压铸AlSi10MnMg合金具有优异的综合力学性能，广泛应用于汽车压铸铝合金结构件。然而，由于冷室压铸过程低速推进，高速充型，高压凝固的特点，使得压铸件存在组织偏析、压室初生相粗大、孔隙率高等问题，限制了压铸件的应用范围。因此，优化压铸AlSi10MnMg合金组织和性能，扩宽其应用范围，具有重要的意义。本论文以压铸AlSi10MnMg合金微观组织特征和力学行为为研究基础，重点研究预结晶组织（ESC）和富铁相的分布特征和断裂行为，在此基础上指导新型压铸合金设计并实现产业化应用。研究结果如下：压铸AlSi10MnMg合金中组织形态包括表层激冷区、共晶带和心部ESC富集区。表层激冷区组织细小，孔洞少，局部区域存在皮肤层。共晶带为Al-Si共晶富集区，与液流充型轨迹吻合。ESC富集区位于试样中心位置，存在大量的孔洞分布，内部ESC枝晶化程度高。压铸过程中，相同低速速度及增压条件设置下，高速速度设置较低会引起ESC枝晶富集，导致试样心部形成大尺寸枝晶网络，阻碍液体补缩，进而形成大尺寸缩松。裂纹起源于大尺寸缩松位置处，进一步以沿晶断裂的模式沿ESC晶界和孔洞边界扩展或以穿晶断裂的模式沿晶粒内部扩展，导致铸件失效，其中，ESC枝晶富集区的大尺寸缩松和沿晶裂纹扩展模式是降低力学性能的主要原因。压铸AlSi10MnMg合金中富铁相包含压室初生富铁相（(P-IMC)I）、型腔初生富铁相（(P-IMC)II）和共晶富铁相。初生富铁相以液相中富锰核心为基础，球状形核后侧向生长为多面体形貌。六面体(P-IMC)I在型腔中的继续生长是沿顶点枝晶化的过程。压铸AlSi10MnMg合金中三种形貌共晶富铁相（针状、网状和汉字状）在Al-Si共晶界面处形成，其生长形貌与冷却速度和剩余液相溶质浓度相关。β相和δ相共存于同一针状富铁相中，二者错配度小，高冷速和高Si含量促进不稳定的β相向稳定的δ相生长转变。压铸富铁相中，(P-IMC)I对力学性能危害最大，易脆断引起应力集中，促进裂纹扩展。通过热力学计算和微量组元调控方式，以AlSi10MnMg合金为基础，添加Zr元素和V元素分别细化ESC和优化(P-IMC)I，开发了非热处理态高强韧压铸THAS-1合金并完成了其在车用减震塔件上的试制。

The high pressure die cast (HPDC) AlSi10MnMg alloy has excellent comprehensive mechanical properties and is widely used in automotive structural parts of HPDC aluminum alloys. However, in high pressure die casting process, due to the characteristics of low-speed injection in the shot sleeve, high-speed filling and high-pressure solidification in the die cavity, heterogeneous microstructures, coarse primary phases and porosities exist in die-cast parts, which limits the application of the process. Therefore, it is of great significance to optimize the microstructure and properties of HPDC AlSi10MnMg alloy and increase its applications. Based on the microstructure and mechanical behavior of HPDC AlSi10MnMg alloy, this dissertation focuses on the distribution characteristics and fracture behavior of externally solidified crystals (ESCs) and iron-rich phases to provide guidelines for new alloy design and promote industrial applications. The results are as follows:The microstructure of HPDC AlSi10MnMg alloy can be roughly divided into a surface chill zone, the eutectic bands and an ESC-rich centre zone. The surface chill zone exhibits fine microstructure and pore-free characteristics. A skin layer might be found at the outer surface of the chill zone. The eutectic bands are Al-Si eutietic-rich zone and their outline is consistent with the direction of the liquid flow, while the ESC-rich zone is located in the center of the casting, with highly distributed porosities and branched ESC dendrites. Under the same slow shot speed and intensification pressure conditions, the decrease of the fast shot speed will cause ESC dendrite enrichment and form large-scale network, which hinders liquid flow feeding and promotes the formation of large-scale interconected shrinkage porosities. The crack originates from the large-scale shrinkage porosities, and then propagates along the ESC boundary and the edge of pores in an intergranular fracture mode or along the interior of the grain in a transgranular fracture mode, resulting in casting failure. The large-scale shrinkage porosities and intergranular fracture mode are important factors to reduce the mechanical properties. The iron-rich phases in HPDC AlSi10MnMg alloy include the primary iron-rich phase formed in the shot sleeve ((P-IMC)I), the primary iron-rich phase formed in the diecavity ((P-IMC)II) and eutectic iron-rich phases. The primary iron-rich phases are based on the manganese (Mn) rich zone in the liquid phase and nucleate in a spherical morphology and then grow laterally into polyhedrons. The continuous growth of hexahedral (P-IMC)I in the die cavity is a dendritic process along its vertex angles. There are three kinds of eutectic iron-rich phases formed near the Al-Si eutectic boundary with varied morphologies (plate shape, net shape and Chinese character shape) in the HPDC alloy, and their morphologies feature is related to cooling rate and the residual liquid solute concentration. The β phase and the δ phase coexist in the same plate-shaped iron-rich phase. The mismatch between them is small, and high cooling rate and high silicon content promote the transformation from the metastable β phase to the stable δ phase. (P-IMC)I is the most harmful iron-rich phase to the mechanical properties compared with other iron-rich phases. The brittle (P-IMC)I is easy to fracture, causing stress concentration and promoting crack propagation. Through thermodynamic calculation and micro alloy component regulation and based on the AlSi10MnMg alloy, a new non-heat treatment HPDC alloy THAS-1 was designed, Zr and V elements are added to optimize the ESC and (P-IMC)I. The new THAS-1 alloy has been applied to the trial production of a Shock Tower casting for automobiles.