Plastic deformation regularity of tailor-welded tube hydroforming

13-19To reveal the deformation characteristics and influence of dissimilar thickness on hydro-bugling of tailor-welded tube (TWT), FEA, experiments and mechanics analysis are conducted. The effects of length ratio, weld-seam movement and work-hardening on deformation compatibility are analyzed. It indicates that the plastic deformation occurs first at the middle zone of the thinner tube, and then extends to the thicker tube crossing the weld-seam. The expansion occurring on the two parts with dissimilar thickness is non-uniform, higher the length ratio and higher the deformation compatibility. Stress-strain analysis reveals that though the whole TWT suffers biaxial tensile stresses and the biaxial elongation occurs in the thinner tube, axial compressive strain occurs in the thicker tube. It is concluded that the mechanism for improving the deformation compatibility is to induce the deformation in the thicker tube by enhancing the bulging pressure needed for the thinner tube through changing the stress state of the thinner tube and flowing stress. Weld-seam movement happens during tailor-welded tube hydroforming, which induces uneven distribution of axial strain and thinning ratio in the TWT

A comparative study on phosphate removal from water using <italic toggle="yes">Phragmites australis</italic> biochars loaded with different metal oxides

Metal oxide-loaded biochars are a promising material to remove phosphate from polluted water to ultra-low concentrations. To facilitate preparing the metal oxide-loaded biochar with the best phosphate adsorption performance, five biochars loaded with Al, Ca, Fe, La and Mg oxides, respectively (Al-BC, Ca-BC, Fe-BC, La-BC and Mg-BC) were produced using Phragmites australis pretreated with 0.1 mol AlCl3, CaCl2, FeCl3, LaCl3 and MgCl2, respectively, characterized, and phosphate adsorption kinetics and isotherms of the biochars were determined. The maximum phosphate adsorption capacities (Qm) of the biochars ranked as Al-BC (219.87 mg g−1) > Mg-BC (112.45 mg g−1) > Ca-BC (81.46 mg g−1) > Fe-BC (46.61 mg g−1) > La-BC (38.93 mg g−1). The time to reach the adsorption equilibrium ranked as La-BC (1 h) < Ca-BC (12 h) < Mg-BC (24 h) = Fe-BC (24 h) <Al-BC (greater than 72 h). Qm of Ca-BC, Fe-BC, La-BC and Mg-BC depend on the molar content of metals in the biochars. The small phosphate adsorption rate of Al-BC is due to the slow intra-particle diffusion of phosphate attributed to the undeveloped porosity and dispersed distribution of AlOOH crystals on the Al-BC surface. Mg-BC is suggested for phosphate removal from water considering adsorption rate and capacity. Al-BC is applicable when a long contact time is allowed, e.g. as a capping material to immobilize phosphate in lake sediments

Microstructure Characterization of Reversed Transformation in Cryogenically Rolled 22MnB5

Hot stamping is a well-known process to produce structural automotive parts with an excellent strength-to-weight ratio. However, this process is more expensive due to the lower energy efficiency and operating cost of the traditional roller-hearth furnace. Additionally, lower ductility and toughness are commonly recognized as the main disadvantages of the current hot stamped ultra-high-strength parts. Refinement of austenite grains could be a profitable way to improve the strength of hot stamped parts. In this work, the evolution of reversed transformation in asymmetrically cryogenically rolled samples was studied in order to control the austenite. Thermomechanical simulation and heat treatment in the salt bath were used to investigate the reversed transformation process, and the typical microstructures were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Compared with symmetric prerolling, ferrite recrystallization could be remarkably inhibited by asymmetric rolling at the liquid nitrogen temperature (LNT) during the reheating process. Additionally, the nucleation of the austenite inner grains can also be promoted and the dynamics of the reversed transformation accelerated by asymmetric prerolling. Such phenomena might be very useful to refine the parent austenite grains before press hardening and enhance the new hot stamping strategy by partial fast reheating

Hot Deformation Behavior, Processing Maps and Microstructural Evolution of the Mg-2.5Nd-0.5Zn-0.5Zr Alloy

Isothermal hot compression experiments were conducted on Mg-2.5Nd-0.5Zn-0.5Zr alloy to investigate hot deformation behavior at the temperature range of 573–773 K and the strain rate range of 0.001 s−1–10 s−1 using a Gleeble-3500D thermomechanical simulator. The results showed that the rheological curve showed a typical work hardening stage, and there were three different stages: work hardening, transition and steady state. A strain compensation constitutive model was established to predict the flow stress of the Mg-2.5Nd-0.5Zn-0.5Zr alloy, and the results proved that it had high predictability. The main deformation mechanism of the Mg-2.5Nd-0.5Zn-0.5Zr alloy was dislocation climbing. The processing maps were established to distinguish the unstable region from the working region. The maps showed that the instability generally occurred at high strain rates and low temperatures, and the common forms of instability were cracking and flow localization. The optimum machining range of the alloy was determined to be 592–773 K and 0.001–0.217 s−1. With the increase in deformation temperature, the grain size of the alloy grew slowly at the 573–673 K temperature range and rapidly at the 673–773 K temperature range