Transactions of Materials Processing (소성∙가공)

The Korean Society for Technology of Plasticity and materials processing (한국소성∙가공학회)
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Microstructure and Wear Properties in an Engine Oil Environment of Extruded Hyper-eutectic Al-15wt.%Si Alloy and Gray Cast Iron

과공정 Al-15wt.%Si 압출재와 회주철의 미세조직 및 엔진 오일 환경에서의 마모 특성

  • Received : 2018.08.09
  • Accepted : 2018.11.08
  • Published : 2018.12.01
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Abstract

This study investigated the microstructure and wear properties of extruded hyper-eutectic Al-Si (15wt.%) alloy in an engine oil environment. The wear mechanism of the material was also analyzed and compared to conventional gray cast iron. In microstructural observation results of Al-15wt.%Si alloy, primary Si phase ($45.3{\mu}m$) and eutectic Si phase ($3.1{\mu}m$) were found in the matrix, and the precipitations of $Mg_2Si({\beta}^{\prime})$, $Al_2Cu({\theta}^{\prime})$ and $Al_6(Mn,Fe)$ were also detected. In the case of gray cast iron, ferrite and pearlite were observed. It was also observed that flake graphite ($20-130{\mu}m$) were randomly distributed. Wear rates were lower in the Al-Si alloy as compared to those of gray cast iron in all load conditions, confirming the outstanding wear resistance of Al-15wt.%Si alloy in engine oil environment. In the $4kg_f$ condition, the wear rate of gray cast iron was $6.0{\times}10^{-5}$ and that of Al-Si measured $0.8{\times}10^{-5}$. The microstructures after wear of the two materials were analyzed using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The primary Si and eutectic Si of Al-Si alloy effectively mitigated the abrasive wear, and the Al matrix effectively endured to accept a significant amount of plastic deformation caused by wear.

Keywords

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Fig. 1 Microstructures of (a) hyper-eutectic Al-15wt.%Si alloy and (b) gray cast iron

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Fig. 2 XRD phase analysis results of Al-15wt.%Si alloy and gray cast iron

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Fig. 3 Low magnification SEM images of (a) Al-15wt.%Si alloy, (b) gray cast iron and high magnification SEM-EDS results of (c) Al-15wt.%Si, and (d) gray cast iron

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Fig. 4 Vickers hardness results for Al-15wt.%Si alloy, primary Si and gray cast iron

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Fig. 5 Wear properties of Al-15wt.%Si and grey cast iron in engine oil environment with (a) wear loss, (b) wear volume and (c) wear rate

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Fig. 6 SEM images showing worn out surface of (a) Al-15wt.%Si alloy (c) grey cast iron tested at 3kgf wear load, (b) Al-15wt.%Si alloy, (d) gray cast iron tested at 4kgf wear load

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Fig. 7 SEM images showing etched worn out crosssectional areas of Al-15wt.%Si alloy ((a), (b)), and grey cast iron ((c), (d)) tested at 4kgf wear load

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Fig. 8 EBSD analysis results of Al-15wt.%Si alloy ((a), (b)) and cast iron using ((c), (d)) tested at 4kgf wear load; (a),(c) inverse pole figures and (b),(d) image quality maps

Table 1 Chemical compositions of hyper-eutectic Al-Si alloy and gray cast iron used in this study

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Table 2 Archimedes density measurement results of Al- 15wt.%Si alloy and gray cast iron

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