Abstract
Type AlSi9Cu3(Fe) alloy has been modified by alloying with iron, manganese, and chromium elements to develop wear-resistant diecast hypoeutectic Al–Si–Cu alloys that can be applied for high-temperature applications. Several alloys have been produced by varying iron, manganese, and chromium levels (0.80, 1.00, 1.20 wt.% for Fe; 0.25, 0.40, 0.55 wt.% for Mn, and 0.06, 0.10 wt.% for Cr). Brinell hardness measurements and pin-on-disk wear tests have been conducted from room temperature up to 200 °C. The microstructural changes that occurred with the different alloying levels have been quantitatively examined by metallographic and image analysis techniques. The results showed how the increasing content of the Fe, Mn, and Cr promoted the precipitation of both primary and secondary Fe-enriched particles, mainly with polyhedral, blocky, and star-like morphologies. These compounds showed high hardness that is not affected by chemical composition and morphology variation. At high temperatures, the diecast alloys always showed lower average hardness and wear resistance, especially at 200 °C; however, a greater amount of Fe-rich particles can compensate the alloy softening.
Highlights
The growing demand of Al-based alloys in the automotive sector is mainly ascribed to the need of vehicles’ weight reduction as well as to increase their performance
Iron is commonly considered an impurity element of Al–Si casting alloys, which detrimentally affects the final mechanical properties. This is typically ascribed to the formation of brittle β-Al5 FeSi (β-Fe) phase, which appears as needles-like particles in the microstructure; as the needle tips act as stress concentration points, the presence of β-Fe phase leads to a general reduction of tensile properties and wear resistance [12]
The measured contents of iron, manganese, and chromium in the final alloys are shown in Table 2; they result to be within the composition tolerance limits of the AlSi9Cu3(Fe) alloy, while the amount of the other elements remains nearly similar to the base alloy; the sludge factor, SF, ranged from 1.32 to 2.90
Summary
The growing demand of Al-based alloys in the automotive sector is mainly ascribed to the need of vehicles’ weight reduction as well as to increase their performance. Iron is commonly considered an impurity element of Al–Si casting alloys, which detrimentally affects the final mechanical properties This is typically ascribed to the formation of brittle β-Al5 FeSi (β-Fe) phase, which appears as needles-like particles in the microstructure; as the needle tips act as stress concentration points, the presence of β-Fe phase leads to a general reduction of tensile properties (ductility and ultimate tensile strength) and wear resistance [12]. The sludge factor can be determined from the initial contents of iron, manganese, and chromium in the alloy as [22,23]: Sludge Factor (SF) = (wt.%Fe × 1) + (wt.%Mn × 2) + (wt.%Cr × 3) In this scenario, the automotive industry requires the best compromise to achieve excellent performances in terms of wear and high-temperature resistance by using materials and processes suitable for mass production. This paper investigates a set of proposed alloys with increasing amounts of Fe, Mn, and Cr alloying elements, taking into account their microstructure, hardness, and wear resistance at high temperature
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