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.

Junction Characterization in a Functionally Graded Aluminum Part

“…Melting of the alloy was performed in an electric furnace with a graphite crucible; the gravity casting process was operated manually and was guided by some key–parameters [25] that play an essential role in the production of an FGM with good interface quality. These parameters are the casting sequence, the soaking temperatures of the two alloys, the mould pre heating temperature and the elapsed time between the casting of the two alloys.…”

“…Recent works have suggested the production of aluminum–FGM pistons by gravity casting [23,24,25,26] adopting a dual, functionally graded, composition: EN AC 48000 (AlSi12CuNiMg) in the piston crown ensuring mechanical strength and thermal resistance, and EN AC 42100 (AlSi7Mg0.3) in the piston skirt providing higher ductility. In fact, pistons are commonly made of Silumin alloy EN AC 48000 and are often subjected to fatigue cracking in the skirt because of the low alloy ductility [27,28,29].…”

“…Since aluminum–silicon alloys are widely adopted in automotive applications, their mechanical properties are well known [23,24,25]; conversely the mechanical properties of the aluminum–FGM are not widely known. Indeed, the joint between the alloys can represent a weak point for low metallurgical bonding due to shrinkage, entrapped air and oxides and bifilm that are intrinsically generated by the casting process [32,33,34,35,36] which may affect the mechanical resistance of the FGM.…”

“…For this reason, the characteristics of the aluminum–aluminum FGM obtained via gravity casting have been investigated in this work. FGMs were obtained as previously seen in [25] and T6 heat treated [37]. The joint between the two alloys, is a metallurgical bonding between them, for this reason this sort of metallurgical interface was studied by means of micro–hardness tests, impact tests, and SEM microstructural analysis, in order to characterize the quality of the bonding between the two alloys and investigate the intermetallic nucleation near the alloys junction.…”

Special Issue on “Mechanical Behaviour of Aluminium Alloys”

“…This challenge has been previously explored by several authors. For example, Fracchia et al [1] focused on the production of bi-metal engine pistons by sequential gravity-casting using both EN-AC 48000 and EN-AC 42100 aluminium alloys, and Zhao et al [2] investigated the stability of single-layer combined lattice shells used as load-bearing structures in aerospace applications.…”