Using Micro-CT Scanning to Quantitative Characterize Porosity in High Pressure Die Castings and Semi-Solid Castings

Porosity is one of the main defects that limits the performance of castings. Porosity in aluminum castings can originate from several sources, including the volumetric shrinkage occurring during solidification, the precipitation of dissolved hydrogen, and entrapment of gasses such as air, boiling water, vaporized lubricants, etc. Traditional methods of identifying and measuring porosity in castings include 2D x-rays, sectioning and polishing, and Archimedes density measurements, but none of these provide a satisfactory quantitative estimate of the size, total volume and distribution of the pores. X-ray CT scanning is a relatively new method that generates not only a 3-dimensional view of the size and distribution of the pores, but can also provide quantitative information of the volume, surface area, size, shape and position of each pore within a casting. Micro-CT scanning is a specialized sub-category of CT scanning, which provides excellent resolution of fine porosity (a resolution limit of 4 microns in one of the case-stores presented in this paper), but it should be noted that the resolution limit in CT scanning techniques is related to sample size. This paper describes results from micro-CT scanning studies of two high pressure die castings and a semi-solid casting, and provides quantitative data on the total porosity content, and the porosity distribution. The paper will also demonstrate the capabilities of the micro-CT scanning process to provide a quantitative comparison of the porosity content in these different types of aluminum castings.

Effects of Post-Treatment to Improve the Surface Quality of 3D Printing Cement Mold Casting

Powder bed 3D printing can be applied to sandcasting mold manufacturing to ensure high quality and economy through process innovation. In this study, refractory alumina cement was used as an aqueous binder to ensure high-temperature thermal stability to minimize the addition of organic matter to reduce gas generation. In addition, spherical silica sand, the study material, was selected to a size of 30 µm to improve the casting mold resolution. To improve the surface quality through the post-treatment process, we confirmed the change in the surface roughness of the mold depending on the surface treatment of colloidal silica and the presence or absence of heat treatment, and finally made the mold through actual casting. Changes in the surface roughness and flowability of the cast body after mold post-treatment were confirmed. For aluminum castings, the shrinkage rate and surface roughness were confirmed in a box-shaped mold via gravity casting, and the flowability of the molten metal in the mold was confirmed in a hand-shaped mold. There was a change in the roughness and porosity of the mold, owing to the post-treatment, and the influence of the surface roughness and flowability of the cast body during actual casting was confirmed.

Subsurface Microstructural Evolution of High-Pressure Diecast A365: From Cast to Cold-Sprayed and Heat-Treated Conditions

The use of cold spray deposition, coupled with diffusion-driven thermal postprocessing, is considered herein as a surface modification process such that near-surface microstructural, micromechanical, and microchemical property improvements can be procured for cost-effective and common aluminum alloy castings. Since the present work was an exploratory investigation into the realm of cold spray induced, high-pressure diecast aluminum subsurface property development and evolution, as well as surface modification, one significant aim was to formalize a set of fundamental observations for continued consideration of such an approach to achieving premium aluminum alloy properties from cost-effective alternatives. Nickel, copper, and titanium cold spray modified near-surface regions of the cost-effective high-pressure diecast A365 system was considered. Near-surface, subsurface, and surface evolution was documented across each of the three pure metal coatings. The analysis was continued across two postprocessing coating-substrate atomic diffusion inspired heat-treated conditions as well. Using energy-dispersive X-ray spectroscopy, field-emission scanning electron microscopy, optical microscopy, and various insights gleaned from an original contextualization of the relevant cold spray literature, noteworthy results were recorded and discussed herein. When copper feedstock was employed alongside thermal postprocessing, diverse surface-based intermetallic compounds formed alongside exotic diffusion zones and severely oxidized regions, thus eliminating thermally activated copper cold-sprayed consolidations from future work too. However, both nickel and titanium cold spray surface modification processing demonstrated potential and promise if correct processing stages were performed directly and chronologically. Consequently, a platform is presented for further research on cold sprayed surface microstructural and property modification of cost-effective alloyed aluminum castings.

Analysis of Aluminium Alloy Wheels Product Quality Improvement Through DMAIC Method in Casting Process: A Case Study of the Wheel Manufacturing Industry in Indonesia

The global market demand for automotive wheels with alloy materials is 55%, which is quite high compared to other materials such as steel, magnesium, chromed, and carbon fiber. The high competition of the global alloy wheels market demands to be able to offer quality alloy wheels. The purpose of this research is to reduce the number of defects in the casting process step by using the Define Measure Analyze Improve Control (DMAIC) method. This study shows the systematic approach to find the root cause of major defects in aluminum castings using the defect diagnostic approach as well as cause and effect diagram. Quality improvement using quality tools, namely the Pareto diagram, fishbone diagram. The major defects for the rejections during production were identified as leak defects, porosity motive holes, and oval defects. In determining the proposed quality improvements using the FMEA tool. The results of data processing on the calculation of process capabilities and product performance show improvements after quality improvements in the casting process. Product performance from DPMO = 15.462, sigma level = 3.6 to DPMO = 8.186 and sigma level = 3.9. The effect of decreasing the percentage of defects could save production costs by IDR 413.350.000. Therefore, the application of the DMAIC method can provide a significant improvement in product quality and impact on production cost savings.

Synthesis of boron carbide reinforced aluminum castings through mechanical stir casting

Nuclear energy is the leading clean energy source in the United States with 99 nuclear power plants generating approximately 20% of the country’s electricity. While the growth of the industry helps to reduce our reliance on fossil fuels, there is also an increase in nuclear waste. The demand for on-site dry cask spent nuclear fuel storage has increased due to complications with the Yucca Mountain Project and diminishing pool capacity. A novel dry cask consisting of an aluminum metal matrix for effective thermal conductivity with boron carbide as a neutron absorbing additive was investigated using gravity sand casting techniques. X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and optical microscopy were used to characterize the resultant microstructure, including boron carbide incorporation and heterogeneity. Results indicate vortex and nonvortex mixing in air with boron carbide (1–10 µm diameter) produces large amounts of porosity and insufficient wetting. Use of a larger particle size distribution of boron carbide (20–60 µm diameter) during high speed vortex mixing prior to casting has shown significant dispersion of up to 12 wt% sufficient for neutron shielding with appropriate wall thickness. These results validate the use of gravity sand casting as a means to produce borated aluminum for an effective alternative to fuel storage.

Technological sample for evaluation of filling capacity of thin-walled body aluminum castings

Prerequisites for development of technological sample design for assessment of filling capacity of thin-walled body parts of complex configuration with wall thickness of 3 mm are considered. The production process of the obtained sample, as well as the results of its application for aluminium alloys are presented.