Materials Science Forum Vols. 628-629

Abstract: Microstructure and impact properties of slow injection A356 die castings with local pressurization have been investigated. The microstructure in the casting different regions were analyzed and compared. The casting impact absorbed energy varies from 1.17 to 2.35J, and is higher than that of other pressure die casting process. Furthermore, fracture mechanisms of different regions in castings are discussed. The results show that, the impact absorbed energy decreases with increase in SDAS. Also significant fluctuations of the impact properties in the thick-walled and local pressurization regions are found.

Abstract: Microstructure and tensile properties of as-cast and T6-treated Al-4%Cu-3%Si alloy with different applied solidification pressures were investigated. The pressure has significant effect on the formed microstructure. It is observed that as the pressures increase, the porosities were removed, and the size and the secondary dendrite arm spacing of primary α-Al grains decreased evidently, and the morphology of eutectic Si particles changed from long acicular to small granular type. Hence, the tensile properties of the alloy were improved. The research has shown that the aspect ratio (A.R.) of the Si particles decreased after the solution and aging treatment. The A.R of the Si particles in the alloys with applied solidification pressure decreased more remarkably and this indicated that the Si particles can be more prone to be dissolved into α-Al matrix. Thus, the increase of the elongation was achieved.

Abstract: In this paper, based on the CAE technology for MIM and fractional factorial design method, the simulation for the filling process was executed in different process conditions by the Moldflow software. And then it was realized that the extent of the effects of the single factor and pairwise interaction between the process parameters on quality of green parts were forecasted. According to that, the relationships of pressure, velocity and time and their optimal combination were researched by the experiments using a FC-80 plastic-Injection-Moulding machine. The experimental results suggested that the pressure, velocity and time have a obvious pairwise interaction which can have more effect on the product than single factor. It was shown that there was a good consistency between the numerical simulation and experiment. The CAE technique and the experiments are combined to optimize the process conditions and improve the part quality automatically by using smaller number of experiments.

Abstract: To decrease weight and increase fuel efficiency, an Al-Cu-Mn alloy frame part with vertical indirect squeeze casting process was fabricated to replace original parts with spheroidal graphite iron, which is used in a special vehicle. Mold filling of the frame with pouring temperature of 700°C and injection velocity of 0.03m/s was simulated. According to the results vents and overflows were designed and the dies were produced with H13 steel. Furthermore, the casting trial producing was conducted. Cross sections of the castings were checked. A number of specimens were obtained from different parts of the castings to evaluate microstructure, and both high dense and fine grain microstructures were found in the specimens. Mechanical properties of the tensile samples with T5 heat treatment were measured, and the average tensile strength and elongation were 387 MPa and 8.8%, respectively.

Abstract: Research was conducted for stretching with horizontal V-shaped anvils (HVA) and common flat anvils (FA). The forgoing research gave the simulation results of single blowing during stretching, and did not pay attention to the influence of the deformation, resulting from the previous blowing, upon the next blowing. ANSYS software is adopted to simulate the through-continuous blowing of HVA and FA forging methods. The transversal stress distribution along the horizontal central axis on the crosssection of the stretched forging is analyzed. The simulation results show that during the stretching with flat anvils, when the ratio of the flat anvil width to the billet height is 1.0 and the ratio of the billet width to the billet height is 0.5, the transversal stress is tensile all the time, and increases as the stretching goes. On the contrary, during the HVA stretching, the stress is compressive and its absolute value increases gradually. The results show that the HVA stretching method is prior to the FA stretching method in the controlling of transversal stress. Conducted physical experiment verified the results.

Abstract: Based on the finite element simulation of tube-hydroforming process with pulsating internal pressure, the influence of the pressure increment p and the time increment t of the pulsating pressure upon the formability of a tube have been investigated by analyzing and comparing the four formability indicators such as thickness distribution, die-filling ability, wall thickness uniformity and potential fracturing. A new indicator f is proposed to estimate the formability of a tube on the basis of the finite element analysis (FEA). The results show that: the indicator f can reasonably reflect the combination formability of a tube in hydroforming including the die-filling ability, the wall-thickness uniformity and the deformation reliability; the p and t values have different influence on the four formability indicators as mentioned above; the smaller the p and t values or the more the internal pressure pulsates during the forming process, the better the combination formability of the tube would be.

Abstract: A novel metal plastic forming technology, cold rotary forging with double symmetry rolls, is presented on the basis of cold rotary forging with single roll. A reasonable 3D elastic-plastic dynamic explicit FE model of cold rotary forging with double symmetry rolls is developed under the ABAQUS software environment. Through simulation, the distributions and histories of different field-variables such as stress, strain and force and power parameters are investigated in detail. The research results not only provide an advanced and innovative technology for metal plastic forming, but also help to better understand cold rotary forging with double symmetry rolls.

Abstract: In the current study, a 3D elastic-plastic FE model for rolling of large-scale aluminum ring on high-voltage switch is developed under the ABAQUS software environment. Based on the 3D FE model, lots of simulation calculations have been carried out. Through simulation, the internal energy and kinetic energy histories during the process are obtained and the optimal mass scaling factor is determined reasonably. Additionally, the stress and stain field-variables and metal flow laws have also been analyzed in detail. The ring rolling experiment was carried out and the experimental results are in good agreement with the simulation ones. The research results provide powerful guidelines for the rolling process design of large-scale aluminum ring on high-voltage switch.

Abstract: In order to investigate the nucleation and growth of after-forging static recrystallization of low-pressure rotor steel 26Cr2Ni4MoV, the thermo-torsion experiment was conducted at 900°C,1000°C and 1100°C, respectively. The outer deformation of the used specimens was 0.21. The specimens were kept under a certain temperature for different periods. Results show that the recrystallization grain grew slowly at 900°C and the grain size became even after 30 minutes. The sizes of most grains were almost constant and only several grains grew bigger after 60 minutes. When the specimens were kept at 1000°C and 1100°C for one minute, static recrystallization was completed and the grain size was even. The said research could provide theoretical base for the controlled forging and after-forging heat treatment.

Abstract: Numerical simulation and experiment of self-piercing riveting with solid rivet joining multi-layer aluminum sheets are carried out in this paper. The forming process of the riveting and the distribution of stress are analyzed, the results show that the simulation is consistent with the experiment. The results of experiment prove that the transition point of the cone-shaped head of the solid rivet, the size and position of groove affect directly the quality of riveting. The fillet at the transition point of the cone-shaped head of the solid rivet can decline the maximum stress of the rivet. When the distance between the center of groove and bottom of rivet is about three quarters of the bottom sheet thickness, the bottom sheet of self-piercing does not fall off. The self-piercing riveting with solid rivet joining multi-layer aluminum sheets is feasible.