فهرست مطالب محمد علی صفرخانیان

Friction stir welding process is solid state welding method that does not have many common defects in fusion methods. In this method for creating optimum weld, some parameters should be optimized, such as welding tool geometry, rotational speed and travel speed. The aim of this study was to investigate the effect of rotational speed on microstructure and mechanical properties of friction stir lap welding AA5456 in rotary state to optimize the parameter values. For this purpose, Welding process was performed in rotating state, rotating tool was plunged from the cold-worked tube (AA 5456-H321 with 5 mm thickness) surface into the surface of Annealed tube (AA 5456-O with 2.5 mm thickness) and lap joints were produced by rotational speeds of 300, 500, 700 and 900 rpm and welding speed of 45 mm/min. Macro and microstructure of weld cross sections by optical microscopy (OM) and scanning electron microscopy (SEM) were studied. Then the hardness profile and tensile shear test were obtained and compared to another. Finally the fracture surfaces of some samples were examined by using a scanning electron microscope (SEM). The Macro and microstructure results show that increasing of rotation speed, increases the vertical flow of material, the height of hook as well as fine-grained sediments in the nugget zone. Increasing the rotational speed, decreases hardness of weld nugget. The results of tensile shear test show that the welding parameter of (700 rpm- 45 mm/min) is the optimal combination of parameters in this study.

The research is based on experimental tests, lap joint welding of 5456 aluminum alloy was carried, so that the hard working H321 sheet with the thickness of 5 mm was placed on an annealed sheet with the thickness of 2.5 mm and has been investigating the simultaneous effects of parameters such as rotation speed and welding speed on metallurgical and mechanical properties in friction stir welding process. The results showed that increasing of rotation speed and reducing of welding speed (increase of welding step) causes increased heat input, increase vertical flux, increase hook height and reduction in effective Sheet thickness and it is causing the failure from the thermomechanical zone where the maximum heat input applied also, increasing of welding speed causes reduction in the material mixing and hook height and it causes an interface failure. It was observed with an examination of the results due to the differences in thickness of the sheets, existence of hook defect and its appropriate height and orientation is useful in this joint and causes an increase in strength and failure was in the base metal of the sheet with a thickness 2.5 mm in a tensile test.

Friction stir welding is suitable for joining series 5000 alloys because no fusion welding problems arise for the alloys in this process. In this project, the effect of tool geometry on mechanical properties and formation of common defects in FSW such Kissing Bond defect and Hooking was investigated. Specimens were welded with three pin, that is, Cone with stair (stair at intersection of two sheets), frustum, and Tri-flute (rotating speeds: 650 , 500 rpm / welding speeds: 50, 25 mm/min). First, the macrostructure and microstructure of weld sections was investigated, and afterwards tensile shear test from retreating side as well as micro hardness test were examined. The results show that from among three pins which were used in this project, Tri-flute is the best pin simply because the specimens which were welded with this pin not only had an appropriate Hooking height, but also Kissing Bond was not destructive in these specimens.

In this study, the friction stir welding process was used for simultaneously joining of AZ31 magnesium alloy and production of Mg/Sic nanocomposite in the stir zone. All combinations of three rotational speeds i.e, 600, 800, and 1000 rpm and four traveling speeds i.e, 25, 75, 125 and 175 mm/min were tested and then the mechanical properties were examined. The joint fabricated with rotational speed of 800 rpm and traveling speeds of 75 mm/min, exhibited the highest mechanical properties, So that the yield strength, tensile strength and percent elongation improved by 11%, 39% and 88%, respectively. The results show that the proper distribution of nanoparticles in the stir zone can reduce the average grain size and improve mechanical properties. The main reason for this change is related to pinning effect and increased nucleation sites associated with SiC nano-particles. Moreover, reinforcement particles resulted in breaking of primary grains in stir zone of friction stir welding.

Friction stir welding is a solid state process developed by the welding institute TWI in 1991¡ as a technique for welding aluminum alloys. In this research¡ lap joint welding of 5456 aluminum alloy was carried¡ so that the hard working H321 sheet with the thickness of 5 mm was placed on an annealed sheet with the thickness of 2.5 mm and has been investigating the simultaneous effects of parameters such as rotational speed¡ feed rate¡ and tool angle¡ on failure force parameters and the hook disadvantage height in friction stir welding were investigated. After evaluation and analysis of the welded samples; the modelling of multilayer perceptron neural network was carried out using experimental results¡ and for the purpose of the trained model verification¡ several verification models was performed where the results of failure force in training model show 2.017 percent average error with respect to the experimental results. Next¡ the multilayer perceptron neural network was used for investigating the effect of welding parameters as in single or group mode on welding mode variations¡ where rotational speed parameter has the greatest effect and tool angle has the least effect than the other two parameters in lap joint friction stir welding.

Friction stir welding is a solid state process which is developed by Twi institute in 1991. In this paper، lap welding of 5456 aluminum alloy sheets were carried out while hard working H321 sheet with a thickness of 5 mm was on top of a 2. 5 mm thickness annealed sheet and the simultaneous effect of rotation speed of tool، feed rate and tool angle parameters on failure force and the height of hook in friction stir welding were investigated using response surface method. After evaluation and analysis of welding samples، response surface method was used using experimental results and several verification models were performed for error estimation. The results of mechanical properties of model show 3. 88 percent average error with experimental results. In proceeding، the analysis of variance was used for investigation of the welding parameters effect on welding mode variations and it was seen that feed rate has the greatest effect on failure force and rotation speed has the greatest effect on the hook height and tool angle has the lowest effect in comparison with this two parameters.

Friction stir welding is a solid state process which is developed by Twi institute in 1991. In present study، lap joint welding of 5456 aluminum alloy sheets were carried out whiles hard working H321 sheet with a thickness of 5 mm was on top of a 2. 5 mm annealed sheet and the simultaneous effect of rotation speed and tool feed rate parameters on microstructure and micro hardness in friction stir welding were investigated. The results show that the friction stir welding causes crush between metal particles، Microstructure homogenization and fine weld beads. The studies showed that increase of rotation speed and reduction of feed rate (increase of welding pitch) causes increase of heat input، vertical flux، grain size and reduction in hardness. With a closer look It was seen that increase in rotation speed from 250 rpm to 750 rpm in constant feed rate and tool angle، increases the grain size from 4. 65 micrometer to 7. 89 micrometer and feed rate with increasing، the grain size reduced from 7. 11 micrometer in speed of 25 mm/min to 4. 77 micrometer in speed of 75 mm/min.

Friction stir welding (FSW) is a new solid-state welding process that can be used to weld aluminum alloys such as Al-2024 that are hard to weld by conventional fusion welding. The grain refining in the stir zone occurs during friction stir welding. The mechanism of grain refining in the stir zone is interest for researchers. The effect of rotational speed and feed speed on the grain size in the stir zone of the 2024 aluminum alloy was investigated in this study. Also the mechanism of grain refining in the stir zone identified. It is found that the grain size of the stir zone increases with the increasing of rotational speed and decreasing of feed speed during FSW. Also it was specified that the mechanism of grain refining in the stir zone is continues dynamic recrystallization (CDRX).

In this study, friction stir spot welding was used to make lap joints on strips of 2024 aluminum alloy. The effects of tool rotational direction (clockwise and counter clockwise) and holding time on bond formation and tensile shear strength of the resulting joints was determined. Macro structure of stir zone was monitored by optical microscopy and it was indicated that interface of sheet metals near the pin hole (Hook) was determined. Also with increasing of the holding time, width of the stir zone and tensile shear failure load increased. An optimum combination of parameters that maximizes joints tensile shear strength was identified.

Friction stir welding (FSW) can be used to join aluminum alloys such as Al-2024 that are hard to weld by conventional fusion welding. Although this welding process can eliminate defects, the softening problem of heat-affected zone can be a non-acceptable problem. To recover the strength of joint, one option is fully post weld heat treatment of welded components. However, it has been reported that fine grains in the stir zone are not stable during solution treatment. In this study, a 2024-T8 aluminum alloy with 5 mm thickness is selected as the experimental material for FSW to reveal the effect of rotational speed of tool before and after post weld heat treatment on the microstructure of stir zone. It was found that the particles are broken up during friction stir welding, and the severity of the breaking up of particles and grain size in the stir zone increase with increasing rotational speed. Consequently stability of grains increases