H. Khalid Rafi

Improving Strength of Stainless Steel/Aluminum Alloy Friction Welds by Modifying Faying Surface Design

Conventionally in friction welding, the rubbing or faying ends of the base material rods are square turned. For the case of dissimilar friction welding, this design is not optimum because of differential flow behavior of the materials. When, only one of the materials deforms preferentially, the actions of cleaning and expulsion of oxides and impurities from the interface would not be as effective. This will adversely affect the joint properties. In this study, alternate designs of faying surfaces such as providing taper (external and internal) and smoother surfaces are compared with the square cut design. The aim was to study how the faying surface conditions of the stronger material affect the flow behavior of the weaker material. By affecting better flow behavior, the intention was to expel intermetallics and other impurities from the interface, and thereby improve joint properties. Friction welding of stainless steel with aluminum alloy (aluminum-magnesium-silicon) was studied. The joints were evaluated for strength and it is found that the external tapered system has the best strength. Different characterization techniques such as optical microscopy, scanning electron microscopy, x-ray diffraction were carried out to observe different phases, microstructure zones, etc., at the interface. Finally, possible reasons for the better strength of tapered system were discussed.

A Generalized Feed Forward Dynamic Adaptive Mesh Refinement and Derefinement Finite Element Framework for Metal Laser Sintering—Part I: Formulation and Algorithm Development

A novel multiscale thermal analysis framework has been formulated to extract the physical interactions involved in localized spatiotemporal additive manufacturing processes such as the metal laser sintering. The method can be extrapolated to any other physical phenomenon involving localized spatiotemporal boundary conditions. The formulated framework, named feed forward dynamic adaptive mesh refinement and derefinement (FFD-AMRD), reduces the computational burden and temporal complexity needed to solve the many classes of problems. The current study is based on application of this framework to metals with temperature independent thermal properties processed using a moving laser heat source. The melt pool diameters computed in the present study were compared with melt pool dimensions measured using optical micrographs. The strategy developed in this study provides motivation for the extension of this simulation framework for future work on simulations of metals with temperature-dependent material properties during metal laser sintering.

Microstructure and Properties of Friction Surfaced Stainless Steel and Tool Steel Coatings

Friction surfacing is a novel solid state surface coating process with several advantages over conventional fusion welding based surfacing processes. In this work, austenitic stainless steel (AISI 310) and tool steel (H13) coatings were friction deposited on mild steel substrates for corrosion and wear protection, respectively. Microstructural studies were carried out by using optical and scanning electron microscopy. Shear tests and bend tests (ASTM A264) were conducted to assess the integrity of the coatings. This study brings out the microstructural features across the coating/substrate interface and its mechanical properties, showing good metallurgical bonding between stainless steel and tool steel coating over mild steel.

Corrosion Resistance of Friction Surfaced AISI 304 Stainless Steel Coatings

Corrosion resistance of friction surfaced AISI 304 coating in boiling nitric acid and chloride containing environments was found to be similar to that of its consumable rod counterpart. This was in contrast to the autogenous fusion zone of GTAW weld which showed inferior corrosion resistance with respect to the consumable rod. The superior corrosion resistance of friction surfaced coatings was attributed to the absence of δ-ferrite in it.