Applied Mechanics and Materials Vols. 217-219

Abstract: In this study, the magnesium alloys AZ31, ZK10, and ZEK100 are investigated through microstructure, texture, and tensile test. The sheets were hot rolled, and different results were found for different chemical compositions. The contained elements affected the grain size, shear band, twins, and intensity of the basal texture of the magnesium alloy. Thus, if a magnesium sheet had finer grains and a weak (00.1) texture because of its chemical composition, it had the most favorable formability.

Abstract: Experiments have been carried out to investigate the ultimate behaviors of single shear bolted connections assembled with four bolts (2 rows×2 columns bolt arrangement) under shear and aluminum alloy plate. End distance parallel to the direction of applied load is considered as main variables. All specimens failed in block shear fracture and curling (out of plane deformation) in the direction parallel to plate thickness was also observed for some bolted connections with a long end distance. The curling led to sudden ultimate strength reduction and test strength was compared with the block shear strength predicted by current design specifications.

Abstract: The fatigue fractography and surface of A7075 aluminum alloy was investigated by means of optical microscope, scanning electron microscope and technology of metallurgic replica. The results show that the fatigue crack generally initiated in the surface or near the surface of the sample area, such as hole and inclusion. The crack propagation regions under high stress amplitude was characterized by furrow and hollow, and obviously presented fine ripple vein. While lots of fatigue striations and sidesteps with the holes and secondary cracks generated in the crack propagation regions of low stress amplitude. Fatigue transient breaking area is a mixed fracture of brittle and ductile fracture. In the fatigue crack propagation stage, with the increasing of cycle times, secondary cracks gradually merged into primary crack on the path of crack propagation. The dislocation of crack tip,grain boundaries and different grain orientations have great influence on the path of crack growth, which can make cracks bending.

Abstract: Bimetal of high-tin aluminum alloy and steel was fabricated by cold-rolling process; microstructure, bonding strength and bonding mechanism for bonding interface of the bimetal were investigated under cold-rolling and recrystallization annealing state, respectively. Experimental results indicate that tin phase of bimetal in cold-rolling state shows a belt type distribution, however, it, in recrystallization annealing state, is uniformly distributed just like some “isolated islands”. A well bonding interface, between layers of high–tin aluminum alloy and pure aluminum, can be obtained, and it is difficult to distinguish one layer from the other; but the interface, between layers of low-carbon steel back and pure aluminum, is clear and uneven. And meanwhile, bonding mechanism of bimetal interface, in cold-rolling state, is cold pressure welding and mechanical occluding, But it, in recrystallization annealing state, is cold pressure welding, mechanical occluding, and metallurgic bonding. After recrystallization annealing, at 350°C for 2h,the bonding strength of bimetal approaches to 92.4MPa, which is about 26% higher than that of cold-rolling state.

Abstract: The corrosion behavior of ZnAl27 alloys in 35g/L NaCl solution has been studied by electrochemical and immersion corrosion tests. The effects of Cu and Sb on the Tafel curves, electrochemical parameters of free corrosion potential, linear polarisation resistance (LPR) and free corrosion current, of the ZnAl27 alloy have been investigated. The surface morphologies of the alloy after immersion corrosion tests have been observed through SEM. The results indicate that addition of proper Cu can improve its corrosion resistance of the alloy, or the free corrosion potential the corrosion current shift towards the positive and negative,respectively. However, excessive addition of Cu can deteriorate the corrosion resistance of the alloy. On the other hand, the corrosion resistance of the ZnAl27 alloy decreases with the increasing of Sb content.

Abstract: Using the ultrasonic fatigue testing technique, specimens of Q345 bridge steel with two types of shape (round and plate) were performed in ambient air at room temperature with a stress ratio of R=-1. The very long life fatigue property of Q345 was studied and the initiation mechanisms of fatigue cracks were investigated and analyzed with SEM. The results show that the two types of specimen present different S-N curve characteristics in the region of 105-109 cycles. The S-N curve of round specimens shows continuously decreasing tendency, while the S-N curve of plate specimens has a steep decreasing step and an asymptotic horizontal one. The fatigue strength of round specimen is higher than that of plate specimen. Fatigue failure initiates from the surface before 107cycles with high stess level while at internal inclusion in the very long life fatigue regime.

Abstract: The new type SFG HSS (super fine grain, high strength steel sheet) has been developed by adding solid-solution strengthening elements to conventional IF steel such as Si, Mn. The precipitation behavior of the second phase particles was observed and studied by a carbon extraction replica technique used transmission electron microscopy (TEM). The shape of the small second particles is similar to spherical and ellipse, the sizes of which are 10~30nm. It is seen that the particles are dispersed on the matrix. The precipitate composition of small particles is Nb (CN) and the precipitate composition of large particles is NbC examined by energy dispersive X-ray (EDX). It is noted that the yield strength is low as well as the tensile strength is high by the PFZ which is free of precipitate called precipitated free zone on the one side of the grain boundary. The results of microstructure shows that the second phase particles pinned on grain boundary not only can inhibit the grain growth, but also the grain can be fined.

Abstract: Different process steps of the workpiece have different effects on the microstructure in the multi-stage forging. In this study, the effect of four different process steps of steering arm on microstructure was studied by FEM. Results have showed that upsetting is beneficial to refine the microstructure as well as finish forging. Especially drawing can make the distribution of microstructure homogeneous while bending has less effect on it. The already-designed forging process for steering arm was reasonable based on the simulation. Eventually, the grain size level of the steering arm was tested as 6.5 based on the conventional standard.

Abstract: The corrosion behaviors of a low carbon bainite steel in three atmosphere environments simulated by corresponding solutions were investigated in this accelerated test. It is found that the corrosion rate of the low carbon bainite steel is lower than that of the commercial weathering steel 09CuPCrNi in all the three solutions. The corrosion rates of the bainite steel in the three solutions are also different, which is most serious in the solution containing both chloride and sulfide. There is no serious selective corrosion, for the corrosion has little effect on the mechanical property of the bainite steel. Corrosion rates are relation to the amount of Cu and Cr enrichment in rust layers, which are well corresponding to the specific surface area values of corrosion products. Inhibit effect can be found in the solution containing both chloride and sulfide.

Abstract: This paper firstly analyzed the desulfurization mechanism of magnesium compound desulfurizer and compound desulfurizer. It is thought that the compound desulfurizer which contains a certain amount of magnesium is better used than the one does not contain. There is also the statistical analysis about these two type desulfurizers in practical Producing. The practical application of contrast verifies the theoretical analysis.The magnesium compound desulfurizer has better performance used in the effect of desulfurization, the consumption of desulfurizer, iron loss, process-time, the loss of hot metal temperature and the lance life than compound desulfurizer.