Weld reliability characterisation of dissimilar friction stir welds of aluminium alloys
- Authors: Azeez, Sarafadeen Tunde
- Date: 2017
- Subjects: Friction stir welding , Dissimilar welding , Welded joints - Reliability , Metals - Weldability , Aluminum
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/269883 , uj:28676
- Description: D.Phil. (Mechanical Engineering) , Abstract: Welding is a crucial joining technique that is generally employed in the fabrication industry. The integrity of weld joints is of great importance, because of its safety and the economic implications. This research provides a glimpse into the basic concept of weld reliability, failure prediction, mechanical and microstructure characterization, with respect to friction stir welding (FSW) of similar and dissimilar Aluminium alloys. The establishment of this concept will enhance welds in service performance and their application in setting criteria for the evaluation of materials’ integrity. Friction stir welding (FSW) of a 6 mm thick AA6082-T6 Aluminium alloy was performed for the preliminary experiment. Three welding speeds of 90 mm/min, 120 mm/min and 150 mm/min at a tool-rotational speed of 950 rpm were used. A solution heat treatment carried out on the specimen revealed a drastic response by an over 120 % increment in strength. The welds at welding speed 150mm/min and the tool-rotation speed of 950rpm (i.e. sample S3) have maximum UTS values of 101MPa at as-weld and 234MPa after heat treatment (i.e. sample H3). The lowest values of strength were observed at 84MPa, at as-weld (i.e. sample S2) and 167MPa when heat-treated (i.e. 90mm/min and 950rpm, sample H1), respectively. The higher the heat input the softer the weld joints. However, the as-weld samples (S1-S6) deviate from the conventional trend unlike the heat treated samples (H1-H6). This is due to overlapping of the temperature field for friction stir bead at the end of each welds. All the samples (i.e. similar welds) fractured at the heat-affected zone (HAZ), due to the reduction in hardness, as a result of a dissolution mechanism. Aside from the point of fracture, the disparities in composition evolution and physical integrity of the weld joints are similar. Ductility is a material property that is inversly related to the strength of the materials. However, a solution heat treatment of the samples (H1-H6) has an increment of over 120% in UTS...
- Full Text:
- Authors: Azeez, Sarafadeen Tunde
- Date: 2017
- Subjects: Friction stir welding , Dissimilar welding , Welded joints - Reliability , Metals - Weldability , Aluminum
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/269883 , uj:28676
- Description: D.Phil. (Mechanical Engineering) , Abstract: Welding is a crucial joining technique that is generally employed in the fabrication industry. The integrity of weld joints is of great importance, because of its safety and the economic implications. This research provides a glimpse into the basic concept of weld reliability, failure prediction, mechanical and microstructure characterization, with respect to friction stir welding (FSW) of similar and dissimilar Aluminium alloys. The establishment of this concept will enhance welds in service performance and their application in setting criteria for the evaluation of materials’ integrity. Friction stir welding (FSW) of a 6 mm thick AA6082-T6 Aluminium alloy was performed for the preliminary experiment. Three welding speeds of 90 mm/min, 120 mm/min and 150 mm/min at a tool-rotational speed of 950 rpm were used. A solution heat treatment carried out on the specimen revealed a drastic response by an over 120 % increment in strength. The welds at welding speed 150mm/min and the tool-rotation speed of 950rpm (i.e. sample S3) have maximum UTS values of 101MPa at as-weld and 234MPa after heat treatment (i.e. sample H3). The lowest values of strength were observed at 84MPa, at as-weld (i.e. sample S2) and 167MPa when heat-treated (i.e. 90mm/min and 950rpm, sample H1), respectively. The higher the heat input the softer the weld joints. However, the as-weld samples (S1-S6) deviate from the conventional trend unlike the heat treated samples (H1-H6). This is due to overlapping of the temperature field for friction stir bead at the end of each welds. All the samples (i.e. similar welds) fractured at the heat-affected zone (HAZ), due to the reduction in hardness, as a result of a dissolution mechanism. Aside from the point of fracture, the disparities in composition evolution and physical integrity of the weld joints are similar. Ductility is a material property that is inversly related to the strength of the materials. However, a solution heat treatment of the samples (H1-H6) has an increment of over 120% in UTS...
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Reinforcement of aluminium AA1100-MIG welds using copper powder
- Authors: Abima, Cynthia Samuel
- Date: 2017
- Subjects: Aluminum alloys - Welding , Welded joints - Reliability , Copper - Welding , Shielded metal arc welding , Gas tungsten arc welding
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269571 , uj:28637
- Description: M.Ing. (Mechanical Engineering) , Abstract: Metal matrix composites have been used in recent times to achieve better mechanical properties of materials and improved general performance of welded structures. Metal Inert Gas (MIG) welding also known as Gas Metal Arc welding (GMAW) is an arc-welding process, which joins metals by heating them with an arc between a continuously fed solid electrode and the work piece. Aluminium and its alloys provides unique properties which makes it one of the most attractive metallic, economical, versatile material for a broad range of uses in engineering applications, such as aerospace, automobile and mineral processing industries. Against this background, aluminium is not suitable for all engineering applications, and it sometimes requires some degree of reinforcement, particularly in a corrosive environment and/or at elevated temperatures. This study focuses on ascertaining the integrity of MIG welded pure aluminium reinforced with copper powder at the weld zone. Material characterizations of the aluminium (Al) and copper (Cu) metal matrix composites produced via the MIG welding process were conducted. The pure aluminium, AA1100 sheets were machined to a 45o v-grooved shape, and then filled with copper powder particles and welded. The welded samples were characterised by performing mechanical tests (tensile testing using the Zwick Roell 2250 tensile machine and microhardness profiling using a digital Vickers microhardness testing machine) and microstructural investigation via the scanning electron microscope (SEM), the energy-dispersive spectroscopy (EDS) and optical microscope. This was followed by X-ray diffraction analysis (XRD), and corrosion test by electrochemical polarization method. The results revealed that the addition of copper powder significantly increased the hardness property of the welds, as the welds with copper powder particles reinforcement showed higher hardness values when compared to those without the copper powder particle reinforcement. The highest tensile strength was obtained from the copper reinforced sample. Furthermore, the microstructures revealed finer grain structures for the reinforced samples. The samples with reinforcement also exhibited better corrosion properties. It was therefore, concluded that the aluminium (Al) and copper (Cu) metal matrix composite welded via MIG welding produced better mechanical properties, as well as increased corrosion resistance behaviour, and it can definitely be recommended for typical aerospace applications
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- Authors: Abima, Cynthia Samuel
- Date: 2017
- Subjects: Aluminum alloys - Welding , Welded joints - Reliability , Copper - Welding , Shielded metal arc welding , Gas tungsten arc welding
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269571 , uj:28637
- Description: M.Ing. (Mechanical Engineering) , Abstract: Metal matrix composites have been used in recent times to achieve better mechanical properties of materials and improved general performance of welded structures. Metal Inert Gas (MIG) welding also known as Gas Metal Arc welding (GMAW) is an arc-welding process, which joins metals by heating them with an arc between a continuously fed solid electrode and the work piece. Aluminium and its alloys provides unique properties which makes it one of the most attractive metallic, economical, versatile material for a broad range of uses in engineering applications, such as aerospace, automobile and mineral processing industries. Against this background, aluminium is not suitable for all engineering applications, and it sometimes requires some degree of reinforcement, particularly in a corrosive environment and/or at elevated temperatures. This study focuses on ascertaining the integrity of MIG welded pure aluminium reinforced with copper powder at the weld zone. Material characterizations of the aluminium (Al) and copper (Cu) metal matrix composites produced via the MIG welding process were conducted. The pure aluminium, AA1100 sheets were machined to a 45o v-grooved shape, and then filled with copper powder particles and welded. The welded samples were characterised by performing mechanical tests (tensile testing using the Zwick Roell 2250 tensile machine and microhardness profiling using a digital Vickers microhardness testing machine) and microstructural investigation via the scanning electron microscope (SEM), the energy-dispersive spectroscopy (EDS) and optical microscope. This was followed by X-ray diffraction analysis (XRD), and corrosion test by electrochemical polarization method. The results revealed that the addition of copper powder significantly increased the hardness property of the welds, as the welds with copper powder particles reinforcement showed higher hardness values when compared to those without the copper powder particle reinforcement. The highest tensile strength was obtained from the copper reinforced sample. Furthermore, the microstructures revealed finer grain structures for the reinforced samples. The samples with reinforcement also exhibited better corrosion properties. It was therefore, concluded that the aluminium (Al) and copper (Cu) metal matrix composite welded via MIG welding produced better mechanical properties, as well as increased corrosion resistance behaviour, and it can definitely be recommended for typical aerospace applications
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Material characterization and optimisation of friction stir welds of 6061-T6 aluminium alloy
- Semakane, Letlhogonolo Nicholas
- Authors: Semakane, Letlhogonolo Nicholas
- Date: 2018
- Subjects: Friction stir welding , Welded joints - Reliability , Welded joints - Testing , Aluminum alloys
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284076 , uj:30668
- Description: Abstract: In this study, the effect of rotational speed and traverse speed on the micro – and macrostructure, and mechanical properties (tensile and microhardness properties) of friction stir butt-welded 6061-T6 aluminium alloy has been investigated. A number of research studies have been conducted on friction stir welding of various aluminium alloys, the rotational and traverse speeds were noticed to have a greater influence on the formation of a quality weld. In this study, welds were fabricated from different parameter combinations by varying the rotational and traverse speeds during the welding procedure. The rotational speeds employed representing the low, medium and high settings are 700, 900, and 1100 rpm respectively while the traverse speeds utilised were 60, 80, and 100 mm/min traverse speeds. To ascertain the joint integrities, the welds were characterised through hardness, microstructure, and tensile tests. The hardness test was performed along the cross-section of the welds. The changes in the microstructure and hardness were analysed and further correlated to the tensile strength of the 6061-T6 aluminium alloy. Optical microscope and Scanning Electron Microscope were used for microstructural analysis. Instron machine and Vickers hardness machine were used to perform tensile and hardness tests, respectively. The results showed that the grain size decreased from the heat affected zone (HAZ) towards the centre of the nugget zone (NZ) due to the stirring during the FSW process. The average hardness in the NZ decreased when the rotational speed varied from 700 rpm to 900 rpm, and then increased with a further increase in the rotational speed to 1100 rpm at constant traverse speeds of 60, 80 and 100 mm/min. Moreover, the ultimate tensile strength increased with an increase in traverse speed at constant rotational speeds of 700, 900, and 1100 rpm. In addition, the tensile results showed that fracture occurred in the relatively weak region which is the HAZ of the advancing side of the weld under a ductile-mode fracture. Additionally, the HAZ was found to be the soft zone in the weld due to thermal action of the FSW process and also due to the heat treatability of the aluminium alloy under investigation. It was observed that welds produced at 1100 rpm and 100 mm/min has the optimum weld quality and can be recommended for future welds in typical applications. , M.Ing. (Mechanical Engineering)
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- Authors: Semakane, Letlhogonolo Nicholas
- Date: 2018
- Subjects: Friction stir welding , Welded joints - Reliability , Welded joints - Testing , Aluminum alloys
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284076 , uj:30668
- Description: Abstract: In this study, the effect of rotational speed and traverse speed on the micro – and macrostructure, and mechanical properties (tensile and microhardness properties) of friction stir butt-welded 6061-T6 aluminium alloy has been investigated. A number of research studies have been conducted on friction stir welding of various aluminium alloys, the rotational and traverse speeds were noticed to have a greater influence on the formation of a quality weld. In this study, welds were fabricated from different parameter combinations by varying the rotational and traverse speeds during the welding procedure. The rotational speeds employed representing the low, medium and high settings are 700, 900, and 1100 rpm respectively while the traverse speeds utilised were 60, 80, and 100 mm/min traverse speeds. To ascertain the joint integrities, the welds were characterised through hardness, microstructure, and tensile tests. The hardness test was performed along the cross-section of the welds. The changes in the microstructure and hardness were analysed and further correlated to the tensile strength of the 6061-T6 aluminium alloy. Optical microscope and Scanning Electron Microscope were used for microstructural analysis. Instron machine and Vickers hardness machine were used to perform tensile and hardness tests, respectively. The results showed that the grain size decreased from the heat affected zone (HAZ) towards the centre of the nugget zone (NZ) due to the stirring during the FSW process. The average hardness in the NZ decreased when the rotational speed varied from 700 rpm to 900 rpm, and then increased with a further increase in the rotational speed to 1100 rpm at constant traverse speeds of 60, 80 and 100 mm/min. Moreover, the ultimate tensile strength increased with an increase in traverse speed at constant rotational speeds of 700, 900, and 1100 rpm. In addition, the tensile results showed that fracture occurred in the relatively weak region which is the HAZ of the advancing side of the weld under a ductile-mode fracture. Additionally, the HAZ was found to be the soft zone in the weld due to thermal action of the FSW process and also due to the heat treatability of the aluminium alloy under investigation. It was observed that welds produced at 1100 rpm and 100 mm/min has the optimum weld quality and can be recommended for future welds in typical applications. , M.Ing. (Mechanical Engineering)
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