Microstructure development, mechanical and tribological properties of a semisolid A356/xSiCp composite

This paper presents the results of experimental investigation on microstructure (size and morphology of eutectic Si), impact toughness and sliding wear properties of A356 Al-Si alloy and composites containing 10, 20 and 25 wt% of SiCp reinforcement produced by semisolid stirring technique. The results revealed that an increase in SiCp content leads to a reduction in the size of eutectic Si and also changes its morphology from plate-like to equiaxed. Furthermore, addition of 10 and 20 wt% silicon carbide reinforcement decreased the impact toughness by 6 and 18%, respectively. A356/25wt%SiCp composite registered the lowest impact toughness with reduction of 33% due to debonding and agglomeration of SiCp in the matrix. The sliding wear results showed that the wear resistance of the composites was significantly higher than that of the matrix alloy due to the increase in hardness as well as reduction in the size and also morphology transformation of eutectic silicon with increase in SiCp content. However, the existence of particle-porosity clustering with increasing the SiCp content to 25 wt% played a significant role in deteriorating the wear behavior of the composite

Role of sr on microstructure, mechanical properties, wear and corrosion behaviour of an al-mg2si-cu in-situ composite

The influence of Sr additions on the microstructure of primary and eutectic Mg2Si phases, wear and corrosion behaviour of Al–Mg2Si–Cu in-situ composite was investigated. The results showed that addition of 0.01 wt% Sr modified the primary Mg2Si morphology but exceeding this level of Sr induced a loss of modification as the primary phase morphology coarsened again. The Al–Mg2Si eutectic phase, on the other hand, still exhibited a refined structure even with higher levels of Sr additions. Thermal analysis results revealed that both modification of the primary Mg2Si and refinement of the eutectic Mg2Si are most likely related to nucleation and growth stages respectively. The results of 0.01 wt% Sr addition showed that the mean size and mean aspect ratio decreased by about 30% and 6% respectively, but the mean density increased by 185% respectively. The highest UTS, El%, impact toughness and hardness were measured at 101.57 MPa, 1.1%, 1.31 J and 81 VHN respectively. Fractography of tensile and impact specimens from the Sr-treated composite revealed that Mg2Si particles suffered cracking with few decohesion indicating higher ductility. The results of wear testing also showed that composites treated with Sr have higher wear resistance compared with those of without Sr. The highest resistance to wear was observed in the composite containing 0.01 wt %Sr which is likely the result of good dispersion of fine Mg2Si particles in the Al matrix. This fine morphology and uniform distribution of Mg2Si particles also contributed to better corrosion resistance by reducing the propagation of corrosion pits

Effect of praseodymium addition on wear properties of Al-15%Mg2Si composites

Nowadays, aluminium metal matrix composites are widely used in various industrial applications, especially in automotive and aerospace industries. In engineering, rare earth elements (RE), such as yttrium, neodymium and cerium are widely used as alloying elements to improve the strength and wear resistance of composite materials. Therefore, this research project was done to investigate the effect of praseodymium (Pr) addition on wear behaviour of aluminium MMC of Al-15%Mg2Si composite. Microstructure analysis was carried out by using optical and SEM analyses. In addition, Vicker hardness and dry sliding wear tests were conducted to measure the effectiveness of Pr addition on mechanical and tribological properties of the fabricated composites. The result showed that Pr addition affected the microstructure and wear properties of aluminium composites. Pr addition with 1.0 wt% concentration gave the highest Mg2Si phase density of area and lowest value of wear rate with average wear rate of 2.3 mm3/km for 20 N applied load compared to 2.4 mm3/km for the base composite which indicated the positive effect of Pr addition on the wear resistance of composites

Microstructure characterization, mechanical, and tribological properties of slow-cooled Sb-treated Al-20Mg2Si-Cu in situ composites

Role of Sb addition on structural characteristics, mechanical properties, and wear behavior of Al-20Mg2Si-Cu in situ composite under slow cooling condition was thoroughly investigated in this study using stereomicroscopy, optical and scanning electron microscopy, thermal analysis, tensile, impact, hardness tests, and wear tester. Results show that addition of 0.8 wt.% Sb was found to produce a change in the morphology of primary Mg2Si from dendrite to fine polygonal shape. At this Sb addition, the primary Mg2Si phase also exhibited a reduction in size from 179.4 to 128.6 μm, an increase in density of Mg2Si per area from 12.5 to 32.2 particle/mm2, and a decrease in the aspect ratio from 1.24 to 1.11. Increasing the amount of Sb added up to 1 wt.% also resulted in a decrease in both nucleation and growth temperatures of the eutectic Mg2Si by 2.6 and 1.7 °C respectively, which is most likely due to change of eutectic Mg2Si morphology from flake to fibrous structure. Thermal analysis technique showed that distribution of Mg2Si particles influences the heat conductivity during the solidification process of Al-Mg2Si composite. The results also showed that improvements in mechanical properties of composite were obtained with increasing Sb content due to modification of both primary and eutectic Mg2Si and due to intermetallic compound transformation from β-Al5FeSi to α-Al15(Fe,Mn)3Si2. Examination of fracture surfaces from tensile and impact samples showed that the base composite failed in a brittle manner with decohered or debonded Mg2Si particles, whereas the 0.8 wt.% Sb-treated composite showed more cracked Mg2Si and ductile fracture in the matrix. Wear properties improved significantly with addition of Sb due to modification and better dispersion of fine Mg2Si particles in matrix

Effect of primary and eutectic Mg2Si crystal modifications on the mechanical properties and sliding wear behaviour of an Al–20Mg2Si–2Cu–xBi composite

This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of primary Mg2Si particles was achieved with the addition of 0.4 wt% Bi. Increasing Bi beyond 0.4 wt% resulted in a loss of modification, possibly due to the formation of Al8MgBiSi4 compound before the precipitation of the primary Mg2Si. Additionally, the structure of the pseudo-eutectic Mg2Si was transformed from plate to fibrous, which was consistent with decrease of growth temperature extracted from the cooling curve thermal analysis. Addition of Bi had an effect on the morphology of Al5FeSi (β), Al2Cu (θ) and Al5Cu2Mg8Si6 (Q) intermetallic compounds. The tensile strength, elongation percentage, impact toughness, and hardness increased by 6%, 13%, 75%, and 23%, respectively, due to modification of both the primary and eutectic Mg2Si crystals. The tensile and impact fracture surfaces showed fewer decohered particles in the Bi-treated composite. The enhancement in wear resistance of the Bi-treated composite could be attributed to solid lubricant function of insoluble soft Bi phase and modification effects on Mg2Si particles

Microstructure characterization and tensile properties of al-15mg2si-xysz hybrid composite

Aluminum matrix composites (AMCs) are widely used in the automotive industry as engine cylinders, pistons, and brake discs. It is due to its ability that better mechanical performance and physical properties are exhibited. Recently, hypereutectic Al-Mg2Si in-situ composite with a large amount of hard Mg2Si particles has attracted considerable attention due to the beneficial features of Mg2Si particles. However, there are some limitations in the application of this composite due to its low tensile and machinability properties. Therefore, the purpose of this study was to fabricate and characterize the microstructure and tensile properties of Al/(15Mg2Si+xYSZ) hybrid composites by using an in-situ reinforcement, namely magnesium silicide (Mg2Si), and ex-situ reinforcement, yttria-stabilized zirconia (YSZ). The effect of different YSZ concentrations (i.e., 3, 6, and 9 wt. %) on the size, shape, and distribution of Mg2Si particles was analyzed accordingly. Microstructure characterization was carried out by using optical microscope (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The microstructure examinations showed that with increasing YSZ concentrations, the size of primary Mg2Si particles was reduced from 74.4 μm (i.e., without YSZ) to 65.2 μm (with 9 wt. % YSZ addition). Similarly, the tensile properties were enhanced parallel to the increasing concentrations from 53.54 to 85.65 MPa with 6 wt. % of YSZ

Influence of barium addition on the formation of primary mg2si crystals from al-mg-si melts

In this study, the influence of different contents of Ba additions on the microstructure evolution, phase reaction characteristic, and mechanical property of Al-Mg-Si alloy was investigated. Microstructural characterization was conducted by means of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) facility, X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical property was examined using hardness test. The results revealed that cubic primary Mg2Si crystals shaped by {100} facets with an average particle size of 35 μm were successfully fabricated through the addition of 0.2 wt. % Ba element to Al-Mg-Si melts. For the first time, it is revealed that the Al4Ba compound can act as the nuclei for the primary Mg2Si during solidification, which leads to the refining of the primary Mg2Si particle size extensively. Furthermore, the formation of Al2Si2Ba and AlSiBa intermetallic compounds (IMCs) are liable for the Mg2Si particle refinement; hence, the hardness of the alloy increased from 60.21 to 67.83 Hv. Besides, thermal analysis showed that the nucleation temperatures of the primary Mg2Si phase increased with the addition of Ba. Ba additions perform a substantial role in determining the shapes of primary Mg2Si crystals, which can be altered from coarse dendritic structure (0 wt. %) to crystals with a combination of eight {111} and four {100} facets (0.08 wt. %), then to truncated cube (0.1 wt. %), and finally to a cube fully bounded by {100} facets (0.2 wt. %) with increasing Ba concentrations. This study revealed that the growth process of the cubic primary Mg2Si is due to the absorption and poisoning effect of Ba atoms, which leads to the fading of the growth rates of {100} faces of primary Mg2Si and as a result the {100} faces are exposed. Furthermore, in the modified alloy, the skeleton-type growth process of the cubic primary Mg2Si was found, in which growth steps with some hillocks were detected

Effect of barium on the structure and characteristics of Mg2Si reinforced particles Al–Mg2Si–Cu in situ composite

Addition of barium (Ba) in various concentrations is susceptible to cause changes on Mg2Si reinforced particles in Al–Mg2Si–Cu in situ composite. In this study, six samples of the composite with different concentrations of Ba (0.1–0.8 wt%) were prepared. The alteration of Mg2Si structure, phase reaction characteristics and cooling curves behaviour of the composite were investigated via optical microscope, scanning electron microscope (SEM), and computer aided cooling curve thermal analysis (CACCTA). The results depicted that 0.2 wt% exhibit the appropriate concentration of Ba added in order to modify and refine the Mg2Si particles. The skeleton and dendrite shape of Mg2Si particles have been transformed into fine polygonal shape accompanied with decreased in average size from 1178.5 µm of the unmodified particles to 289.1 µm. In fact, the refinement of Mg2Si particles is associated with the increased of nucleation temperature, TN of the respective phase together with the least undercooling, ΔU correspond to the easiness of the particles to be formed prior to its growth. Meanwhile, the decrement of TN respective to other concentrations of Ba indicates the opposite refinement effect of the particles as it became coarser. Besides, the refinement of Mg2Si has induced more nucleation of the particles resulting the increment of the density of particles and better distribution over the composite area. Therefore, the corresponding mechanical and tribological properties of the composite are believed to be improved accordingly