Papers by Keyword: Weld Microstructure

Abstract: The features of the formation of the structure of welded joints for various welding modes and energy parameters of welding capsules for hot isostatic pressing are given. Mechanical properties are investigated for each of the modes.

Abstract: The welding of WELDOX960 ultra-high strength steel must consider not only the strength but also the toughness of the welding zone. In this paper, a new welding process with low strength matching backing layer is studied, that is, we choose ER50-6 wire for backing welding, use T union gm120 wire for MAG welding filling, and complete the cover welding. We prepared two groups of welding samples of ER50-6 wire backing welding and T union gm120 wire backing welding. Then we test the samples by optical metallography, tensile test, impact test and hardness test. The results show that the properties of the two kinds of backing weld can meet the requirements. The basic structure of the weld outside the backing layer of the two welding methods is similar, which are acicular ferrite and carbide. Using ER50-6 welding wire as backing, the microstructure of the weld is uniform and fine ferrite grain and a small amount of pearlite. Using T union GM120 high strength steel as backing, the microstructure of the weld is acicular ferrite and carbide. The toughness of ER50-6 is higher than that of T union GM120, and the hardness is lower than that of T union GM120.The research results have been successfully applied to the welding of large tonnage truck crane boom, and the enterprise has achieved high economic benefits.

Abstract: This work focuses on the analysis of the compositional variation made during stir casting of Al-B₄C metal matrix composite (MMC) and the properties of GTA weldments. Pulsed current gas tungsten arc (GTA) welding, a novel variant of traditional GTA weld process, was tried on two different composites, viz. 2 % and 4 % B₄C particulates in aluminium matrix. For a chosen current and voltage, two different pulsing frequencies (2Hz & 5Hz) were combined with three different pulse on time periods (40%, 50 % & 60%) and the weldments were compared with that of constant current weldments. An attempt has been made to study the time-temperature effect of pulsed GTA welding process parameters on microhardness in as-welded condition. Pulsed current resulted in better grain refinement and the same is reflected in the microhardness values. The increase in the reinforcing composition showed increased effect on the fusion zone weld hardness levels. Increase in Pulse on time and pulse frequency of PC weldments resulted in increased hardness of both the compositions.

Abstract: Through traditional corrosion method of aluminum alloy weld could only get a black-and-white metallographic structure. Color metallographic structure could be got by using color metallographic technique, which could improve discrimination of metallographic structure. The welding test pieces were got by using A7N01 and A6N01 aluminum sheets as base metal and E5356 and E4043 as welding wire. Through sampling, mounting, grinding and polishing process, metallographic specimens were obtained. Contrast test of aluminum alloy specimens was investigated. Conventional Keller’s reagent corrosion results showed the grain outline was not very clear and the grain boundary was fuzzy. Color metallographic corrosion results showed both the grain outline and boundary were very clear. Grains of different orientation and composition segregation presented different color. So color can be used to distinguish orientation and composition segregation. Color metallographic technique was better than black-and-white metallographic technique to observe the metallographic structure.

Abstract: Ultrasonic spot welding of galvanized steel sheets has been conducted to investigate formation process of the weld microstructure, and effect of zinc coat on joint property. The joint strength showed a rapidly increase at the weld time of 0.8s, and it has the maximum value over 1.0 s. In the weld time range from 0.1s to 0.8s, fracture occurred in zinc coat/ steel interface. In contrast, the fracture partially occurred in the base steel in the weld time over 1.0s, and concaves in which the steel substrate of one specimen partially remains on the other specimen were observed. The formation process of weld microstructure of ultrasonic welding was proposed to be a two-steps process. First, zinc coat in the interface was mechanically removed by the vibration and clamping force, and some zinc particles dispersed in the weld interface. Second, the zinc particles melted due to the friction, and partially bonded regions were simultaneously formed around the zinc particles. The partially bonded regions were stirred with the steel substrate as the weld time increased. The joint strength increased by development of the stirred zone. At the weld time over 1.2s, the joint strength decreased due to growth of crack around the stirred zone.

Abstract: A novel process of ultrasonic-assisted underwater wet arc welding was proposed to improve the joint properties, a number of ultrasonic-assisted underwater welding experiments were then carried out, and the effects of pulse frequency on weld formation, joint hardness and microstructure were investigated. Experimental results show that the ultrasonic frequency pulsation of arc can improve weld penetration while reducing effectively the hardness of joint HAZ in the arc axial direction and refining the grain of microstructure, and the effects of which are related closely to the pulse frequency.

Abstract: Through the metal inert gas welding (MIG) experiment, the effects of the different welding parameters on the microstructure, the weld configuration and the mechanical properties of the joint of the magnesium (Mg) alloy AZ31B were analyzed. The results indicate that with the increase in the welding current, the microstructure change of the weld is characterized by the grain coarsening, and the microstructure change of the heat affected zone is characterized by the grain coarsening and the broadening of the heat affected zone. An exorbitant welding current is inimical to the weld configuration. With the increase in the welding speed, the welding linear energy decreases, inducing the formation of the finer equiaxed grains in the weld. Moreover, the grains in the heat affected zone are also with the trend of the refinement, and thus the mechanical properties of the joint increase. The optimal welding current and speed in our experiment are 160-170A and 400-450mm/min, respectively.

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: A new flux based on NaCl – CaCl2 – CaF2 – Na3AlF6 was developed for the gas welding of aluminium and its alloys. The flux was generated by the application of the Hadamard multivariate chemical composition model. The model uses a 8 x 8 matrix and a full factorial analysis to generate several compositions within given ranges of the constituent flux elements. Mechanical and field tests were carried out on weldments made with the flux. The tensile strength, Izod impact strength and hardness of the all – weld metal were 310MPa, 5.35J and 100BHN. The weld deposition efficiency was 90.3%.The new flux and two popular commercial fluxes were given to five expert aluminium welders to use for three months, and were requested to rate the performances. The results showed that there was an agreement between the responses of the welders that the new flux performed better than the commercial versions available in Nigeria.