There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

비만아 부모의 돌봄 경험: q 방법론

A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

A review of selective laser melting of aluminum alloys: Processing, microstructure, property and developing trends

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

Review: friction stir welding tools

Electron beam, CO 2 , and Nd:YAG laser beam welding were performed on four different aluminium alloys, namely alloys 5005, 2024, 6061, and 7020. The plate thickness was 5 mm except alloy 5005 which was 3 mm thick in all cases and Nd:YAG laser beam welding was performed on 3 mm thick plates for all four alloys. Microstructural characterization of the weld metals was made by optical and scanning electron microscopies. A very low level of porosity was observed in all EB welds due to surface cleaning prior to welding and the vacuum environment of the EB welding process. In the case of CO 2 laser beam welding, high porosity level was observed. The pores observed in laser beam welded joints were varied small to large in size. Furthermore, the loss of Mg apparently took place in electron beam welding of all the alloys, which leads to the loss of strength in fusion zone (strength undermatching). The use of filler wire in laser beam welding processes improved the base metal property (strength) degradation to some extent in some cases. However, the strength undermatching was still to be observed in almost all of the cases.

Characterization of Laser and Electron Beam Welded Al Alloys / Charakterisierung von laser- und elektronenstrahlgeschweißten Aluminiumlegierungen

This study showed that sound joints without defects can be produced in a large array of weld parameters including numerous rotational and traverse speeds.

Microstructural and Mechanical Characterization of Friction Stir Butt Joint Welded 63% Cu-37% Zn Brass Plate

Intensive alloy development studies on intermetallic gamma (γ) based alloys in recent years has led to the development of several aerospace engine components using advanced γ-TiAl based alloys by ingot and powder metallurgical routes. These materials are of great interest to the aerospace industry owing to their very low density and good high temperature properties. Further application of this material will require the development of successful joining and cost effective fabrication methods. Joining of this intermetallic alloy by fusion joining processes, however, requires very careful process controlling, i.e. low cooling rates and very high preheat temperatures. On the other hand, solid state joining processes, particularly diffusion bonding, brazing, and friction welding, can readily be used to join this material. In the present work, successful application of solid state diffusion bonding to weld investment cast γ-TiAl alloys has been demonstrated. A series of diffusion bonds were produced without using an interlayer at temperatures ranging from 950 to 1100°C with different pressure levels and holding times. Bonds have been characterized using optical and scanning electron microscopy. Defect-free bonds were achieved for all the conditions studied. The bond qualities were assessed by shear testing at room temperature. Reasonable shear strength levels were obtained by bonding at 1000 and 1100°C for 3 h at pressures of 20 and 40 MPa, respectively. The bonds were also post bond heat treated at 1430°C for 30 min, which improved the bond quality in all cases.

Diffusion bonding of investment cast γ-TiAl

Abstract Numerous industrial applications, particularly those in the transport industry, require the joining of dissimilar materials which offers considerable benefits in terms of low cost, design flexibility, and weight reduction for overall structures. The problems associated with conventional fusion welding processes have stimulated researchers in recent years to develop new joining methods for dissimilar materials which are particularly difficult to join. Friction stir welding (FSW) originally developed for joining difficult-to-weld Al-alloys and FSSW (a variant of FSW for spot welding) have exhibited great potential for obtaining sound joints in various dissimilar alloy systems in different configurations namely butt-, lap- and spot-welding, particularly in dissimilar Al-alloys systems with different properties, which are very difficult to weld using conventional fusion welding techniques. A major difficulty in joining dissimilar Al-alloys by FSW/FSSW lies in the discontinuity in mechanical and technological properties (such as high-temperature strength, plastic deformation capacity, viscosity, etc.) of the materials to be welded across the abutting surfaces. This discontinuity as well as inherent asymmetry in heat generation and material flow of FWS/FSSW processes causes a higher asymmetry in materials flow behavior in dissimilar welding. However, it is relatively easier to implement the FSW/FSSW process to dissimilar Al-alloys in contrast to FSW of dissimilar materials combinations with very differing properties, such as Al-alloy to Mg-alloy or Al-alloy to steel.

/pdf/advances-in-fsw-and-fssw-of-dissimilar-al-alloy-plates-atn0vuts.pdf

Gürel Çam

Papers

Characterization of Laser and Electron Beam Welded Al Alloys / Charakterisierung von laser- und elektronenstrahlgeschweißten Aluminiumlegierungen

Microstructural and Mechanical Characterization of Friction Stir Butt Joint Welded 63% Cu-37% Zn Brass Plate

Diffusion bonding of investment cast γ-TiAl

Advances in FSW and FSSW of dissimilar Al-alloy plates

Prospects of producing aluminum parts by wire arc additive manufacturing (WAAM)