Materials Science Forum Vols. 706-709

Abstract: Technique of including a thermoplastic film as the outermost layer of thermoset composites have been developed as an attempt to join the thermoset composites using fusion bonding methods. Special thermoplastic in the form of film was incorporated onto the surface of thermoset composites during co-curing process. Semi-Interpenetration Polymer Network [s-IPN] was formed between thermoplastic and thermoset polymers. The thermoset composites can be fusion bonded using co-consolidation and localized heating through their incorporated thermoplastic surfaces. The mechanical properties of thermoset composites bonded with thermoplastic adhesive were equivalent or superior to the benchmark composites bonded with Cytec FM300K adhesive in terms of lap shear strength, high temperature, low temperature and anti-chemical resistance.

Abstract: Car manufactures have been asked to avoid the unnecessary waste of energy and reduce pollution. Replacing steel with lightweight materials on car bodies is considered as one method to reduce the vehicle weight to achieve these requirements. Therefore, in this study, we selected a modified metal inert gas welding-brazing process to join aluminum to zinc coated steel on the lap geometry. The main purpose of this research was to reveal the relationship between weldability and various process parameters such as Zn coated thickness, kind of coated treatment type, filler wire type and welding condition. Metallurgical observations and mechanical testes were carried out to evaluate the weld quality. Based on these results, we could find that the weldability of dissimilar materials were depend on sufficient and regular wetting by heat input and gap condition. The tensile-shear test results, all the fracture occurred in the HAZ of aluminum and the strength was up to 70% of base metal of aluminum. However zinc coated thickness in the range of 10㎛ to 30㎛ was no related with welded strength. Also we could find that silicon content of filler wire is very important to minimize the thickness of intermetallic compound layer. Silicon might be disturbed to the growth intermetallic compounds.

Abstract: The objective of this study is to determine an optimal welding procedure that can be implemented to repair damaged Nickel Aluminium Bronze (NAB) components. NAB is commonly used in marine applications where components are subject to a constant corrosive environment and high stresses. Research into ideal NAB microstructure for a marine application, was performed in order to gain a baseline for experimental analysis of potential welding procedures. The results indicated that the welding repair can be performed with a wide range of heat input. The effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties in the heat affected zone (HAZ) and weld metal was also investigated in this research. The dominant microstructure in weld metal at as-welded condition is coarse Widmanstatten type structure with high hardness; post-weld heat treatment resulted in significant grain refinement and hardness reduction in weld metal.

Abstract: Regarding the friction stir welding (FSW) of heat–treatable aluminum alloys, although the thermal flow does not cause any material fusion, it can still deteriorate the local mechanical properties of the joints due to coarsening or dissolution of the strengthening precipitates. Therefore, it is of significance and possible to improve the joint properties by controlling the temperature level. For this purpose, a 2219-T6 aluminum alloy was underwater friction stir welded in the present study, and the temperature histories, grain structures and the general mechanical properties of the joints were investigated in order to illuminate the effect of water cooling. The results reveal that the water cooling action can effectively control the temperature level in the joint. The recrystallized grains in the weld nugget zone (WNZ) are significantly refined under the water cooling effect. The mechanical analysis indicates that the tensile strength of the joint can be improved by 6% through the external water cooling action. Additionally, the underwater joint also exhibits superior bend and impact properties to the normal joint, indicating the positive effect of water cooling on the general mechanical properties of the joints.

Abstract: High strength low alloy (HSLA) steel, namely HSLA-65, has shown promise as a replacement for more common high strength shipbuilding steels. However, conventional high heat input welding processes can cause significant distortion, often requiring expensive post-weld reworking. Butt welds in HSLA-65 steel were fabricated using a hybrid fibre laser-gas metal arc welding (GMAW) procedure to investigate the efficacy of distortion mitigation via low heat input joining. Heat input from the laser and arc sources were roughly equal at ~5.2 kW each, and plates were welded in either the laser-leading or arc-leading configuration. In either case, butt welds in ~9 mm thick plates could be made in a single pass at a total heat input of ~0.4 kJ/mm. Welding induced distortion was minimal. Analysis of the microstructure and microhardness of the welds is provided, along with some preliminary results of mechanical and impact testing.

Abstract: In this paper laser welding AA5182 of aluminum alloy with AA5356 filler wire were performed with respect to laser power, welding speed, and wire feed rate. The experiments showed that the tensile strength of the weld was higher than that of the base material under sufficient heat input conditions. A genetic algorithm was used to optimize process parameters which were the laser power, welding speed, and wire feed rate. To do that, a fitness function was formulated, taking into account weldability and productivity. A factor for the weldabilty used tensile strength estimation model which was made by neural network, and as the productivity, welding speed, and wire feed rate were used. Weld monitoring system for aluminum laser welding with filler wire was constructed through the optical sensors to measure the plasma light intensity. Relationship between monitoring signal and plasma and keyhole behavior according to welding condition was analyzed and it was found that sensor signal could express the information for weld quality. Weld quality estimation algorithm was formulated fuzzy multi feature pattern recognition algorithm using the monitoring signals. Quality prediction system was also developed to apply this algorithm to production line.

Abstract: Resistive Implant Welding involves an electrically conductive implant (welding rod) placed between the parts to be joined. Heat generation by Joule effect raises the temperature of the implant above the melting temperature of the thermoplastic being joined and a weld is reached. In the present study, resistive implants have been used to weld two HDPE components that make up a tank. RIW represents a good welding technique for advanced thermoplastic polymers contributing to increase the use of those materials and their industrial applications.

Abstract: A new bonding technique of titanium and zirconium conducted at low temperatures was developed utilizing the hydrogen-induced transformation. Hydrogen charge treatment of the faying surfaces of titanium and zirconium was conducted with varying the charging time between 3.6-700ks prior to diffusion bonding. Diffusion bonding of hydrogen-charged titanium and zirconium was carried out at 600-800°C for 0.6-1.8ks applying the bonding pressure of 5-10MPa in vacuum. Titanium and zirconium hydrides were formed at faying surfaces after hydrogen charge treatment. The β-transus temperature at faying surfaces of titanium and zirconium was reduced to approx. 450-550°C with hydrogen-charging. The bond layer was phase transformed to a bcc structure (β) at the bonding temperature due to the hydrogen diffusion during bonding process. Grain growth across the prior bond interface was observed in the joints bonded at 750-800°C after hydrogen-charging for 300-500ks. Tensile strength of titanium joints bonded at 800°C attained approx. 70% of the base metal strength (approx. 1.6 times as high as non-charged joints), and corrosion resistance of the joints was comparable to that of the base metal. Furthermore, tensile strength of zirconium joints bonded at 800°C was approx. 1.7 times as high as non-charged joints. It follows that the solid-state bondability of titanium and zirconium at low temperatures was improved compared to the conventional diffusion bonding (direct bonding without hydrogen-charging).

Abstract: Friction spot welding (FSpW) is a recent solid state welding process developed and patented by GKSS Forschungszentrum (now Helmholtz-Zentrum Geesthacht), Germany. A spot-like connection is produced by means of an especially designed non-consumable tool consisting of pin, sleeve and clamping ring that creates a joint between sheets in overlap configuration through frictional heat and plastic deformation. FSpW offers many advantages over conventional spot joining techniques including high energy efficiency, surface quality and environmental compatibility. Comparing with friction stir spot welding, FSpW produces a weld without keyhole on the surface at the end of the joining process. In the present study, the possibility of joining AZ31 magnesium alloy by FSpW technique was evaluated by using different welding parameters (rotational speed, plunge depth and dwell time), aiming to produce high quality connections. Microstructural features were analyzed by light optical microscope and mechanical performance was investigated by microhardness test and lap shear test. Microstructure analysis revealed that defects free welds could be produced. A slight decrease in grain size of the stir zone was observed causing a slight increase in the microhardness of this region. The preliminary lap shear data demonstrated that the weld strength is comparable to other welding process.

Abstract: The effect of forging pressure on linear friction welding (LFW) behaviour of a single crystal Ni-based superalloy was investigated. Crystal orientations of the specimens were controlled and results indicated that welding success is dependent on proximity of the oscillation direction to the <011> direction. Characterization of the welds included optical examination of the microstructural features of the weld and thermomechanically affected zones (TMAZ) in relation to the parent material. Mechanical properties of the welded material examined via microhardness testing showed an increase in strength in the weld zone (WZ). Microstructural examination indicated that some recrystallization occurred in the WZ, as well as a small amount of distortion of the dendrites in the TMAZ. With increased forge pressure, recrystallized grains remaining in the weld were minimized.