Advancing the Casting Art
This article was first published in the May 2000 issue of Foundry Trade Journal, England.
The Metal Processing Institute (MPI) in the US is centred at Worcester Polytechnic Institute and is dedicated to advancing the state of the art in the metal processing industry. Within the MPI is the Aluminium Casting Research Laboratory (ACRL) an industry and university alliance established to address the scientific and engineering problems associated with the production and use of advanced aluminium components and to provide a technological base for the aluminium casting industry. During the past few years, ACRL staff and students have worked on structure property relationships in Al-Si-Cu alloys, on microstructure control in Al based alloys, and on shortening the heat treatment cycle of Al-Si-Mg alloys. In addition, the ACRL is active and aggressive in securing outside funding for developmental research.
The laboratory entered a $2.8 million cooperative agreement with the US Department of Energy (DOE) to conduct a five year research project on clean metal casting. In addition, DOE and the North American Die-Casting Association (NADCA) have awarded ACRL a two year, $500,000 co-operative agreement for a research project to investigate alloy chemistry, microstructure, and performance interactions in aluminium diecasting alloys. ACRL researchers, through a cooperative agreement with the Metal Casting Coalition (CMC) and DOE worth $500,000, are also investigating the casting characteristics of aluminium diecasting alloys.
The goals of the DOE funded programme on clean metal casting are to secure for the US metal casting industry a pre-eminent position in the global market through technological competence and innovation, and through monitoring of international standards via benchmarking. The programme of research focuses on four major areas:
Development to melt cleanliness assessment technology.
Two distinct projects are pursued in this task. One is to optimise the reduced pressure test, which is widely used in industry. A comprehensive study has been compiled into an optimised test method that has become the AFS's recommended practice for performing the reduced pressure test.
A second project is devoted to develop a novel sensor to detect inclusions in molten aluminium. The WPI team has developed a novel sensor where Lorrentz forces are applied to molten aluminium in a proprietary manner, forcing the inclusions present in the melt to separate out and to agglomerate.
Subsequently, optical and other ancillary devices are utilised to detect the presence of inclusions. An alliance has been established with Heraeus Electro-Nite to commercialise such a device.
Development of melt contamination avoidance technology.
The objective of this project is to study and understand the aluminium melt contamination process and particularly to develop and prescribe methods to reduce both melt oxidation and hydrogen pickup. In order to achieve these goals, the following strategy is followed:
- Characterise the physical properties and effectiveness of various fluxes using thermal analysis, x-ray diffraction and microscopy.
- Determine the effect of flux composition on the interfacial tension between aluminium alloy melts and fluxes.
- Develop and optimise the composition of environmentally friendly fluxes.
- Conduct laboratory trials with the optimised fluxes and evaluate their effectiveness.
- Development of high temperature phase separation technology.
The objective of this project is to expand existing knowledge about phase separation technology used in clean metal processing of aluminium alloys. Specifically, the research focuses on sedimentation, flotation and electromagnetic separation.
To design and implement efficient melt treatment processes, it is important to develop a clear understanding of the physics of the basic mechanisms involved in phase separation. The goal is to develop comprehensive, reliable models of the processes which will be used in the design of a reactor, rotor spinning nozzle for melt treatment, in the optimisation of the operating parameters, and in the investigation at the effectiveness and the ideal method of deploying electromagnetic separation in aluminium melt treatment.
Establishment of a correlation between the level of melt cleanliness, processing effects, and the resultant as cast mechanical properties.
The primary goal is to develop a technology base for clean metal processing that is capable of consistently providing a metal cleanliness level fit for a given application. In this context, performance and mechanical properties of the resultant casting are also influenced by the processing methodologies used in addition to the level of melt cleanliness.
Two of the portfolio of consortium funded projects outside of the Clean Metal Casting project include:
The effect of key elements on the feeding characteristics of aluminium silicon casting alloys. The main objective of this project is to investigate the effect of alloying elements that are common in aluminium silicon casting alloys on the feeding characteristics of these alloys.
Evolution of the eutectic microstructure in aluminium silicon casting alloys.
The main objective of this research project is to understand the mechanism and the sequence of events that lead to the formation of the eutectic microstructure in aluminium silicon hypoeutectic casting alloys. Understanding the mechanism of eutectic formation is essential to analysing resistance to melt flow which influences feeding efficiency and in turn shrinkage, porosity formation, and segregation.
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