A357合金中的介金屬化合物主要為β′-Mg2Si析出硬化相以及富鐵相，隨著富鐵相成份與形態的改變，合金的機械性質也會跟著有顯著的改變。許多學者曾經針對Al-Si-Mg合金中添加Be對合金機械性質的影響做過詳細的研究，但其中並不包括抗應力腐蝕性。本研究配製四組Fe與Be含量不同之A357合金，並施以T6熱處理後，利用微結構分析、機械性質量測、電化學量測以及慢應變速率拉伸測試，來探討Be與Fe含量對A357鋁合金微結構(富鐵相介金屬化合物、共晶Si粒子、Mg2Si析出強化相)、機械性質以及應力腐蝕性質之影響。 粗大的富鐵相容易因應力集中成為破裂的起始點，富鐵相的含量越多，材料的機械性質越差。不加Be的A357合金，含有大量的針狀富鐵相及文字型含Mg的富鐵相，Be的添加可減少富鐵相的含量，並改善其成分與形狀，使針狀富鐵相與含Mg的文字型富鐵相被不含Mg的結節狀(球、塊狀)富鐵相取代，含Mg文字型富鐵相的減少，使固溶於基地內的Mg含量增加，促進Mg2Si的析出動力與析出量，藉以提昇材料的機械性質。 富鐵相數量的增加使材料的抗腐蝕能力降低，然而在晶界處並沒有富鐵相的存在，故富鐵相的數量與形態對合金抗應力腐蝕性質無明顯之影響。A357合金晶界析出物數量少，析出物彼此之間沒有連結，且其活性與基地相近，不利於應力腐蝕裂縫成長，故具有良好的抗應力腐蝕性質。 β′-Mg2Si and iron-beraing phases are the main intermetallic compounds in A357 alloys.With the changes of composition and shape,mechanical properties of the alloys change evidently.Many people researched the relation between Be content and mechanical properties but rsearchs on stress corrosion cracking are absent.Effects of Be and Fe Content on Microstructure and Stress corrosion cracking in A357 Alloys are investigated. A larger amount of acicular shape and scrip morphology of Mg-containing structure of iron-bearing phases were found in Be-free alloys. These structures are replaced by nodular shape Mg-free structure of iron-bearing constituents when Be is added.The addition of Be reduce the amount of iron-bearing phases,increase amount of solid solution of Mg.The addition of Be could enhance the precipitation kinetics and increase the amounts of Mg2Si to promote the tensile properties.With the increasing the amount of iron-bearing phases,the corrosion resistane is reduced.The amounts,composition and shape of iron-bearing phases are insignificant about SCC resistance because of the absence of the iron-bearing pricipitations at the grainboundaries. Less amounts,discontinuous arrangement and similar activity to matrix of the precipitations at grainboundary are unfavorable for grow of the crevices. Therefore A357 alloys have excellent SCC resistance.
