Materials Science Forum Vols. 697-698

Abstract: To enhance the forming quality of pneumatic bulging for abnormity thin-wall pot and reduce such forming defects as severe wall thickness reduction and fold breaks. Based on numerical simulation, this article analyzes the impact of the friction factor, die radius of curvature, pot wall thickness and load pressure on the wall thickness reduction rate, maximum stress and axial contraction. The experiment result is consistent with the numerical simulation. The research results have greater practical value to process optimization and process control.

Abstract: In this paper, the dissolution mechanism of copper weld brazing has been researched. The thickness losses of Cu foil in contact with molten Cu-P and Cu-Ag binary alloys at different temperatures have been studied. And the dissolution rate constants in both alloys is calculated and exists following relation: k_Cu-P (T)=10k_Cu-Ag (T), which explains the special phenomenon that the dissolving amount of copper in Cu-P liquid alloys is larger than that in Cu-Ag liquid alloys by using weld brazing technology. The dissolution rate of copper in filler metals is the main reason to realize weld brazing. It can be concluded that element P is indispensable in filler metals as the function of accelerating dissolution during weld brazing.

Abstract: Nowadays, the tailor-welded blanks (TWBs) technology has been developing very rapidly in China. The quality of tailor-welded blanks becomes more and more important for the stable manufacturing of automotive panels. therefore, it’s very necessary to find out the key factors that influence the forming performance of tailor-welded blanks. This paper experimentally studies the effect of weld line direction on drawing performance. The tailor-welded blanks with the same material pair were used in the experiment, in which the weld line is straight and forms a certain angle with drawing force. The drawing tests were done with the different angles and values of relative position. The results show that the forming performance is related to the relative position of weld line and the angle between weld line and drawing force.

Abstract: Surface-strengthening treatment was performed on the welded joints and base material specimens of AISI304 austenitic stainless steel using ultrasonic peening treatment. Stress-corrosion test in a 42% boiling magnesium chloride solution were conducted with treated and untreated specimens. Four-point loaded specimens were employed in the stress-corrosion test. Residual stress in the surface layer of the specimens was analyzed with an x-ray stress analyzer before the stress corrosion test. The microstructure of the specimens was observed by a scanning electron microscope after the stress corrosion test. The state of stress in the surface layer of the specimens affected by the ultrasonic peening treatment was analyzed. The stress corrosion cracking behavior was studied by observing the corrosion fractographs. The results showed that the stress corrosion resistance of the welded joint and base material specimens was remarkably improved because of the compressive residual stress employed by the ultrasonic peening treatment. Fracture modes were of the same kinds in the treated and untreated specimens.

Abstract: The new welding material – ERCuTi alloys filler metals were developed specially for gas tungsten arc welding (GTAW) of copper. The hot cracking in welding copper is inhibited completely as the addition of de-oxidant element Ti in copper welding material. The degree of addition of Ti (2-4wt%) is critical when the susceptibility of cracking is to be suppressed. If the level is allowed to exceed 4wt%, more low-melting point eutectics (β-TiCu₄ and TiCu₂) will be formed in the welds, and cracking susceptibility will be increased again. Results of mechanical properties tests show that although adding Ti increases the hardness and strength of the weld compared to the base metal, the impact ductility and the plastic properties are not decreased significantly.

Abstract: Conceptual design method for the upper beam of the press is proposed. Based on the technical parameters (nominal load and tablesize) and press structural scheme (number and layout of the hydraulic cylinder), simplified mechanical model of upper beam is established and then the conceptual design model is derived. According to the model, conceptual prototype with equivalent moment of inertia of the cross section is achieved. The structure prototype of upper beam is then obtained based on the conceptual prototype by introducing the design rules and experience and solving an optimization model. The method is applied to the structure prototype design of upper beam of a 100MN hydraulic press.

Abstract: Powder forging combines powder metallurgy and forging technology, thus possess the advantages of both processes that result in both stronger and yet more versatile products with complicated geometry and arbitrary alloy compositions. For complete filling up, predicting the power requirement and final face width is an important feature of the powder forging process. In this paper, a finite element method is used to investigate the forging force, the final face width and the density variation of the spur gear powder forging process. In order to verify the FEM simulation results, the experimental data are compared with the results of the current simulation for the forging force and the final face width of spur gear. The influences of the parameters such as modules, number of teeth, the initial relative density, the ratio of the height to diameter of billet and friction factor on the forging force and the final face width of the billets are also examined.

Abstract: Determination of the stiffness specification is essential to subsequent structure design of a hydropress. Through the analysis of the press-die-workpiece system, it is found that the forming precision of the workpiece is significantly affected by the deflection of the lower beam of press frame. According to this finding, a mapping model between the forming precision of the workpiece and the stiffness of the lower beam is established. With this mapping model, the forming precision of the workpiece can be mapped into the stiffness requirement of the lower beam to form the stiffness specification of the hydropress frame.

Abstract: A new comparative propagation property parameter CP suitable to judge the propagation of the interface crack in the cladding part is proposed. The propagation criterion for the crack inclined across the interface is established. The theoretical research on the CP_xA and CP_xB of this interface crack propagating in the clad and substrate separately is carried out. The propagation law of the interface crack in the cermet cladding part is investigated with an example. The research results show that, within the ranges of the studied parameters, CP_xA is bigger than CP_xB, and that the crack initially propagates in the clad.

Abstract: The paper reports a comparative study of the tribological properties of the most employed hard coatings like TiN, TiAlN and CrAlN. Ball-on-disc wear tests were performed on the CETR UMT-2 test system against Si₃N₄ balls with a relatively high speed of 100m/min. The coating character and test results were obtained through SEM, XRD and Wyko surface profilometer. The results are as follows: The friction coefficients of the three coatings are relatively high because of the superabundant wear debris during tests. The wear behaviour and wear tracks exist distinct differences for different coatings. As for wear rates, the sequence of three coatings is TiN>TiAlN>CrAlN, the combination property of CrAlN is the best.