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

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.

Development and application of inverse heat transfer model between liquid metal and shot sleeve in high pressure die casting process under non-shooting condition

To predict the heat transfer behavior of A380 alloy in a shot sleeve, a numerical approach(inverse method) is used and validated by high pressure die casting(HPDC) experiment under non-shooting condition. The maximum difference between the measured and calculated temperature profiles is smaller than 3 °C, which suggests that the inverse method can be used to predict the heat transfer behavior of alloys in a shot sleeve. Furthermore, the results indicate an increase in maximum interfacial heat flux density(q_(max)) and heat transfer coefficient(h_(max)) with an increase in sleeve filling ratio, especially at the pouring zone(S2 zone). In addition, the values of initial temperature(T_(IDS)) and maximum shot sleeve surface temperature(T_(simax)) at the two end zones(S2 and S10) are higher than those at the middle zone(S5). Moreover, in comparison with fluctuations in heat transfer coefficient(h) with time at the two end zones(S2 and S10), 2.4-6.5 kW ·m^(-2)·K^(-1), 3.5-12.5 kW ·m^(-2)·K^(-1), respectively, more fluctuations are found at S5 zone, 2.1-14.7 kW ·m^(-2)·K^(-1). These differences could theoretically explain the formation of the three zones: smooth pouring zone, un-smooth middle zone and smooth zone, with different morphologies in the metal log under the non-shot casting condition. Finally, our calculations also reveal that the values of q_(max) and h_(max) cast at 680 °C are smaller than those cast at 660 °C and at 700 °C.

Effects of viral infection and microbial diversity on patients with sepsis:A retrospective study based on metagenomic next-generation sequencing

BACKGROUND: The study aims to investigate the performance of a metagenomic next-generationsequencing (NGS)-based diagnostic technique for the identifi cation of potential bacterial and viral infectionsand eff ects of concomitant viral infection on the survival rate of intensive care unit (ICU) sepsis patients.METHODS: A total of 74 ICU patients with sepsis who were admitted to our institution from February1, 2018 to June 30, 2019 were enrolled. Separate blood samples were collected from patients for bloodcultures and metagenomic NGS when the patients’ body temperature was higher than 38 °C. Patients’demographic data, including gender, age, ICU duration, ICU scores, and laboratory results, were recorded.The correlations between pathogen types and sepsis severity and survival rate were evaluated.RESULTS: NGS produced higher positive results (105 of 118;88.98%) than blood cultures(18 of 118;15.25%) over the whole study period. Concomitant viral infection correlated closelywith sepsis severity and had the negative effect on the survival of patients with sepsis. However,correlation analysis indicated that the bacterial variety did not correlate with the severity of sepsis.CONCLUSIONS: Concurrent viral load correlates closely with the severity of sepsis and thesurvival rate of the ICU sepsis patients. This suggests that prophylactic administration of antiviraldrugs combined with antibiotics may be benefi cial to ICU sepsis patients.

Characterization of A390 aluminum alloy produced at different slow shot speeds using vacuum assisted high pressure die casting

The effects of vacuum assistance on the microstructure and mechanical properties of high pressure die cast A390alloy at different slow shot speeds were evaluated.Plate-shaped specimens of hypereutectic A390aluminum alloy were produced on a TOYO BD?350V5cold chamber die casting machine incorporated with a self-improved TOYO vacuum system.According to the results,the vacuum pressure inside the die cavity increased linearly with the increasing slow shot speed at the beginning of mold filling.Meanwhile,tensile properties of vacuum die castings were deteriorated by the porosity content.In addition,the average primary silicon size decreased from23to14μm when the slow shot speed increased from0.05to0.2m/s,which has a binary functional relationship with the slow shot speed.After heat treatment,microstructural morphologies revealed that needle-shaped and thin-flaked eutectic silicon particles became rounded while Al2Cu dissolved intoα(Al)matrix.Furthermore,the fractography revealed that the fracture mechanism has evolved from brittle transgranular fracture to a fracture mode with many dimples after heat treatment.

Effect of different processing parameters on interfacial heat-transfer behavior in high-pressure die-casting process

Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),high shot speed(VH),pouring temperature(Tp)and initial die temperature(Tm),inverse method was developed to determine the interfacial heat transfer coefficient(IHTC).The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used.It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings.The IHTC could have a higher peak value with increasing the Tp from680to720℃or the VL from0.1to0.4m/s.In addition,the influence of the VH and Tm on IHTC could be negligible.

Interfacial heat transfer behavior at metal/die in finger-plated casting during high pressure die casting process

Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m^(-2) and 64.3 kW ·m^(-2)·K^(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s^(-1) to 110 m·s^(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m^(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).

Influence of different high pressure die casting processes on 3D porosity distribution of Mg-3.0Nd-0.3Zn-0.6Zr alloy

3D reconstruction was adopted to characterize the microstructural morphologies of Mg-3.0Nd-0.3Zn-0.6Zr alloy castings produced by high pressure die casting(HPDC)processes with different parameters,including low slow-shot speed,solidification pressurization and fast slow-shot speed.At low slow-shot speeds of 0.1 m·s^(-1),0.2 m·s^(-1) and 0.3 m·s^(-1),the porosity is concentrated in the center of the castings with one spiral staggered shape along the liquid flow direction.The porosity volume simultaneously decreases with the reduction of quantity and size of externally solidified crystals(ESCs),while the shrinkage pores become more and more dispersed with the increasing low slow-shot speed.Pressurization not only reduces the porosity volume due to the improvement of feeding ability,but also transformes the center gathered porosity into one layer-by-layer distribution form.Accompanied with the increasing fast slow-shot speed,the central porosity dramatically decreases and transforms into a large-scale spiral staggered shape along the liquid flow direction.However,the porosity is much more dispersed when the speed is increased from 2 m·s^(-1) to 3 m·s^(-1).

Cognitive characteristics in Chinese non-demented PD patients based on gender difference

Background:Cognitive impairment is one of the non-motor symptoms in Parkinson’s disease(PD).In the present study,we aim to examine the cognitive function of non-demented Parkinson’s disease patients and compare the results between male and female patients as well as control groups in search of any gender effect.Methods:Sixty PD Patients(30 males and 30 females)from the Movement Disorders Clinic at Huashan Hospital Affiliated to Fudan University were recruited to participate in the study.One hundred age and gender matched control subjects without neurological or psychiatric disorders were voluntarily recruited.The participants were administered measures of cognition in five domains including memory,language,spatial processing abilities,attention and executive function.Results:PD patients attained significantly lower scores in the visual spatial function,language and attention/executive function compared with the control group.Anti-parkinsonian treated patients performed worse in Rey-copy score,Clock Drawing Test(CDT)and Verbal Fluency-City than untreated ones.In regard to gender differences,though no general cognitive differences were found in Mini-mental State Examination(MMSE),men surpassed women on Boston naming test(BNT)while women were superior on Auditory Verbal Learning Test-long(AVLT)delayed cued recall test.Conclusions:Cognitive impairments were common in PD patients even in the absence of dementia.PD patients with anti-parkinsonian medication had worse cognitive impairment than untreated patients.Genders may have different manifestations of cognitive impairment in PD patients.