Advanced Materials Research Vols. 299-300

Abstract: The influence of pulse electric field on the columnar crystals growth has been studied by employing pulse electric field vertically to the solid/liquid interface during unidirectional solidification. The results showed that the pulse electric field was favorable to columnar crystals growth with the increase of pulse electric field intensity when the liquid phase was the positive electrode of pulse electric field. The formation of equiaxed crystal was accelerated when the degree of composition supercooling in front edge of solid/liquid interface reached the degree of nucleation supercooling by pulse electric field. When the liquid phase was the negative electrode of pulse electric field, the growth of columnar crystals was hindered, and the formation of equiaxed crystal was accelerated by pulse electric field.

Abstract: The testing device self-designed was used to measure the shrinkage ratio of Fe-0.18%C alloy in the length direction of cast ingot with the dimension of 200×80×100 mm. The results show that the total linear shrinkage mass of cast ingot is 0.0281 mm in the range of 4 mm near the inner surface of water-cooled crystallizer from the beginning of solidification to the end of δ→γ transformation. The shrinkage mass of δ phase and δ→γ transformation is 0.0211 mm and 0.007 mm, which is 75% and 25% of total shrinkage mass, respectively. The shrinkage rate of δ phase and δ→γ transformation is 0.45 μm·s^-1 and 1.45 μm·s^-1, respectively. The shrinkage mass in the cross section of cast ingot is less than the free shrinkage mass observed by using a confocal laser scanning microscope.

Abstract: It is not difficult to prepare self-compacting concrete (SCC) in laboratory now. The problem researchers faced is how SCC can be popularized in civil engineering. A modified densification mixture design algorithm (DMDA) is used in this study to prepare the control mixture. And on the basis of the system analysis for exist studies, 6 factors are chosen as experimental factor and 25 experiments are designed by orthogonal design experiment method. The results analysis indicates that only 3 factors are significant on SCC and their recommend value is obtained respectively. It may shed light on the application of SCC.

Abstract: The annealing process of 800MPa grade hot dip galvanized DP steel was simulated on Gleeble-1500 thermo-mechanical simulator. The recovery and recrystallization of ferrite and the formation of austenite during the continuous heating process were studied in this paper. The results show that the fine equiaxed recrystallized nucleus started emerging nearby grain boundaries of deformed ferrites when the heating temperature was 630°C. With the increase of temperature, the recrystallized grain began to grow up, some new crystallized nucleus formed in other places with high stored energy of deformation. when the heating temperature was 690°C, the recrystallization process was basically finished, the deformed microstructure had been replaced by equiaxed ferrite grains. When the heating temperature was 730°C, the austenite nucleated on the carbide particles of the ferrite grain boundaries in the original pearlite area mainly. Some austenite also nucleated on the ferrite grain boundaries or the carbide particles within the ferrite grain. When the temperature was 750°C, the austenite began to grow along and parallel to ferrite grain boundaries.

Abstract: Deep drawing processes are widely utilized in mechanical industries for producing several typologies of products ranging from computer industry to automotive components, from house products to furniture products. The goal of this study is to verify experimentally the warm deep drawing process assisted with hydraulic counter pressure as a suitable alternative to conventional deep drawing as a means for producing defect-free sheet metal parts. Using specific process parameters like blank holding pressure, blank diameter and temperature, wrinkle-free parts with deeper draws could be produced. An enhancement in LDR from 2.06 in conventional deep drawing to 2.16 in warm deep drawing with a lower blank holding pressure is achieved. The lower blank holding pressure leads to lesser thickness variation in the product this reducing the occurrence of fracture at the punch radius. The hydraulic counter pressure helps in reduction of wrinkles and enhancement of formability. The improvement in the LDR was observed around 200°C for warm deep drawing. This process reduces the forming restrictions of many materials, can produce complicated shapes and reduces the costs of material and die.

Abstract: AZ31 alloy sheets were produced by twin-roll casting (TRC) and sequential hot rolling. Uniaxial tensile tests were used to evaluate the deformation properties of the AZ31 alloy at a strain rate of 7×10^-4s^-1 and a temperature range from room temperature to 400°C. The microstructure evolution and fracture behaviour were observed by optical microscopy and scanning electronic microscope. The results show that the elongation of the AZ31 alloy increases with increasing temperature at a strain rate of 7×10^-4s^-1. The AZ31 alloy begins to exhibit superplasticity at 300°C. The elongation of 497.8% is achieved at 400°C. The deformation of the AZ31 alloy at low temperature is controlled by dislocation motion, and with increasing temperature (above 300°C), grain boundary sliding (GBS) begins to play a dominant role during superplastic deformation.

Abstract: In order to improve toughness of the weld heat affected zone (HAZ) of ultra-fine grained (UFG) steel, a thermal simulation procedure of Fe-Mn-Si UFG steels with different Al addition was conducted and the corresponding microstructure was characterized and investigated. The results indicate that the maximum value on driving force of nucleation is ultra-fine grain steel with wtAl=0.6%, it has been explained in Nucleation kinetics that the grains are fine in UFG2. On the other hand, the bainite ferrite growth orientation has been increased. The toughness was remarkably enhanced in the steel welded heat affected zone. The formation of strie retained austenite and grain refinement of bainite ferrite in Fe-Mn-Si UFG steels with Al additions results in the increasing toughness of weld HAZ.

Abstract: The mouthparts of female mosquitoes have evolved to form a special proboscis, a natural biomicroelectromechanical system, which is used for painlessly penetrating human skin and sucking blood. The structure of the mosquito fascicle is observed using a scanning electron microscope, and the mechanical property of the labrum and maxillae, two of the most important parts of the mosquito’s fascicle is studied. The micronano structure and the special biomaterials of the mosquito’s proboscis make the mosquito penetrate easily into human skin with a surprising low force, which is measured to be only tens of micro-Newton. Our obtained results are helpful for the optimum design of the microneedles and transdermal drug delivery system.

Abstract: Stress-induced melt activation (SIMA) has a certain advantage during the preparation of semi-solid billet of Mg alloy. However, Equal-Channel Angular Pressing (ECAP) only can produce small billet by several channels to achieve large equivalent strain. To conquer this problem, the forward extrusion/(ECAP) method, a new process for preparing semi-solid Mg alloy was proposed. And the feasibility of forward extrusion/ECAP was analyzed. This new method simplified the processing procedure for providing commercial semisolid billets of Mg alloy. The experimental dies and experimental procedure were designed. The effect of extrusion ratio and equivalent strain on the microstructure of semisolid Mg alloy was investigated. It was found that when the extrusion ratio was larger than 10, the semisolid microstructure is refined, with increasing extrusion ratio, the microstructure is refined further.

Abstract: The tensile process of 800MPa grade dual-phase steel was observed in-situ by SEM. The initiation and propagation of crack in dual-phase steel, the initiation of micro-pores, the deformation behavior of ferrite and martensite were analyzed in this paper. The results show that the main crack goes across the soft ferrite and around the hard martensite during its propagation in the beginning. When the applied stress is small, the micro-pores are easy to form inside the ferrite grain or on the interface of ferrite and martensite. The micro-pores can also form in the fracture site of martensite with the increase of applied stress. The fracture morphology of the dual-phase steel is dimple and the formation of fracture belongs to plastic fracture.