Squeeze-cast Composites Research Articles

Investigation on microstructure and tribological performance of zirconium boride reinforced AZ91D magnesium alloy: Effect of processing routes

The present research explored the effects of spatially dispersed ZrB2 particles on mechanical characteristics, surface-modified tribo layer and the dry sliding wear of the AZ91D alloy composite. The objective of this study was to reduce the porosity and improve the tribo performance of the AZ91D/ZrB2 composite by a squeeze casting, and the results were compared with those of a stir-cast composite. The influence of ZrB2 on mechanical properties such as hardness, tensile strength, and wear analysis of composites by the pin-on-disk technique was studied. The squeeze cast composite showed a higher hardness of 115 HV and ultimate tensile strength of 275 MPa than the stir cast composite. Stir-cast composite reduces particle rearrangement due to cluster formation, resulting in higher porosity and lower mechanical strength, reducing tribo performance. The refinement of grain structure and porosity reduction of up to 31.61% improves strength, leading to better tribological properties for the squeeze cast composites. The squeeze cast composite containing 12 wt% of ZrB2 showed a minimum wear of 0.024 mm3/m, which is 25.14% less than the stir cast composite. The improved wear resistance resulted from a lubricating boron oxide layer (B2O3), confirmed through Raman spectroscopy. Tribo layer, delamination, and plastic deformation were found to be the primary wear mechanisms for the AZ91D/ZrB2 composite that were active throughout the sliding period.

Influence of CeO2 reinforcement on microstructure, mechanical and wear behaviour of AA2219 squeeze cast composites

The present investigation deals with development of AA2219 composites with different weight fractions of Cerium oxide (CeO2) reinforcement and characterizing the microstructure and mechanical properties thereof. XRD and SEM micrograph confirm the presence of CeO2 particles and Al2Cu precipitate. The grain size of 0, 0.5, 1.0, 1.5 and 2 wt% CeO2 composites are 483, 453, 411, 362 and 328 μm, respectively. Addition of CeO2 significantly reduces the dendritic morphology and refines the α-Al grain structure. 2 wt% CeO2 addition has yielded the maximum hardness of 124 HV and yield strength of 87 MPa in all the composites developed. Additionally, the developed composites were evaluated by examining the wear characteristics with the co-efficient of friction (COF) and the specific wear rate. In this study, Taguchi's L25 orthogonal array was used to optimize the parameters like reinforcement fraction, load and sliding distance. Signal-to-noise ratio (S/N ratio) and analysis of variance (ANOVA) are used to obtain the parameters highly influencing the wear behaviour. Adhesive wear is exhibited by ploughing at lower loads and delamination is observed with increasing load. Deep shallow ploughs with embarked abrasion are observed at higher loads.

Beneficial effect of CeO2 on the corrosion behaviour of AA2219 squeeze cast composites – An experimental investigation

This research emphasizes the impact of Cerium oxide on grain size and corrosion behavior of AA2219 fabricated by the Squeeze casting technique. The composites were effectively characterized by electron backscatter diffraction EBSD, which indicates a significant reduction in grain size inherited by the thermo-physical properties of the dispersoids, which in turn enhances the mechanical properties. The Corrosion behavior of squeeze cast samples was examined through the potentiodynamic polarization technique with Tafel polarization using a standard solution of 3.5% NaCl. The microscopic characterization of the corroded regions reveals that the sample with higher reinforcement of 2% CeO2 is more resistant to the pitting attack due to the hydrophobic nature of the dispersoids.

Study the Stability of A 356 Al Alloy/ZrO2 Composites Fabricated by Vortex and Squeeze Casting in Acid Rain

Electrochemical behavior of A 356 Al alloy and its composites reinforced by zirconia and prepared by vortex and squeeze casting was studied in acid rain using open circuit potential, poteniodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The open circuit potential for the A 356 alloy and its vortex cast composites increases in noble direction very slowly with time till reaches a steady state value indicating growth of the pre-immersion passive oxide film on the tested materials in the acid rain to a certain thickness which increases with increasing of the zirconia content of the composites. Also, the open circuit potential values for the squeeze cast composites are higher than that for vortex composite. This means that the surface of squeeze composite allows for formation passive film with large thickness than that formed on vortex one. The results of polarization and EIS indicated that the corrosion resistance of the vortex composites increases with the increase in the vol. % of ZrO2 up to 20 % then decreases again. Also, the corrosion resistance of the squeeze composites increases as the squeeze pressure increases. Additional, the micrographs of scanning electron microscopy (SEM) well-showed that the surface of squeeze composite is covered by a passive film and less exposure to corrosion in comparing with the surface of vortex composite. Energy dispersive spectroscopy (EDS) found out the presence of a protective passive aluminium oxide on the two types of the test composites in acid rain.

Appraisal of tribological properties of A356 with 20% SiC composites under dry sliding condition

The goal of this research work is to assess the tribological properties of A356 alloy reinforced with 20 wt% SiC composite prepared by liquid metallurgy route. A356 alloy and A356 with 20 wt% SiC composites were manufactured through three different casting techniques such as gravity die casting, stir casting and stir cum squeeze casting. The fabricated castings exhibit improved hardness value of around 680 MPa, 840 MPa and 950 MPa for A356 alloy, A356 with 20 wt% SiC stir cast composite and A356 with 20 wt% SiC stir with squeeze cast composite, respectively. Further, an ultimate tensile strength of 256 MPa, 298 MPa and 331 MPa was obtained for A356 alloy, A356 with 20 wt% SiC stir cast composite and A356 with 20 wt% SiC stir with squeeze cast composite, respectively. The tribological properties of prepared samples were tested using a pin-on-disk tribometer at room temperature under dry sliding condition. The wear results explained that the wear rate and coefficient of friction started to increase with the function of load (10–40 N) under both the sliding distance of 1000 m and 2000 m. The squeeze cast A356 with 20 wt% SiC composite produced less wear rate and a higher coefficient of friction when compared to other samples. This was attributed to effective embedding, bonding and load-carrying capacity of SiC particles over the A356 matrix. This result indicates improved adhesive properties and abrasion resistance in the squeeze cast A356 with 20 wt% SiC composite. Further, the worn surface morphology of squeeze cast samples was examined using a scanning electron microscope to observe mild adhesive wear and damages due to the delamination effect.

Elucidation on the Microstructural and Mechanical Properties of Tailored VAL12 Hybrid Composites with ZrO<sub>2</sub> Dispersoids Fabricated by Squeeze Casting Technique

The effect of ZrO2 (2, 4, 6 and 8 wt%) dispersoids with 1 wt% graphite on the microstructural, mechanical properties on squeeze cast VAL12 matrix hybrid composite is investigated in the present study. The hybrid composites were characterized using advanced characterization techniques to reveal its microstructural and physical properties. The microscopic examinations using optical and SEM technique reveal that the addition of dispersoids accelerates the nucleation kinetics, thus attaining fine, equiaxial grains in hybrid composites. The squeeze cast composites show almost nil porosity, defects and owing to it, the actual density of the composites are found to be more than 95% as that of the theoretical density values. The hardness values and tensile values increase with respect to the increase in percentage addition of ZrO2. The tensile results show that there is an appreciable increase in the UTS values of composites without much loss in its ductility as the addition of graphite improves the self-lubricating property and provides wettability during the casting. Fractographic studies on tensile tested specimen reveal that the crack occurs in both matrix and particles showing the good interface between matrix and dispersoids. Machinability studies reveal the formation of continuous chips in hybrid composites with a lower percentage of reinforcement (up to 4% ZrO2 + 1%Gr) and segmented chips in case of the composite with 8% ZrO2 + 1%Gr, as the increase in the percentage of dispersoids improve the chip breakability of the composites. On an overall, the hybrid aluminium matrix composites with 1%Gr and 6 % ZrO2 unveiled better optimal results.

Microstructure and thermal/mechanical properties of hot-extruded aluminum/graphite composites with Al–Si alloy addition

Al/graphite composites with small amounts of Al–Si alloy were consolidated by spark plasma sintering and hot-extrusion processes. The effect of Al–Si alloy addition on densification behavior, microstructure, thermal conductivity (TC), coefficient of thermal expansion (CTE), and compressive strength has been systematically investigated. The results showed that the addition of Al–Si alloy resulted in improvements in relative density of the composites, interfacial bonding between Al and graphite, and orientation degree of graphite. The composites with Al–Si alloy showed improved TC and reduced CTE values in comparison with those without Al–Si alloy. For example, the 450 °C-extruded Al/60 vol% graphite/9 vol% Al–Si composite showed a maximum TC of 297 W m−1 K−1 and a minimum CTE of 7.95 ppm K−1. Moreover, the hot-extruded Al/graphite composites containing Al–Si alloy exhibited higher compressive strength compared to conventional squeeze-cast composites and hot-extruded composites without Al–Si alloy.

A Comparative Study of Thermal Conductivity and Tribological Behavior of Squeeze Cast A359/AlN and A359/SiC Composites

A comparative study of thermal and wear behavior of squeeze cast A359 alloy and composites containing 5, 10 and 15 wt.% AlN and SiC particulates was investigated. It was pointed out that A359/AlN composites have a superior thermal conductivity as compared to A359 alloy or even to A359/SiC composites. Composites wear characteristics were achieved by pins-on-disk instrument over a load range of 20-60 N and a sliding speed of 2.75 m/s. Results showed that A359/AlN and A359/SiC composites exhibited higher wear resistance values compared to A359 alloy. Moreover, A359/AlN composites showed superior values of wear resistance than A359/SiC composites at relatively high loads. Friction coefficients and contact surface temperature for A359/AlN specimens decreased as AlN content increased, while they increased for A359/SiC. Investigations of worn surfaces revealed that A359/AlN composites were covered up by aluminum nitrides and iron oxides, which acted as smooth layers. However, A359/SiC composites were mainly covered only by iron oxides. The superior thermal conductivity and the significant wear resistance of the developed A359/AlN composites provided a high durable material suitable for industrial applications.

Fabrication and characterization of squeeze cast A413-CSF composites

Abstract A413 aluminum matrix composites reinforced with short carbon fibers (CSFs) were produced using a combination of vortex and squeeze casting processes and the effects of reinforcement volume fraction and reinforcement coating on density, porosity, reinforcement distribution and mechanical properties of the produced composites were studied. The results showed that increasing the volume fraction of CSFs led to decreased density and increased porosity of the cast composites. Distribution of uncoated CSFs in the matrix of the reinforced samples was poor and most of the fibers were in agglomerated bundle form. Utilization of coated CSFs resulted in a rather uniform distribution of the reinforcement in the matrix. Mechanical properties of squeeze cast composites fabricated using uncoated CSFs improved by increasing the reinforcement volume fraction up to 2% and decreased beyond it. Mechanical properties of the squeeze cast composites fabricated using coated CSFs improved steadily by increasing the reinforcement volume fraction up to 3%. Ultimate tensile strength and hardness values of the composites reinforced with 3 vol% coated CSFs increased by more than 100% and 60%, respectively, in comparison with those of the monolithic cast sample.

Prediction of Cooling Curves for Squeeze Cast Al/SiCp Composites Using Finite Element Analysis

This paper reports the experimental and finite element analyses of the solidification behavior of Al/SiCp composites, fabricated by the squeeze casting technique. Experiments were carried out by varying the melt temperatures for cylindrical-shaped composite castings. The composite samples were produced at the following constant temperatures: melt—1023 K, 1073 K, 1123 K, and 1173 K (750 °C, 800 °C, 850 °C, and 900 °C); and die—673 K (400 °C). The pressure applied throughout the experiment is 100 MPa. The melt temperature shows significant influence on the solidification behavior of the metal matrix composite. It was observed that the solidification time was 40 seconds when the melt temperature was 1023 K (750 °C) but it increased to 51 seconds when the melt temperature was at 1173 K (900 °C). The results also showed that the cooling rate decreased on increasing the melt temperature. Cooling curves for our system, squeeze cast composites, were predicted using the finite element software ANSYS. K-type thermocouples were interfaced to the die and the microcomputer from which the experimental cooling curves were constructed. The experimental and predicted cooling curves were then compared. While both show similar trends, the finite element analysis consistently under-predicts the temperature. In addition, finite element stress analysis reveals that both radial and tangential thermal stresses increase with the melt temperature.

Tribological Properties of Al–SiC Metal Matrix Composites: A Comparison Between Sand Cast and Squeeze Cast Techniques

Tribological behaviour of Al–SiC metal matrix composites prepared using two different fabrication techniques, viz. sand cast and squeeze cast techniques are studied in a multi- tribotester (TR-25, DUCOM, India) under dry sliding conditions and ambient atmosphere for varying volume fraction of reinforcement, applied load and sliding speed. Friction increases with increase in applied load and sliding speed and volume fraction of reinforcement. Wear test results show increased wear rates at higher load and speed, while increase in SiC volume fraction yields decrease in wear rate. Corrosion study conducted in 3.5 % NaCl solution shows that squeeze cast composites have better corrosion resistance than sand cast composites. Vickers’s microhardness test shows improved hardness properties for squeeze cast composites compared to sand cast ones. The microstructure study of wear tracks reveals domination of abrasive wear with minor traces of adhesive wear.

The Effect of the Die Temperature on the Solidification Behaviour of the Al/SiC<sub>p</sub> Metal Matrix Composite: A Comparative Study of Experimental and Finite Element Analysis

This paper discusses the influence of die temperature on the solidification behaviour of A356/SiCp composites fabricated by squeeze casting method. Information on the solidification studies of squeeze cast composites is somewhat scarce. Experiments were carried out by varying the die temperatures for cylindrical shaped composite castings K-type thermocouples were interfaced to the die and the temperature-time history was recorded to construct the cooling curves. The cooling curves are also predicted from the finite element analysis (FEA) software ANSYS 13. The experimental and predicted cooling curves are not in good agreement. In addition to, the experimental and theoretical solidification times are studied. It was understood that the increase in the die temperature decreases the cooling rate.

Effect of the squeeze pressure on the mechanical properties of the squeeze cast Al/SiC<SUB align="right">p Metal Matrix Composite

This paper presents the results of a study carried out to understand the effect of the squeeze pressure on the mechanical properties of Al/SiCp composites, fabricated by the squeeze casting technique. Aluminium (A356) alloy reinforced with SiC particles were prepared using the stir casting route. The SiC particles are distributed in the liquid Al alloy matrix by mechanical stirring, and the melt is then subjected to different squeeze pressure during solidification. Microstructure examination of the squeeze cast composites showed the SiC particle distribution and the grain refinement in the Al alloy matrix due to the applied pressure. The hardness and density distribution also carried out to correlate with the particle distribution. The tensile and impact strength value linearly increase with the applied squeeze pressure due to the uniform distribution of particle and effect of grain refinement. At 100 MPa, the sound cast Al/SiCp composites are produced with superior hardness and tensile properties.

Effect of Squeeze Pressure on Microstructure, Aging and Mechanical Properties of A357/ ZrO<sub>2</sub> Composite

AlSiMg (A357) composites containing 10 vol. % zirconia (ZrO2) particulates have been synthesized by the stir process followed by squeeze casting. Pressures of 25 and 50 MPa were maintained during solidification in specially designed die and ram and maintained at 250°C. Results show that with increasing squeeze pressure, the density increases while porosity decreases. The hardness of squeeze cast composite is higher than that of stir casting by about 10%. The compression properties have been evaluated and compared. The results show that compressive strength increases with squeeze pressure.

Effect of Squeeze Pressure on Aging and Mechanical Properties of AA2218-5 Wt Pct Al2O3 (TiO2) Composites

Metal matrix composites (MMCs) based on AA2218 alloy have been successfully developed by stirring powder mix of TiO2 particles along with Al2O3 particles prepared by milling into the alloy melt. The chemical reaction of TiO2 particles with molten Al alloy results in alumina and simultaneously releases into the alloy elemental titanium, which forms intermetallic phase Al3Ti in the last freezing liquid at the dendrite cell boundary. Application of squeeze pressure during casting of melt-particle slurry in the pressure range from 100 to 220 MPa results in decreasing the cell size and porosity. Following T61 heat treatment recommended for AA2218 alloy, the composites have been solutionized; their aging response at 170 °C shows significant increase due to squeeze pressure, but the peak hardness at 10 hours is relatively insensitive to variation in squeeze pressure. The 0.2 pct offset proof stress and the UTS of squeeze-cast composites after solutionizing and those aged following solutionizing increases with increasing squeeze pressure. The influence of aging as evident from the comparison of their properties starts increasing significantly in composites squeeze cast at 140 MPa but becomes steady after 180 MPa. The ductility of the composites also improves across the pressure range between 140 and 180 MPa, and there is increased improvement in ductility after aging at higher squeeze pressures. The scanning electron microscopy (SEM) micrographs show that squeeze-cast composites show more dimpled regions than those observed in gravity-cast composites.

Effect of Al<SUB>2</SUB>O<SUB>3</SUB> Particles on the Microstructure and Sliding Wear of 7075 Al Alloy Manufactured by Squeeze Casting Method

Aluminum (Al) alloy 7075 reinforced with Al2O3 particles was prepared using the stir casting method. The microstructure of the cast composites showed some degree of porosity and sites of Al2O3 particle clustering, especially at high-volume fractions of Al2O3 particles. Different squeeze pressures (25 and 50 MPa) were applied to the cast composite during solidification to reduce porosity and particle clusters. Microstructure examinations of the squeeze cast composites showed remarkable grain refining compared with that of the matrix alloy. As the volume fraction of particles and applied squeeze pressure increased, the hardness linearly increased. This increase was related to the modified structure and the decrease in the porosity. The effect of particle volume fraction and squeeze pressure on the dry-sliding wear of the composites was studied. Experiments were performed at 10, 30, and 50 N with a sliding speed of 1 m/s using a pin-on-ring apparatus. Increasing the particle volume fraction and squeeze pressure improved the wear resistance of the composite compared with that of the monolithic alloy, because the Al2O3 particles acted as load-bearing constituents. Also, these results can be attributed to the fact that the application of squeeze pressure during solidification led to a reduction in the porosity, and an increase in the solidification rate, leading to a finer structure. Moreover, the application of squeeze pressure improved the interface strength between the matrix and Al2O3 particles by elimination of the porosity at the interface, thereby providing better mechanical locking.

Tensile and wear properties of aluminum composites

Beryl/Al–Si–Mg composites containing 2.0–10.0% of beryl particles have been fabricated by squeeze casting. Pressure of 80 MPa was maintained during solidification in a specially designed die and punch maintained at 400 °C. The tensile and wear properties have been evaluated and compared with gravity cast beryl–aluminum composites. The squeeze cast composites show a peak strength of 216 MPa showing an increase of 11.6% in tensile strength. The new composites also have improved wear resistance when compared to gravity cast composites. Squeeze cast composites with 6 wt.% of beryl particles showed almost 1.2 times reduced adhesive wear rate at 2400 m sliding distance when compared to that at 600 m.

Fabrication of 6061 aluminium alloy/Al18B4O33(w) composite by using sol–gel alumina binder

For fabrication of aluminium borate whisker (Al18B4O33(w)) reinforced 6061 aluminium alloy composites, a sol–gel alumina binder instead of conventional silica binder was used for preparing the whisker preforms of the squeeze cast composites. The results show that a sound whisker preform and a uniform composite can be made by this method. Unlike the reactive silica binder, the sol–gel alumina binder is rather stable throughout the entire high temperature fabrication process. Under appropriate conditions, the sol–gel alumina binder can also serve as a thermal barrier for minimising interfacial reactions between aluminium borate whiskers and the matrix alloy. With a binder concentration of 0.6 mol L-1, the ultimate tensile strength of the composite is as high as 277.6 MPa at room temperature and moderate at elevated temperatures. The tensile fracture of the alumina bound composite shows a mixed mode of dimple fracture and interface debonding.

The structure and bending properties of squeeze-cast composites of A356 aluminium alloy reinforced with alumina particles

In the present work, variations in the microstructure, mechanical properties and fracture character of Al 2O 3/A356 composites fabricated by squeeze casting at different solidification cooling rates were investigated. Experimental results showed that when the solidification cooling rate decreased, the crystalline grain size of the matrix alloy and the eutectic silicon phase increased gradually, but the bending strength and the elastic modulus decreased. For Al 2O 3/A356 composites fabricated by squeeze casting, solidification occurred first in the interstices between particles and the particle surface was the substrate for the heterogeneous nucleation of the eutectic silicon phase. Fracture surfaces of the Al 2O 3/A356 composites showed brittle fracture characteristics and broken and cleaved Al 2O 3 particles were observed on the fracture surfaces of the composites.

Influence of fibre interconnections on the thermomechanical behaviour of metal matrix composites consisting of a Zn–Al alloy reinforced with steel fibres

Interconnected fibre networks presenting transverse isotropic symmetry with variable fibre interconnectivity were prepared by sintering assemblies of low carbon steel fibres. The strength and stiffness of these fibre preforms was found to increase very much when increasing sintering temperature or sintering time. Squeeze cast composites were prepared by infiltrating these preforms with alloy ZA8. Creep tests and tensile tests were carried out at 150°C. Both the creep strength and the back-flow strains at unloading drastically increase with increasing preform sintering temperature or time. Also thermal expansion is much affected by fibre interconnectivity. Especially, during cooling, the matrix dilatation strains brought about by thermal mismatches increase with increasing fibre interconnectivity. These results demonstrate that plastic and viscoplastic behaviours of network reinforced composites depend on the mechanical properties of the network as a whole.