Papers by Author: Chun Mei Yang

Abstract: The simulation rolling and actual rolling of AZ31 strip with a thickness of 3mm prepared by a vertical twin roll caster (Ø250×150mm) have been made by both Gleeble-1500D thermal simulation testing machine and Ø170×300mm rolling-mill. The influence of various rolling parameters such as temperature (250°C, 300°C, 350°C and 400°C) and reduction (40%, 50% and 60%) on the microstructure of the rolled AZ31B thin strip have been investigated by means of metallographic observation and grain size measurment. The results indicate that when the temperature increases, the grain size of the rolled strip increases and the uniformity decreases. When the reduction is 50% the grain size is 10~30μm and the grains are fine and uniform. When the reduction is 40% or 60%, the grain size is 5~180μm and the grains are coarse in some areas. An optimized rolling process, 350°C×50% is suggested for actual rolling and a uniform microstructure of rolled AZ31 strip is obtained.

Abstract: The residual stress in epoxy adhesive layer deposited on metal and other substrate at room temperature is studied. With embedded strain gauges in arranged depth of epoxy layer, the strain changes in the adhesive layer induced by the curing procedure and the changes of ambient temperature were measured to evaluate the changes of residual stress in place during a period after the curing procedure finished. The actual strain in epoxy adhesive layer from curing is used to estimate the residual stresses in it. While taking the strain obtained from the surface of the adhesive layer as free strain, the residual stress can be calculated and presented a strongly cyclic variation with a period of 24 h. The inner stress is also analyzed using the finite element method.

Abstract: Magnesium has a hexagonal close-packed crystal structure which makes it more difficult to deform than aluminum. Conventional strip production usually requires several process steps to reach the final strip thickness. Strip casting can reduce some of the process steps and make strip processing simpler and easier, especially for alloys with poor deformability. The twin-roll casting process can directly obtain strips with thickness less than one or two millimeters. In this paper, the metallurgical characteristics of the twin-roll strip casting process were analyzed and discussed. A laboratory scale vertical twin roll caster in prepared AZ31 magnesium alloy strips, with 1.0 to 2.0 mm thick and 150mm wide. Process stability in the thin strip casting process of the alloy has been studied, the casting temperature (superheat) was proven to be a key factor influencing process stability and casting strip quality. The as-cast microstructure of the alloy was analyzed and evaluated by optical microscopy, which showed that the as-cast microstructure was composed of developed dendrites when the superheat was high, and of a rosebush-like structure when the superheat was low. When the casting temperature was close to the liquid phase temperature，the as-cast microstructure became global or grainy, and the grain size of the cast strip was very small. This remarkably improved the deformability of the as-cast strip.

Abstract: The influence of various homogenizing parameters on the microstructure of ZK60 magnesium alloy ingot has been investigated. By means of metalography observation and micro-hardness measurement, the effect of annealing temperature and time on the homogenization processes were studied, which indicated that the homogenized microstructure was more sensitive to annealing temperature than to annealing time. An optimized homogenizing process 470°Cx14h was suggested to improve the deformability of ZK60 alloy.

Abstract: In this paper, the influence of the cooling rate on the solidified structure of ZK60 Mg alloy has been studied by means of Gleeble-1500D thermal simulation instrument. The result showed that the grain size and grain shape depended on the cooling rate, Primary Dendrite Arm Space ( λI ) and Secondary Dendrite Arm Space ( λII) sharply decreased with the increasing of solidifying cooling rate (v) in the range of experimental cooling rate (0.2~100K/s). When superheat was constant, the empirical formulas of the relation between λI λII and v was obtained. In addition, the dependence between micro-hardness (HV) and Secondary Dendrite Arm Space ( λII) for ZK60 casting alloy was proved to be similar with Hall-Petch formula. The empirical formula for λII-HV has been proposed.