Edited by A. Nurul Amin. Published: January 14th DOI: Jonas Open access peer-reviewed 3. Microstructure and Properties of Elektron 21 Magnesium Alloy. By Andrzej Kielbus Open access peer-reviewed Kim Open access peer-reviewed Edited Volume and chapters are indexed in.
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Shin: Mater. Forum Vol. Park, J. Lim, D. Eliezer and K. Forum, Vol. All Rights Reserved. Log In. The major problems encountered in welding of Mg-alloys are the presence of porosity and the emission of large volumes of non-toxic fumes in arc welding. There are numerous experimental and numerical studies on the investigation of the welding performance of the plates joined by the friction stir welding method. In the most of the experimental examinations, first, researchers tried to obtain optimum parameters for best welding performance. However, Gharacheh et al. Xunhong and Kuaishe, aimed to obtain the best parameters for FSWed AZ31 Mg alloy joint with excellent appearance and no distortion in their study.
Albakri et al. They showed the asymmetric nature of temperature distribution and material movements and their effects on flow during the FSW process so slightly higher temperatures in the range of K were developed on the advancing side of the sheet as compared to the retreating side under all processing conditions. They also reported a combination of high translation and low rotational tool speeds were ideal to cause effective grain refinement. Darras, referred that more grain refinement can be achieved at lower rotational speeds.
This is believed to be related to the thermal histories associated with the process because more heat is generated at higher rotational speeds and therefore, more grain growth takes place. Wen et al. Cao and Jahazi, studied about effect of various welding speed of FSWed AZ31B-H24 magnesium alloys and they showed defect, microstructure, hardness and tensile strength.
Yang et al. Also they researched grain refinement in welding zone, fracture features and ultimate tensile strength. Chowdhury et al. They tried to characterize the microstructure, texture and tensile properties and they reported that rotational rate has stronger effect on the yield stress than ultimate tensile stress.
Processing and Characterization of Magnesium Alloys
Chang et al. Chai et al. They applied FSW in air and under water. They investigated thermal distribution on workpiece, microstructure and mechanical properties. Suhuddin et al. Padmanaban et al. They compared to the results of each technique about microstructure, tensile properties and hardness. Fu et al. They reported that the joints which performed by higher rotational speed have better tensile properties. Soundararajan et al.
The objective of this study is to investigate the effect of the rotation a land translational speeds on the mechanical properties both experimentally and numerically. In the experimental study, tensile tests, metallography and Vickers micro hardness measurements of FSWed AZ31 Mg-alloy plates were carried out.
AZ31 Mg-alloy plates with a thickness of 6. Figure 1 shows the view of the FSW process. The welding trials were used clamping and steel-backing plate. The tool used in the study was manufactured from H13 tool steel. Friction stir welding tools must have some special features such as ambient and elevated temperature strength, elevated temperature stability, wear resistance, fracture toughness. H13 is a chromium-molybdenum hot-worked air-hardening steel and is well known with its good high-temperature strength, thermal fatigue resistance and wear resistance Mishra and Mahoney, H13 chromium hot-work steel is widely used in hot and cold work tooling applications.
The shoulder diameter was 20 mm. The pin was threaded with a diameter of 8 mm M8. For the metals and alloys having high melting point, the heat generated by friction and stirring may be inadequate to soften and plasticize the material around the pin and shoulder. Therefore, preheating or additional external heating sources can help the material flow and welding process. Preheating of theworkpiecebeforeweldingshould be beneficialforimprovingweldingspeedandminimizingtoolwear Jabbari, In this study, pre-heat was provided by holding of the tool to be rotated but not to be translated at the beginning of the welding process for 40 s.
Pin used in the experimental study can be seen in Figure 2. Figure 3 shows the measurement setup used to determine the temperature histories on the plate during the welding operation. Positions of the thermocouples are shown in Figure 4. Thermocouples were placed near the shoulder of the pin.
Temperature values obtained by the measurements were compared with those predicted by the numerical analyses. In the experiments, K-type thermocouples with a diameter of 0. Holes with a diameter of 3 mm were drilled on both sides of the workpiece to accommodate the thermocouples. The thermocouples were embedded in the holes. The distance between sequent thermocouples is 45 mm.
Thermocouples N1 to N5 were located on the advancing side of the workpiece whereas N6 to N10 were on the retreating side of the workpiece.
In the numerical analyses, the thermomechanical analyses were carried out using ANSYS commercial software. These analyses were carried out in two stages. Transient thermal analysis is the first stage followed by nonlinear transient structural analysis in the second stage.
Since the problem involves nonlinear analysis, full Newton-Raphson option is used to solve the nonlinear equations. The thermomechanical coupled three-dimensional model was used in the numerical analyses. Detailed explanations about the numerical models and stages of the numerical study were given in previous study Serindag et al.
Torque required to rotate the tool, heat generated by the shoulder and pin were determined in order to use them as the boundary conditions in the finite element analyses Serindag et al. Transient finite element analyses were performed considering moving heat source. Heat source during welding were considered as the friction between the rotating tool and the welded workpieces. In modeling the thermal analyses, the moving heat sources of the shoulder and the pin were represented as moving the heat generation.
Figure 6 shows the boundary conditions used in the thermal and structural finite element analyses. Mechanical and physical properties of the AZ31 Mg alloy change with the temperature; so in the nonlinear finite element analyses, material properties were defined depending on the temperature. Tables 2 and 3 show the thermal conductivity, k and heat capacity, C p values of AZ31 Mg-alloy depending on temperature used in the thermal analyses Gok and Aydin, , Yang et al. Figure 7 shows the stress-strain curves of AZ31 used in the nonlinear structural analyses under different ambient conditions.
Stress-strain curves are used in the structural analyses Gok and Aydin, In the present study, the modeling of friction stir welding was carried out using ANSYS commercial software. Transient thermal finite element analyses were performed in order to obtain the temperature histories in the welded AZ31 Mg alloy plates during the welding operation.