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

Investigating the Machinability of Al-Si-Cu cast alloy containing bismuth and antimony using coated carbide insert

Surface roughness and cutting force are two key measures that describe machined surface integrity and power requirement evaluation, respectively. This investigation presents the effect of melt treatment with addition of bismuth and antimony on machinability when turning Al-11 Si-2 Cu alloy. The experiments are carried out under oblique dry cutting conditions using a PVD TIN-coated insert at three cutting speeds of 70, 130 and 250 m/min, feed rates of 0.05, 0.1, 0.15 mm/rev, and 0.05 mm constant depth of cut. It was found that the Bi-containing workpiece possess the best surface roughness value and lowest cutting force due to formation of pure Bi which plays an important role as a lubricant in turning process, while Sb-containing workpiece produced the highest cutting force and highest surface roughness value. Additionally, change of silicon morphology from flake-like to lamellar structure changed value of cutting force and surface roughness during turning. (C) 2014 Elsevier Ltd. All rights reserved

Oxidation and melting characterizations of AZ91D granules during in-situ melting

In this research, the oxidation and melting behaviour of AZ91D magnesium alloy granules was investigated throughout using in-situ melting technique when the granules were covered by flux. The granules were heated inside an electrical resistance furnace at four different temperatures of 650, 700, 750 and 800 °C for 30 min. Thermal analysis was used to detect the granules characteristic temperatures during the technique. The products of the heating process were examined visually and characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that due to occurrence of severe oxidation and combustion, particularly at 800 °C, a significant amount of the granules transformed to a powdered state. The presence of the mould materials within the oxidation residue was detected indicating that severe mould-magnesium reaction occurred during heating. It was found that the granules melted during the heating process. However, the presence of oxides on the granules prevented them from fusing to form a single melt

Effects of pouring temperature and slurry viscosity on heat transfer and surface roughness in lost foam casting

The effects of pouring temperature and slurry viscosity in terms of heat transfer on surface roughness during lost foam casting (LFC) of LM6 alloy were investigated experimentally. Heat transfer of molten materials is an important factors to changes the microstructure which is considered in the present study. It is primarily dependent on the pouring temperature, casting thickness, mould material, mould temperature and surrounding medium. The pouring temperature changed from 700 to740°C and slurry viscosity altered from 20 to 36 sec. A full 2-level factorial design experimental technique was used to identify the significant factors that effect on surface roughness of castings. The results show that surface roughness improved by lower pouring temperature, whereas slurry viscosity has less influence on the quality of surface

Relationship between the corrosion behavior and the thermal characteristics and microstructure of Mg-0.5Ca-Xzn alloys

Effects of secondary phases on corrosion behaviour of the Mg-0.5Ca-xZn alloys were investigated by polarization, immersion and hydrogen evolution tests. The Mg 2Ca phase nucleated at 520°C while, Ca 2Mg 6Zn 3 and Mg 51Zn 20 phases were formed at 420°C and 330°C respectively. The corrosion resistance of Mg-0.5Ca alloy was enhanced with the addition of Zn up to 1%, while further addition reversed the effect. The Mg-0.5Ca-1Zn alloys with (α-Mg+Ca 2Mg 6Zn 3+Mg 2Ca) phase showed lower corrosion rate than the alloys with (α-Mg+Ca 2Mg 6Zn 3) and (α-Mg+Ca 2Mg 6Zn 3+Mg 51Ca 20) phases. The amount of corrosion product, composed of Mg(OH) 2 and hydroxyapatite on the surface of the alloy, increased with increasing Zn content

Microstructure analysis and corrosion behavior of biodegradable Mg-Ca implant alloys

The calcium content in binary Mg-xCa alloys affects the microstructure, corrosion and solidification behavior of the alloys. In this study, binary Mg-xCa alloys with various Ca contents from 0.5 to 10wt.% were produced by casting process. Microstructural evolutions were characterized by optical microscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Solidification behavior was assessed via two thermocouple thermal analysis method. The corrosion resistance was examined in vitro by potentiodynamic polarization and immersion test in Kokubo solution at room temperature. The results revealed that the grain size and dendrite cell size decreased significantly with rising Ca content, whilst the content of Mg2Ca intermetallic phase in grain boundaries increased with increasing Ca content. Potentiodynamic polarization tests in simulated body fluid (SBF) indicated that corrosion rates of Mg-xCa alloy increased significantly with rising Ca content. Immersion tests in Kokubo solution also showed that dissolution rate of Mg-xCa alloy increased with increasing Mg2Ca content which lead to an increase in pH value. It was observed that corrosion damage in specimens with lower Ca content was more moderate and uniform than higher Ca content. Thermal analysis results showed that the fraction of primary a-Mg at dendrite coherency point (faDCP) decreased with increasing Ca content but the liquid fraction fL increased causing the rise in eutectic Mg2Ca intermetallic phase in grain boundaries, thus increasing the corrosion rate. Our analyses showed that Mg-0.5Ca alloy is a promising alloy to be used as biodegradable implants

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 modifier elements on machinability of Al-20Mg2Si metal matrix composite during dry turning

The principle aim of this study was to observe the effect of machining parameters as well as the separate additions of 0.4 wt% bismuth, 0.01 wt% strontium, and 0.8 wt% antimony on the machinability of Al-20%Mg2Si in situ metal matrix composite. Microstructure alteration, surface roughness, main cutting force, and chip morphology were taken into account as indices to examine the effect of modifiers and machinability during dry turning. It was found that the additives modify the Mg2SiP particles by changing the particle shape from coarse primary to polygonal shape and decrease the particle size and aspect ratio as well as increase the particle density. Results show that the modified work-pieces present adequate machinability with respect to cutting force and surface roughness. The smaller reinforcements enable lower surface roughness values to be obtained even if they are pulled out, fractured, or elongated. In addition, the modified work-pieces encourage lower surface roughness values in comparison with unmodified work-piece due to less built-up-edge formation. A scenario for surface roughness of Al-Mg2Si composite with respect to the size and aspect ratio of reinforcement particles is proposed in this study