Semisolid melt squeezing procedure for production of open-cell Al–Si foams Ramin Jamshidi-Alashti ⇑ , Mehdi Kaskani, Behzad Niroumand Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran article info Article history: Received 6 August 2013 Accepted 16 November 2013 Available online 26 November 2013 Keywords: Al–Si open-cell foam Melt squeezing procedure Semisolid process Microstructure Mechanical properties abstract Melt squeezing process in semisolid state was used for the first time for production of open-cell Al–Si foams with improved microstructural and mechanical characteristics. First a given amount of preheated NaCl particles was stirred into molten A356 alloy. Stirring continued during solidification of the slurry until reaching a given solid fraction of primary particles. The resulting mixture was pressed by a perfo- rated piston to squeeze a controlled amount of the residual meltout. Open-cell foams were achieved by leaching the final Al–Si–NaCl composites in water. The suitable values of the NaCl particle size, pressur- izing temperature, melt to salt ratio and piston pressure for production of uniform and high integrity foams were obtained to be 3400 lm, 605 °C, 1.5:1 and 10 MPa, respectively. The results showed that the semisolid processing employed could refine and modify the microstructure of the cell ligaments in the final foams. Mechanical properties of the foams such as energy absorption and fracture toughness were also improved by the semisolid processing. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction High impact energy absorption capability of metal foams has created a large market for their structural applications. Aside from the arrangement and macrostructure of the cells, energy absorp- tion of a foam is directly dependent on its mean plateau stress and densification strain which in turn are related to strength and ductility of the parent solid alloy, respectively [1]. In order to im- prove the mechanical properties of metal foams, researchers have conducted numerous works on composition adjustment, heat as well as surface treatments or reinforcing with foreign ceramic par- ticles [2–4]. Although many of these efforts have resulted in in- creased strength and energy absorption capacity of the foams, most of these procedures are costly or only partially successful. Incorporation of reinforcement particles in metal matrices also poses new difficulties such as wettability problems between the particles and the foam matrix, brittleness and/or processing chal- lenges [5]. Design and tailoring of the microstructures of the metal part of the foams is a more promising way to improve their mechanical properties. It is known that such defects as shrinkage porosity, hot tearing, microsegregation, and residual stresses associated with dendritic microstructure of conventionally cast products re- sult in their lower mechanical properties [6]. In recent years, with development of semisolid casting techniques, many attempts have been devoted to creation of non-dendritic microstructures during solidification [7]. Some of the proven advantages of semisolid cast- ings over conventionally cast components include lower gas and shrinkage porosity, less chemical segregation, improved structural integrity and mechanical properties as well as longer tool life [7,8]. Introduction of shear to a solidifying molten alloy within its solidus and liquidus temperature range is a common way of producing non-dendritic microstructures. Such a microstructure consists of coarser non-dendritic primary particles formed during shearing enveloped by a much finer dendritic matrix formed upon casting the slurry in a mold [8,9]. Mechanical stirring is the most common way of producing semisolid slurries. In this method, the alloy is continuously cooled and stirred from a superheat temperature to a given temperature in the semisolid range. Upon reaching a given solid fraction of pri- mary particles, or after some isothermal stirring at this tempera- ture, the slurry is cast into a mold where the liquid part of the slurry rapidly solidifies rendering a high quality component. Despite the advantages of semisolid products, the authors are unaware of any attempt to utilize this technique in processing of open-cell metal foams. There are some limited studies on direct foaming of magnesium and aluminum alloys by gas injection into semisolid melt yielding closed-cell foams [10–13]. The purpose was the better entrapment of gas bubbles and the more stable expansion of closed cells in the semisolid slurry. Furthermore, some of these works do not discuss the mechanical properties of the foams made by semisolid procedure in comparison with those produced by liquid-based techniques. 0261-3069/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2013.11.033 ⇑ Corresponding author. Tel.: +98 311 3915731; fax: +98 311 3912752. E-mail addresses: r.jamshidialashti@ma.iut.ac.ir (R. Jamshidi-Alashti), m.kaskani @ma.iut.ac.ir (M. Kaskani), behzn@cc.iut.ac.ir (B. Niroumand). Materials and Design 56 (2014) 325–333 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes