Advanced Materials Research Vols. 83-86

Abstract: In this study the effects of two welding positions included in flat and upward vertical on the mechanical properties and microstructure of high strength weld metal deposited with shielded metal arc welding (SMAW) using an electrode of ASME SFA 5.5-96 E9018B3 type have been investigated. The aim of the present work is to study the effects of these two welding positions for a weld metal alloyed with 1%Mo, 2%Cr, 0.79%Mn, and 0.08% C in the stress relieved condition. For studying mechanical properties Tensile, Impact and hardness experiments have been conducted; meanwhile chemical analysis and microstructure studying have been carried out on specimens. The results show that welding position does not have any significant effect on tensile and hardness of the weld metal but in vertical position welding metal toughness is lower than toughness in flat position in all temperatures. Transition temperature of ductile fracture to brittle fracture is -50 °C for E9018B3 in welding of high strength micro alloyed steels.

Abstract: This paper proposes an alternative ultrasonic welding technique capable of welding plastic parts with different shapes and sizes. In this method, a thin plastic sheet of less than 0.5 mm in thickness is fixed to the ultrasonic vibration body called the horn, and two plastic workpieces to be welded are pressed upon the sheet from both sides at a constant normal pressure. Once the horn starts to ultrasonically vibrate, frictional heat is momentarily generated between the sheet and the plastic workpieces, increasing the frictional temperature to a high level. When the temperature increases to over the melting point of all the materials, the materials melt and eventually are welded after the ultrasonic vibration stops. In the current work, an experimental apparatus was designed and constructed. A series of experiments was subsequently carried out on the apparatus to investigate how the surface roughness of the workpieces, the welding time, and the normal welding pressure affect the actual welding area and the tensile strength of the welded workpieces. The experimental results showed that a bigger welding area and a higher tensile strength can be obtained under the appropriate welding conditions, providing validation of the new welding method.

Abstract: Evaluation of the formability of tubes is an important issue in tube hydroforming processes. Since tubular materials during tube hydroforming are under a biaxial even triaxial stress state, other biaxial-stress-based testing methods are needed. In this paper, uniaxial tensile tests at different temperatures are firstly employed to evaluate the material properties of magnesium alloy AZ61 tubes. A hydraulic bulge warm forming machine, which is used for hydraulic bulge tests with a fixed tube length, is also designed and manufactured. Using this self-designed testing machine, experiments of bulge tests of magnesium alloy AZ61 tubes at elevated temperatures are carried out. From the experimental results, the bulge formability of the magnesium alloy tubes at different temperatures is discussed.

Abstract: Friction stir spot welding (FSSW) is a relatively new welding technique which has already been successfully commercially applied on automotive aluminum alloys which, in turn, lead to significant energy savings and infrastructure cost-reductions. Due to the success of FSSW on Al alloys FSSW has generated tremendous interest in the automotive industry as an alternative joining process to resistance sport welding for steel body panels. Currently there is limited data on the mechanical properties and microstructure of friction stir spot welded steel thus the current aim was to investigate how these parameters chamged as a function of some critical process variables. In this instance spot welding of 2 mm thick high strength dual phase steel (DP800) was undertaken using a 3.5mm pin length tungsten rhenium tool with a tool rotation speed of 1000 rpm and plunge rate of 100 mm/min. Different dwell times of 0, 0.5, 1, 2 and 4 seconds were then applied prior to tool retraction to study the effect of dwell time on the microstructure and mechanical properties of the spot welds. Investigation of the weld spot joints revealed three distinct microstructural zones; a) thermo-mechanically affected zone (TMAZ), b) heat affected zone (HAZ), and c) parent material zone. The TMAZ shows an acicular martensite microstructure while the HAZ shows a ferrite/martensite structure in a very fine scale when compared to parent material zone. The Parent material is a typical dual phase structure which is ferrite matrix with a dispersion of martensite. Therefore, the TMAZ was harder while HAZ was softer when compared with parent material zone. The tensile strength obtained from tensile tests and the bonding ligament which has been reported to be measures of strength were also found to increase with dwell time.

Abstract: The use of laser energy in material processing for boring, cutting and welding has been state of the art for many years [1]. The good focussing ability of the laser allows power densities that are hardly possible with conventional welding processes. Thus, the desired component processing can be carried out on a limited area with low overall power where component and material are subjected to minimum thermal loading. The laser build-up welding process which is particularly suited for low distortion applications, as well as materials that are difficult to weld using conventional methods, is explained in detail. Co2 laser, nd:yag laser and diode laser as established beam sources in laser material processing are compared with newer, innovative beam sources like the fiber laser and disk laser that have been developed in the recent years. Where the possible spectrum of use ranges from small parts to large components weighing tons, the need for a universal handling system is discussed together with laser safety issues. Several industrial applications for laser build-up welding are presented.

Abstract: Tailor welded blanks had been widely used in automobile industries. In this paper, the formability of tailor-welded blanks with curved seams had been studied in experiments, and compared with that of tailor-welded blanks with straight seams. For tailor welded blanks with curved welded seams, the effects of thickness ratio on the limited forming height are the same under various welded seam shape, and the limited forming heights are decreased and then increased with the increase of thickness ratio, which different to that obtained from tailor-welded blanks with straight seam. The reasons that the shapes of welded seam how to influence the formability of tailor welded blank are deduced in the paper. Results show that the shape of the welded seam can change the blank’s deformation condition, which one of the main factors of determining the sheets formability.

Abstract: The ferritic stainless steel is a low cost alternative to the most often adopted austenitic stainless steel due to its higher strength, better ductility and superior corrosion resistance in caustic and chloride environments. However, the application of ferritic steel is limited because of poor ductility and notch impact toughness of its weld section with differential grain structures. Several techniques have been explored to control the grain features of the weld to minimize these problems. In the present effort, a review of these options in relation to the degree of grain refinement in ferritic stainless steel weld is conducted in order to have a better understanding about the grain refining phenomenon in the weld microstructure. So far, the most effective technique is found to be the pulse AC TIG welding which can produce weld with mechanical properties equivalent to 65% to those of the base metal. The refinement in this process occurred through dendrite fragmentation and grain detachment in the weld pool producing small-grained microstructures with a large fraction of equiaxed grains. However, in friction welding process where heat input and heat transfer are effectively controlled, the strength can be as high as 95% of the parent metal. This suggests that the total energy input for welding and heat transfer phenomenon mainly control the development of microstructural feature in the weld pool and hence the strength.

Abstract: Friction stir welding (FSW) is a fairly recent technique that utilizes a non-consumable rotating welding tool to generate frictional heat and plastic deformation at the welding location in the continuously-fed work piece. In the present investigation this welding process is applied to join 1050 cold-rolled aluminium plates. The effects of varying the welding parameters namely welding speed [56, 90 and 140 mm/min] and tool rotational speed [850 and 1070 rpm] on the mechanical and microstructural properties were studied. Vickers micro hardness results across the weldment showed that the weld nugget hardness is dependant upon the welding speed and the tool rotational speed. Increasing the welding speed at 850 rpm reduced the hardness at the weld nugget, whereas, at 1070 rpm the weld nugget hardness merely did not change. However, the hardness achieved at 850 rpm was constantly higher than that achieved with 1070 rpm irrespective to welding speeds. In the same fashion, the yield and ultimate strengths of the joints were influenced by varying the welding parameters. Increasing the welding speed at 850 rpm reduced both strengths whereas; at 1070 rpm they were almost unchanged. Microstructural study showed that the weld region is composed of unaffected base metal and the stir zoned [weld nugget] which is characterised by a fine equiaxed grain structure. Increasing the welding speed at constant tool rotational speed has caused a slight refinement in the weld nugget's grain size, whereas, decreasing the rotational speed has also led to weld nugget grain refinement.

Abstract: In this research, variations of tensile properties and fracture behavior of 316L austenitic stainless steel weld metal as a function of aging temperature and time have been investigated. Stainless steel plates were butt-welded using GTAW process. Weld metal tensile specimens were subjected to various aging heat treatments at temperatures of 750 and 850°C for periods of 1 to 100 hours prior to tensile tests at 25 and 500°C. Dissolution of delta-ferrite and formation of sigma phase network during aging resulted in a mild increase in tensile strength and significant reduction in ductility, particularly at 25°C. Although fracture surfaces exhibited ductile features, the dimple morphology and the macroscopic fracture mode were found to be affected by aging. The unaged weld metal exhibited a classic mode of cup and cone fracture, whereas slant and flat types of fracture modes were observed in the aged weld metals, with the slant mode being dominant at 500°C. The slant mode was associated with deformation localization along arrays of primary voids, nucleated at cracked sigma phase particles, oriented at about 45° to loading direction. The transition in the fracture mode is further discussed based on variations in the dimple morphologies and strain hardening exponent.

Abstract: Transport variables in plasma column are analytically investigated in this paper. Low-energy electrons and ions are produced from electron beam evaporation of a metal target in the technological vacuum chamber of an electron beam welding machine. Assuming collisionless plasma motion in the radial direction, the electrostatic potential is obtained from model of plasma expansion. Transport variables such as ion density, electron density, conduction heat of the ions and electrons are calculated using the electrostatic potential and are compared with the available experimental data.