Materials Science Forum Vols. 704-705

Abstract: Fine-blanking with negative clearance is a kind of fine blanking processes. The punch size of fine-blanking with negative clearance is larger than the die size. The paper does lots of simulations for the changes of blanking force in fine-blanking with negative clearance and common blanking by DEFORM software, and the blanking force curves are gained by these experiments. The changing principle of blanking force and internal material is obtained through the simulation and experiments. The result shows that simulation blanking force of AISI-1045 is lager than the actual blanking force. According to the curves derived from experiments, we can see that the maximum blanking force of fine-blanking with negative clearance is higher than common blanking force. Compared with fine-blanking with negative clearance, the common blanking force reduces faster after the blanking force reaches maximum value. The experiment result shows that the force of fine-blanking with negative clearance under a smaller blanking clearance is a bit bigger than the force of common blanking force, and the blanking quality of fine-blanking with negative clearance is much better than that of common blanking. Cracks can be closed effectively by the special squeeze forming in fine blanking with negative clearance. Then, the crack can not expand continuously, and the bonding force is enhanced. The squeeze forming can restrain intergranular deformation and reduce the damage. However, the stretch forming easily leads to the inner crack and defect of materials. By means of the analysis on experimental curves, the paper further studies the changing law of fine-blanking with negative clearance blanking force.

Abstract: Machining experiments of fine-blanking with negative clearance show that the blanking force is very different from ordinary blanking in different blanking stages. Studying on the blanking force size of fine-blanking with negative clearance in different blanking stages is a very important significance for studying die wear and analyzing the state of material stress-strain. Firstly, numerical simulation and stress state analysis of the fine-blanking with negative clearance are carried out, with DEFORM-metal forming finite element analysis software. Afterward the relationship curve of blanking force and stroke are measured, and the blanking force with different blanking stages of fine-blanking with negative clearance is analyzed by the simulation and the experiment. The analysis result shows that the simulation blanking force is bigger than the experimental result (error about 15%), but the blanking force variation tendency is accordant. while the punch pushes down within 0.1mm, the blanking force changes quickly. The metal sheet will enter into the state of plastic deformation after the blanking force reaching maximum value. Along with the punch continues to move down, the area of shear zone is decrescent so that the blanking force inches down, and the blanking force reaches a certain value in the place of blanking allowance value finally. With punch pushing the metal sheet to enter the plastic state and punch downward the place of the allowance value, the metal sheet sustained the big blanking force all the time as well as the deformation zone material keeps the plastic deformation. The research result provides theoretic reference and the experimental data for the practice application of fine-blanking with negative clearance, and has instructive significance and reference value to mould design.

Abstract: The effects of shielding gas and external longitudinal magnetic field on arc shape and weld quality of AZ31+1%Ce+1%Sb magnesium alloy TIG welding were investigated. The results show that a weld joint with a good appearance, few defects and enough penetration can be obtained under the protection of helium-argon gas mixture, especially when the helium ratio is about 50%. However, the weld quality is significantly decreased by adding additional CO₂ or N₂ in He-Ar gas mixture. The weld seam consisted of fine equiaxed grains which mostly grow in a certain direction were formed when a longitudinal magnetic field is added, due to its electromagnetic stirring in weld pool. The grains of weld seam formed under the alternating current longitudinal magnetic field are much finer than those under the direct current magnetic field. A weld joint with good formability and finer microstructure is obtained when the exciting voltage of AC longitudinal magnetic field is 20 V. The average microhardness of the corresponding weld joint is 68.5 HV0.1, and its average tensile strength is 220 MPa which is up to 88% of that of the base plate.

Abstract: In this paper a new technology for purification of molten aluminum, namely flux jet technology has been presented. The basic principle of this method is that the molten flux is forced to inject into the molten aluminum and create strong vortex and is uniformly mixed with the molten aluminum under the pressure differential. The flux and the molten aluminum will mix fully to contact each other. In this way, the inclusions in the aluminum will transfer into the flux because of the absorption of the flux to the inclusions. As the result, the molten aluminum will be purified. The experiments were carried out for A357 aluminum foundry alloy with the flux (40% NaCl, 30% KCl, 10% NaF and 20% Na₃AlF₆). The results show that after 3 cycles, the inclusion contents dramatically decreases from 1.61% to 0.333%, a decline rate of 79.4%; and hydrogen concentration decreased from 0.32ml/100gAl to 0.09ml/100gAl, with hydrogen removal rate being 72%.

Abstract: The impact specimens with different hydrogen contents were solution treated at 540±3°C for 12h; water quenched at 60-100°C; and aged at 165±1°C for 6h. The impact test was carried out at Roell450 pendulum impact testing machine. The impact test results show that the impact energy has strong relation with the hydrogen content. The total absorption energy increases with the increasing of hydrogen content. The crack propagation energy A_vp and present larger proportion than the initial crack energy A_vi in the total absorption energy A_v. The number of the pinholes increases and the pinholes turn from smaller irregular ones into sub-circular shape ones. The specimen with irregular sub-circular pinholes has larger K_I, and has more crack propagation resistance.

Abstract: Hydrogen is a harmful element in aluminum. How to accurately measure hydrogen content in molten aluminum alloy has been significant for improving the metallurgical qualities of aluminum products. Currently, Reduced Pressure Test (RPT) based on the famous Sievert’ law is the most commonly used method to measure the hydrogen in aluminum. However, due to the changes in solidification morphology of alloys under different solidification conditions, hydrogen will be closed more or less in the sample by the developed dendrites, which results in the dispersion of test results. According to the principle of solute redistribution, an improved reduced pressure technology under directional solidification was proposed in this paper. The solidification interface was pushed on along the single direction by controlling the temperature gradient of solid-liquid interface. Hydrogen is released in front of the solid-liquid interface through the solute redistribution. The result shows that the hydrogen content increases and the mean variance decreases with the increasing of the temperature gradients. The method was proved to be of higher accuracy.

Abstract: To research the tribological properties of micro-arc oxidized ceramic coating in extreme friction condition, ceramic coatings were tested with 1000# waterproof sand paper friction pair for the first time. The phase composition of ceramic coating was analyzed by X-ray diffraction (XRD).Micro structures of ceramic coating surface were observed by scanning electron microscopy (SEM). Friction coefficient of ceramic coating was measured by ball-on-disc wear tester with a 3 mm steel ball. Wear weight loss and wear rate of ceramic coating were measured and calculated by photoelectron balance. The results show that ceramic coatings in various roughnesses have different former wear rates and close wear rates at stable stage. Under water-lubricated condition, wear rate is as low as 0.2 mg/min to 0.3 mg/min. The antiwear behavior of ceramic coating is about 5.3 times compared to aluminium alloy at dry friction. While under water-lubricated condition, the antiwear behavior of ceramic coating improves about 94 times compared to aluminium alloy. The friction coefficient of loose layer is higher than compact layer at dry friction. And there are positive correlation between wear rate and surface roughness of ceramic coating. So it can be verified that compact layer has well antiwear behavior better than loose layer.

Abstract: It’s an important content to treat on the magnesium alloy surface for improving it’s abrasion performance and corrosion resistance in the field of surface engineering nowerdays. This research takes the AZ91D magnesium alloy and Aluminum as a substrate and powdered alloy respectively.It takes the laser surface modified technology as the method so that to enhance the corrosion resistance of the magnesium alloy surface.The optimization technological parameters are obtained by discussing the influence rule on laser power to corrosion resistance of AZ91D substrate and Mg-Al modified level.

Abstract: The surface integrity of NAK80 steel by grinding and electrical discharge machining (EDM) was studied in this paper. Microhardness, 3D topography and surface roughness of machined surface precipitation hardening layer were measured respectively. And the residual stress of the machined steel surface was measured with X-ray diffraction. Further experiments indicated that, compared with EDM, grinding method can obtain better surface integrity, and lower stress concentration sensitivity of NAK80 steel. But when machining the parts with complex shapes, EDM has the unparalleled advantages to grinding method.

Abstract: In allusion to the non-linear relation in key parameters (internal pressure, axial extrusion force, radial back force) of Three-way tube hydroforming process, forecast and optimization models are established based on genetic algorithms and back propagation algorithms. By using the capacity of non-linear mappings of Artifical Neural Network and the capacity of global optimization of Genetic Algorithms，and using dynaform Finite Element simulation software to get samples and check results, the models can forecast and optimize parameters of T tube hydroforming process. The original tube could be in any bore, length, and wall thickness of a certain range. The results show that by using these models, parameters’ matching test numbers could be reduced, and the quality of T tube is excellent.