Freiberg, TU Bergakademie, Diss., 2001.

Freiberg (Sachsen), Techn. University, Diss., 2001.

Zugl.: Kassel, Univ., Diss., 2006 / Download lizenzpflichtig

Zugl.: Kassel, Univ., Diss., 2006

Zugl.: Kassel, Universiẗat, Diss., 2006. / Download lizenzpflichtig.

Universiẗat, Diss., 2003--Kassel. / Lizenzpflichtig.

In the production of parts for direct industrial application and for developing research purposes, it is of utmost importance to understand the defects associated with the material system. In this work, the microstructural and mechanical properties of 316L Stainless Steel deposits and cast Aluminum A356 and Magnesium AZ91 alloys are investigated. The study first examines the design of efficient gating systems utilizing the Electromagnetic Pump Green Sand system to produce vertically cast A356 plates. A series of numerical simulations were developed for each of the four gating designs in order to compare modeling results with actual castings. The method of four-point bend (FPB) testing was used to obtain information about the effect of oxide entrainment on the mechanical properties of the parts, and from this data, a two-parameter Weibull statistical analysis was performed in order to quantify specimen failure rate for each of the configurations. Metallographic analysis was carried out using optical microscopy, and fractography using Scanning Electron Microscopy (SEM). In keeping with light alloys focus, the determination of superior casting processes for AZ91 alloys is also studied. Passenger car control arms were cast by Indirect Squeeze Cast, Low Pressure Permanent Mold, T-Mag, and Ablation processes. The microstructure, grain size, porosity distribution, and defect analyses were obtained with optical microscopy and the ImageAnalyzer program. The mechanical behavior was characterized from the FPB and tensile tests. The four casting processes were evaluated in terms of reliability again using a Weibull analysis of the ultimate bending strength determined from the FPB test samples. Metallographic analysis was performed on these samples, revealing noticeable microstructural differences between them, with some even showing possible evidence of oxide films. Lastly, the study of process parameters such as beam and laser current, translation speed, and wire feed and deposition rate associated with 316L stainless steel deposits produced by both Laser Engineered Net Shaping and Electron Beam Freeform Fabrication becomes the research objective. Tensile tests, optical microscopy, and SEM were used to determine mechanical properties, characterize solidification grain structure, porosity, secondary dendrite arm spacing, and possible modes of failure.

Zugl.: Magdeburg, Univ., Diss., 2005

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This study investigates the possibility of fabricating periodic cellular materials (PCMs) via the lost foam casting (LFC) process using aluminum alloy A356 and magnesium alloy AZ91. This approach combines the structural efficiency of PCM architectures with the processing advantages of near-net-shape LFC. An initial feasibility study fabricated corrugated A356 panels. This was followed by a study of casting variables such as pattern design, vacuum assistance, and alloying additions in order to improve the fillability of the small cross-section struts. Finally, integrated pyramidal sandwich panels having different relative densities were subjected to artificial aging treatments and subsequently tested in uniaxial compression. The A356 PCMs experienced a continuous increase after yielding while the AZ91 PCMs exhibited strut fracture after peak strength. The results showed the compressive yield strengths of this study are comparable with those previously reported PCMs produced by different fabrication methods.