S. Rajakumar

Establishing empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints

AA 6061-T6 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance. Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys, friction stir welding (FSW) process is an emerging solid state joining process in which the material welded does not melt and recast. Joint strength is influenced by the grain size and tensile strength of the weld nugget region. Hence, an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints. The empirical relationships are developed by response surface methodology (RSM) incorporating FSW tool and process parameters. A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.

Multi-objective optimization of friction stir welding parameters using desirability approach to join Al/SiCp metal matrix composites

Silicon carbide particulate (SiCp) reinforced cast aluminium (Al) based metal matrix composites (MMCs) have gained wide acceptance in the fabrication of light weight structures requiring high specific strength, high temperature capability and good wear resistance. Friction stir welding (FSW) process parameters play major role in deciding the performance of welded joints. The ultimate tensile strength, notch tensile strength and weld nugget hardness of friction stir butt welded joints of cast Al/SiCp MMCs (AA6061 with 20% (volume fraction) of SiCp) were investigated. The relationships between the FSW process parameters (rotational speed, welding speed and axial force) and the responses (ultimate tensile strength, notch tensile strength and weld nugget hardness) were established. The optimal welding parameters to maximize the mechanical properties were identified by using desirability approach. From this investigation, it is found that the joints fabricated with the tool rotational speed of 1370 r/min, welding speed of 88.9 mm/min, and axial force of 9.6 kN yield the maximum ultimate tensile strength, notch tensile strength and hardness of 265 MPa, 201 MPa and HV114, respectively.

Optimizing Diffusion Bonding Parameters to Maximize the Strength of AA6061 Aluminum and AZ61A Magnesium Alloy Joints

The main difficulty when joining magnesium (Mg) and aluminum (Al) alloys by fusion welding process lies in the existence of oxide films and formation of brittle intermetallic in the weld region. However, solid-state welding processes such as friction welding and diffusion bonding are suitable processes to join these two materials. The diffusion bonding process parameters such as bonding temperature, bonding pressure, holding time, and surface roughness of the bond specimen play a major role to determine the joint strength. In this investigation, an attempt was made to develop empirical relationships to predict the lap shear strength and bonding strength of diffusion bonded dissimilar joints of AZ61A magnesium and AA6061 aluminum alloys, incorporating the above-mentioned parameters. Response surface methodology (RSM) was applied to optimize the diffusion bonding process parameters to attain the maximum shear strength and bonding strength of the joint. From this investigation, it is found that the bonds fabricated with the bonding temperature of 420.43°C, bonding pressure of 7.70 MPa, holding time of 27.15 min, and surface roughness of 0.10 μm exhibited maximum shear strength and bonding strength of 51.24 and 72.10 MPa, respectively.

Developing Empirical Relationships to Predict Grain Size and Hardness of the Weld Nugget of Friction Stir Welded AA7075-T6 Aluminium Alloy Joints

High-strength, precipitation-hardening AA7075-T6 alloy is used extensively in aircraft primary structures. Friction stir welding process is an emerging solid state joining process in which the material that is being welded does not melt and recast. The FSW process and tool parameters play a major role in deciding the joint strength. Joint strength is influenced by the grain size and hardness of the weld nugget region. Hence, in this investigation an attempt has been made to develop empirical relationships to predict the grain size and hardness of the weld nugget of the friction stir welded AA7075-T6 aluminium alloy joints. Six factors, five levels, central composite, rotatable design matrix is used to optimize the experimental conditions. The empirical relationships are developed by response surface methodology incorporating tool and process parameters. A linear regression relationship is also established between grain size and hardness of the weld nugget of friction stir welded joints. The weld nugget grain size is related with hardness of the joint. The developed relationships can be effectively used to predict the weld nugget grain size of the joint non-destructively by measuring the weld nugget hardness.