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To improve robustness of mechanical properties of semi-solid cast A356 alloy using taguchi design method

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china Foundry 2024年第2期21卷 175-184页

作者： Yi-wu Xu Hong-yi Zhan Wei Tong Jin-ping Li Le-peng Zhang De-jiang Li Xiao-qin Zeng School of Materials science and Engineering Shanghai Jiao Tong UniversityShanghai 200240China china science lab General Motors Global Research&DevelopmentShanghai 201206China general motors(china)Investment Co. Ltd.Shanghai 201206China china International Intellectech Corporation(CIIC) Beijing 100004China

Mechanical properties of semi-solid casting are dependent on multiple processing parameters,and improper processing parameters will not only reduce mean data but also increase variations.The present study investigated the impact of parameters in slurry preparation and heat treatment on the yield strength and ductility of T6 heat-treated A356 Al-Si alloy using rapid slurry forming(RSF)semi-solid casting.The focus was primarily on the robustness of mechanical properties based on Taguchi design method.By analyzing signal-to-noise ratio and minimum value calculated from-3S,the optimum slurry preparation parameters and heat treatment parameters were determined to be no quench,enthalpy exchange material(EEM)temperature of 140℃,EEM-to-melt ratio of 6mass%,stirring time of 18 s,solution heat treated at 520℃ for 2 h,and ageing heat treated at 190℃ for 6 h.In a small batch validation,the-3S yield strength and-3S elongation reach 256.1 MPa and 5.03% respectively,showing a satisfactory robustness.The hardness and microstructure of heat-treated samples with the best and worst properties were characterized to gain insight into the underlying mechanisms affecting the mean value and variations of mechanical properties.

关键词： semi-solid casting taguchi design method signal-to-noise ratio mechanical property microstructure

Unified casting(UniCast)aluminum alloy—a sustainable and low-carbon materials solution for vehicle lightweighting

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Journal of Materials science & Technology 2023年第23期154卷 251-268页

作者： Hongyi Zhan Guang Zeng Qigui Wang Congjie Wang Pan Wang Zhou Wang Yiwu Xu Devin Hess Paul Crepeau Jianfeng Wang china science lab General Motors Global Research & Development Shanghai 201206 China School of Materials science and Engineering Central South University Changsha 410083 China Advanced Materials Technology Global Technical Center General Motors Company Warren MI 48093 USA School of Materials science and Engineering Shanghai Jiao Tong University Shanghai 200240 China general motors (china) Investment Co. Ltd. Shanghai 201206 China

Casting aluminum(Al)alloys have been widely used in the automotive industry to improve fuel economy as well as to reduce greenhouse gas(GHG)emissions in the vehicle use phase.However,the casting Al alloys used for load-bearing body and chassis components today are mostly made from primary Al with a low impurity Fe content typically less than 0.2 wt.%,owing to the requirements for high ductility and adequate fatigue strength.Primary Al is made directly from alumina which was refined from aluminum ore(bauxite),using an electrolytic process which consumes a lot of energy and produces GHG emissions that are much higher than those from steel making.The objective of this paper is to present a Unified Casting(UniCast)Al alloy concept as a sustainable materials solution for vehicle lightweighting.The UniCast alloy chemistry is intentionally designed to be more tolerant of Fe impurity.This chemistry can not only satisfy the requirements on castability,but also deliver mechanical properties needed for a variety of thin-walled and thick-walled automotive structural components that are produced by various casting processes.The UniCast alloy concept will contribute to the establishment of a closed-loop recycling system in the future as the shredded scrap obtained from the disposed end-of-life vehicles can be directly recycled back into UniCast alloy ingot with a more efficient sorting process.In addition,by setting the upper limit of Fe content in the UniCast alloy to a higher level,it will become possible to use a high fraction of post-consumer scraps to produce this alloy.To demonstrate the feasibility of this concept,an exemplary UniCast alloy chemistry has been elaborated in this article.Furthermore,challenges and future research opportunities related to the realization of UniCast alloy concept in the automotive industry are discussed.It is hoped that this article will be of great implication to industrial researchers and academicians for making concerted efforts to establish closed-loop recycling of Al castings for the a

关键词： Recycled aluminum Closed-loop recycling Automotive application Casting Mechanical properties Unicast al alloy

Microstructural evolution of Mg-Al-Re alloy reinforced with alumina fibers

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Journal of Magnesium and Alloys 2020年第3期8卷 565-577页

作者： Li Li Dejiang Li Xiaoqin Zeng Alan A.Luo Bin Hu Anil K.Sachdev Liangliang Gu Wenjiang Ding Shanghai Jiao Tong University ShanghaiChina The Ohio State University ColumbusOHUnited States General Motors China Science Lab ShanghaiChina general motors Global R&D Center WarrenMIUnited States

Few studies were reported on the phases'relationships of AE44(Mg-4.0Al-4.1RE-0.3Mn,wt.%)and its composites.In this work,AE44 alloy and Saffil(6-Al2O3)/AE44 Metal matrix composite(MMC)were both prepared by slow shot high pressure die casting(SS-HPDC)technology and their phase constitutions were all studied in detail using experimental techniques combined with CALPHAD(Calculation of Phase Diagram)modeling.The results revealed that the alloy consists of the a-Mg matrix,A1hRE3 intermetallic phase,and one trace phase AI3RE,while the composite contains five major phases:a-Mg,5-AI2O3,AI3RE,MgO and Mg2Si.and two trace phases of A12RE and AI11RE3,respectively.A1hRE3 is partly derived from ALRE,while A13RE is a product of the peritectoid reaction between the two precipitates.The presence of MgO and Mg2Si is due to the interfacial reaction between the SiO2 binder in the fiber preforms and the molten magnesium during infiltration.The use of SiO2 binder in the preform manufacturing was limited/minimized to reduce the MgO formation in the MMC casting process,which can be detrimental to the fatigue performance of the MMC materials.

关键词： Mg-Al-RE Magnesium composite Slow shot high pressure die casting Microstructure CALPHAD AlxREy

Review on Hydrogen Embrittlement of Press-hardened Steels for Automotive Applications

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Acta Metallurgica Sinica(English Letters) 2023年第7期36卷 1123-1143页

作者： Z.Wang Q.Lu Z.H.Cao H.Chen M.X.Huang J.F.Wang General Motors China Science Lab Shanghai201206China Department of Mechanical Engineering The University of Hong KongPokfulam RoadHong Kong999077China Key laboratory for Advanced Materials of Ministry of Education School of Materials Science and EngineeringTsinghua UniversityBeijing100084China

Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achieved by hot stamping process.However,the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement.To reduce this kind of risk,recent research efforts have been focused on various ways to optimize the microstructure of PHS.The present review intends to summarize these efforts,to highlight present solutions to address hydrogen embrittlement,and to shed light on directions for future improvement.The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition.The substrate part covers the influence of martensite,carbides,inclusions,and retained austenite,while the surface part covers decarburization and oxidation,pre-coating,and trimming.

关键词： Hot stamping Press-hardened steels Coating-free Hydrogen embrittlement Fracture Al-Si coating

Dynamic response of a Q&P steel to high-strain-rate tension

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Acta Mechanica Solida Sinica 2017年第5期30卷 484-492页

作者： Huanran Wang Wenchao Zhang Dongfang Ma Bohan Ma Danian Chen Xin Yang Chunlei Fan Mechanics and Materials science Research Center Ningbo UniversityNingboZhejiang 315211China china science lab Research&Development CenterGeneral Motors CompanyShanghai 202106China

The experimental study on the volume fraction of retained austenite for QP980CR steel under high-strain-rate tension is briefly described. An interrupted tensile split Hopkinson bar （TSHB） is developed to control the elongation of specimens. The QP980CR steel sam- ples recovered from the interrupted TSt-IB tests are investigated using synchrotron X-ray diffraction （XRD） to analyze the effects of strain and strain rate on the martensitic trans- formation of retained austenite. A constitutive model of QP980CR steel coupling with the transformation-induced plasticity （TRIP） effect is presented based on Delannay＇s mean-field modeling. The stress-strain curves of quasi-static and dynamic tensile tests for QP980CR steel are compared with the results predicted by the presented constitutive model. The dif- fuse necking of QP980CR steel sheet specimens in TSHB tests is analyzed using Batra and Vv＇ei＇s instability criterion and the presented constitutive model. The effects of strain rate and temperature on the dynamic tensile fracture strain of QP980CR steel are also given.

关键词： Interrupted Hopkinson testPhase transformationMultiphase constitutive modelDynamic fractureQP980CR steel

generalized multipath planning model for ride-sharing systems

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Frontiers of Computer science 2014年第1期8卷 100-118页

作者： Jamal YOUSAF JuanziLI Lu CHEN Jie TANG Xiaowen DAI Department of Computer science and Technology Tsinghua National Laboratory for Information Science and Technology Tsinghua University Beijing 100084 China. general motors China Science Lab Shanghai 201303 China

Ride-sharing systems should combine environ- mental protection （through a reduction of fossil fuel usage）, socialization, and security. Encouraging people to use ride- sharing systems by satisfying their demands for safety, pri- vacy and convenience is challenging. Most previous works on this topic have focused on finding a fixed path between the driver and the riders either based solely on their loca- tions or using social information. The drivers＇ and riders＇ lack of options to change or compute the path according to their own preferences and requirements is problematic. With the advancement of mobile social networking technologies, it is necessary to reconsider the principles and desired character- istics of ride-sharing systems. In this paper, we formalized the ride-sharing problem as a multi source-destination path plan- ning problem. An objective function that models different ob- jectives in a unified framework was developed. Moreover, we provide a similarity model, which can reflect the personal preferences of the rides and utilize social media to obtain the current interests of the riders and drivers. The model also al- lows each driver to generate sub-optimal paths according to his own requirements by suitably adjusting the weights. Two case studies have shown that our system has the potential to find the best possible match and computes the multiple opti- mal paths against different user-defined objective functions.

关键词： ride-sharing path planning dynamic optimiza-tion

Understanding grain refining and anti Si-poisoning effect in Al-10Si/Al-5Nb-B system

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Journal of Materials science & Technology 2021年第6期65卷 190-201页

作者： Yang Li Ying Jiang Bin Liu Qun Luo Bin Hu Qian Li Materials Genome Institute State Key Laboratory of Advanced Special SteelsShanghai Key Laboratory of Advanced FerrometallurgySchool of Materials Science and EngineeringShanghai UniversityShanghai 200444China china science lab General Motors Global Research and Development56Jinwan RoadShanghai 201206China

Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB_(2)provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB_(2)and(1-100)NbB_(2)surface can be substituted by Al to form(Al,Nb)B_(2)intermedia layers.In addition,a layer of NbAl_(3)-like compound(NbAl_(3)')can cover the surface of NbB_(2)with the orientation relation of(1-100)[11-20]NbB_(2/)/(110)[110]NbAl_(3)'.Both of the(Al,Nb)B_(2)and NbAl_(3)'intermedia layers contribute to enhancing the nucleation potency of NbB_(2)particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.

关键词： Al-Si casting alloys Grain refinement Niobium diboride Interface Anti Si-poisoning

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

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china Foundry 2023年第1期20卷 12-22页

作者： Hong-yi Zhan Yi-wu Xu Pan Wang Jian-feng Wang Jin-ping Li Le-peng Zhang general motors Global Research&Development China Science LaboratoryShanghai 201206China School of Materials science and Engineering Shanghai Jiao Tong UniversityShanghai 200240China general motors(china)Investment Co. Ltd.Shanghai 201206China china International Intellectech Corporation(CIIC) Beijing 100004China

Aluminum high pressure die casting(HPDC)technology has evolved in the past decades,enabling stronger and larger one-piece casting with significant part consolidation.It also offers a higher design freedom for more mass-efficient thin-walled body structures.For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance,shock towers and hinge pillars,etc.),a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

关键词： Al-Si alloy intermetallics high pressure die casting tensile property T7 heat treatment

Effect of retained austenite on the fracture behavior of a novel press-hardened steel

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Journal of Materials science & Technology 2023年第4期135卷 34-45页

作者： Zhisong Chai Qi Lu Jun Hu Lingyu Wang Zhou Wang Jianfeng Wang Wei Xu State Key laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China china science laboratory General Motors Global Research&DevelopmentShanghai 201206China

Tensile and bending properties are two critical attributes of press hardened steels(PHSs)for automotive body structural components.However,the research on these properties of PHSs with retained austenite(RA),which is introduced to improve the mechanical properties,has not been well reported.In this study,the effect of RA on the quasi-static uniaxial tensile and three-point bending behaviors has been systematically investigated for a newly developed Cr and Si alloyed PHS.RA with various degrees of mechanical stabilities was obtained by tuning the auto-tempering of martensite through the control of the die contact pressure during the press hardening process.Mechanically stable RA provides the optimal combination of tensile and bending performance,while the PHS with RA of poor mechanical stability has a deteriorated bending toughness as manifested by a reduction of bending angle from approximately 61.6°to56.8°.However,itstensileproperties,incontrast,arethebestintermsof theproductofulti-mate tensile strength and total elongation(15.9 GPa%).This is mainly attributed to the unstable RA on the outermost surface of the bending sample.The unstable RA can easily transform into brittle martensite under local plane strain and strain gradient conditions in the bending test compared with uniaxial stress in the tensile test,promoting crack initiation and propagation.Furthermore,the effect of martensitic auto-tempering or contact pressure on the quantity and stability of RA are also discussed.This study would provide a useful reference to guide hot stamping process optimization for the newly developed Cr and Si-containing press-hardened steel.

关键词： Press-hardened steel Retained austenite Tensile property Bending toughness Crack initiation