Loading...

An Investigation into Microstructure and Mechanical Properties of Al/Mgo Composite Fabricated by Friction Stir Processing

| 2023

43 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56424 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahedi, Mojtaba; Kokabi, Amir Hossein
  7. Abstract:
  8. In this research, the strength and wear resistance of aluminum 5083 was improved by using composites with magnesium oxide nanoparticles (MgO-20nm) and friction stir processing. The effect of the number of process passes and rotational speed variables, considering the number of one, three, and five passes at rotational speeds of 700, 1000, 1300, 1600, and 1900 rpm, was investigated on the mechanical properties and wear behavior of the composite. To determine the appropriate weight percentage of MgO powder, the longitudinal tensile strength of three composites with different weight percentages of 3, 4.7, and 6 were compared. The linear movement speed of the tool was selected as a constant value equal to 100 mm/min using preliminary tests. The geometry of the tool used for the process was considered as a threaded and triflute pin with a shoulder and pin diameter of 20 mm and 5 mm. Optical and scanning electron microscopes were used to examine the microstructure of the stir zone, including the grain size and distribution of reinforcing powder, and scanning electron microscopes were used to examine the fracture surface and wear surface. Longitudinal and transverse tensile tests, microhardness testing, and pin-on-disc wear were used to check the mechanical properties of the composite. The longitudinal tensile test was used to determine the yield strength and longitudinal tensile strength of the composite and elongation up to the breaking point, and the transverse tensile test was used to determine the fracture location and transverse tensile strength. Microhardness measurement and wear test were used to determine the hardness and wear resistance of the composite, respectively. Microstructural observations showed that the grain size became finer with the increase of rotation speed from rpm700 to rpm1300 in both three-pass mode and five-pass mode, but the grain size increased from rpm1300 to rpm1900. The smallest grain size with a value of 1.6 μm was obtained for the 1300-5 sample, which has a significant change compared to the base metal with a grain size of 100 μm. Also, the electron microscope images of the powder distribution show that with the increase in the number of passes, smaller agglomerated particles of MgO powder were created, and the smallest size of agglomerated particles was created at a rotation speed of 1300 rpm. The maximum tensile strength and elongation obtained for the five-pass sample and the rotational speed of 1300 rpm are 377 MPa and 24%, which have increased by 14% and 70%, respectively, compared to the base metal. The fracture surface of longitudinal tensile samples showed softer behavior with the increase of microstructure uniformity and reduction of particle agglomeration at high rotational speed and more passes, with the formation of smaller dimples. In the transverse tension test, the optimal mode was established for the sample with five passes and a rotation speed of 1000 rpm, in this mode, the bearing stress was 339 MPa and failure occurred from the HAZ. The results of the microhardness test show that by increasing the rotational speed up to 1300 rpm, the highest average hardness equal to 95 Vickers was obtained in the stir zone, and at all rotational speeds by applying 5 passes, more uniformity was created in the microhardness process. The results of the wear test show that increasing the hardness of the composite has played an important role in improving the wear resistance of the composite. The wear resistance obtained for the sample with five passes and 1300 rpm shows a 36% improvement compared to the base metal. The mechanisms observed in the wear samples are of a mechanical type, so in the samples with low rotational speeds, the adhesive mechanism was the main mechanism, and in the high rotational speeds, the abrasive mechanism was the main mechanism
  9. Keywords:
  10. Magnesium Oxide ; Mechanical Properties ; Friction Stir Welding ; Aluminum Alloy 5083 ; Wear Resistance ; Nanocomposite

 Digital Object List

 Bookmark

No TOC