# Case Study of a Functionally Graded Aluminum Part
###### Abstract  
The growing interest in aluminum alloys is due to the excellent ductility and mechanical strength, especially in relation with their lightness. These properties make aluminum alloys one of the most used and competitive materials in the automotive sectors. In fact, at the present day, automotive components must guarantee high mechanical and thermal properties in order to ensure low emissions of the vehicle. Despite that, harsh operating conditions can lead to a rupture in aluminum components, especially if subjected to both thermal and mechanical loads. In this panorama, aluminum functionally graded materials (FGMs) could be introduced, in order to produce a single piece with different properties that fulfill all the piece requirements. In this work, considering the typical application of the aluminum alloys as engine pistons, FGMs are realized by sequential gravity casting with the piston alloy EN AB 48000 and the alloy EN AB 42100. Tensile tests on these bi-metal parts give good results in terms of mechanical strength, elongation rates and alloys bonding. aluminum FGM; gravity casting; sequential casting; mechanical properties 4000 000-0000-0000-0000-0000-0000-0000-00000-0000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-000000-00000-00000-000000-000000-00000  
This casting process causes a certain grade of defects, intrinsically generated by the process [6], and the final properties of castings are related to defects as well as to die design and microstructures. Parameters that could affect the casting process causing defects are: (i) temperatures (pouring, pre-heat); (ii) time (pouring, melt holding, degasification); (iii) material and thickness of the mould-coating; (iv) mould design; and (v) pouring velocity. The types of defects and their ranking in gravity casting were classified in [7] as: (i) gas/air porosity, about 45%; (ii) shrinkage, 44%; (iii) filling related problems, 38%; (iv) cracks, 33%; (v) inclusions, 28%; and (vi) metal/die interactions, 23%. Focusing on the combination FGM-automotive applications, and considering the high presence of the aluminum alloys in this sector [8], it is certainly possible to combine the aluminum alloys with the concept of FGM [9; 10; 11; 12]. In fact, aluminum alloys are considered as very interesting materials, because of their lightweight, especially if compared with ferrous alloys, which lead to an important decrease in fuel consumption reducing the polluting emissions, and their high specific resistance and ductility [13; 14]. Particularly, FGMs in the automotive industries could be used for engine pistons [9], leaf springs [15] and many other applications. Focusing on the piston production techniques, the most employed processes are casting and forging [16; 17; 18; 19; 20; 21]. In [22], [PERSON] et al. optimized the forging process to produce aluminum pistons employing aluminum powder; in the research [23], high performance pistons were produced by additive manufacturing; and in [24], the forging process was performed on the piston-wrought-alloy EN AW 4032 (AlSi12,5 MgCuNi). In [9], a microstructure-gradient FGM aluminum piston was produced by centrifugal casting: the hypereutectic alloy A390 was melted and poured into a spinning mould, and the design of the die leads to obtain a strong segregation of the primary silicon particles on the head portion of the piston that leads to an increase in wear and hardness. Similarly, with the same producing process, [PERSON] et al. [25] realized a chemical-composition-gradient FGMs with AlSi18 CuMgNi alloy. Engine pistons are commonly produced employing aluminum-silicon alloys because of their high mechanical resistance at high temperature and good fatigue behavior [16; 25; 26; 27; 28; 29; 30; 31; 32]. Particularly, the most widely used piston alloy is the EN AC 48000. However, this alloy exhibits poor ductility and low elongation at rupture that could lead to fatigue failure in the piston skirt.