JOURNAL OF WELDING SCIENCE AND TECHNOLOGY OF IRAN
Year:2019 | Volume:5 | Issue:1 |Papers Count:12

In present study, the effect of heat treatment after friction stir welding dissimilar welds 7075-T6 and 2024-T4 aluminum alloys were investigated. Friction stir welding was performed at a constant rotation speed of 1140 rpm and welding speed 32 mm/min. After welding samples are taken under various heat treatment processes at different aging temperature and time period. Microstructural observations, phase analysis characterization and mechanical properties were performed on welded before and after heat treatment in cross section of welds joint. The results showed that postweld heat treatment causes abnormal grain growth turns destructive effect on the mechanical properties, while formation of fine and uniform precipitation recovery strength and ductility of welds joints. It is found heat treatment based on 7075-T6 and 2024-T6-procedure has highest and lowest impact on the restore of weld strength. Tensile test indicate that fracture occurred on the interface between TMAZ and HAZ in retreating side (7075) at as-weld joint, if that failure happens in the stir zone by applying PWHT. Surface fracture suggested fractures in PWHT samples are predominantly inter-granular, while in as-weld joint the fractures of joints are mostly trans-granular.

In the present Study, a dissimilar joint of carbon steel sheet EN 10025 with 316L has been welded by FSW and the welding parameters were optimized by RSM software method. For investigation of mechanical properties and microstructural analysis carried out by using optical, scanning electron microscopes with EDS analysis, tensile and hardness test of different area of joints, SZ, TMAZ, HAZ, their interfaces and Base metal. The optimized result were shown that best of joints within maximum strength (UTS) 312 MPa by rotational speed 950 rpm, transverse speed 90 mm/min and tool angle 3° was achieved. The failures were happened at base metal of EN 10025 to advancing side. Metallographic results were shown that grain size at SZ is 10 to 20 time more reduced caused improved of mechanical properties. Also chemical analysis and hardness result on welded samples by optimized parameters were shown that quite good mixing was happened at SZ.

In this study, friction stir butt welding of Mg and Al alloys with applying Zn interlayer was performed. To obtain optimum condition, a combination of two travel and three rotation speeds were selected. Mg-Zn and Mg-Al-Zn IMCs, Al solid solution and residual Zn, were the most common phases in the stirred zone, which eliminated the formation of Al-Mg intermetallics. The maximum mechanical properties were achieved for the joint fabricated at 35 mm/min and 600 rpm, caused to 24% improvement in tensile strength and around 3 times enhancement of elongation compared with Zn free sample FSWed at the same conditions. The fracture micrographs were consistent with corresponding ductility results. Fracture surfaces of Zn-added samples presenteda fine texture with a mixture of brittle and ductile fracture feature, which was different from the coarse cleavage plane and fully brittle fracture of the joint without Zn interlayer.

This paper introduces a novel soldering method for joining aluminum foams to aluminum plates. In this method, a rotating aluminum plate is soldered to the aluminum foam using zinc-based solder material. Rotation of the aluminum plate over the solder material drags the solder material and stirring it. Excellent tensile strength was obtained compared to those samples that are welded with the soldering flux but with no rotation involved. It was concluded that the stirring of the zinc-based solder material in the liquid state and just before the solidification break the oxide layers and help the wetting process done. Scanning electron microscopy examinations showed diffusion has occurred between the solder alloy and the aluminum foam and the aluminum plate.

Shielded metal arc welding on the high strength low alloy steels in pipelines to transport natural gas from Iran is of great importance. In this article the effects of annealing heat treatment on properties of multi pass welding in different situations (6-4: 30, 4: 30-3, 3-1: 30, 1: 30-12) with 36 in outside diameter is evaluated by chemical, metallography, tensile, toughness and hardness. Tensile test results showed the lowest yield strength (Vertical to weld and in position 6-4: 30) equal to 348 MPa, and the lowest energy impact (Vertical to weld and in position 1: 30-3) equal to 108J. The impact energy alignment to weld had a rate of 12 percent increase before the heat treatment. The amount of hardness variation in different areas and positions is negligible (less than 5 percent). Images of metallographic test made by light and electron microscopes demonstrated that the amount of perlite cap pass weld and heat affected zone near the weld metal were decreased compared to main metal to respectively 29 and 8 percent. The elongation weld of was increased ratio than before the heat treatment in base metal respectively 75 and 23 percent. The increase rate of C, V and Ti in the weld zone according to base metal in situation of 3-4: 30 are respectively 0. 02, 0. 003 and 0. 006.

In the present study, effect of Ni alloying element on the characteristics of deposited weld metal of E7018-G electrode was evaluated. Therefore, electrodes contained different amounts of Ni (0-1. 7wt. %) were designed, manufactured and welded via SMAW process. Microstructural studies revealed dichotomy effect of Ni on the deposited weld metal microstructure, i. e. increasing the Ni content up to 1. 2wt. % improved the formation of acicular ferrite in the weld metal microstructure and caused significant grain refinement at the reheated zone of weld metal. While, higher Ni content (>1. 2wt. %) resulted in some raising in the widmannstatten ferrite content in the weld metal. Strength multiplied by impact energy parameter (UTS×CVN) was used for mechanical properties assessment. Mechanical properties evaluation revealed the highest UTS×CVN parameter achieved in the weld metal contained 1. 2wt. % Ni. Hardness of the weld metal increased with increasing Ni content which is related to the formation of micro constituents in the microstructure of weld metal and increasing their content with increasing Ni content.

In the present study, effect of inclusions characteristics changing on the formation of acicular ferritein submerged arc welding of API5l-X65 low alloy steel was investigated. Three different welding fluxes with different chemical composition and basicity index of 0. 72, 0. 82 and 0. 99, and two different welding heat inputs of 1. 6 kJ / mm and 2. 4 kJ / mm were used to create inclusions with different characteristics such as chemical composition and size. The results indicate that inclusions acting as acicular ferrite nucleation sites and improvement of the microstructure and resulted mechanical properties, can be observed in welding conditions in which the welding flux with lowest basicity index and higher welding heat input. Under these conditions, the percentage of inclusions with a high titanium oxide value and size range of 0. 5 to 1. 5 micrometers is increased, which increases the amount of acicular ferrite in the microstructure. However, in other welding conditions, formation of grain boundary ferrite reduces amount of acicular ferrite and weakens mechanical properties of weld metal compared to the base metal.

The effect of electromagnetic vibration on the microstructure and impact toughness of API-X70 steel weld metal was investigated. The welding was carried out by gas tungsten arc welding process and using filler metals including ER80S-G and ER309L. Electromagnetic vibration under voltages 0-30 volts concurrent with welding was applied. The microstructure of the base and weld metals using optical microscope and SEM was studied. The impact energy of weld metals at TR, 0° C and-20℃ using charpy impact test was measured. Microstructural investigations revealed that applying electromagnetic vibration have caused the finer and more uniform of Martensitic-Austenitic (MA) islands in the ER80S-G weld metal. The results showed that, due to electromagnetic vibration, the microstructure became finer and the average size of dendrites in the ER309L weld metal decreased from 18. 19 to 8. 01 μ m. . The impact test result, illustrated that the applied vibration cause improvement of impact energy of weld metals at different temperature (TR, 0° C and-20℃ ). It was found that with vibration under 30V, impact energy of ER80S-D weld metal in TR, 0° C and-20℃ was increased equal to 53, 29 and 36 percents, respectively. Besides for ER309L weld metal, the impact energy in TR and-20℃ was increased equal to 18 and 5 percents, respectively. (TR= Room Temperature).

In this paper experimentally, the friction-stir welding of the polypropylene sheets with 40% glass fiber has been investigated. Comparison to other welding methods, the strength of the joint is the most important feature in this process. Many parameters such as tool geometry, rotational speed, linear velocity, and tilt angle are very important as input parameters in this type of welding. Therefore, in the present study, the effect of these parameters on the frictionstir welding of the polypropylene composite sheets have been extracted. Experiments are based on the Taguchi method and the orthogonal L9 array that are suitable for three-level designs. Statistical analysis have been performed as variance (ANOVA) and signal-to-noise ratio. Based on the results, the tool with a screw cone-cylindrical pin has a better apparent quality and higher tensile-shear strength. Results analyze show the rotational speed has the most significant effect on the tensile-shear strength and appearance of the weld. The joint with maximum tensile strength is obtained at rotational speed of 1000 rev/min, welding speed of 20 mm/min and tilt angle of 1 degree.

In this paper, failure mechanism of a 17th stage blade of an 82. 5 MW steam turbine that caused damage to the internal turbine compartment and the adjacent blade equipment has been studied. In order to determine the cause of failure and prevent similar events, various metallurgical and mechanical investigations including chemical composition analysis, metallography and microstructural analysis, fractography using scanning electron microscope and hardness and tensile tests were carried out. The initial results showed that the alloy had a chemical composition, microstructure and mechanical properties in the acceptable range, and the fracture failure was not due to the mechanical and metallurgical degradation during the service. The results of the fractography indicate high cycle fatigue as the main mechanism of the failure and shows that the fatigue crack has initiated from the adjacent hole relative to the vibration damped wire near to the brazing region on the blade, due to inadequate quality and incomplete connection of the brazing and its stress concentration effect the hole, which eventually has propagated and reached a critical level, and a sudden failure of the blade has occurred.

Dissimilar joint with good quality and mechanical properties is one of the major problems the industries. One of the most commonly used methods to solve this problem is friction stir welding process. In this paper two different tool pin with simple cylindrical and screwed profile were used to finding optimization of friction stir welding parameters to reach best mixing flow, composite structure and maximum tensile strength in dissimilar joint between AA6065 aluminum alloy and pure copper. In this research 1130 rpm tool rotation, 24, 40 and 65 mm/min travelling speed, 0. 3 mm plunge depth and 3o tool tilt angle were carried out. The results shows that internal material flow that produced with screw pin was better than simple cylindrical in constant process parameters. According to the results, at lower tool travelling speed the strength of joint increases. The tensile test results revealed the maximum strength of joint of screw pin was 345MPa with 2. 6mm elongation and simple cylindrical pin was 272MPa with 2. 2mm elongation which welded with 1130 rpm and 24 mm/min travelling speed.

In this research, the effect of vibration at the resonant range (75 Hz) on the hardness and tensile strength of AA5083-H321 aluminum alloy, were welded by gas metal arc welding (GMAW) investigated. Vibration forces were ranged from 850 N to 2200 N, under identical welding parameters. Tensile strength and hardness testing of welded samples were performed. After mechanical tests, the fracture surfaces of welds were examined using scanning electron microscope (SEM) and discussed. The results showed that with increasing vibration force, the tensile strength and fracture strength of the specimens were welded during vibration, were increased by about 3 and 9 percent, respectively, compared to the non-vibrated weld sample. However, no significant change was observed in the hardness of the welded specimens. Mean grains size and heat affected zone of the sample was welded was welded with conventional GMAW, were about 200 μ m and 1800 μ m, but due to inducing vibration, as vibration force increased from 850 N to N 2200 N, Mean grains size was reduced to about 75 μ m and HAZ was reduced from about 1000 μ m to 700 μ m, that is, about 44 to 61%.