Microstructural Evaluation and Corrosion Resistance of Semisolid Cast A356 Alloy Processed by Equal Channel Angular Pressing

Mohamed Gebril,Norinsan Othman,Mohd Omar,Intan Mohamed

doi:10.3390/met9030303

Mohamed Gebril, Norinsan Othman + Show 2 more

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https://doi.org/10.3390/met9030303

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Journal: Metals	Publication Date: Mar 8, 2019
Citations: 12	License type: CC BY 4.0

Affiliation: National University of Malaysia, University of Benghazi

Abstract

As-cast and semisolid casting using a cooling slope A356 alloy were processed by equal channel angular pressing (ECAP) for Si and grain refinement. The ECAP was conducted at room temperature in a mold, with a channel angle of 120°, and this resulted in a significant size reduction of grain and Si particles from 170.5 and 4.22 to 23.12 and 0.71 µm, respectively, after six passes of heat-treated cooling slope casting, using the ECAP process. The hardness increased with ECAP processing, from 61 HV, for the as-cast alloy, to 134 Hv, after six passes of heat-treated cooling slope casting. The corrosion resistance of the alloy improved, from 0.042 to 0.0012 mmy−1, after the ECAP process. In this work both the strength and corrosion resistance of the ECAPed A356 alloys were improved with the application of the cooling slope process than without (i.e., from the as-cast condition).

Highlights

A356 alloy is an Al–Si casting alloy that contains ~7 wt.% Si, mostly developed for automotive powertrain components such as the engine block and automotive transmission cases
This study further examined the effects of microstructure changes and its effect on strength as well as corrosion resistance for both ECAPed as-cast and ECAPed cooling slope-cast A356 alloy
Considering that the mold itself has a the evolution of the coarsen dendritic to finer dendritic could be observed from the center zones relatively low initial temperature, the cooling rate is more rapid near the wall of the mold, approaching the thin wall zone

Summary

Introduction

A356 alloy is an Al–Si casting alloy that contains ~7 wt.% Si, mostly developed for automotive powertrain components such as the engine block and automotive transmission cases. The coarse flake Si particles can cause the initiation of premature cracks during deformation. This shape weakens the workability of the alloy at room temperature, reducing the ductility of the alloy [1]. The reduction in the area ratio of noble Si particles (cathode) to less-noble eutectic Al phase (anode) around Si particles largely improves pitting corrosion resistance. The reduction in the area ratio of cathode to anode (Ac/Aa) reduces the corrosion current density. In the Al–Si alloy, the size reduction of Si particles which as cathode, facilitates the re-passivation of protective film with improved stability [5,6,7]

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