中文摘要：

本文以A319合金作为研究对象,通过在合金熔体中添加变质剂、分层铸造以及对铸造后的合金进行T6热处理等方法来研究这些因素对合金显微组织和性能的影响。本文的主要研究内容包括：（1）研究了Sr变质剂对铸造A319铝合金的微观组织和力学性能的影响。结果发现Sr变质过的合金中硅颗粒的大小和长径比显著减小,得到了很好的粒状化效果,即变质后的组织更加细密,孔洞也减少了,因此力学性能得到了提高。（2）探讨了铸造固化过程中不同冷却速率对A319铝合金的微观组织和力学性能的影响。结果表明随冷却速率的提高,合金中硅颗粒的大小和长径比及二次枝晶臂间距减小,组织变得细密。宏观上表现为合金的屈服强度、抗拉强度及延伸率等力学性能都随着冷却速率的提高而变好。

英文摘要：

A319 alloy is the research object in this article.The effects of modification by adding the modifier in the melt,casting with different layers and T6 heat treatment on the microstructure and mechanical properties of alloys have been investigated.The following are the main research of this article：（1）The effects of Sr modification on the microstructure and mechanical properties of alloys have been investigated.The results shows that strontium modification reduces the size and aspect ratio of the eutectic silicon particles,thus,the particles get spheroidization effects.Strontium modification can refine the grains of the microstructure,both of the number and size of the holes in the alloys decrease,leading to better mechanical properties.（2）The effect of cooling rate during solidification on the microstructure and mechanical properties of alloys have been investigated.It is clear from this work that increasing the cooling rate during solidification will reduce the size and aspect ratio of the eutectic silicon particles,as well as secondary dendrite arm spacing.The mechanical properties,such as hardness,the yield strength,the fracture strength and ductility get better as the cooling rate increased.