## 1 Introduction  
Over the past decades, the demand for lightweight materials with superior mechanical properties has gained significant attention from researchers around the world [1; 2; 3]. A wide range of research is focused on developing lightweight materials because of their superior properties when compared to conventional materials [4; 5; 6; 7]. Among various composite materials, metal matrix composite (MMC) has gained a lot of attention in automobile [8; 9], defense, marine, and aerospace sectors [10; 11]. Aluminum metal matrix composites (AMMCs) are known for their high performance and have attracted the attention of most industries due to their provocative properties such as higher strength-to-weight ratio, high hardness, good wear resistance, low density, and decent resistance to corrosion [12; 13; 14]. These inviting properties make them attractive for a wide variety of applications. Recently, the application of AMMCs has surged in the above-mentioned sectors, which require high strength-to-weight ratio, low density, high elastic modulus, excellent thermal stability, and wear resistance. For this purpose, many AMMCs have been developed using various reinforcements, such as alumina (Al2O3) [15], silicon carbide (SiC) [16], boron nitride (BN) [17], titanium carbide (TiC) [18], silicon nitride (Si3N4) [19], boron carbide (B4C) [20], Al-Cu-Li [21], nitinol (NiTi) [22], aluminum nitride (AlN) [23], zirconium dioxide (ZrO2) [24], cerium dioxide (CeO2) [25], and titanium dioxide (TiO2) [26], that have shown distinctive contributions in enhancing the structural, thermal, damping, mechanical, and corrosion properties of AMMCs [27; 28]. However, there are some limitations in choosing the type of preparation method. Powder metallurgy, forging and stir casting methods are the popular manufacturing techniques to synthesize AMMCs [29; 30; 31; 32; 33]. Among these, powder metallurgy (PM) is a simple and cost-effective synthesis technique and provides better results when compared to other processes [34]. Furthermore, PM along with hybrid microwave sintering (HMWS) is suitable for the development of Al-based composites, because it can control the growth in particle size and the changes in microstructure and the volume fraction between the reinforcement and matrix [15; 16; 17; 18; 19; 20; 21; 22]. Our research group has reinforced Al2O3, TiC, Si3N4, B4C, BN, and SiC successfully to develop Al-based nanocomposites through the PM technique along with HMWS process.  
Tin-bismuth (BiSn) alloy exhibits high strength and hardness, low melting point, superior creep resistance, low thermal expansion coefficient, and low cost, which enables it to be a preferable reinforcement to enhance the mechanical properties of monolithic materials [35]. BiSn composites have been developed by various techniques demonstrating improved properties, such as electrochemical deposition process [36], ball milling with low-temperature melting [37], directional solidification [38], and hydrolysis process [39]; however, there is no reported attempt to use BiSn reinforcement to synthesize aluminum/tin-bismuth (Al-BiSn) composites using microwave-assisted PM technique followed by hot extrusion process. Therefore, the present work focuses on the development of Al-BiSn composites using HMWS technique followed by the hot extrusion process. The structural, mechanical, and thermal properties of the developed Al-BiSn composites with various weight percentages of BiSn particles were investigated.