【作者】 孙健；

【导师】 魏尊杰；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2017， 硕士

【摘要】 铝合金被用于船舶制造已有上百年的历史。随着造船业的发展,船舶轻量化越来越受重视,舰船材料对于铝合金材料的屈服强度和耐蚀性的要求越来越高。A357合金铸造性能优异,抗疲劳、抗腐蚀性能、气密性好,在航空航天、汽车工业已广泛使用。通过优化A357合金的成分和工艺,在不降低其耐蚀性的前提下提高屈服强度,具有非常重要的实用价值。本文研究了Si、Cu、Mg、Mn合金元素对金属型铸造铝硅合金屈服强度和耐蚀性能的影响。设计四因素三水平正交实验,综合各因素对合金屈服强度、延伸率和耐蚀性的影响,确定最优成分;分析了不同Sr浓度对优化成分合金的变质效果;通过金相显微镜、SEM观察合金的微观组织;研究了最优成分合金的最佳时效工艺;观察合金的断口形貌并分析断裂机理;分析对比了最优成分合金和A357合金的耐腐蚀性。研究表明随着Si、Mg、Cu元素浓度的升高,合金的屈服强度增大;随着Si元素浓度的升高,合金的延伸率减小,耐蚀性先略微减弱后增强;随着Cu元素浓度的升高,耐蚀性显著减弱;优化后的成分为Si:8.3 wt.%,Cu:0.1 wt.%,Mg:1.0 wt.%,Mn:0.1 wt.%。0.06 wt.%Sr对最优成分合金中的硅具有良好的变质和细化效果;热处理后硅相呈颗粒状分布在基体中,粒度在5μm左右;富锰相呈细小颗粒状分布;Cu、Mg元素主要以弥散的脱溶相的形式分布在基体中;过变质的铝合金晶界元素富集严重,延伸率很低。最优成分的合金的最佳时效工艺为时效温度170℃时,时效时间为8h;此工艺下合金的屈服强度为322.5MPa,延伸率3.2%,耐蚀性优于A357铝合金。不同成分的合金断口形貌均为穿晶韧性断口;硅含量不同对断口形貌影响显著,随着硅含量的升高,韧窝面积逐渐变小,深度逐渐变浅;基体中脆性相逐渐增多,撕裂棱也逐渐增多,合金塑性变差。更多还原

【Abstract】 Aluminum alloy is used for shipbuilding for hundreds of years.With the development of shipbuilding industry,increasingly importance has been attached to light-weighting of ship.Yield strength and corrosion-resistance requirements of materials for shipbuilding are getting higher and higher.A357 alloy has a good performance in casting,anti-fatigue,corrosion-resistance and airtightness.It has been used widely in the aviation industry and the automotive industry.And it is of great practical value to improve its yield strength without reducing the corrosion resistance through optimizing the composition and process of A357 alloy.In this paper,the effects of Si,Cu,Mg and Mn on the mechanical properties and corrosion-resistance of metal mold casting Al-Si alloy were studied.The orthogonal experiment with four factors and three levels was designed to determine the optimal composition of the alloy.The modification effects of optimal composition alloy with different Sr concentration were analyzed.The aging process of the new alloy was optimized.The microstructure of the alloy was observed by SEM.The fracture morphology of the alloy was observed and the fracture mechanism was analyzed.The corrosion-resistance of the new alloy and A357 alloy was compared.The results show that with the increase of the concentration of Si,Mg and Cu,the yield strength of the alloy increases.With the increase of Si concentration,the elongation of the alloy decreases and corrosion resistance is first slightly weakened and then enhanced.With the increase of Cu concentration,the corrosion resistance is obviously weakened.The optimized composition is Si: 8.3 wt.%,Cu: 0.1 wt.%,Mg: 1.0 wt.%,Mn: 0.1 wt.%.0.06 wt.% Sr has good modification and refinement effects on the silicon in the new alloy.The silicon phase is distributed in the matrix after the heat treatment and the particle size is about 5μm.The manganese-rich phase is in the form of fine particles.Cu and Mg are mainly distributed in the matrix in the form of dispersed desorption phase.The elements of hypermetamorphic aluminum alloy are enriched in grain boundary and the plasticity of alloy is poor.When the aging temperature is 170 ℃,the aging time of 8 hours can get the desired yield strength and elongation.The yield strength of the new alloy is 322.5MPa.The elongation of the new alloy is 3.2% and the corrosion resistance of the new alloy is better than that of A357 aluminum alloy.The alloy with different content exhibits ductile fracture with dimples.The effects of silicon content on fracture morphology are significant.With the increase of silicon content,the dimple area gradually becomes smaller and the depth gradually becomes lighter.The amount of brittle phase in the matrix and the tear edge also gradually increased with plasticity decreased.更多还原