## 1 Introduction  
A357-type aluminum (Al-Si-Mg) alloy is mostly known for its excellent strength and quality index value, and is widely used in various engineering applications, particularly in the automotive industry [1; 2; 3; 4]. The vehicle suspension system is the assembly of mechanical components located between the frame (chassis) of the vehicle and road wheels. The suspension system is responsible of absorbing shocks from the road, maintaining contact between vehicle tires and the road, transmitting applied power from vehicle wheels to the chassis, and maintaining the proper kinematics of suspension. The suspension system usually consists of three main components: springs, dampers, and suspension linkage. Springs and dampers are responsible for the response of the vehicle under random excitations from different road conditions (and they are the subjects of research in many automotive vibration studies), while suspension linkages are the assemblies of mechanical components, linking the whole suspension system and transmitting forces to the chassis of the vehicle [5; 6]. Manufacturing this mechanical component from light metals helps with enhancing vehicle performance by decreasing the unsprung mass. Several studies indicate superior mechanical performance by using semi-solidcasting technology for producing such automotive suspension mechanical components of aluminum alloy [1; 5; 6; 7]. Semi-solid forming (SSF) is a forming technique that combines the processes of casting, forming, and extrusion. Force is applied, either mechanical or electromagnetic, to fragment the semi-solid structure in the mushy zone of liquid-solid range. Temperature is retained above melting point for the whole process. It is then compressed inside the mold cavity under high pressure to take its final geometry [8; 9]. Semi-solid is classified into two casting techniques: thioxcasting and rheocasting. Thioxcasting involves the formation of the required billets with desired microstructure from continuous casting, which is obtained, usually, by electromagnetic stirring. While in rheocasting, liquid metal is poured in an equal size container with the die to be filled, and is then fed to the die chamber; this avoids the reheating process of stock metal. The semi-solid materials (SSM) mix is produced and injected on demand, which decreases the total cycle time and, thus, cost. The desired structure is obtained by cooling, grain refinement, and stirring. The semi-solid casting process is characterized by the presence of equiaxed grain structure compared to the dendritic structure found in conventional casting [8; 9; 10; 11; 12]. In addition to the positive effects of using semi solid casting technique, the accelerating thermal aging treatments, using multiple and interrupted cycles, result in superior mechanical properties compared to traditional thermal treatments. A study done by [PERSON] et al. [13] showed the effect of multiple thermal aging over traditional single step aging for alloy A357. Samples were solution heat treated at 543 \({}^{\circ}\)C for 12 h then quenched in water maintained at 80 \({}^{\circ}\)C. Single stage aging was done at temperatures of 155, 165, and 175 \({}^{\circ}\)C for 4 h to 16 h. For step aging, samples were pre-aged at 155 \({}^{\circ}\)C for 4 h then finally aged at 175 \({}^{\circ}\)C for 3 h to 18 h. The results showed an enhancement in the strength and ductility values of samples that were step aged for 12 h. What was also observed were the general enhancements in the tensile properties of the step aged samples on the single aged samples. The explanation of the high strength and ductility was related to the presence of different precipitate sizes of Mg\({}_{2}\)Si. Other studies [14; 15] applied TEM study on the effect of multiple thermal aging treatments on performance and precipitate evolution of A357 semi-solid samples. Moreover, the formation of different sizes of Mg\({}_{2}\)Si precipitates that compromise between excellent strength and high ductility was observed.