The Discussion of Graduate student (MSc) Ahmed Ali Sakar was Held on Sunday 6/10/2019 at the discussion room in Building C at 9:00 am at the Department of Materials Engineering, University of Technology her thesis entitled

"Mechanical Behavior Optimization of friction stir welding for aluminum Alloy "

By the following gentlemen

The Thesis was scientifically evaluated by   Asst. Professor Dr. Muhsin Abdulla Al-Hussain from the University of Baghdad College of Engineering Department of Mechanical Engineering. And Linguistically Evaluated by Asst. Professor Dr. Omar Farooq Lutfi University of Technology/Department of Control and Systems Engineering. The discussion was done in a scientific atmosphere and The student was Awarded a Pass with credit after finishing all the correction recommended by the commute

Abstract

Friction stir welding (FSW) is a relatively modern joining technology, it is a solid-state welding process used for welding similar and dissimilar materials.

          In this study, the (FSW) process was conducted for two kinds of aluminum alloys (similar and dissimilar joint) of (AA2024-T3, and AA6061-T6) with a plate thickness of (3.5 mm) at three levels of different control parameters. The control parameters were: tool rotation speeds of (710, 1000 and 1400 rpm), linear speeds (feed rate) of (40, 56 and 80 mm/min), tapered pin geometry with three different shoulder diameters of (12, 14 and 16 mm), tilting angles of (1, 2 and 3 degrees), and welding directions of (1, 2 and 3 passes). The design of experiments (DOE), using the Taguchi method according to the orthogonal array (L₂₇) system, was used.

         Mechanical tests, such as tensile and bending test, were carried out to evaluate the joint quality of weldments. Microstructure and microhardness tests were done on cross-section of the welds in order to study the various welding zones. (XRD) and (SEM-EDS) inspections were used to study the phases that formed during welding process and the fractography of fracture surface after tensile test of (FSW) joints.

          A hybrid approach of Taguchi method and Fuzzy logic-based desirability function have been applied for multi-objective (Multiple response) optimization applied for (FSW) parameters to achieve better mechanical properties. The influence of the (FSW) parameters on the mechanical properties were determined using the analysis of variance (ANOVA). Characteristics (i.e. tensile strength, yield strength, elongation (%), microhardness, toughness and bending strength) have been considered for the optimization process.

          The work includes firstly, single optimization process using (Minitab®17) statistical software (Taguchi method); secondly, multi-objective optimization using (Matlab) software (Fuzzy logic application). The optimum condition of the optimization process had high acceptance with the results of the experimental work which was obtained from confirmation tests.

          The optimum condition that resulted from multi-objective optimization technique of shoulder diameter, rotation speed, linear speed, tilting angle and welding direction were found to be (14 mm), (1400 rpm), (40 mm/min), (3°) and (3 passes), respectively.

          The results showed that the multi-objective optimization exhibited better mechanical properties for similar joints of tensile strength, yield strength, elongation (%), microhardness, toughness and bending strength which were found to be (386 MPa), (251 MPa), (3.62 %), (279.3 VH), (138.965 MJ/m³) and (7.61 MPa), respectively; and for dissimilar joints of tensile strength, yield strength, elongation (%), microhardness, toughness and bending strength were (268 MPa), (227 MPa), (7.6 %), (224.3 VH), (36.754 MJ/m³) and (4.51 MPa), respectively, compared to single optimization.