Saad Khodir - Academia.edu (original) (raw)

Papers by Saad Khodir

Materials & Design, Feb 1, 2016

Abstract Friction stir spot welding of high-Mn twinning-induced plasticity steel was studied. Wel... more Abstract Friction stir spot welding of high-Mn twinning-induced plasticity steel was studied. Welds were made at different tool rotation speeds and constant plunge rate and dwell time. The microstructure evolution was examined by optical microscopy, scanning electron microscopy and electron backscattered diffraction technique. In addition, the microhardness distribution and tensile-shear load bearing capacity were measured. The friction stir spot welding process successfully produced high integrity completely defect-free joints at all the proposed welding parameters. However, the complex plastic deformation and high thermal cycle experienced had a significant effect on the weld region, which consisted of three distinct zones. The flow transition zone, stir zone and torsion zone were all characterized by a recrystallized grain structure. The heat affected zone was characterized by a coarse grain structure as a result of grain growth caused by the high thermal cycles experienced. The hardness was significantly affected by friction stir spot welding, resulting in a softened region in the joint area. The softening increased as the rotation rate increased. The maximum peak tensile shear load of 13 kN was obtained at 750 rpm, and a considerable amount of extension was obtained in all the joints with a maximum of 4 mm at 500 rpm.

Materials transactions, 2006

AA2024-T3 Aluminum alloy plates of 3 mm thickness were friction stir butt welded at a constant we... more AA2024-T3 Aluminum alloy plates of 3 mm thickness were friction stir butt welded at a constant welding speed of 50 mm/min and rotation speeds of 400, 600, 800, 1000, 1250, and 1500 min À1. Effects of rotation speed on microstructures, hardness distributions, and tensile properties of the joints were investigated. Equiaxed grain size increased with increasing rotation speed till 1000 min À1 of rotation speed. Increase of rotation speed more than 1000 min À1 brought about no significant increase of grain size in the stir zone. Also, increasing rotation speed resulted in finer and more homogenous distributions of second phase particles in the stir zone. Hardness increased both in the stir zone and thermo mechanically affected zone as the rotation speed increased and reached to that of base metal. Kissing bond-free joints were fractured at the heat affected zone on the retreating side and a maximum tensile strength of the joints was 402 MPa which was achieved at 1250 min À1 of rotation speed. The joint efficiency was 88%.

John Wiley & Sons, Inc. eBooks, Jun 28, 2011

Journal of Polymer Research

International Journal of Materials Technology and Innovation

Steam boiler flange, made of steel ASTM A105 welded to spool pipe, experienced a failure near the... more Steam boiler flange, made of steel ASTM A105 welded to spool pipe, experienced a failure near the welding area after six years of service. The operator company has reported that a sudden increase in operating pressure and temperature exceeded the normal operation conditions. As a result, the failed flange and welded spool pipe segments were received for further investigation using root cause analysis to determine the reason for the failure. The failed parts were visually inspected (VT) and tested for subsurface defects with a fluorescent wet magnetic particle test (MT). Chemical analysis, microstructure observations, and hardness tests are conducted for the failed flange and pipe. It is noticed that there were no abnormalities or indications of creep or overheating were found in the microstructure and hardness values. Upon examining the macro & microstructure of the connecting weld joint, several welding defects, such as non-metallic conclusions, few porosities, and lack of fusion between welded passes, were noticed. Scanning Electron Microscope (SEM) observations showed that fine striations as beach marks on the fractured surface provided strong evidence of fatigue failure. The identified crack originated from welding defects and progressed through the flange material due to fluctuating radial stresses due to the cyclic changes in working pressure during service. To prevent similar failures, it is recommended to apply proper welding procedure specifications (WPS) by qualified welders, conduct regular inspections and maintenance of the steam boiler, and keep working conditions stable.

Procedia Structural Integrity, 2018

During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.

Materials Transactions, 2007

Dissimilar aluminum alloys such as 2024-T3 and 7075-T6 plates 3 mm thickness were friction stir b... more Dissimilar aluminum alloys such as 2024-T3 and 7075-T6 plates 3 mm thickness were friction stir butt welded. The welding was carried out at a constant welding speed of 100 mm/min and rotation speeds of 400, 800, 1200, 1600 and 2000 min -1 . Effects of rotation speeds and fixed location of two alloys on microstructures especially the homogeneity of elemental distribution in the stir zone (SZ), hardness distributions, and tensile properties of the joints were investigated. The homogeneity of constituents of the two alloys in the SZ was analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). At the lowest rotation speed of 400 min -1 there was no mixing of two alloys in the SZ and a border between them was observed regardless of the fixed location. Increase of rotation speed more than 400 min -1 brought about a mixed structure likewise onion ring with periodic change of equiaxed grain size and heterogeneous distribution of alloying ...

MATERIALS TRANSACTIONS, 2007

Dissimilar alloys such as 2024-T3 Al alloy and AZ31 Mg alloy of plates in 3 mm thickness has been... more Dissimilar alloys such as 2024-T3 Al alloy and AZ31 Mg alloy of plates in 3 mm thickness has been friction stir butt welded. The welding was carried out at a constant rotation speed of 2500 min À1 and welding speeds of 200, 300, 400 and 550 mm/min. Effects of welding speeds on microstructures and hardness distributions of the joints were investigated. Distribution of phases in the stir zone (SZ) was analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). Increasing welding speed brought about a redistribution of phases in SZ where the regions occupied by 2024 Al alloy concentrated in the lower portion of SZ while AZ31 Mg alloy concentrated in the upper region beneath the tool shoulder. The laminated structure was formed in the SZ near the boundary between SZ and TMAZ on the advancing side of 2024 Al alloy regardless of the welding speed. The hardness value fluctuates in the SZ due to formation of intermetallic compounds that formed by constitutional liquation during welding.

Materials Science and Engineering: B, 2008

The present study focuses on the microstructure and mechanical properties of dissimilar joints of... more The present study focuses on the microstructure and mechanical properties of dissimilar joints of 2024-T3 Al alloy to 7075-T6 Al alloy produced by friction stir welding. Effects of welding speed and fixed location of base metals on microstructures, hardness distributions, and tensile properties of the welded joints were investigated. SEM-EDS analysis revealed that the stir zone contains a mixed structure and onion ring pattern with a periodic change of grain size as well as a heterogeneous distribution of alloying elements. The maximum tensile strength of 423.0 MPa was achieved for the joint produced at welding speed of 1.67 mm/s when 2024 Al alloy was located on the advancing side.

Materials Science and Engineering: A, 2007

Friction stir welding (FSW) has received a great deal of attention as a new solid-state welding t... more Friction stir welding (FSW) has received a great deal of attention as a new solid-state welding technique. In the present study, the relationship between the microstructure of stir zone and the mechanical property of FS-welded 5083 aluminum alloy was investigated. The microstructures of the stir zones consisted of fine equiaxed grains at various FSW conditions in FS-welded 5083 Al alloy.

Journal of Materials Engineering and Performance, 2016

Types and distribution of intermetallic compound phases and their effects on the mechanical prope... more Types and distribution of intermetallic compound phases and their effects on the mechanical properties of dissimilar Al/Cu friction stir welded joints were investigated. Three different rotation speeds of 1000, 1200 and 1400 rpm were used with two welding speeds of 20 and 50 mm/min. The results show that the microstructures inside the stir zone were greatly affected by the rotation speed. Complex layered structures that containing intermetallic compound phases such as CuAl 2 , Al 4 Cu 9 were formed in the stir zone. Their amount found to be increased with increasing rotation speed. However, the increasing of the rotation speed slightly lowered the hardness of the stir zone. Many sharp hardness peaks in the stir zones were found as a result of the intermetallic compounds formed, and the highest peaks of 420 Hv were observed at a rotation speed of 1400 rpm. The joints ultimate tensile strength reached a maximum value of 105 MPa at the rotation speed of 1200 rpm and travel speed of 20 mm/min with the joint efficiency ranged between 88 and 96% of the aluminum base metal. At the travel speed of 50 mm/min, the maximum value of the ultimate tensile strength was 96 MPa at rotation speed of 1400 rpm with the joint efficiency ranged between 79 and 90%. The fracture surfaces of tensile test specimens showed no evidence for the effect of the brittle intermetallic compounds in the stir zones on the tensile strength of the joints.

Journal of Materials Science, 2013

MATERIALS TRANSACTIONS, 2006

AA 2024-T3 Aluminum alloy plates of 3 mm thickness were friction stir butt welded at a constant r... more AA 2024-T3 Aluminum alloy plates of 3 mm thickness were friction stir butt welded at a constant rotation speed of 1250 min À1 and welding speeds of 50 and 100 mm/min. Three types of backing materials such as SUS304, pure copper block, and a combination of copper-block with 0.5 mm SUS304 were used. Controls of temperature history were achieved and their effects on microstructures, hardness distributions, and tensile properties of the joints were investigated. Grain size of the stir zone decreased from 7.4 mm in the case of stainless steel to 4.4 and 1.7 mm for the cases of a combination backing type and copper-block respectively. As a result of higher heating/or cooling rates, both higher welding speed and copper-block backing material resulted in increased hardness in HAZ and a maximum value was achieved for the combined backing plate at 100 mm/min of welding speed. Higher peak temperature was beneficial for higher hardness in stir zone while lower one in HAZ. A maximum tensile strength of the joint was achieved at a welding speed of 100 mm/min when the combined backing type was used. The joint efficiency of this case was 93.6% and this value was the highest among the present joints.

Materials & Design, 2014

The microstructures and mechanical properties of weld metals of high strength steels having 3–9% ... more The microstructures and mechanical properties of weld metals of high strength steels having 3–9% Ni content have been investigated with getting a better insight into the role of retained austenite. The weld metals were produced autogenously by electron beam welding (EBW) process. The results showed that once Ni content exceeded 4% prior austenitic grains of the weld metals were rapidly coarsened and solidified into a cellular dendritic structure. The content of retained austenite increased with Ni addition and was preferentially distributed along the lath boundary, edges of coalesced bainite, cellular dendritic boundaries and at prior austenite grain boundaries. Retained austenite morphology was also changed on increasing nickel content from a discontinuous film into a continuous one. The impact toughness for half-size specimens has shown a significant drop from 126 J to 40 J when Ni content increased from 3% to 5%, while further addition of Ni partially recovered the toughness. Tho...

Ultrasonic bonding is relatively new and very useful technique for bonding dissimilar metals in w... more Ultrasonic bonding is relatively new and very useful technique for bonding dissimilar metals in which brittle intermetallic compounds are easily developed in conventional fusion welding processes The possibility of evaluations of ultrasonic bonds by ultrasonic testing was discussed in detail. In order to evaluate the quality of bonds it is necessary to obtain the correlation between the results by ultrasonic testing as non destructive test and mechanical properties, tensile shear strength in this work as a destructive test. It was confirmed that ultrasonic testing (C-scope mode) was useful to evaluate the bonding situations of the bonds by ultrasonic bonding when the appropriate threshold level was selected. In this study it was found that the threshold level of 200 had a good correlation between the result of ultrasonic testing and a tensile shear test.

ABSTRACT Thixoforming process is a semisolid metal processing route, which involves forming of al... more ABSTRACT Thixoforming process is a semisolid metal processing route, which involves forming of alloys in the semisolid state to near net shaped products. To investigate the effects of thixoextrusion parameters on microstructure and mechanical properties of commercial 6061 aluminum alloy, forward extrusion experiments were carried out in the semisolid state. The results showed that fine and globular microstructure can be achieved using semisolid forming. SEM micrographs and mechanical tests results showed that the tensile behavior of thixoformed specimens at billet temperatures below 620 °C is relatively elastic and brittle. With increasing die temperature up to 620 °C more elongation value and ductility were obtained in the thixoformed specimens.