Fabrication of Al-Si/Mg 2 Si in-situ composite by friction stir processing M.H. Daneshifar a,⇑ , A. Papi a , M. Alishahi a,b a Department of Materials and Polymer Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar, P.O. Box 397, Iran b Department of Physical Electronics, Faculty of Science, Masaryk University, CZ-61137 Brno, Czech Republic article info Article history: Received 16 June 2020 Received in revised form 3 October 2020 Accepted 10 October 2020 Available online 15 October 2020 Keywords: Metallic composite In-situ Mg 2 Si Friction stir processing Microstructure abstract Al/Mg 2 Si in-situ cast composites are very popular in Al casting industries, but they suffer low toughness due to very coarse Mg 2 Si particles. The friction stir processing (FSP) method can produce composites with very fine and uniform distribution of the reinforcement phase. Hence, in the present research, for the first time, FSP was used to fabricate Al/Mg 2 Si in-situ composites. For this purpose, pure Mg was added to Al-Si cast eutectic alloy by FSP. The formation of Mg 2 Si was studied by a variety of analysis techniques. The results prove the applicability of FSP for producing of Al/Mg 2 Si composite. The hardness of the prepared composite shows moderate improvement (~15%) compared to the FSPed base alloy. Ó 2020 Elsevier B.V. All rights reserved. 1. Introduction Friction stir processing (FSP) is a processing technique that works based on friction stir welding (FSW) principals, developed by Mishra et al. [1]. During the last two decades, its imminent ben- efits as a green technology were understood, and extensive inves- tigations were carried out on its science and technology. The main applications of FSP are cast structure modification [2], metal matrix composites (MMCs) fabrication [3], preparing nanostruc- tured materials [4], and mechanical alloying [5,6]. Fabrication of MMCs by FSP was studied by either ex-situ or in-situ methods, and the reader may refer to [3] for a recent review on the in-situ composites by FSP. Different Al-based composites with transition metals such as Ti, Ni, Fe, Mo, and Cu were investigated so far [3], where some intermetallic phases form and strengthen the matrix. Aluminum and its alloys are a major engineering material group because of high property to weight ratio, good corrosion resistance, and excellent formability. The main drawback is lower strength and modulus than steels, which can be overcome by either alloying or Al-based composites. Al/Mg 2 Si is a popular group of Al-based composites that can be prepared in-situ by casting technique. These composites show low density (1.88 kg/m 3 ), High hardness (4.5 Â 10 9 N/m 2 ), low thermal expansion (7.5 Â 10 -6 /K), and high elastic modulus (120 GPa) [7]. But cast structure suffers the large and improper distribution of Mg 2 Si particles that reduce the work- ability and toughness. Chemical methods have usually been used to solve this problem [8]. Although magnesium is one of the major alloying elements in Al alloys, because of very high affinity to oxi- dation, high vapor pressure at casting temperatures, and usually wide solidification range is prone to different casting defects such as pores and trapped oxide films. Therefore, using Mg as an alloy- ing element in casting causes several technical and metallurgical difficulties. Based on the above literature review, Al/Mg 2 Si com- posites have never been tried to be prepared by FSP in solid- state. Hence, the present investigation aims to study the feasibility of FSP to fabricate sound Al/Mg 2 Si in-situ composite. 2. Experimental procedure In the present research, Al-13wt.%Si eutectic cast alloy was used as the base metal. Pre-weighted A356 (Al-7Si-0.5Mg) blocks were melted in an induction furnace, and the proper amount of Al-70% Si master alloy was added to the melt to reach the desired compo- sition. The melt was then cast into a steel mold to form a slab. The slab was cut into plates with dimensions of (L Â W Â t) 80 Â 40 Â 10 mm. Commercially pure Mg ingot (purity ~99%) was cut into blocks of suitable size by wire cut EDM machine. A FP4M vertical milling machine was used to process the plates by FSP. Two tools were used for FSP; a pinless tool for capping and the main FSP tool. The geometry and dimensions of the tools are depicted in Fig. 1-(a) and (b). For FSP, plates were fixed on the milling machine table and a groove with dimensions of 60 Â 3 Â 2 mm was machined on their surfaces. The pre-cut Mg blocks were placed in the groove and capped by the pinless tool to prevent it from moving during FSP. Based on the preliminary tri- https://doi.org/10.1016/j.matlet.2020.128832 0167-577X/Ó 2020 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: mh.daneshifar@hsu.ac.ir (M.H. Daneshifar). Materials Letters 282 (2021) 128832 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue