Materials Science Forum Vols. 773-774

Abstract: The press bonding experiments of Ti-17 alloy were conducted at the bonding temperatures ranging from 730°C to 880°C, a bonding pressure of 20 MPa and a bonding time of 15 min. The results show that the plastic deformation is a main bonding mechanism in the press bonding of Ti-17 alloy. With an increase in bonding temperature, the plastic deformation enhances and voids in the bonding interface disappear gradually. The grain boundary migration and grain growth spanning the bonding interface start to activate, which is of benefit to obtaining a sound bond. The failure mode of bonding interface changes from a brittle fracture to a ductile fracture. However, a higher bonding temperature will induce grain coarsening which result in strength decreasing. The SEM of lap shear fracture surfaces indicates that a bond with superior strength can be obtained at a bonding temperature of 860°C.

Abstract: The effects of heating rate, heating temperature and cooling rate on the microstructures and mechanical properties of four pipeline steels for high frequency electric resistance welded pipe have been studied by using a Gleeble-3500 thermo-mechanical simulator. The results show that the heating rates have an effect on austenizing phase transformation temperature (A_c1 and A_c3). It shows that there is a linear relationship between heating rate and austennizing temperature (A_c1 and A_c3) in the range of tested heating rate. With the heating temperature increasing, the strength property goes up, on the contrary, the strength begins to go down when the heating temperature exceeds 900 °C, then a lowest strength point appears on 925 °C in the testing scope. As the further increase of the heating temperature, the strength goes up again. Moreover, the cooling rate has a great effect on the microstructure and the mechanical properties. With the decrease of cooling rate, the strength decrease significantly, meanwhile, the microstructure becomes coarse, even the banded structure can be found. As the conclusion, the optimum heating temperature is 950 °C, and cooling rate is from 8.5 to 13 °C/s.

Abstract: Determination of the optimal welding parameters to achieve specific weldments on a new material is usually an expensive and time consuming. To determine the welding parameters using Artificial Intelligence (AI) technologies, one must consider many factors including productivity, thermal input, defect formation, and process robustness. Determination of the welding parameters for pipeline welding is based on a skilled welders long-term experience rather than on a theoretical and analytical technique. In this paper, a smart system develops which determines welding parameters and position for each weld pass in pipeline welding based on one database and FEM model, two BP neural network models and a C-NN model. The preliminary test of the system has indicated that the system could determine the welding parameters for pipeline welding quickly, from which good weldments can be produced without experienced welding personnel. Experiments using the predicted welding parameters from the developed system proved the feasibility of interface standards and intelligent control technology to increase productivity, improve quality, and reduce the cost of system integration.

Abstract: In robotic GMA (Gas Metal Arc) welding process, heat and mass inputs are coupled and transferred by the weld arc and molten base material to the weld pool. The amount and distribution of the input energy are basically controlled by the obvious and careful choices of welding process parameters in order to accomplish the optimal bead geometry and the desired mechanical properties of the quality weldment. To make effective use of automated and robotic GMA welding, it is imperative to predict online faults for bead geometry and welding quality with respect to welding parameters, applicable to all welding positions and covering a wide range of material thickness. To successfully accomplish this objective, two sets of experiment were performed with different welding parameters; the welded samples from SM 490A steel flats adopting the bead-on-plate technique were employed in the experiment. The experimental results of current and voltage waveforms were used to predict the magnitude of bead geometry and welding quality, and to establish the relationships between weld process parameters and online welding faults. MD (Mahalanobis Distance) technique is employed for investigating and modeling of GMA welding process and significance test techniques were applied for the interpretation of the experimental data. Statistical models developed from experimental results which can be used to control the welding process parameters in order to achieve the desired bead geometry based on weld quality criteria.

Abstract: One of the main concerns of the automotive industry is reduction in structural weight of automobiles. Reduction of weight on vehicles has been proven to lower the usage of fuel, and therefore save a lot of energy in order to move from one place to another. At the same time, reduction of weight often means reduction in material usage, often regarded to be threatening structural strength of parts, components or vehicles body in white (BIW). Truss Core Panel, which has been developed from the study of origami engineering, specifically plane-tilings and space fillings, is a suitable candidate because it can be produced from thin sheet metals and can be joined using spot welding. In this paper, method for evaluating truss core panels for crashworthiness has been established based previous research on crashworthiness evaluation on thin shells. The effect of different configuration of spot welding has been investigated. The number of spot weld (n) along central member and side members of truss core panel has been varied and modeled from n = 2, 4, 6 ... to n = 30, and compared to a truss core panel model that is fully welded along central member and side members. The results also show that it is possible to attain similar mean crush force to fully welded structure with smaller number of spot welds.

Abstract: The aim of this study was to value the possibility to join, for pulsed Nd:YAG laser welding, thin foils lap joints for sealing components in corrosive environment. Experimental investigations were carried out using a pulsed neodymium: yttrium aluminum garnet laser weld to examine the influence of the pulse energy in the characteristics of the weld fillet. The pulse energy was varied from 1.0 to 2.5 J at increments of 0.25 J with a 4 ms pulse duration. The base materials used for this study were AISI 316L stainless steel and Ni-based alloys foils with 100μm thickness. The welds were analyzed by electronic and optical microscopy, tensile shear tests and micro hardness. The results indicate that pulse energy control is of considerable importance to thin foil weld quality because it can generate good mechanical properties and reduce discontinuities in weld joints. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. In all the specimens, fracture occurred in the top foil heat-affected zone next to the fusion line. The microhardness was almost uniform across the parent metal, HAZ and weld metal. A slight increase in the fusion zone and heat-affected zone compared to those measured in the base metal was observed. This is related to the microstructural refinement in the fusion zone, induced by rapid cooling of the laser welding. The process appeared to be very sensitive to the gap between couples.

Abstract: In this investigation, AISI321 steel was solution - stabilizing post heat treated in various temperatures and times after SMAW welding. Results show, increasing of temperature in solution and stabilizing heat treatment, raise sensitization; in addition, by increasing of the solution heat treatment time, sensitization enhances. However, increasing the time of stabilizing heat treatment creates less chrome carbides, so the sensitization decreases. These heat treatments reduce the amount of delta ferrite and change its morphology from narrow and acicular shape to discontinues and separate globular particles. Moreover, more carbide and carbonitrid of Ti and Nb are also created.

Abstract: The microstructure and mechanical properties of an X100 grade pipeline steel were investigated by the thermal simulation tests performed on a Gleeble-3500 thermal simulator. The results show that the steel has excellent weldability. Even if the weld heat input gets 40 kJ mm^-1, the low impact toughness energy in welding coarse grain heat affected zone (CGHAZ) is still higher than 200 J. Yet, an embrittlement zone emerges in inter-critical HAZ (ICHAZ) at the peak temperature of 750 °C, and the lowest strength appears in fine grained HAZ (FGHAZ) at the peak temperature of 950 °C. Moreover, the strength and toughness decrease with the increase of heat input.

Abstract: Friction stir welding of AA 7020-T6 aluminum alloys, 5 mm thick plate is an Al-Zn-Mg grade alloy of 7XXX series heat treatable of medium strength alloys and employed for welded engineering structural components. The effect of FSW parameters (rotational speeds and travel speeds) on joint strength and welding zone dimensions have been investigated experimentally. Four different rotational speeds are used: 450, 560, 710 and 900 r.p.m. with three travel speeds 16, 25 and 40 mm.min-1. The experimental investigation included tensile test and weld pool geometry determination. It was found the that best welding conditions for FSW was the weldments which have 247 Mpa yield strength, 340 MPa ultimate tensile strength, 7.3% elongation, 11020N bending forces for both face and root and hardness value ranging from (133-138) Hv 0.05 for the different welding regions under the optimal welding conditions at a rotational speed of 900 r.p.m. and travel speed of 25mm.min-1.

Abstract: In this paper analytical predictions of the fusion zone shapes around the welding cavity produced by a moving electron beam are provided. A three-dimensional analytical model in the molten and heat-affected regions surrounding a paraboloid of revolution-shaped cavity is used to predict the shapes of the fusion zones. This work avoids the defect of the infinite temperature at the cavity base for the line-source model. Introducing a new image method, a new analytical solution is provided by satisfying exactly the adiabatic condition at the top surface. The shape of a fusion zone is governed by dimensionless parameters related to beam power per unit penetration, and the depth and shape of the cavity in this work. A three-dimensional shape of fusion zone is computed and presented in this paper. The effect of beam power per unit penetration on the shape of fusion is also discussed.