Key Engineering Materials Vol. 837

Abstract: Resistance spot welding is an important technology widely used in manufacturing industry. It is a coupling process which involves thermal, electrical and mechanical physics fields. Due to the formation of weld nugget is transient and non-visible, the experimental analysis is difficult. In this paper, a thermal electrical-mechanical coupling technique is carried out by finite element method to study the effect of electrode strips on weld nugget formation and surface indentation under different processing parameters. Experimental and numerical analysis results show that the electrode strips can reduce the surface indentation depth effectively and is helpful to the formation of weld nugget.

Abstract: This study presents manufacturing cryogenic tanks for aerospace applications. Since most high strength aerospace alloys like titanium alloys and Al-Li alloys exhibit low formability due to low ductility and work hardening, superplastic forming technology is applied to manufacture hemispherical shapes. Superplasticity is the ability of materials to deform plastically to show very large amount of strains. Advantages of superplastic forming technology include its design flexibility, low tooling cost and short leading time to produce. In this study, various manufacturing processes, like superplastic forming, diffusion bonding, laser beam welding and friction stir welding, are applied to manufacture titanium and aluminum cryogenic tanks. Using these technologies in manufacturing process makes the aerospace components lighter and stiffer, with efficient energy and cost saving.

Abstract: This study presents manufacturing lightweight aerospace components by solid state joining technologies. The advantages of solid state joining are due to the lack of hot cracking from solidification, since there is no liquid phase involved in joining process. This produces a high quality joint as compared to that from conventional fusion welding process. In diffusion bonding process, two different surfaces are matched together at elevated temperature under a low pressure without macroscopic plastic deformation in the interface. In friction stir welding process, the rotating shoulder of the tool generates frictional heat on the surface. As the pin rotates it forces the plastic material to mix mechanically in the vicinity of the pin and produces a heavily deformed microstructure around the pin. In this study, solid state joining processes of diffusion bonding and friction welding, are applied to manufacture several launcher components with lightweight, efficient and cost saving.

Abstract: In view of the special requirements of rails to ensure the safe and stable operation of Railways in China, the formation characteristics of austenite grains in high carbon rail are revealed through industrial exploration, the process of industrial rail heating and rolling is simulated, innovative experimental research methods such as different heating and heat treatment are carried out on the actual rails in the laboratory. Transfer characteristics of austenite grain size, microstructures and key properties of high carbon rail during the process are also revealed. The results show that the austenite grain size of industrial produced U75V rail is about 9.0 grade. When the holding temperature is increased from 800 C to 1300 C, the austenite grain size of high carbon rail steel decreases, the austenite grain are gradually coarsened, and the tensile strength increases slightly. The tensile strength is affected by the heating temperature. With the increase of heating temperature, the elongation and impact toughness of high carbon rail decrease. The heating temperature of high carbon rail combined with austenite grain size shows that the heating temperature has a great influence on austenite grain size, and has the most obvious influence on the toughness of high carbon rail.

Abstract: An innovative study on the high strength of U shaped steel plate was carried out. Through the two different cooling systems of hot stamping die obtained the two U shaped steel plates, founding that the cooling rate of U shaped steel plate obtained by bath water cooling system in the die was significantly higher than the steel plate obtained by cooling pipe in the die system, and had a smaller temperature difference, Which is a good solution to the problem the cooling rate of blank decreases with the thickness of blank increasing and the blank had a large temperature difference for badly uniform temperature quenching. This system is also greatly shorten the quenching time and improve the production efficiency in hot forming process.

Abstract: Pulverized coal ash can be used as an additive to reduce corrosion on heating surface of biomass boiler. Biomass ash and pulverized coal ash were mixed and coated on the metal surface for experiment; the results showed that the corrosion rate of the metal decreases by adding pulverized coal ash. With the increase of additive content, the corrosion gradually reduces. The effect of different pulverized coal ash on corrosion is different, but as the proportion of pulverized coal ash increases, the effect tends to be close. When the molar content of (Si+Al)/(Na+K) is about 2 and the ratio of Si/Al is about 1, the pulverized coal ash additive works best.

Abstract: This paper focuses on the problems of ash deposition and corrosion caused by alkali metal chloride in biomass boiler. Kaolin, pulverized coal ash, silica fume, dolomite, limestone and bauxite are used as additives in this study, to investigate the degree of corrosion of four metal materials on biomass boiler. The results show that the corrosion rate of metal samples is significantly reduced after adding additives. Kaolin, pulverized coal ash, silica fume and bauxite show much obvious effect on corrosion inhibition. Corrosion resistance of four pipe metals: T91>15CrMoG>12CrMoVG>20G, in which the corrosion resistance of T91 is much better than the other three metals.

Abstract: Electrochemical preparation of binary alloy of Cu-Ni from acid sulphate bath containing citric acid using Potentiostatic method. The effects of alloy composition were monitored. Copper is widely used in industry, because of its good thermal conductivity and mechanical characteristics. The accumulation of Nickel & Manganese to Copper enhances itspotency, vigour, toughness, endurance, permanence&also the corrosion-resistanceas well asattrition. Corrosion controls of metal have technical environmental and economical importance. The Cu-Ni-Mn alloyswere used commercially for decorative and protective purpose and also in marine applications. The thin film coating characterized by SEM, EDAX and XRD shows morphological, compositional and structural properties of alloys respectively.

Abstract: In order to understand the influence of the tensile stress on the corrosion of reinforcement bars in civil engineering, the reinforcement bars specimens were put into the liquid corrosion tank made of hydrochloric acid and distilled water by applying the tension stress on the reinforcing frame to carry out rapid corrosion. The corrosion of reinforcement bars under different tension stresses was tested by using electrochemical polarization method. The metallographic examination of reinforcement bars was carried out through the section of reinforcement bars. The corrosion mechanism of the stressed reinforcement bar was tested and analyzed. It can be known from the experimental study: First in the same corrosion condition, the larger the tensile stress is, the faster the corrosion of steel bar will be; Second corrosion current density or corrosion rate are index for evaluating corrosion rate of reinforcement bars with different tensile stresses. Corrosion potential can not be used as an index for evaluating corrosion rate of reinforcement bars with different tensile stresses; Third intercrystalline corrosion occurs inside the reinforcement bar due to micro-defects after rolling and moulding, which directly affects the mechanical properties of reinforcement bar.

Abstract: Limestone and slag blended concrete is an innovative concrete which belongs to the family of limestone calcined clay cement (LC3) concrete. Strength is an important property of structural concrete. This study shows artificial neural networks (ANN) and gene expression programming (GEP) models for predicting strength development of limestone and slag blended concrete. ANN model consists of an input layer, a hidden layer, and output layer. GEP model consists of the sum of three expression trees. The input parameters of ANN and GEP models are mixtures and ages. The output parameter is a strength. The correlation coefficients of ANN and GEP model are 0.99 and 0.98, respectively. Both ANN and GEP model can produce prediction results of the strength of ternary blended concrete reliably.