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Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

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China Foundry 2024年第1期21卷 11-19页

作者： Wen-ning Liu Wei Zhang Peng-yue Wang Yi-xian Liu Xiang-yi Jiao Ao-xiang Wan Cheng-gang Wang Guo-dong Tong shou-mei xiong School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Key Laboratory for Advanced Materials Processing Technology Tsinghua UniversityBeijing 100084Beijing China FAW Group Co. Ltd.Changchun 130013China China FAW Foundry Co. Ltd.Changchun 130013China

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

关键词： hypoeutectic Al-Si alloy high pressure die casting porosity externally solidified crystal tensile property

Defect band formation in high pressure die casting AE44 magnesium alloy

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China Foundry 2022年第3期19卷 201-210页

作者： Ying-ying Hou Meng-wu Wu Feng Huang Xiao-bo Li shou-mei xiong Hubei Key Laboratory of Advanced Technology for Automotive Components Wuhan University of TechnologyWuhan 430070China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China

The characteristics of defect bands in the microstructure of high pressure die casting(HPDC)AE44 magnesium alloy were investigated.Special attention was paid to the effects of process parameters during the HPDC process and casting structure on the distribution of defect bands.Results show that the defect bands are solute segregation bands with the enrichment of Al,Ce and La elements,which are basically in the form of Al_(11)RE_(3) phase.There is no obvious aggregation of porosities in the defect bands.The width of the inner defect band is 4-8 times larger than that of the outer one.The variation trends of the distribution of the inner and outer defect bands are not consistent under different process parameters and at different locations of castings.This is due to the discrepancy between the formation mechanisms of double defect bands.The filling and solidification behavior of the melt near the chilling layer is very complicated,which finally leads to a fluctuation of the width and location of the outer defect band.By affecting the content and aggregation degree of externally solidified crystals(ESCs)in the cross section of die castings,the process parameters and casting structure have a great influence on the distribution of the inner defect band.

关键词： high pressure die casting magnesium alloy AE44 defect band microstructure

The effect of different high pressure die casting parameters on 3D microstructure and mechanical properties of AE44 magnesium alloy

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Journal of Magnesium and Alloys 2023年第9期11卷 3141-3150页

作者： Tong-tong Zhang Wen-bo Yu Chao-sheng Ma Wan-tong Chen Lin Zhang shou-mei xiong Center of Materials Science and Engineering School of Mechanical and Electronic Control EngineeringBeijing Jiaotong UniversityBeijing 100044China China Academy of Machinery Science and Technology Group Co. LtdBeijing 100044China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China

To understand the relationship between the process-microstructure-mechanical properties of the high-pressure die-casting(HPDC) AE44 magnesium alloy, 3D reconstruction and 2D characterization were carried out on the HPDC castings produced with different process parameters(low slow-shot speed, fast slow-shot speed, solidification pressure). Microstructural characterization revealed that the formation of shrinkage pores are closely related to ESCs, which were mainly controlled by the low slow-shot speed in shot sleeve(ESCs growth time) and fast slow-shot speed into the die cavity(distribution of ESCs). In addition, solidification pressure can significantly reduce the shrinkage porosity in the center by improving the feeding capacity of liquid metal. Tensile fracture revealed that the tearing ridge is mainly evolved from the slip band of ESCs. The quantity and distribution of ESCs determine the fracture mode of castings. The relationship between mechanical properties of castings and the morphology of ESCs and porosity is also statistically discussed.

关键词： HPDC parameters Porosity Externally solidified crystals(ESCs) Tensile fracture 3D reconstruction

Characterization of the Grain Structures in Vacuum-Assist HighPressure Die Casting AM60B Alloy

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Acta Metallurgica Sinica(English Letters) 2016年第7期29卷 619-628页

作者： Xiao-Bo Li shou-mei xiong Zhi-Peng Guo School of Materials Science and Engineering Tsinghua University Key Laboratory for Advanced Materials Processing Technology Ministry of EducationTsinghua University

The structures in vacuum-assist high-pressure die casting （HPDC） AM60B alloy were studied by using an optical microscope and a scanning electron microscope with an energy dispersive spectrometer. It was found that the HPDC under the vacuum could significantly change the morphology and distribution of the microstructure. For both conventional and vacuum-assist HPDC processes, the externally solidified crystals （ESCs） tended to aggregate in the center along the thickness direction of the castings. Besides, the aggregation was more pronounced, and the number of ESCs decreased, and the ESCs tended to become smaller and more globular, as the distance between the specimen location and runner increased. Compared with the conventional castings, the vacuum-assist HPDC can significantly reduce the size and amount of ESCs, and the ESCs tended to be more globular. For the distribution of ESCs along the thickness of the specimens, the aggregation tendency was more pronounced in vacuum-assist die castings than that in conventional castings. Besides, the distribution of ESCs at different locations was more converged in the vacuum-assist HPDC than that in the conventional HPDC.

关键词： AM60B alloy Grain structure Vacuum-assist high-pressure die casting Externally solidifiedcrystals

An improved mathematical model to simulate mold filling process in high pressure die casting using CLSVOF method and CSF model

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China Foundry 2015年第3期12卷 180-188页

作者： Cheng Bi Zhi-peng Guo shou-mei xiong School of Materials Science and Engineering Tsinghua University

A 3D mathematical model was proposed to simulate the mold filling process in high-pressure die casting(HPDC) to improve accuracy considering the surface tension. Piecewise liner interface calculation(PLIC) and volume of fluid(VOF) methods were used to construct the pattern of the liquid interface. A coupled levelset and VOF method(CLSVOF) was proposed to capture the interface pattern and obtain its normal vector. A continuum surface force(CSF) model was used to consider the surface tension. Two water analogy experiments were carried out using the proposed model. Simulation and experimental results were analyzed and compared; and the effects of surface tension were also discussed. The simulation results agreed well with the experiments and the simulation accuracy was an improvement on interface geometries, liquid flows, and gas entrapments.

关键词： mold filling HPDC CLSVOF CSF surface tension force

Phase-field-lattice Boltzmann study for lamellar eutectic growth in a natural convection melt

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China Foundry 2017年第5期14卷 373-378页

作者： Ang Zhang Zhi-peng Guo shou-mei xiong School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Key Laboratory for Advanced Materials Processing Technology Ministry of Education Tsinghua UniversityBeijing 100084China

In the present study, the influence of natural convection on the lamellar eutectic growth is determined by a phase-field-lattice Boltzmann study for Al-Cu eutectic alloy. The mass difference resulting from concentration difference led to the fluid flow, and a robust parallel and adaptive mesh refinement algorithm was employed to improve the computational efficiency without any compromising accuracy. Results show that the existence of natural convection would affect the growth undercooling and thus control the interface shape by adjusting the lamellar width. In particular, by alternating the magnitude of the solute expansion coefficient, the strength of the natural convection is changed. Corresponding microstructure patterns are discussed and compared with those under no-convection conditions.

关键词：自然传送对流薄片状的宽度阶段地模型格子 Boltzmann 方法 TP391.99 一

Modeling studies on divorced eutectic formation of high pressure die cast magnesium alloy

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China Foundry 2018年第1期15卷 58-65页

作者： Meng-wu Wu Lin Hua shou-mei xiong Hubei Key Laboratory of Advanced Technology for Automotive Components Wuhan University of Technology Wuhan 430070 China Hubei Collaborative Innovation Center for Automotive Components Technology Wuhan 430070 China School of Materials Science and Engineering Tsinghua University Beijing 100084 China

The morphology and content of the divorced eutectic in the microstructure of high pressure die casting(HPDC) magnesium alloy have a great influence on the final performance of castings. Based on the previous work concerning simulation of the nucleation and dendritic growth of primary α-Mg during the solidification of magnesium alloy under HPDC process, an extension was made to the formerly established CA(Cellular Automaton) model with the purpose of modeling the nucleation and growth of Mg-Al eutectic. With a temperature field and solute field obtained during simulation of the primary α-Mg dendrites as the initial condition of the modified CA model, modeling of the Mg-Al eutectic with a divorced morphology was achieved. Moreover, the simulated results were in accordance with the experimental ones regarding the distribution and content of the divorced eutectic. Taking a "cover-plate" die casting with AM60 magnesium alloy as an example, the rapid solidification with a high cooling rate at the surface layer of the casting led to a fine and uniform grain size of primary α-Mg, while the divorced eutectic at the grain boundary revealed a more dispersed and granular morphology. Islands of divorced eutectic were observed at the central region of the casting, due to the existence of ESCs(Externally Solidified Crystals) which contributed to a coarse and non-uniform grain size of primary α-Mg. The volume percentage of the eutectic β-Mg_(17)Al_(12) phase is about 2%-6% in the die casting as a whole. The numerical model established in this study is of great significance to the study of the divorced eutectic in the microstructure of die cast magnesium alloy.

关键词： magnesium alloy high pressure die casting divorced eutectic microstructure simulation

Different aging behaviors at surface layer and central region of a die-casting A380 alloy during heat treatment

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China Foundry 2017年第6期14卷 506-512页

作者： Zi-hao Yuan Zhi-peng Guo shou-mei xiong School of CMaterials Science and Engineering Tsinghua University Beijing 100084 China State Key Laboratory of Automobile Safety and Energy Tsinghua University Beijing 100084 China

Microstructural and hardness evolutions of a vacuum-assistant die-cast A380(Al-8.67 wt.%Si-3.27 wt.%Cu) alloy during heat treatment were investigated. Isothermal DSC test at 200 °C revealed that the precipitation reaction in the surface layer was faster than that in the central region. This corresponded with the hardness evolution that the surface layer hardened faster. The hardness increment in the surface layer was higher than that in the central region. Further experimental evidences indicated that the differences were due to the different amounts of heterogeneous nucleation sites for precipitation in the two parts. The influence of the characteristic as-cast microstructure on the artificial aging process is analyzed and discussed in detail.

关键词： high pressure die casting(HPDC) heat treatment macro-segregation kinetics precipitation externally solidified crystals(ESCs)

Simulation of dendritic growth of magnesium al oys with fluid flow

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China Foundry 2017年第5期14卷 359-364页

作者： Meng-wu Wu Zhi-peng Guo shou-mei xiong Hubei Key Laboratory of Advanced Technology for Automotive Components Wuhan University of Technology Wuhan 430070China Hubei Collaborative innovation Center for Automotive Components Technology Wuhan 430070China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China

Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp(hexagonal closepacked) structure, an extension was made to the formerly established CA(cellular automaton) model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.

关键词： magnesium alloy dendritic growth cellular automaton method fluid flow