Aluminum Foams as Permanent Cores in Casting

Their low density and high specific stiffness and impact energy/vibration absorption ability make Al-based metal foams promising materials in applications for which a light weight and energy/vibration absorption abilities are crucial. In view of these properties, Al-based foams can be extremely interesting as cores in cast components in order to improve their performances and simplify their whole technological process. However, both in the scientific literature and in technological application, this topic is still poorly explored. In the present work, Al-based metal foams (Cymat foams and Havel metal foams in the form of rectangular bars) are used in a gravity casting experiment of an Al-Si-Cu-Mg alloy (EN AB-46400). The foams were fully characterized before and after insertion in casting. Porosity, cell wall and external skin thickness, microstructure, infiltration degree, and the quality of the interface between the foam core and the dense cast shell, have been investigated by means of optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS). The analyses evidenced that a continuous and thick external skin protect the foam from infiltration by molten metal, preserving the initial porosity and insert shape. A detailed analysis of the foam’s external skin highlights that the composition of this external skin is crucial for the obtaining of a good joining between the molten metal and the Al foam core. In fact, the presence of Mg oxides on the foam surface prevents bonding, and maintains a gap between the core and the shell. This point opens up the opportunity to design innovative surface modifications for this external skin as promising strategies for the optimization of cast components with a foam core.

Gas Pressure Effect on Sand Collapse in Kinetic Zone of Lost-Foam Casting

Pressure of the kinetic zone is an essential factor for making defect-free castings in lost-foam casting process. The extremely high pressure causes many problems, such as reducing the melt velocity and inclusion of residual decomposition of the pattern in the castings, and very low pressure causes sand collapse. Therefore, the minimum gas pressure for preventing sand collapse is required. When the minimum gas pressure can be predicted, computer simulation becomes possible. Successful computer simulations can help reduce the number of trials and the lead time while designing new casting products. A preliminary sand experiment was conducted to predict the gas pressure and reduce the number of actual casting experiments. In this preliminary sand experiment, compressed air was used instead of gas in the kinetic zone. A new mathematical equation was proposed from the results of the preliminary sand experiment. The void ratio of the sand effect on the minimum gas pressure was included in the equation. An actual casting experiment was conducted by melting nodular cast iron to verify this equation. In the actual casting experiment, pressure of the kinetic zone in front of the metal tip was directly measured. The results obtained from the preliminary sand experiment and the actual casting experiment validated the equation.

Mg-Based Materials with Quasiamorphous Phase Produced by Vertical Twin-Roll Casting Process

Metallic materials with micron grains, submicron grains, or amorphous structures have attracted great interest in recent decades owing to their excellent mechanical properties and corrosion resistance. Compared with traditional forming processes, rapid solidification technology has shown great superiority and potential in the preparation of materials in such structures. In this study, fine-grained quasiamorphous Mg-based alloy strips fabricated by a twin-roll strip casting process were explored using simulation and experimental methods. The concept of critical casting speed was proposed to reflect the optimum casting conditions. The product of critical casting speed and strip thickness was used to evaluate the cooling capacity of the casting system. Based on simulation results, a twin-roll strip-casting experiment was performed on a Mg-rare earth alloy. A novel puddle-like microstructure of the as-cast alloy strip was obtained. Tensile testing results showed that the novel strip exhibited improved ductility.

Surface Pretreatment and Fabrication Technology of Woven Carbon Fiber Cloth Aluminium Alloy Matrix Composite

Carbon fiber is mainly distributed in the shape of short fibers and unidirectional fibers as the reinforcing phase in metal matrix composites, and it is seldom studied as woven-cloth shaped to reinforce the matrix. In this paper, the pretreatment and the surface metallization of the woven carbon fiber were studied. Besides, the casting experiment without external pressure was carried out under the application of magnetic field. The result shows that when burning about 45mins at 500°C in the atmospheric environment, the pretreatment can achieve the best result according to differential thermal analysis and weight-time variation curve. Meanwhile the surface wettability between the carbon fiber and the matrix is greatly improved after the surface treatment and at the same time the reaction between the carbon fiber and molten aluminium alloy matrix is necessarily avoided, and it can consequently achieve an excellent bonding between the woven carbon fiber and aluminium alloy matrix. The application of magnetic field also provides magnetic force to promote the penetration of the molten matrix into the carbon fiber bundles.

Ceramic Foam Filters in Runner System Design for Castings

In the design of runner systems, ceramic foam filters are used for reducing the velocity of liquid metal in order to avoid so called bifilm defect resulting from a high gating velocity (over its critical gating velocity) in aluminum gravity casting. In this study, two types of runner systems incorporated with the ceramic foam filters were designed. In order to observe the flow phenomena in these two runner systems with and without the filters, a water analogy experiment in a transparent plastic mold was utilized. Furthermore, in order to understand the effect of the filters used in these systems, an aluminum sand casting experiment was conducted. The quality of the cast metal in the outlet area of the filter for these systems was investigated. The defect content of this casting sample was measured by the re-melt reduced pressure test (re-melt RPT) and followed by measuring its bulk density. An optimized runner system with the filter was suggested in this study. Keywords: ceramic foam filter, runner system design, gravity casting, critical gating velocity, bifilm defect.

Numerical Simulation of Die Casting for Semi-Solid Aluminum Alloy and its Mould Research

Design and manufacture an aluminum alloy semi-solid die-casting. Simulate the process of rheological semi-solid aluminum alloy die-casting, and verification it by casting experiment. The result is that, the heating system of the semi-solid die-casting mold play an important role in the process of forming, and the size of gate has great impact on the quality of casting.