Muralimohan Cheepu

Fabrication and Analysis of Accumulative Roll Bonding Process between Magnesium and Aluminum Multi-Layers

In the present study commercially pure magnesium and aluminum strips were fabricated using the process of accumulative roll bonding. It is a prominent solid state joining process to manufacture similar and dissimilar materials for various applications. Three layers of stack was used for bonding of multilayered composite and preheated at 250 °C for 20 min. The effects of rolling parameters on bond strength and deformation of the strips were analyzed. The interface between aluminum and magnesium were characterized to identify the formation of diffusion compounds, and are found to be the presence of Al12Mg17 intermetallic compounds. Tensile strength of the bonds was increased with the decreasing of thickness of the strips. The interface characteristics were analyzed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDAX) to reveal the intermetallic compounds, micro cracks and bonding properties. The strength of the composites is varying with width of the intermediate strip and maximum strength values were obtained after three passes of the roll bonding.

Improving Mechanical Properties of Dissimilar Material Friction Welds

Friction welding of stainless steel to titanium with aluminum insert metal was investigated to improve the mechanical properties of the joints. Two different methods were used to insert the aluminum as a barrier between to substrates. The process parameters were found to be different for these two methods to obtain the sound welds. The friction welds between stainless steel and titanium with aluminum insert prevented the formation of brittle intermetallic compounds in the weld interface. A new intermetallic compounds such as AlTi and Al3Ti were formed between titanium and aluminum insert metal interface which are more ductile than the FeTi and CrTi intermetallic compounds. The joints characterized that the aluminum insert metal improved the metallurgical reaction at the weld interfaces thus indicates the results of decrease in microhardness of the intermetallic compounds which have major influence on the strength of the joints. The tensile strength of the aluminum insert welds was higher than the direct joints between the stainless steel and titanium. Higher tensile properties were attained at higher upset pressure condition due to the effect of higher force upon the welded materials and the remnant narrower thickness of insert metal.

Influence of Water Cooling and Post-Weld Ageing on Mechanical and Microstructural Properties of the Friction-Stir Welded 6061 Aluminium Alloy Joints

A 6061-T6 aluminium alloy was friction stir welded in submerged water as well as in air cool at a constant traverse speed and different rotational speed in order to investigate the microstructural characterization and mechanical behaviour of the joints. In order to improve the tensile strength of the joints, weldments were studied at different heat treatment processes such as post weld aged condition and solutionized condition. It is observed that, water cooled joints are resulted in enhancing of both strength and ductility with the lower strain hardening ability than the air cooled joints. The width of the hardness distribution varies with the different cooling process of the joints. The highest hardness peak observed to be located in the heat affected zone of the joints. The maximum tensile strength of the joints achieved for welds under water cooled conditions in contrast to air cooled conditions. Moreover, a combination of water cooling and post weld ageing is proven to be the optimal path to improving the microstructural and mechanical properties of the joints with a maximum efficiency of 89.87% of the base metal strength. The microstructural observations of the joints revealed the presence of voids defects for the low rotational speed joints due to the insufficient heat input. The nugget of the higher tensile strength joints were free from defects and showed the fine grained material flow patterns which are constructive to obtain better mechanical properties.

Dissimilar Friction Welding of AISI 304 Austenitic Stainless Steel and AISI D3 Tool Steel: Mechanical Properties and Microstructural Characterization

In recent years, the continuous demand for dissimilar joining combination of various materials increasing in manufacturing sector for various applications such as power plants, nuclear, and aerospace applications. The joining of dissimilar metals using conventional fusion welding methods is exhibited in unsatisfactory joint strength. The use of solid-state welding methods is most suitable for joining of dissimilar combination in the current scenario. In this study, dissimilar joining of 304 austenitic stainless steel and D3 tool steel are joined using friction welding process to investigate the properties and joint interface characteristics. To identify the feasibility of joining dissimilar materials using friction welding process, the experiment is performed at different input welding conditions such as friction pressure and upset pressure were varying from minimum to maximum values to obtain the reliable joint strength. The friction welded joints were characterized using microscope observations at the weld interface and failure modes are discussed.

Interfacial Microstructures and Characterization of the Titanium—Stainless Steel Friction Welds Using Interlayer Technique

The joints of dissimilar metals and alloys are increasing demand as essential parts of aerospace, nuclear and cryogenic applications. One of the greatest challenges for design engineers is to develop and implement fast and cost-effective industrial procedures to join titanium with stainless steel and aluminum. Regardless of the welding conditions, such high specific properties of the metal combinations cannot be fusion welded in conventional method, because of the formation of highly brittle intermetallic compounds in the fusion zone. However, solid-state joining processes, friction-welding process contemplated to offer the highest potential for successful joining of bimetallic components. The friction welding techniques are highly efficient and it has the advantage of far greater weldability and reduces the risk of interfacial reaction. In the present investigation, microstructure formation at the interfaces of friction welds between titanium and stainless steel with and without interlayer are discussed. The formation of fragile intermetallic compounds like Fe–Ti and Cr–Ti are completely avoided between the titanium and stainless steel by introducing of interlayer material. The interlayer material successfully controlled the undesirable compounds from the weld interface and developed a new weld interface. The new microstructure formation at weld interface enhanced the final properties of the titanium to stainless friction welds.