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

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.

Role B4C Addition on Microstructure, Mechanical, and Wear Characteristics of Al-20%Mg2Si Hybrid Metal Matrix Composite

In the current study, the effect of different B4C additions (0, 2.5, 5, and 10 wt%) on the microstructural, solidification behavior, mechanical, and tribological properties of Al-20%Mg2Si composite were studied by means of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness, tensile, and dry sliding wear tests. The cooling curve thermal analysis (CCTA) approach was utilized to monitor the influence of B4C particles on the solidification behavior of Al-20%Mg2Si composite. The results revealed that the addition of B4C particles up to 10 wt% reduced the nucleation temperature (TN) and growth temperature (TG) of the primary Mg2Si phase. Moreover, the proper amount of B4C added to Al-20%Mg2Si composite has a significant effect on the microstructural alteration, mechanical, and tribological properties of the composite. The mean size of primary Mg2Si in Al-Mg2Si composite was 47 μm, in which with the addition of 5 wt% B4C, the particle size decreased to 33 μm. The highest UTS (217 MPa) and El% (7%) was achieved in Al-20%Mg2Si-5%B4C hybrid composite. The cast Al-20%Mg2Si composite revealed the brittle mode of fracture with some cleavage characterization, in which with the addition of 5%B4C, the fracture mode altered to a more ductile fracture. The wear results revealed that the Al-20%Mg2Si-5%B4C hybrid composite has the highest wear resistance with the lowest wear rate (0.46 mm3/Km) and friction coefficient (µ = 0.52) under 20 N applied load compared to other fabricated composites with mild abrasion as the governed wear mechanism.

Morphology evolution of primary Mg2Si in Ca-modified Al-Mg2Si alloy with various contents of Mg\Si

Combined influence of the Mg\Si and Ca contents on crystallization of primary Mg2Si in Al-Mg2Si alloy is investigated. Embryos formation of primary Mg2Si can be restricted by the addition of...

Influence of Superheating Melt Treatment on Microstructure of Gd-Modified Al-15wt.% Mg2Si In-Situ Composite

The influence of melt superheating treatment with different superheating temperatures (750, 800, 850, and 900°C) on the microstructure of Al-15wt. % Mg2Si composites before and after addition of Gd (1.0 wt.%) were studied. Microstructure characterisation was carried out via optical microscopy (OM) and x-ray diffraction (XRD).The results showed that in the unmodified composite, when the temperature of superheating raised from 750°C to 900°C, the primary Mg2Si experienced a decrease of the average grain size from 40 to about 32 µm, while, in the Gd-modified composite, the particle size was refined considerably from 27 to 13 µm by increasing the temperature from 750°C to 850°C. Furthermore, with a further increase in temperature to 900°C, the particle size slightly increased to about 15 µm which might be due to the burning loss of Gd in the melt. Nevertheless, for both unmodified and Gd-modified composites, the superheating temperature exhibited minor influence on the Mg2Si crystals morphologies. It is believed that compiling of Gd addition and superheating melt treatment is efficient to improve the composite properties that could encounter the application requirements.

Microstructure Evolution and Performance Improvement of Hypereutectic Al–Mg2Si Metallic Composite with Ca or Sb

In this article, the modification effects on Al–Mg2Si before and after heat treatment were investigated with Ca, Sb, and (Ca + Sb). In comparison with single Ca or Sb, the samples with composition modifiers (Ca + Sb) had the optimal microstructure. The sample with a molar ratio for Ca-to-Sb of 1:1 obtained relatively higher properties, for which the Brinell hardness values before and after heat treatment were remarkably increased by 31.74% and 28.93% in comparison with bare alloy. According to differential scanning calorimetry analysis (DSC), it was found that the nucleation behavior of the primary Mg2Si phase could be significantly improved by using chemical modifiers. Some white particles were found to be embedded in the center of Mg2Si phases, which were deduced to be Ca5Sb3 through X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM) analyses. Furthermore, Ca5Sb3 articles possess a rather low mismatch degree with Mg2Si particles based on Phase Transformation Crystallography Lab software (PTCLab) calculation, meaning that the efficient nucleation capability of Ca5Sb3 for Mg2Si particles could be estimated.

Effect of Mg2Si Concentration on the Dry Sliding Wear Behavior of Al–Mg2Si Composite

The microstructural morphology and wear behavior of as-cast Al–X wt% Mg2Si (X = 0.0, 5.0, 10.0, 15.0, and 20.0) composites were investigated through optical microscopy (OM), energy dispersive X-ray (EDX) spectrometry, scanning electron microscopy (SEM), and field emission scanning electron microscopy (FESEM). The dry sliding wear behavior was studied against an EN 31 hardened steel disk at four different applied loads (19.6 N, 29.4 N, 39.2 N, and 49 N) with a sliding speed of 62.8 m/min for 1 h. The optical microscopy analysis exhibits that the primary Mg2Si particles average equivalent diameter and volume fraction are increased with an increase in Mg2Si (Mg and Si) concentration in the Al–Mg2Si composite. Therefore, the bulk hardness of the composites is increased, whereas the primary Mg2Si hardness decreased because the coarser primary Mg2Si particles have less compactness. The wear resistance of the commercially pure aluminum significantly improved due to Mg2Si reinforcement, and the wear resistance is increased with the increase in Mg2Si concentration up to 15.0 wt% and then decreased at 20.0 wt%. The tested composites worn surfaces and debris exhibit adhesion, delamination, microcutting-abrasion, abrasive- and oxidation-type wear mechanism.