臺灣博碩士論文加值系統

本研究主要探討低溫時效處理對壓鑄鋁合金356的顯微組織和機械性質之影響。
將AA（Aluminum Association）規格之356鋁合金，採用壓鑄法（die casting）來鑄造，藉由壓鑄過程中，鑄件急速凝固，可得到較砂模、金屬模鑄件細的晶粒顯微組織；再施以低溫時效硬化處理，使強化相Mg--2Si析出，和改善共晶Si的幾何形狀及分佈，進而改善機械性質。壓鑄鑄件本身包含大量之空孔、縮孔，是影響其機械性質之重要因素之一，本實驗利用不同溫度和時間做低溫時效硬化處理，以防止高溫時潛在之氣孔膨脹，因此忽略孔洞之影響，以平均值來計算，並觀察顯微組織和機械性質兩者之相互關係。
實驗結果顯示，以壓鑄法製造之鑄件雖含有大量空孔，但本身即具有良好之機械性質，且經過適當的熱處理後，其拉伸強度（tensile strength）和伸長量（elongation）與砂模及金屬鑄模的鑄件之機械性質相比較，除了可高於砂模鑄件外，也可直逼金屬模鑄件的高強度性質。
在低溫155℃時效處理時，時間增加，強化相Mg2-Si逐漸析出且散佈廣泛，使其抗拉強度增加，但Si由叢聚變成細密之網狀結構、兩端變小且尖銳，使得伸長量下降，為脆性破壞，衝擊值降低；在較高溫220℃以上，當時效溫度和時間都逐漸增加時，其抗拉強度有下降趨勢，伸長量增加，代表逐漸由脆性轉變成延性，所以破壞時吸收的能量增加了，衝擊值也就隨著增加。
根據本實驗所得之數據可提供鑄件所要求之機械性質，而給予適當之熱處理條件，可增加以壓鑄法製造356鋁合金之可行性。

This research aims to study the relationship of die cast aluminum alloy Grade 356 between microstructure and mechanism properties.
Using 356 aluminum alloys, which is one of the aluminum-silicon-magnesium systems to produce specimens. During the casting process, the castings rapidly cooled to room temperature, and get finer microstructure than specimens made by sand-cast or gravity cast ones. Then in the aging precipitation hardening heat treatment, the Mg-Si compounds are precipitation and the geometry and distribution of Si will be provided. Die-castings include a large quantity of pore, shrinkage hole, and shrinkage porosity, etc. which is one important factor of the effects of the mechanism properties. This research aims to study die cast aluminum alloy Grade 356 in as-cast condition directly apply the low temperature aging process (less then 300℃) at different temperature and time to attain precipitation hardening effect, and ignored the effect of porosity. The properties-structures relationship of the die cast aluminum 356 alloy subjected to the low temperature aging heat-treatments will be compared with that of the sand-cast / gravity cast ones.
Though the as-cast specimens, which produced by die-casting, include high porosity, they still have good mechanism properties. And the tensile strength and elongation of 356 aluminum alloy with proper heat treatment were found to be up to 249.8MPa

TABLE OF CONTENTS
ABSTRACT
ACKNOWLEDGEMENTS
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
CHAPTER ⅠINTRODUCTION
CHAPTER ⅡLITERATURE SURVEY
2.1 Decomposition products created by the aging of the supersaturated solid solution
2.2 Hardening reaction[5, 6]
2.3 Aging hardening treatment
2.3.1 The classification of aging treatment
2.3.2 The aging heat-treated subdivisions
2.4 The effect of microstructure for mechanism properties
2.4.1 Grain size
2.4.2 The size and shape of Si
2.4.3 The distribution of Mg2-Si
2.4.4 Fe compound
2.4.5 Voids or shrinkage holes
2.5 The fracture characteristics
2.5.1 Macrofractography
2.5.2 Microfractography
2.6 The applications and development of die-casting
CHAPTER ⅢEXPERIMENT PROCEDURE
3.1 Prepare Specimens
3.2 Heat Treatment
3.3 Impact Test
3.4 Tensile Test
3.5 Take A View Of Porosity
3.6 Metallographical Examination
3.7 X-Ray Diffractometry
3.8 Fracture Surfaces Observation
3.8.1 Macrofractography
3.8.2 Microfractography
CHAPTER ⅣRESULTS AND DISCUSSION
4.1 Metallographic Observation
4.1.1 Precipitation
4.1.2 Effect Of Aging Temperature
4.1.3 Effect Of Aging Treating Time
4.2 Porosity
4.3 Tensile Strength
4.3.1 Effect Of Aging Treating Time
4.3.2 Effect Of Aging Temperature
4.4 Elongation
4.4.1 Effect Of Aging Temperature
4.4.2 Effect Of Aging Treating Time
4.5 Impact Toughness
4.5.1 Effect Of Aging Treating Time
4.5.2 Effect Of Aging Temperature
4.6 Fracture Surfaces Observation
4.6.1 Macrofractography
4.6.2 Microfractography
4.7 Summary On The Heat Treatment Effect
CHAPTER ⅤCONCLUSIONS
CHAPTER ⅥREFERENCE

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