Casting and (b)spray Casting2 rubbed at the applied load of 5N and sliding distance of 50m. Fig. 22. SEM micrographs and X-ray image of Al-Kα, Si-Kα, Fe-Kα and O-Kα for surface and (b)sem micrographs and X-ray diffraction analysis of the wear debris of Permanent mold Casting rubbed at the applied load of 5N and sliding distance of 1,000m. Fig. 23. SEM micrographs of the worn surface of (a)permanent mold Casting, (b) Squeeze Casting, (c)spray Casting1 and (d)spray Casting2 rubbed at the applied load of 15N and sliding distance of 1,000m. Fig. 24. Wear behavior of the Hyper-eutectic Al-Si alloys with different Si particle size. Fig. 25. Variation of percent of linear change and coefficient of thermal expansion by hot extrusion ; (a)permanent mold casting and (b)squeeze casting. Fig. 26. Variation of (a)percent of linear change and (b)coefficient of thermal expansion versus each of the processes. Fig. 27. Relationship between coefficient of thermal expansion(25 200 ) and Si particle size. Fig. 28. (a)variation of CTEs and (b)increasement of CTEs during thermal
cycle. Fig. 29. Schematic illustration of dislocation extermination in matrix during thermal cycle ; (a)large Si particle and (b)small Si particle.
Molten metal Atomizer Orifice Gas Gas Droplet Deposit Substrate Fig. 1. Schematic representation of spray-forming process. Spray Forming Process (a) Spray Deposition Process Deposit Thickness R D time solid Laminated & Columnar structure (b) Spray Casting Process Deposit Thickness R D time liquid solid Equaxed structure Fig. 2. Schematic illustration of Spray-deposition process and Spraycasting process involved in spray-forming process.[14]
1. Superheat 2. Flow Rate 3. Gas Flow Rate 1.Metal Delivery 2. Atomization Stage of the process Critical Dependent Parameter Independent Process Parameter 4. Gas Type 5. Gas Pressure 6. Stand-off Distance 3. Transfer of Droplet(Spray) State of the Spray at Impact State of the Surface 7. Substrate -Material -Surface Quality -Temperature 8. Substrate Motion & Config. 4. Consolidation 5. Preform cooling & Solidification Fig. 3. Flow chart depicting independent process parameters at each intermediate stage in Spray-casting.[14]
Fig. 4. Interrelationship between processing, microstructure and properties.[24]
Table. 1. Chemical composition of 390 alloy (wt.%).[54] Table. 2. Reactions during solidification of A390.1 alloy.[54]
Table. 3. Reactions during solidification of A390.1 alloy.[54] Table. 4. Characteristics of phases observed by Micrography/SEM/EDX.[54]
Fig. 5. The tensile strength variation of unrefined and phosphorus refined Hyper-eutectic alloys.[4]
Table. 5. Chemical composition of Al-Si alloy(a390) used. (wt.%)
Table. 6. Experimental conditions for each of the processes. Table. 7. Experimental condition for the hot extrusion.
Load Counter part Specimen 45º PC Metal plate Motor Fig. 6. Schematic illustration of the tribology tester. Table. 8. Experimental condition for tribology test. V = m ρ
W = m/ρ Pl m ρ l (a) (b) Temperature 450 7 /min 1.0 7 /min 0.8 20 PLC(%) 0.6 0.4 0.2 Time 0.0 Cycle 1 Cycle 2 Cycle 3 0 100 200 300 400 500 Temperature( ) Fig. 7. (a)schematic diagram and (b)variation of Percent Linear Change of the thermal cycle test.
➀ ➁ Fig. 8. Microstructure of specimens before and after hot-extrusion. ➀ ➁
50 50 50 50 40 40 40 40 30 20 30 20 30 20 30 20 10 10 10 10 0 0 0 0 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 50 50 50 50 40 40 40 40 30 30 30 30 20 20 20 20 10 10 10 10 ➀ 0 0 0 0 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 50 50 50 50 40 40 40 40 30 30 30 30 20 20 20 20 10 10 10 10 0 0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 50 50 0 50 0 1 2 3 4 5 6 7 8 9 10 0 50 0 1 2 3 4 5 6 7 8 9 10 40 30 40 30 40 30 40 30 ➁ 20 10 20 10 20 10 20 10 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Primary Si particle size(μm) 30 25 20 15 10 5 0 As Fabricated 5:1 25:1 50:1 Extrusion Ratio Aspect ratio 2.2 2.0 1.8 1.6 As Fabricated 5:1 25:1 50:1 Extrusion Ratio Permanent Mold Casting Squeeze Casting Spray Casting 1 Spray Casting 2 Fig. 9. Distribution of the Si particle measured by Image Analyzer before and extrusion.
Fig. 10. Microstructure of specimens before hot-extrusion;(a)permanent Mold Casting, (b)squeeze Casting and (c)spray Casting 1 ➀
98 96 Density Ratio(%) 94 92 90 88 86 84 82 Permanent Mold Casting Squeeze Casting Spray Casting 1 Spray Casting 2 As fabricated 5:1 25:1 50:1 Extrusion Ratio Fig. 11. Variation of density of specimens before and after hot extrusion measured by principle of the Archimedian. ➀ ➁
4-2. 인장 특성 각 시편을 25:1의 압출비로 열간압출한 시편의 조직사진을 그림 12에 나타내었다. 또한 각 시편들의 영상분석 결과와 상온 인장시험의 최대인 장강도와 파괴 연신율의 값을 표 9에 나타내었다. (a) (b) 50 (c) 50 (d) 5 5 Fig. 12. Microstructure of specimens after hot extrusion and T6 treatment ; (a)permanent Mold Casting, (b)squeeze Casting, (c)spray casting① and (d) Spray Casting ② Table. 8. Variation of size and aspect ratio of Si particles of the cast specimens before and after hot extrusion, and U.T.S and elongation of the extruded specimens. Permanent Mold Casting Squeeze Casting Spray Casting① Spray Casting② As As As As casted extruded casted extruded casted extruded casted extruded Average Si Particle Size( ) Average Aspect Ratio Ultimate Tensile Strength(MPa) Elongation(%) 27.0 20.3 24.3 18.5 2.9 2.0 1.3 1.1 3.1 3.0 3.1 3.0 2.9 2.8 1.8 1.8 187.6 208.2 305.2 317.2 2.01 2.40 3.62 3.95-30 -
U.T.S (MPa) 320 300 280 260 240 220 200 180 160 UTS Elongation 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Elomgation (%) 0 5 10 15 20 Average Si Paticle Size(μm) Fig. 13. Ultimate tensile strength and elongation versus average size of the primary Si particles.
(a) (b) 20 20 (d) (c) 20 10 Fig. 14. Microstructure of the fractured surface of extruded and T6 treated specimens after tensile test ; (a)permanent mold Casting, (b)squeeze Casting and (c),(d)spray Casting② 그림 14는 금형주조, 용탕단조, 분사주조② 압출재의 인장시험 후 파단 면을 관찰한 미세조직 사진이다. 금형주조와 용탕단조의 경우 파단된 초 정 Si입자의 일부와 공정조직에서 딤플(Dimple)이 관찰되었다. Si입자의 경우 전형적인 취성파괴를, 공정조직에서는 Al기지에 의해 전형적인 연성 파괴를 확인 할 수 있었다. 그림 14(c),(d)에서 알 수 있는 것처럼 Si입자 의 크기가 미세한 Spray② 시편의 경우는 파단면 전반에 걸쳐서 미세한 딤플이 형성되어 있으며 이로 인하여 금형주조재에 비해 강도와 연신율 이 크게 향상되었음을 알 수 있다. 본 연구에서는 Si입자의 크기와 인장 특성과의 관계를 확립하기 위하여 4가지 시편 외에 분사주조의 공정 조건을 변화시켜 Si입자의 크기를 조절 한 추가의 시편에 대한 인장 특성을 평가하였다. 추가 제작 시편의 미세 조직을 그림 15에 나타내었으며 Image Analyzer 분석으로 얻어진 Si 입 자의 크기와 인장시험 결과를 본 연구의 결과에 추가하여 그림 16에 나 타내었다. 그래프에서 나타나는 것처럼 분사주조 공정에 의해 제조된 시 편의 인장강도와 연신률도 Si 입자의 크기에 대하여 기존의 결과 범위에 - 32 -
서 크게 벗어나지 않는 것을 알 수 있다. 기지의 결정립 크기나 금속간 화합물 등 다른 요인에 의한 인장강도의 차이도 발생할 수 있을 것으로 여겨지나 과공정 Al-Si합금은 취성을 갖는 Si입자의 분율이 높아 재료의 물성을 좌우하는 주 요인으로 작용하는 것으로 알려져 있다. 따라서 본 연구에서 A390합금의 물성 평가에 Si 입자외의 다른 금속학적 요인은 큰 영향을 주지 않을 것으로 여겨진다. 50 50 Fig. 15. Microstructure of extruded and T6 treated specimens by Spray Casting 5.0 300 UTS 280 Elongation 4.5 4.0 260 3.5 240 220 3.0 Elomgation (%) U.T.S (MPa) 320 200 2.5 180 2.0 160 0 5 10 15 20 Average Si Paticle Size( ) Fig. 16. Ultimate tensile strength and elongation versus average size of Si particles. - 33 -
Wear volume(mm 3 ) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 (a) Applied Load : 5N Sliding Velocity : 25cm/sec Permanent mold casting Squeeze casting Spray casting 1 Spray casting 2 0 200 400 600 800 1000 Sliding distance(m) Specific wear rate(mm 2 /N)x10-7 2.5 2.0 1.5 1.0 0.5 0.0 (b) Permanent Squeeze Mold casting casting Applied Load : 5N Sliding Velocity : 25cm/sec Sliding Distance: 1000m Spray Spray casting1 casting2 1.8 1.7 1.6 1.5 Friction Coefficient, f Specific Wear Rate Friction Coefficient Fig. 17. Wear characteristics of extruded specimens at the applied loads of 5N ; (a)wear volume and (b)specific wear rate and Friction coefficient.
3 (a) (b) 3 Applied Load : 5N Sliding Velocity : 25cm/sec Sliding Distance: 1000m 2 1 2 1 Applied Load : 10N Sliding Velocity : 25cm/sec Sliding Distance: 1000m Wear volume(mm 3 ) 0 3 2 1 0 3 0 3 2 1 0 3 Applied Load : 15N Sliding Velocity : 25cm/sec Sliding Distance: 1000m 2 1 2 1 0 Spray Casting2 Spray Casting1 Squeeze casting Permanent Mold casting 0 0 5 10 15 20 Average Si Paticle Size(μm) Fig. 18. Variation of wear volume versus (a)each of the process and (b)average Si particle size at the applied load 5,10,15N and sliding distance of 1,000m.
Sliding direction (a) (b) (c) (d) 200 Fig. 19. SEM micrographs of the worn surface (a)permanent mold Casting, (b)squeeze Casting, (c)spray Casting① and (d)spray Casting② rubbed at the applied load of 5N and sliding distance of 1,000m. 그림 19는 마모시험 후 시편의 마모면을 SEM을 이용하여 관찰한 것이 다. 마모량의 차이에도 불구하고 마모면의 미세조직은 모든 시편이 유사 한 형상을 띄고 있다. 그림 20은 마모량의 차이가 가장 컸던 금형주조 압 출재와 분사주조 압출재인 Spray②시편의 마모면을 고배율로 관찰한 조 직 사진이다. 사진에서 확인되는 것처럼 전형적인 연삭마모(Abrasive wear)와 함께 층분리 마모(Delamination wear)의 흔적을 나타냄을 알 수 있다. - 36 -
Sliding direction (a) (b) Fig. 20. High magnification image of the worn surface of (a)permanent mold casting and (b)spray Casting rubbed at the applied load of 5N and sliding distance of 1,000m. 그림 21은 마모초기 단계인 활주거리 50m의 경우에 Spray② 시편과 금형주조재의 마모면을 SEM으로 관찰한 사진이다. 분사주조 압출재의 경우 마모 초기에는 연삭마모만이 발생한 반면 금형주조 압출재의 경우 연삭 마모 뿐 아니라 층분리 마모도 함께 발생함을 알 수 있다. 이러한 초기의 층분리 마모의 발생 유무가 마모량의 결과에 영향을 주는 것으로 여겨진다. - 37 -
Sliding direction (a) (b) Fig. 21. SEM micrographs of the worn surface of (a)permanent mold Casting and (b)spray Casting② rubbed at the applied load of 5N and sliding distance of 50m. 그림 22(a)는 마모시험 후 미끄럼 직하를 관찰하기 위해서 금형주조 압 출재에 대하여 Cross section을 SEM/EDX를 이용하여 분석한 결과이다. 또한 마모실험 후 마모분에 대한 분석결과를 그림 22(b)에 나타내었다. Cross section이나 마모분의 분석결과 마모면의 표면은 마모시험 시 발 생하는 열로 인하여 전체적으로 산화된 것으로 여겨지나 그 직하는 국부 적으로 산화된 부분과 그렇지 않은 부분이 존재함을 확인할 수 있다. 마 모분의 분석결과에서도 실험에 사용된 A390합금의 성분 외에 산소의 Peak이 생겼음을 확인 할 수 있다. - 38 -
(a) Al Ka1 Si Ka1 Fe Ka1 O Ka1 (b) Intensity Fig. 22. SEM micrographs and X-ray image of Al-Kα, Si-Kα, Fe-Kα and O-Kα for surface and (b)sem micrographs and X-ray diffraction analysis of the wear debris of Permanent mold Casting rubbed at the applied load of 5N and sliding distance of 1,000m.
Sliding direction (a) (b) (c) (d) Fig. 23. SEM micrographs of the worn surface of (a)permanent mold Casting, (b)squeeze Casting, (c)spray Casting① and (d)spray Casting ② rubbed at the applied load of 15N and sliding distance of 1,000m. 그림 23에 15N의 하중과 활주거리 1,000m일 경우 시편의 마모면을 나 타낸 결과이다. 하중의 증가에도 불구하고 모든 시편에서 하중 5N일 경 우와 유사한 마모면의 형상을 나타냄을 알 수 있다. 그림 24는 이상의 결과를 종합하여 활주거리와 하중의 증가에 따른 마 모기구의 변화를 나타낸 모식도이다. 과공정 Al-Si 합금에서 Si입자가 미 세할수록 기지 전체에 고르게 분포하기 때문에 조대한 초정 Si입자가 분 포하고 있는 경우에 비하여 마모시험 시 발생하는 응력을 효과적으로 분 산 시킬 뿐 아니라 발생 열에 대하여서도 기지조직 전체로의 효과적인 분산효과를 갖는 것으로 여겨진다.[70] - 40 -
Matrix Si particle Matrix Si particle Small Si particle size Large Si particle size - Sliding distance - Applied load Fig. 24. Wear behavior of the Hyper-eutectic Al-Si alloys with different Si particle size.
1.0 0.8 (a) 1.0 0.8 (b) PLC(%) 0.6 0.4 PLC(%) 0.6 0.4 0.2 0.2 0.0 0.0 CTEs(x10-6μm /μm ) 26 24 22 20 18 16 14 0 50 100 150 200 250 300 350 400 450 Temperature( ) (a) CTEs(x10-6μm /μm ) 24 22 20 18 16 14 0 50 100 150 200 250 300 350 400 450 Temperature( ) (b) 12 12 25-50 25-100 25-150 25-200 25-250 25-300 25-35025-400 25-50 25-100 25-150 25-200 25-250 25-300 25-35025-400 As cast Extrusion Fig. 25. Variation of percent of linear change and coefficient of thermal expansion by hot extrusion ; (a)permanent mold casting and (b)squeeze casting.
PLC(%) 1.0 0.8 0.6 0.4 0.2 (a) CTEs(x10-6μm /μm ) 25 24 23 22 21 20 19 18 17 16 15 (b) 14 0.0 13 12 0 50 100 150 200 250 300 350 400 450 Temperature( ) 11 25-50 25-100 25-150 25-200 25-250 25-300 25-350 25-400 Permanent Mold Casting + Hot Extrusion Permanent Mold Casting + Hot Extrusion Squeeze Casting + Hot Extrusion Squeeze Casting + Hot Extrusion Spray Casting 1 + Hot Extrusion Spray Casting 1 + Hot Extrusion Spray Casting 2 + Hot Extrusion Spray Casting 2 + Hot Extrusion Fig. 26. Variation of (a)percent of linear change and (b)coefficient of thermal expansion versus each of the processes. 23 22 CTEs(x10-6 μm/μm ) 21 20 19 18 0 5 10 15 20 25 30 Average Si Paticle Size(μm) Fig. 27. Relationship between coefficient of thermal expansion(25~200 ) and Si particle size.
28 (a) 0.8 0.7 (b) CTEs(x10-6 μm/μm ) 26 24 22 ΔCTEs(x10-6 μm/μm ) 0.6 0.5 0.4 0.3 0.2 20 0.1 Cycle 1 Cycle 2 Cycle 3 0.0 Cycle2-Cycle1 Cycle3-Cycle2 Permanent Mold Casting + Hot Extrusion Spray Casting 2 + Hot Extrusion Permanent Mold Casting + Hot Extrusion Spray Casting 2 + Hot Extrusion Fig. 28. (a)variation of CTEs and (b)increasement of CTEs during thermal cycle.
c b a 제조온도 상온 a : Elastic Particle zone (Si) b : Elastoplastic zone C : Elastic Matrix zone Cycle 1 Cycle 2 Cycle 3 Fig. 29. Schematic illustration of dislocation extermination in matrix during thermal cycle ; (a)large Si particle and (b)small Si particle.