Lap joints of commercially pure magnesium plates to aluminium plates (Magnesium plate on the top, and Aluminium plate, grade 1100, on the bottom side) were conducted by friction STIR welding using various traveling and rotation speeds of the tool to investigate the effects of the welding parameters on the joint characteristics and strength. Defect-free lap joints were obtained in the welding traveling speed range of 40-80 mm/min, and rotational speed range of 1200-1600 rpm. The shear tensile strength of Mg/Al joints increased as a result of decreasing the welding speed from 120 to 40 mm/min at constant rotation speed of 1600 rpm. DEFECTS such as surface grooves, excessive flash, tunnels, and voids were observed if the joints prepared out of the mentioned range. The effects of the welding parameters are discussed metallographically based on observations with optical and scanning electron microscopes.

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 the present study, friction STIR processing (FSP) technique was carried out on the AA2024 sheet at different traverse speed (63 to 250 mm/min) and rotation speed (315 to 800 rpm). The temperature and grain size of STIRred ZONE (SZ) were measured and their relationship was analyzed and effect of FSP parameters on the grain size of SZ was determined. Experiment and analytical investigations revealed that SZ grain size complies the exponential temperature-dependent relationship and can be defined the mathematical equation. Calculations indicate that a change in operational variables (rotation and traverse speeds) makes no variation in strain rate, and it is constant.

Friction STIR welding is a new and effective method for joining the alloys with welding problems and also for the dissimilar alloys. In the present study, friction STIR welding is used to join st37 low carbon to AISI 304 stainless steel plates at different tool rotation speeds. The STIR ZONE in AISI 304 stainless steel shows evidence of dynamic recrystallization with a moderate dislocation density. The STIR ZONE in st37 steel appears to experience dynamic recrystallization too, although the allotropic transformation during cooling cycle of the welds removes the features of dynamic recrystallization and produces a fine ferritepearlite microstructure with a low dislocation density. The relationship between hardness and microstructure is investigated through the Hall-Petch equation for the STIR ZONE of both steels. The results of weighted least-squares fit also show that the average hardness of austenite in AISI 304 steel and ferrite in st37 steel inside the STIR ZONEs has a reverse relation with hardness according to the Hall-Petch equation. The hardness of the base metal and the STIR ZONEs of AISI 304 stainless steel does not stand on a same Hall-Petch line that can be attributed to the relatively higher dislocations due to the dynamic recrystallization of STIR ZONEs.

In this study, the effects of friction STIR welding parameters on the formation of intennetallic compounds, DEFECTS and tensile strength of AAII00 aluminum joints A441 AISI steel were studied. Thick Intermetallic compound formed at high tool rotational speed and low traverse welding speed. iChemical compositions of these components were Al6Fe2 and Al6Fe that formed in joints interfaces. Tunnel DEFECTS were main voids that formed in the STIR ZONE. Due to improper heat generation in lower rotational speeds, this void made in low rotational tool speeds and these voids vanished with increasing the frictional heat. Frictional heat increased by tool plunge depth and STIR ZONE void became smaller. By controlling mechanical parameters of the process strongest joint produced in 800rpm tool speed, 63 mm/min traverse speed and 0.2 mm tool plunge depth. This joint had 90% of the aluminum base metal strength.

2Background: MRI is the imaging modality of choice for the detection of diabetic pedal osteomyelitis. The aim of this study is to compare the STIR sequence, as the most important fluid-sensitive sequence, with contrast-enhanced images for diagnosing diabetic pedal osteomyelitis. Methods: Medical images were compared. Moreover, the effect of adding T1W image findings to the STIR sequence was evaluated. This cross sectional study was collected and analyzed at Namazi Hospital, Shiraz University of Medical Sciences, from 20 March 2016 to 22 September 2017. Results: The final diagnosis of osteomyelitis was confirmed for 47 bones (78%). 13 bones (22%) didn't have osteomyelitis. The specificity of contrast-enhanced and STIR sequences was 92.3% and 53.8%, respectively; whereas the sensitivity of the two sequences was similar (100%). Records of 48 diabetic patients suspected of having pedal osteomyelitis referred to one of the university hospitals, who underwent foot MRI with and without contrast injection, were assessed. Overall, 48 Patient MRIs and 60 separate bony parts were evaluated. Diagnoses were confirmed by clinical correlation. Finally, sensitivity, specificity and diagnostic accuracy of STIR sequence and contrast-enhanced images were compared. Moreover, the effect of addition of T1W image findings to STIR sequence was evaluated. Conclusion: This study was performed to suggest a pulse sequence that doesn’t need contrast media injection for diagnosing diabetic pedal osteomyelitis since the previous studies showed that gadolinium-based contrast media shouldn’t be applied in patients with renal failure (glomerular filtration rate<30 ml/min/1.73m2. According to the results STIR images had the same sensitivity as T1 post-contrast images; therefore, it can be concluded that contrast media injection can be avoided using this pulse sequence. The specificity of the STIR pulse sequence was lower than that of post-contrast images which was due to the lower ability of this pulse sequence to detect secondary symptoms of osteomyelitis such as cortex disruption, sinus path, and abscess. Using the T1 pre-contrast images, specificity and diagnostic accuracy increased. Finally, it can be concluded that MRI without contrast including STIR and pre-contrast T1W images is a reliable modality for the detection of osteomyelitis in suspected diabetic patients who are more prone to renal disorders.

This study aims to examine how friction STIR welding parameters, such as welding speed and rotational rate, affect the microstructure, DEFECTS, and mechanical properties of AA7075-T651 aluminum alloy joints. It also assesses the relation of the DEFECTS and microstructure to the mechanical properties. Microstructural investigations using optical microscopy (OM) and scanning electron microscopy (SEM) indicated remarkable grain structure variations among the different welding ZONEs. Especially, it was found out that the interface between welding nugget ZONE (WNZ) and thermo-mechanically affected ZONE (TMAZ) is a dominant determinant of the mechanical properties of joints. The importance of the interface comes from the fact that it is the most prone region to cracks, micro-cavities and tunneling DEFECTS. WNZ and TMAZ interfaces as well as their grain structures can be influenced by the heat generated from the friction between rotating tool and workpiece material. Therefore, coarser grain structures observed at the WNZ-TMAZ interfaces of the samples welded at higher rotational rates or lower welding speeds is due to the greater heat generated in such cases. Besides, microstructural variations in the weld ZONE affect the hardness and mechanical properties of weld joints. Thus, samples with coarse-grained structures display lower values of yield stress and microhardness.

In this article, effects of Friction STIR welding tool rotational and traverse speeds were studied on the temperature distribution, material flow and formation of DEFECTS in the welding ZONE. Computational fluid dynamics method was used to simulate the process with commercial CFD Fluent 6.4 package. To enhance the accuracy of simulation in this Study, the welding line that is located between two workpieces, defined with pseudo melt behavior around the FSW pin tool. Simulation results showed that with increase of FSW tool rotational speed to linear speed, the material flow in front of tool became more and dimensions of the STIR ZONE will be bigger. The calculation result also shows that the maximum temperature and STIR of the material was occurred on the advancing side. The computed results showed that with incompetent heat generation, insufficient material flow caused around the pin and DEFECTS formed in weld root. The computed results were in good agreement with the experimental results of other researchers. Based on the welding parameters that used in this simulation, the maximum strain rate is predicted between -4 (S-1) to +4 (S-1) in the STIR ZONE.

The present research aims to study the liquation and re-solidification of liquid during friction STIR spot welding of AZ91 alloy. Although friction STIR spot welding is a solid-state process, the presence of Mg17Al12 intermetallic compounds results in liquation during the welding process. In this study, friction STIR spot welding was performed with a tool rotational speed of 2500 rev/min and a tool dwell time of 5 seconds. The microstructural assessment was carried out by optical and scanning electron microscopes. The results showed that initiation of liquation from the inner and outer edge of the eutectic precipitates occurred based on the melting of residual eutectic. Moving toward STIRred ZONE, a liquid film formed along the grain boundaries. The liquid re-solidified as a composite structure of α-Mg/, which α-Mg phase dispersed in γ-Mg17Al12 matrix. Also, the results showed that eutectic morphology resulting from re-solidification is related to the cooling rate. Eutectic morphology changed from granular to fibrous by increasing the cooling rate. Also, the liquid film along the grain boundaries re-solidified as a divorced eutectic.

In this paper, the effects of welding parameters involving tool shape, title angle, rotational speed and welding speed on the S-shape defect formation have been investigated. For this purpose friction STIR welding process were done on the Al-1085 plates by cylindrical, Triangle and square pins. The welded sections were studied by metallographic, radiography and SEM methods. The results showed that the S-shape defect was formed in the 1120 rpm, 1º title angle, 160mm/min welding condition. It is believed that the higher heat input in this welding condition with low welding speed would lead to more oxidation of Aluminum and so oxide particles formation. These oxide particles precipitate in a S shape pattern during the materials transfer between Advancing Side and Retreating Side sites which leads to S-shape defect formation.