Numerical simulation of DC casting of AZ31 magnesium slab at different casting speeds

A mathematical model of the direct chill(DC)casting process for AZ31magnesium slab has been developed to predict the temperature evolution in the slab.The temperature fields at different casting speeds were compared and the optimum casting speed of 300 mm×800 mm magnesium slab in the certain pouring temperature and cooling-water flow rate was obtained.The casting speed during the plant trial was consistent with the calculation.

Timing of early laparoscopic cholecystectomy after endoscopic retrograde cholangiopancreatography

Objective:This study was performed to compare the effect of different time intervals between endoscopic retrograde cholangiopancreatography(ERCP)and early laparoscopic cholecystectomy(LC)on the operation duration,postoperative hospitalization,and postoperative complications.Materials and methods:We retrospectively reviewed data for 105 patients with cholecystocholedocholithiasis who underwent ERCP and LC from January 2016 to May 2019.The patients were divided into three groups.In Group A,the interval from ERCP to LC was3 days;in Group B,the interval was 4e6 days;and in Group C,the interval was>6 days.We compared operation duration,blood loss volume,postoperative hospitalization,and rate of biliary complications among the three groups and analyzed the risk factors for postoperative complications.Results:Operation duration differed significantly between Groups A and B(47.5 min vs.60.0 min,p?0.033)and between Groups B and C(60.0 min vs.47.5 min,p?0.033).The median blood loss volume was significantly less in Group A than in Group B(8 ml vs.10 ml,p?0.041),and the postoperative hospitalization and rate of postoperative complications did not differ significantly.Conclusion:The best time for patients with cholecystocholedocholithiasis to undergo LC is 0e3 days after ERCP.If the operation cannot be performed within 3 days,we recommend 6 days after ERCP.

Effects of Extrusion Speed on the Microstructure and Mechanical Properties of Mg-9Gd-3Y-1.5Zn-0.8Zr alloy

The effects of the extrusion speed on the microstructures, mechanical properties and aging hardening behaviors of Mg-9Gd-3Y-1.5Zn-0.8Zr alloy have been investigated. The microstructure evolution during hot extrusion has also been discussed. The microstructures of the extruded alloys mainly consist of the equiaxed dynamically recrystallized grains and fiber-like long period stacking ordered （LPSO） phase. The increasing extrusion speed results in grain coarsening and the mechanical properties deterioration. Mean- while, it could also retard the aging hardening response. The extrudability of the investigated alloy is limited. Cracks nucleate and grow up rapidly when the extrusion speed is over 0.3 m/min. It should be closely related to the large amount of LPSO phase and the unique microstructure evolution. The rapidly precipitating fine lamella during extrusion could pin the dislocations and grain boundaries effectively. It could strengthen the alloy but also limit the extrudability of the investigated alloy.