October 2021, Vol. 21, No. 5 MANUFACTURING TECHNOLOGY ISSN 1213–2489 indexed on: http://www.scopus.com 725 DOI: 10.21062/mft.2021.074 © 2021 Manufacturing Technology. All rights reserved. http://www.journalmt.com Comparison of the Porosity of Aluminum Alloys Castings Produced by Squeeze Casting Andrzej Zyska (0000-0001-9307-4364), Kinga Boroń (0000-0002-8421-3745) Czestochowa University of Technology, Department of Metallurgy and Metal Technology, Al. Armii Krajowej 19, 42-200 Częstochowa, Poland. E-mail: [email protected], [email protected] The results of researches on porosity and structure of castings from AlMg9, AlSi7Mg and AlCu4Ti alloys produced by squeeze casting and for comparison by gravity die casting are presented. The tests were carried out on 200x100x25mm plates squeeze casted under 90MPa pressure. Prior to the commencement of experimental studies, numerical simulations of solidification were made for the selected alloy (AlSi7Mg) in order to determine the potential locations of shrinkage porosity. As part of the study, the porosity distribution in the plate cast was assessed by taking samples for measurements from the center and edge of the casting. It was found that the area particularly vulnerable to the presence of shrinkage porosity is the central part of the casting and the zone extending from its center to the upper surface. Due to the wide temperature range of solidification of the examined alloys, diffused porosity occurs in cast- ings, and the shape of the pores formed is conditioned on the solidification morphology. The average porosity of squeeze castings is two times smaller than gravity die castings and is at the level of 1.0-1.5% depending on the type of alloy. In addition, as a result of pressing, the shrinkage porosity in the central part of the plate is reduced and its distribution becomes uniform throughout the volume. High pressure acting on solidifying castings ensures a significant increase of grains density in microstructure and de- crease of SDAS. Keywords: Squeeze Casting, Aluminum Alloys, Porosity, Structure Introduction Squeeze casting method is a technology that com- bines three methods such as forging, pressure casting and die casting. Thanks to the combination of these methods, the metal solidifies under pressure, which in turn results in a significant improvement in the prope- rties of castings [1,2]. This technology is designed for casting of light metals, especially aluminum alloys due to the good properties obtained with the alloys cast with this method. Squeeze casting in terms of quality is more effective than high pressure die casting and die casting, while economically is better than forging. Comparing the squeeze casting technology for high pressure die casting, there are several significant diffe- rences in the quality of castings. The development of the squeeze casting technology allowed to make casts with negligible shrinkage and gas porosity, fine-crys- talline structure and high tightness of castings. This is conditioned by the fact that in comparison to die casts, the pressure affecting the liquid metal causes accelera- ted heat exchange, thus eliminating the air gap at the contact point of the casting and mould, and creates permanent contact between the molten metal and the mould surface [3]. Thanks to the use of external pres- sure in the squeeze casting method during solidifica- tion of the metal, noticeable improvement of strength parameters of castings can be observed. These casts are characterized by an increase in the yield point of 10-15% and an improvement in overall elongation by 50-80%, dimensional accuracy is 0.25 mm for casting a length of 100 mm and 0.6 mm for the casting of 500 mm [4-6]. Castings produced by this method are also characterized by a smooth surface, no surface defects and a shape very similar to the final product. The cost- effectiveness of the process is also associated with the fact of lower energy and material consumption, even up to 98% of molten metal, by eliminating the gate assembly, strain relief and feeding head [7]. Due to the lack of a running gate system and limited flow of liquid metal, even low-castability plastic alloys can be used in this method, however, it can not be too small, because it leads to casting defects such as cold laps [8,9]. However, one of the most important advantages of the squeeze casting technology compared to pressure casting is to enable complete heat treatment of castings [10-12]. Applying pressure at a temperature close to the solidify point is the most effective. The highest growth rate of nucleation and the maximum undercooling of the alloy occur then. On the other hand, too much overheating can almost completely disrupt the effect of elevated pressure [3,4,13-17]. In the literature, one can find various theories about what factorinfluences the fragmentation of the structure in castings made with the squeeze casting
Comparison of the Porosity of Aluminum Alloys Castings Produced by Squeeze Casting
Jun 17, 2023
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