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

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.

Microstructure and mechanical properties of a high ductility Mg–Zn–Mn–Ce magnesium alloy

A high-ductility ZME200(Mg–2.3Zn–0.4Mn–0.2Ce^(1))alloy was newly developed for vehicle closure and structure applications,based on an earlier ZE20(Mg–2.0Zn–0.2Ce)alloy for extrusion applications.Previous study indicates that the hot deformation behavior of as-cast ZME200 alloy varies with processing parameters,namely temperature and strain rate.In this follow-up study,a conventional rolling process was optimized to obtain magnesium sheets with a very fine grain structure and high ductility.The microstructure,mechanical properties,and corrosion resistances of ZME200 alloy were investigated,and compared with those of commercial AZ31 magnesium alloy.It was demonstrated that the ZME200 alloy sheet exhibits extraordinarily higher ductility(36%in tensile elongation),much superior stretch formability(an Erichsen value of 9.5),lower anisotropy,comparable strength and corrosion resistance to AZ31 alloy.The unique RD–TD double split texture with remarkably reduced intensity and grain refinement gives rise to the significantly improved ductility and formability at room-temperature.

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

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.

Microstructural evolution of Mg-7Al-2Sn Mg alloy during multi-directional impact forging

Multi-directional impact forging(MDIF)was applied to a Mg-7Al-2Sn(wt.%)Mg alloy to investigate its effect on the microstructural evolution.MDIF process exhibited high grain refinement efficiency.After MDIF 200 passes,the grain size drastically decreased to 20µm from the initial coarse grains of~500µm due to dynamic recrystallization(DRX).Meanwhile,original grain boundaries remained during MDIF and large numbers of fine sphericalβ-Mg_(17)Al_(12) particles dynamically precipitated along the original grain boundaries with high Al concentration,acting as effective pinning obstacles for the suppression of DRXed grain growth.Besides,micro-cracks nucleated during MDIF and propagated along the interface between the remained globular or cubic Al-Mn particles and Mg matrix.

Preparation and characterization of the micro-arc oxidation composite coatings on magnesium alloys

The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MCC)coatings on AZ91D magnesium alloys were prepared by Micro-arc Oxidation(MAO)and electrophoresis technologies.The microstructure,corrosion resistance,abrasion resistance,stone impact resistance and adhesion of MCC coatings were studied respectively.The cross section morphologies showed that the outer organic coating was filled into the hole on surface of MAO coating,and it acted as a shelter against corrosive products.The copper-accelerated acetic acid salt spray Test,abrasion resistance test,stone impact resistance test,thermal shock resistance test and adhesion test were used to evaluate the protective characterization by the third testing organization which approved by GM.The test results showed the composite coatings meet all the requirements.The MCC coating on Mg presents excellent properties,and it is a promising surface treatment technology on magnesium alloys for production vehicles.

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

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 automotive and other transportation industry segments.

Enhancing Fe content tolerance in A356 alloys for achieving low carbon footprint aluminum structure castings

Low carbon footprint aluminum structure castings are the mainstream development direction of alu-minum alloys in the future.Enhancing the Fe content tolerance upper limit in casting aluminum alloys is considered an effective way to promote the application of recycled aluminum production.In this work,it was found that with the Ce and TiCN NPs(nanoparticles)addition simultaneously to A356 alloys,the acicular Fe-rich phases(β-Al 5 FeSi)which damages the properties can be changed into beneficial phases(core-shell heterostructures)for the alloy,and hence the mechanical properties of A356 alloys can be im-proved.The TiCN nanoparticles and rare element Ce play crucial roles in the formation of core-shell het-erostructures.The formation mechanism of core-shell heterostructure was also systematically researched from the perspective of thermodynamics and kinetics.This study provides a simple and feasible strategy to eliminate the harmful effects of Fe impurity and contributes to the industrialization of low carbon footprint aluminum structure castings.

Low‑Carbon‑Emission Hot Stamping:A Review from the Perspectives of Steel Grade,Heating Process,and Part Design

Hot stamping steels have become a crucial strategy for achieving lightweighting and enhancing crash safety in the automo-tive industry over the past two decades.However,the carbon emissions of the materials and their related stamping processes have been frequently overlooked.It is essential to consider these emissions during the design stage.Emerging materials and technologies in hot stamping pose challenges to the automotive industry's future development in carbon emission reduc-tion.This review discusses the promising materials for future application and their special features,as well as the emerging manufacturing and part design processes that have extended the limit of application for new materials.Advanced heating processes and corresponding equipment have been proven to improve heating efficiency and control temperature uniformity.The material utilization and the overall performance of the components are improved by tailored blanks and an integrated part design approach.To achieve low-carbon-emission(LCE)hot stamping,it is necessary to systematically consider the steel grade,heating process,and part design,rather than solely focusing on reducing carbon emissions during the manufacturing process stage.This review aims to present the latest progress in steel grade,heating process,and part design of hot stamping in the automotive industry,providing solutions for LCE from a holistic perspective.

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

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.

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

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.

Generalized multipath planning model for ride-sharing systems

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.

The Portevin-Le Chatelier effect of gradient nanostructured 5182 aluminum alloy by surface mechanical attrition treatment

Nanocrystalline surface layers and gradient nanostructure in 5182 aluminum alloy have been produced through surface mechanical attrition treatment(SMAT). The results indicate that the gradient nanostructure can not only improve the mechanical properties of 5182 Al alloy, but also has a certain effect on the Portevin-Le Chatelier(PLC) effect. The yield and ultimate tensile strength of 5182 Al alloy with SMAT are significantly improved combining with the decrease of fracture elongation compared with the as-received one. The PLC effect of 5182 Al alloy could be effectively postponed by the formation of gradient nanostructure after SMAT. It leads to the increase of critical strain of the PLC effect, more concentrated distribution of serrated strain, and increase of average stress amplitude in special strain range. The influence of grain size and gradient nanostructure on the PLC effect of 5182 Al alloy was also discussed in detail. Grain refinement could sharply increase the density of dislocations and hinder the movement of dislocations, which results in the decrease of moving speed of dislocations and the more concentrated distribution of solute atoms. The solute atoms would aggregate to form nano precipitates and further impede movement of dislocation. The stronger interaction between the dislocations and the nano precipitates is the main mechanism of postponed PLC effect.

Influence of strain rate and crystallographic orientation on dynamic recrystallization of pure Zn during room-temperature compression

This work investigates the strain rate dependence of dynamic recrystallization behaviour of high-purity zinc in room temperature compression under strain rates of 10^(-4)s^(-1),10-2s^(-1)and 0.5 s^(-1).Results from electron backscatter diffraction provide insight into the deformation and dynamic recrystallization mechanisms operative.Continuous dynamic recrystallization,twin-induced dynamic recrystallization,and discontinuous dynamic recrystallization are all active under compressive deformation at room temperature.Due to the high stacking fault energy of Zn,continuous dynamic recrystallization is the dominant mechanism while discontinuous dynamic recrystallization only operates in the early stages of compression at 10^(-4)s^(-1).Dynamic recrystallization kinetics are enhanced at higher strain rates(10^(-2)s^(-1)and 0.5s^(-1))due to an increased contribution from twin-induced dynamic recrystallization.The present study reveals that the controlling mechanisms for continuous dynamic recrystallization are basalslip and 2ndorder pyramidalslip activity.Because the activation of slip systems is mainly determined by crystallographic orientation,continuous dynamic recrystallization behaviour varies with grain orientation according to their propensity for basal and 2ndorder pyramidal slip.

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

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.