Advanced Materials Research Vols. 634-638

Abstract: In order to solve the problem of rivet head tending to crack in riveting, the effect of die forms on TA1 rivet deformation and microstructure was investigated by experimental method from macro and micro aspects in electromagnetic riveting. The results show that rivet material axial and radial flow can be controlled using different die forms, and thus the distribution of adiabatic shear band and grains in two sides of that in formed rivet head can be changed. With flat head die, severe axial and radial flows result in the nonuniform deformation and crack is prone to produced in rivet head. The adiabatic shear band of rivet head is obvious and grains in both sides of that deform severely. Material radial flows of rivet head are well constrained by spherical and 400 head die. The deformations are relatively uniform and the adiabatic shear bands are not obvious. It is an effective way to avoid crack formation and improve riveting quality using different die forms.

Abstract: Surface quality including residual stresses and surface roughness due to turning operations in Inconel 718 were studied as a function of cutting speed, feed rate and depth of cut. By means of X-ray radiation diffraction method, the influence of cutting parameters on residual stress was investigated. The results show that dry cutting of Inconel 718 resulted in predominantly tensile residual stresses at the machined surface and the surface roughness increased with the increase of cutting parameters.The effects of the cutting parameters on surface integrity are investigated while employing the range analysis. From these results it was possible to select a combination of cutting speed, feed rate and depth of cut that generate favorable surface characteristics.

Abstract: During plastic deformation of materials, part of the plastic work is converted into heat, and the temperature field will be changed, this phenomenon is well known as thermoplastic effect. Based on the analysis of thermoplastic effect, the surface temperature of Q235 steel during quasi-static tensile tests was measured by using an infrared camera, and the surface temperature field and it versus time for different strain rate were obtained. A numerical procedure was devised to model the thermoplastic effect during the tensile tests by using ANSYS software. The results showed that, the heat loss during deformation process will be smaller as the strain rate increase, and the temperature increase on the specimen surface generated by the plastic deformation will be higher. The simulation results matched well with the experiment results showed that it was a good way to analyse the thermoplastic effect by the commercial finite element software.

Abstract: The purpose of present paper is to fabricate tungsten rods with diameter of 200 μm to micro-pin electrodes, which have small conical angle and high aspect ratio, by the use of electrochemical machining process. The influence of working parameters, such as: applied voltage, electrolyte concentration, anode depth, and drawing speed on the machining process is investigated. Experimental results show that the applied voltage and electrolyte concentrate will affect the surface precision as the machining current is small than the limiting current. The anode immersed depth combined with a suitable drawing velocity has a significant effect on the conical angle (conicity) and aspect ratio.

Abstract: Thermo-mechanical experiments were carried out to study the effect of deformation speed and temperature on the behaviour of a non-quenched and tempered steel during hot forging. And an effective method for correction of friction was used to amend the tested flow stress, Meanwhile, the constitutive equations of flow stress-strain for TL1438 steel during hot forming was established based on the amended flow stress and hyperbolic sine which includes Zener-Hollomon parameter, and related parameters of TL1438 during hot forming was obtained by analyzing the data.

Abstract: On account of the self-excited vibration in No. 5 stand of 1420 cold rolling mill, the relationship between rolling lubrications and self-excited vibration of rolling mill was theoretically studied. The self-excited vibration in No.5 stand of the mill was restrained by optimizing the lubrication technical parameters, and the critical stabilized rolling speed was increased from650 m/min to above 900m/min. The important problem disturbing the mill was accordingly resolved.

Abstract: The forming process of automobile trunk side panel was investigated, using numerical simulation technology, to acquire the feasible process parameters and improve the formability of the product. With the technology, the manufacturability working procedures and drawing process parameters of the product were analyzed, calculated and simulated to achieve optimum formability characteristics. The method effectively lowers the probability of springback, wrinkling and thickness reduction, and shortens design cycle and cost. Based on the simulation results including forming limit diagram and thickness distribution diagram, the feasible process parameters are determined.

Abstract: The assumption of uniform stress in a test specimen is fundamental to SHPB test technique. In the present paper, a numerical simulation of wave propagation in SHPB is performed to validate the assumption. A one-dimensional model based on CSPM is firstly developed. Then the wave propagations in SHPB with various area ratios of bar/specimen are simulated. The results show that the condition of stress uniformity is not satisfied, especially at the beginning of wave propagation. For the large area specimen, the stress tends to be uniform. While for the small area specimen, the non-uniformity of stress is more apparent.

Abstract: The AuSn20 (mass fraction) solder was prepared by laminate rolling-annealing method, the AuSn20/Ni solder joints were prepared by the reflow process. The effects of the aging times and temperatures on the microstructure and shear strength of the AuSn20/Ni joints were investigated by the scanning electron microscope (SEM) with an energy dispersive X-ray (EDX). The results show that, the AuSn20 solder is composed of lamellar ζ-Au5Sn and δ-AuSn phases after preparing and the melting point approximates to the eutectic temperature of Au-20Sn alloy. A eutectic ζ-Au5Sn+δ-AuSn microstructure forms in the solder matrix and hexagon (Ni,Au)3Sn2 intermetallics nuclear at the as-reflowed joint. Then the AuSn20/Ni joint was aged at 150 and 200 °C for various times，and the thickness of the IMC layer at 150 °C changes few with the aging time increasing from 150 h to 1000 h, however, it grows rapidly at 200 °C.

Abstract: Viscous pressure forming(VPF) using a semi-solid, flowable, highly viscous and certain rate sensitive macromolecule polymer as the forming flexible-die is a good forming method for high strength, low plasticity, complex sheet metal parts. In this paper, the bulging process of aluminum alloy 2024 sheet is carried out by combining methods of experiments with numerical simulation. Influences of viscous medium properties on the geometry of bulging specimens, thickness distribution and the pressure field of viscous medium are analyzed, and the limit bulging heights of aluminum alloy 2024 sheets are obtained. The research results show that choosing viscous medium with high rate sensitivity in the forming process can increase the non-uniformity of viscous pressure field, improve the viscous pressure bulging property of aluminum alloy 2024 sheet, and ameliorate the distribution uniformity of wall thickness of bulging specimens.