中文摘要：

借助光学显微镜（OM）、扫描电镜（SEM）以及X射线衍射（XRD）等分析手段研究了真空低压消失模壳型铸造（EPSC-VL）A356铸态和T6态铝合金的微观组织特征和拉伸性能,并对拉伸断口进行了分析.试验结果表明：真空低压消失模壳型铸造A356铝合金组织主要由α-Al初生相、共晶硅和Mg2Si相组成,T6热处理后共晶硅边角更加圆润,均匀分布于晶界,热处理后共晶硅长宽比减小.T6热处理后真空低压消失模壳型铸造A356铝合金抗拉强度、延伸率、布氏硬度均明显提高.真空低压消失模壳型铸造A356铝合金经T6热处理后,其二次枝晶臂间距和共晶硅尺寸较小,致使胞界不连续,硅粒子的开裂优先出现在晶界处,最终呈现出晶间断裂的模式,其拉伸断口呈现明显的韧窝形貌.

英文摘要：

The microstructure,tensile properties and fractography of as-cast and T6A356 alloy were investigated using optical microscopy（OM）,scanning electron microscope（SEM）and X-ray diffraction（XRD）,which were produced by expendable pattern shell casting process with vacuum and lowpressure（EPSC-VL）.The results show that the microstructure of A356 alloy made by this casting process consists ofα-Al prime phase,eutectic silicon phase and Mg2Si phase.The corners of eutectic silicon show more roundly,and uniformly distributed in the grain boundary,and the aspect ratio of silicon particles decreased after T6treatment.The tensile strength,elongation as well as hardness of A356-T6 alloy obviously increase.Because secondary dendrite arm spacing and size of eutectic silicon decreased after T6treatment,it makes the grain cell boundaries more discontinuous.The cracking of eutectic silicon particles taken place in the grain boundaries,and the final fracture path tends to pass through the eutectic phase along the grain boundaries of α-Al primary phase.The eutectic silicon particles firstly cracked in the grain boundary,and the fractography displayed an obvious dimple rupture as intergranular fracture mode.