Microstructure Examination and Sliding Wear Behavior of Al-15%Mg2Si-xGd In Situ Composites before and after Hot Extrusion

Hamidreza Ghandvar,Katsuyoshi Kondoh,Abdollah Bahador,Tuty Asma Abu Bakar,Nor Akmal Fadil,Mostafa Abbas Jabbar

doi:10.3390/lubricants10010003

Hamidreza Ghandvar, Katsuyoshi Kondoh + Show 4 more

Open Access

https://doi.org/10.3390/lubricants10010003

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Abstract

In current study; the effect of various Gadolinium (Gd) additions on the microstructure and sliding wear behaviour of Al-15%Mg2Si composite before and after the hot extrusion process was examined. Optical microscopy (OM), scanning electron microscopy (SEM) equipped with EDX facility and X-ray diffraction (XRD) were used to characterize the microstructure. The results showed that with addition of 1.0 wt.% Gd to Al-15%Mg2Si composite, the primary Mg2Si particles size reduced from 44 µm to 23 µm and its morphology altered from dendritic to polygonal shape. Further refinement of primary Mg2Si particles was achieved after conducting hot extrusion which resulted in a decrease in its size to 19 µm with a transfer to near-spherical morphology. The Vickers hardness value increased from 55.6 HV in the as-cast and unmodified composite to 72.9 HV in the extruded 1.0% Gd modified composite. The wear test results revealed that composites treated with Gd possess higher wear resistance in comparison with those of without Gd. The highest wear resistance obtained with the lowest wear rates of 0.19 mm3/km and 0.14 mm3/km in the Al-15%Mg2Si-1.0% Gd before and after the hot extrusion, respectively. The high wear resistance of extruded Gd-modified Al-15%Mg2Si composite is due to the refinement of primary Mg2Si particles with uniform distribution in the composite matrix along with fragmentation of Gd intermetallic compounds.

Highlights

Al–Mg–Si alloys are extensively utilized in the aerospace and automotive applications owing to their high strength to weight ratio, good formability and favorable cast ability [1]
It is claimed that the excellent features of the Al–Mg–Si alloy comes from Mg2Si particles due to its attractive features which made the Al-Mg2Si system a replacement for Al–Si alloys [2]
As seen in Figure 1(1a), in the unmodified composite, the primary Mg2Si particles possess dendritic and irregular morphology which are surrounded with eutectic Mg2Si cells

Summary

Introduction

Al–Mg–Si alloys are extensively utilized in the aerospace and automotive applications owing to their high strength to weight ratio, good formability and favorable cast ability [1]. Wu el al., [5] found that by increasing the Bi content to 4 wt.%, the morphology of primary Mg2Si changes from irregular or dendritic to polyhedral shape with decreasing in its average size significantly which results in enhancement of wear and friction properties of the composite. The reason for the refinement of Mg2Si crystals by the addition of Bi may be related to the composition supercooling caused by the segregation of Bi at the front of the solid/liquid interface of Mg2Si during solidification. Wu et al, [7] found that with the addition of 0.5 wt.% Nd addition to Al-18%Mg2Si composite, the dendritic morphology of primary Mg2Si changed to polyhedral shape with a decrease in its average size as well as enhancement in wear properties. In the present study the effect of various contents of Gd additions and the hot extrusion process on microstructural and sliding wear behaviour of Al-15%Mg2Si composite is investigated

Materials Fabrication

Hot Extrusion

Microstructural Examination

Hardness and Dry Sliding Wear Test

Microstructural Characterization

Mechanical Properties