Semisolid Stirring Research Articles

Microstructures, interface structure and room temperature tensile properties of magnesium materials reinforced by high content submicron SiCp

Abstract The present work aims to research the treatment processing of magnesium reinforced with 1 μmsilicon carbide particle (SiCp) using stir casting combined by ultrasonic vibration. Present studies have been done on six different materials: (a) AZ31B alloy without particles, (b) 5 vol.% SiCp/AZ31B composites fabricated with different semi-solid stirring time (5 min, 10 min, 15 min and 20 min), (c) composite with 20 vol.% SiCp. The effects of 1 μm/SiCp pretreatment and stirring time on microstructure and interfacial wettability as well as mechanical properties of the materials were confirmed. Both short and long stirring time for the particle dispersion brought particle agglomeration. Results of SEM microstructure and tensile properties exhibited that the optimal stirring parameters of 625 °C/1500 rpm/15 min are exploited, and 20 vol.% SiCp/AZ31B composite was fabricated by the optimal stirring parameters. The application of optimal stirring parameters for the treatment resulted in homogeneous particle distribution. The addition of SiCp leads to a reduced matrix grain, and 20 vol.% SiCp/AZ31B composite showed smaller grain size than. 5 vol.% SiCp/AZ31B composite. The interface between SiCp and matrix is clear and interfacial wettability well. Tensile test results show that with increasing SiCp content, strengths increase while ductility decreases.

Effect of Particle Size and Weight Percent of SiC Particles on Microstructure and Hardness of A356-SiC Composites Produced by Semi-Solid Stir Casting

This research investigates the effects of particle size and weight percent on the hardness of A356 matrix composite reinforced with SiC particulates produced by semi-solid stir casting. The particle sizes of the reinforcing phase were in the form of 37 and 100 μm SiC powders with loading content of 5, 10, 15 and 20 percent by weight. A356 alloy was melted and SiC powder was then gradually added into the continuously stirred slurry to promote uniform distribution of the particulates. It has been found that in the as cast condition, the average hardness values of A356 reinforced with different amounts of 37μm SiC, increase as expected with increasing amounts of particulates. A356 reinforced with 100 μm 10 wt% SiC, followed by T6 treatment, exhibited the highest percentage of hardness increment.

Microstructure, Mechanical Properties and Wear Behaviour of Semisolid Stir Casting SiC Reinforced Zn-40Al Based Composites

The Zn-40Al composites with various contents of SiC were fabricated by the semi-solid stir casting process. The influence of the SiC on the microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that the microstructures of as-cast Zn-Al alloys are refined by the addition of SiC. However, with the increase of SiC content, a number of shrinkage porosity occur. The hardness of the composites increases with the increase content of SiC. The tensile strength of the composites declines significantly with the increase content of SiC. The most effective strengthening achieves in Zn-40Al/0.5wt.% SiC, with a maximum increment of 20% in tensile strength compared to non-SiC addition alloy. The overall results reveal that the composites possess similar friction coefficients but the abrasion loss is reduced to less than a tenth after adding 0.5% SiC.

Simultaneously improving the strength and ductility of extruded bimodal size SiCp/AZ61 composites: Synergistic effect of micron/nano SiCp and submicron Mg17Al12 precipitates

AZ61 matrix reinforced by micro- and nano-scaled SiC particles fabricated via semisolid stirring assisted ultrasonic vibration was subjected to extruded at different speeds (0.1, 0.5 and 2.5 mm/s) with a constant temperature of 280 ℃. The effect of extrusion speed on the microstructure and tensile properties of the extruded composite was investigated. Grain size, precipitates fraction and texture were found to be greatly affected by the extrusion speed, resulting in tensile properties showing superior strength and ductility as the extrusion speed being of 0.1 mm/s. The improved strength and ductility were ascribed to the synergistic effect of micron/nano SiCp and submicron Mg17Al12 precipitates. The strengthening mechanism of extruded composites was also discussed.

Effect of Remelting Temperature and Soaking Time on Microstructure and Mechanical Properties of the Thixoformed Part of Nano-Sized SiCp/7075 Composite

Semisolid billet of the 7075 aluminum matrix composite reinforced with nano-sized SiC particles was first fabricated by an ultrasonic-assisted semisolid stirring method and rheoforming technology. Then it was thixoformed into a cylinder part under different remelting temperatures and soak times. The effects of the remelting temperature and soaking time on the mechanical properties and microstructure of the thixoformed composite part were investigated. The results show that parts of good quality were thixoformed successfully. The microstructure of the top side wall of the thixoformed part consisted of near spheroidal grains. A large quantity of elongated grains occurred in the medium and bottom side walls and the bottom itself. With increasing remelting temperatures, the size of the solid grains of the thixoformed parts showed a trend of first to increase and afterwards to decrease. High density dislocations were found in the microstructure when the remelting temperatures were 590 °C and 600 °C. When the soaking time was 15 min, the severest deformation occurred in the thixoformed part. High mechanical properties of the thixoformed parts were achieved under conditions such as a remelting temperature between 590 °C and 600 °C and a soaking time between 10 min and 15 min. The fracture mode of the thixoformed part changed from transgranular fracture to intergranular fracture when the remelting temperature was elevated from 580 °C to 610 °C. After the thixoformed parts were treated by T6, the ultimate tensile strength (UTS) and elongation of the side wall were improved to 552 MPa and 7.9%, respectively. Dispersed MgZn2 precipitates created by T6 heat treatment led to an improvement of the mechanical properties.

Achieving high-strength magnesium matrix nanocomposite through synergistical effect of external hybrid (SiC+TiC) nanoparticles and dynamic precipitated phase

Hybrid (SiC+TiC)p/AZ91 nanocomposites were successfully fabricated by the combination of semisolid stirring and ultrasonic vibration. Then the nanocomposites were extruded at a low temperature of 270 °C with slow extrusion speeds of 1, 0.5 and 0.1 mm/s, respectively. The result showed that the distribution of hybrid nanoparticles was uniform both in the as-cast and as-extruded conditions. With decreasing the extrusion speed from 1 mm/s to 0.1 mm/s, the grain sizes of the nanocomposites were gradually decreased. The volume fraction of precipitated Mg17Al12 phases was gradually increased while the average diameter was decreased. The externally applied hybrid nanoparticles and dynamic precipitated Mg17Al12 phase could hinder the movement of grain boundary, contributing to the grain refinement. The yield strength of ∼345.6 MPa, ultimate tensile strength of ∼397.2 MPa and elongation of ∼5.2% was obtained in case of the nanocomposite extruded at 0.1 mm/s. The increment in the strength could be attributed to the addition of hybrid (SiC+TiC) nanoparticles, ultra-fine matrix grains and large amount of precipitated Mg17Al12 phases. For the stage Ⅲ on the work hardening rate curve for the (SiC+TiC)p/AZ91 nanocomposite, the hybrid nanoparticles and dynamic precipitated Mg17Al12 could impede the annihilation of dislocation while the refined matrix grains had the opposite effects.

Distribution of SiC particles in semisolid electromagnetic-mechanical stir-casting Al-SiC composite

The distribution of SiC particles in Al-SiC composite can greatly influence the mechanical performances of Al-SiC composite. To realize the homogeneous distribution of SiC particles in stir-casting Al-SiC composite, semisolid stir casting of Al-4.25vol.%SiC composite was conducted using a special electromagnetic-mechanical stirring equipment made by our team, in which there are three uniformly-distributed blades with a horizontal tilt angle of 25 ° to mechanically raise the SiC particles by creating an upward movement of slurry under electromagnetic stirring. The microstructure of the as-cast Al-SiC composites was observed by Scanning Electron Mcroscopy (SEM). The volume fraction of SiC particles was measured by image analysis using the Quantimet 520 Image Processing and Analysis System. The tensile strength of the Al-4.25vol.%SiC composites was measured by tensile testing. Results show that the Al-4.25vol.%SiC composites with the homogeneous distrbutin of SiC particles can be obtained by the electromagnetic-mechanical stirring casting with the speed of 300 and 600 r·min−1 at 620 °C. The differences between the volume fraction of SiC particles at the top of ingot and that at the bottom are both ~0.04vol.% with the stirring speed of 300 and 600 r·min−1, which are so small that the distribution of SiC particles can be seen as the homogeneous. The tensile strength of the Al matrix is enhanced by 51.2% due to the uniformly distributed SiC particles. The porosity of the composite mainly results from the solidification shrinkage of slurry and it is less than 0.04vol.%.

Estimation of High Cycle Fatigue Life of AZ91E-Ni Coated Al2O3 Particulate Nano Composites Using Reliability Based Approach

This paper presents a method to determine sample size for estimating fatigue life of Magnesium alloy composites. Semi solid stir casting methodology was employed for the preparation of composites and the effect of nano Al2O3 as well as Nickel coated nano Al2O3 reinforcements on the fatigue life of AZ91E Magnesium alloy has been studied. Rotating beam bending machine is used to calculate the high cycle fatigue strength under fully reversed conditions. Fatigue tests are conducted at five different stress levels and at each stress level, minimum sample size is determined using statistical design. S–N curve for AZ91E and its composites are presented and compared. A regression analysis is performed for the S–N curve and the developed equations are validated through analysis of variance.

Incorporation of Silicon Carbide and Alumina Particles into the Melt of A356 via Electroless Metallic Coating Followed by Stir Casting

It is known that Cu and Ni coating layers provide different surface energy functionalities when coated onto ceramic particles with a range of particle sizes. This is known to be due to some extent to the kinetic aspects in the bath during the electroless deposition process. In this study, A356-based composites reinforced by 1.5 wt. % large Al2O3 and 1.5 wt. % fine SiC particles were fabricated by a two-step process, semi-solid stir casting followed by rolling. For wettability improvement, the Ni and Cu layers were coated on both the ceramic particles, separately. The results indicated that the best mechanical properties were obtained for a composite, which contained 1.5 % wt. SiC and 1.5 % wt. Al2O3, in which SiC particles were coated by the copper and alumina particles were coated by the nickel.

Microstructure, Mechanical Properties and Wear Behavior of the Rheoformed 2024 Aluminum Matrix Composite Component Reinforced by Al2O3 Nanoparticles

The 2024 nanocomposite reinforced with Al2O3 nanoparticles was fabricated by the ultrasonic assisted semisolid stirring (UASS) method and rheoformed into a cylinder component. Microstructure, mechanical properties, and wear behavior of the rheoformed composite components were investigated. The results showed that the composite components with complete filling status and a good surface were rheoformed successfully. The deformation of semisolid slurries was mainly dominated by flow of liquid incorporating solid grains (FLS), sliding between solid grains (SSG), and plastic deformation of solid grains (PDS). Mechanical properties of the rheoformed composite components were influenced by stirring temperature, stirring time, and volume fraction of Al2O3 nanoparticles. The optimal ultimate tensile strength (UTS) of 358 MPa and YS of 245 MPa were obtained at the bottom of the rheoformed composite components after a 25-min stirring of composite semisolid slurry with 5% Al2O3 nanoparticles at 620 °C. Enhancement of mechanical properties was attributed to high density dislocations and dislocation tangles and uniform dispersed Al2O3 nanoparticles in the aluminum matrix. Natural ageing led to the occurrence of needle-like Al2CuMg phase and short-rod-like Al2Cu phase. UTS of 417 MPa and YS of 328 MPa of the rheoformed composite components were achieved after T6 heat treatment. Improvement of mechanical properties is due to the more precipitated needle-like Al2CuMg phase and short-rod-like Al2Cu phase. Wear resistance of the rheoformed composite components was higher than that of the rheoformed matrix component. Wear resistance of the rheoformed composite component increased with an increase in Al2O3 nanoparticles from 1% to 7%. A slight decrease in wear rate resulted from 10% Al2O3 nanoparticles due to greater agglomeration of Al2O3 nanoparticles. A combination mechanism of adhesion and delamination was determined according to worn surface morphology.

Tribological Behavior of Nano-Sized SiCp/7075 Composite Parts Formed by Semisolid Processing

The tribological behavior of the rheoformed and thixoformed nano-sized SiCp/7075 composite parts is investigated. The semisolid stirring temperature has a little influence on the friction coefficient and wear resistance of the rheoformed composite parts. As for the thixoformed composite parts, the average value of the steady-state coefficient of friction increases firstly and then decreases with increasing reheating temperature. Higher wear resistance is achieved at a reheating temperature of 580 °C. The average value of the steady-state friction coefficient of the rheoformed composite parts varies from 0.37 to 0.45 upon applied loads of from 20 to 50 N. Weight loss increases slightly upon an increase of applied load from 20 to 40 N. An applied load of 50 N leads to a significant increase of the weight loss. The wear rate decreases firstly and then increases with increasing applied load. As for the thixoformed composite part, the average value of the steady-state friction coefficient and the weight loss decreased with an increasing applied load. However, the wear rate decreases firstly with increasing applied load and then increases. As for the rheoformed composite part, the average value of the steady-state friction coefficient decreases firstly and then increases a little with increasing sliding velocity. Weight loss and wear rate show a first increase and a followed decrease with increasing sliding velocity. As for the thixoformed composite part, the average value of the steady-state friction coefficient shows a decrease with increasing sliding velocity. Weight loss and wear rate exhibit, at first, an increase, and then a decrease with increasing sliding velocity. The average friction coefficient varies from 0.4 to 0.44 with increasing volume fraction of SiC. Weight loss and wear rate decrease with increasing volume fraction of SiC. An increase in dislocation density around the nano-sized SiC particles and the mismatch of the coefficient of thermal expansion (CTE) between 7075 matrix and nano-sized SiC particles during solidification improve the wear resistance of the composite. The dominant wear mechanisms of the rheoformed and thixoformed composite parts are adhesive wear, abrasive wear and delamination wear.

A comprehensive analysis of extrusion behavior, microstructural evolution, and mechanical properties of 6063 Al–B4C composites produced by semisolid stir casting

In this study, composites of aluminum alloy 6063 reinforced with 10 wt% boron carbide microparticles were successfully fabricated by a combination of spark plasma sintering and stir casting methods, followed by hot extrusion. A systematic study on the relationship between extrusion process variables (i.e. extrusion ratio, temperature, and punch speed) and porosity, particle refinement, particle distribution and consequently tensile properties and fracture behavior of the composites was performed. Extensive electron microscopy analysis and tensile testing of the composites revealed a multifactoral interdependency of microstructural evolution and mechanical properties on the extrusion process variables. For example, while increasing the extrusion ratio at higher temperatures led to moderate particle refinement, better densification of the composites, and improvement in mechanical properties, concurrent particle fragmentation and microvoid formation around the particles at lower temperatures had opposing effects on the mechanical behavior. We show that the dependency of mechanical properties on all such microstructural factors makes it difficult to predict optimum extrusion conditions in aluminum matrix composites. That is, unlike the common approach, extruding the composites at higher temperatures and achieving more reduction in area may not necessarily lead to the most favorable mechanical properties.

Microstructure and properties of SiC/Gr composite reinforced aluminum matrix composites material

SiC/Gr/ZL101 aluminum-based composites were prepared by semi-solid stirring and gravity pouring method. The effects of SiC/Gr with different volume fractions on the microstructure and property of aluminum-based composites were studied by means of microstructure observation, tensile test, fracture scanning analysis and damping capacity test. The results show that the primary phase α-Al of ZL101 alloy prepared by semi-solid stirring and gravity pouring method is fragmented dendrite, along with the rising SiC volume fractions, the tensile strength of the composites first increases and then decreases while its elongation gradually decreases, the maximum tensile strength of the material can reach 168 MPa, up to 16% than that of ZL101 alloy, the fracture morphology is obviously brittle fracture. They also show that the addition of SiC and Gr improves the damping capacity of ZL101 alloy, the internal dissipation Q-1 of the composites is obviously higher than that of matrix alloy and gradually increases along with the rising SiC volume fractions. The damping mechanism of the composites is mainly the combined effects of both dislocation damping and interfacial damping.

Development of SiC Nanoparticles and Second Phases Synergistically Reinforced Mg-Based Composites Processed by Multi-Pass Forging with Varying Temperatures.

In this study, SiC nanoparticles were added into matrix alloy through a combination of semisolid stirring and ultrasonic vibration while dynamic precipitation of second phases was obtained through multi-pass forging with varying temperatures. During single-pass forging of the present composite, as the deformation temperature increased, the extent of recrystallization increased, and grains were refined due to the inhibition effect of the increasing amount of dispersed SiC nanoparticles. A small amount of twins within the SiC nanoparticle dense zone could be found while the precipitated phases of Mg17Al12 in long strips and deformation bands with high density dislocations were formed in the particle sparse zone after single-pass forging at 350 °C. This indicated that the particle sparse zone was mainly deformed by dislocation slip while the nanoparticle dense zone may have been deformed by twinning. The yield strength and ultimate tensile strength of the composites were gradually enhanced through increasing the single-pass forging temperature from 300 °C to 400 °C, which demonstrated that initial high forging temperature contributed to the improvement of the mechanical properties. During multi-pass forging with varying temperatures, the grain size of the composite was gradually decreased while the grain size distribution tended to be uniform with reducing the deformation temperature and extending the forging passes. In addition, the amount of precipitated second phases was significantly increased compared with that after multi-pass forging under a constant temperature. The improvement in the yield strength of the developed composite was related to grain refinement strengthening and Orowan strengthening resulting from synergistical effect of the externally applied SiC nanoparticles and internally precipitated second phases.

Investigation of Mechanical Properties of Al7Si/ SiC and Al7SiMg/SiC Composites Produced by Semi Solid Stir Casting Technique

Mechanical characteristic of silicon carbide particle reinforced aluminum matrix composites produced by semi solid stir casting technique was investigated. Al7Si and Al7SiMg were used as metal matrix. High purity silicon carbida with average particle size mesh 400 was used as reinforcement particle. Aluminum matrix composites with variation of SiC: 5 %, 7.5 % and 10 % wt were manufactured by the semi solid stir casting technique. Stiring process was performed by 45 ° degree carbide impeller at rotation of 600 rpm and temperature of 570 °C for 15 minutes. Characteritation of composites speciment were: microscopic examination, density, hardness, tensile and impact test. Hardness and density were tested randomly at top, midlle and bottom of composites product. Based on distribution of density, distribution of hardness and SEM photomicrograph, it can be concluded that semisolid stir casting produces the uniform distribution of particles in the matrix alloy. The results also indicate that introducing SiC reinforcement in aluminum matrix increases the hardness of Al7Si composite and Al7SiMg composite. Calculated porosities increases with increasing wt % of SiC reinforcements in composite. The addition of 1 % Mg also increases the hardness of composites, reduces porosities of composite and enhances the mechanical properties of composites.

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

Abstract 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.

Experimental Investigation of Process Parameters in Drilling LM25 Composites Coated with Multi Wall Carbon Nano Tubes Using Sonication Process

AbstractAluminium based metal matrix composites are widely used in automobile components such as cardan shaft of Chevrolet corvette, disc brake and engine push rod. In this experiment a Hybrid Metal Matrix Composites (HMMC) are fabricated and drilled. Drilling is the process of making slots in disc brake and thread in the engine parts. The surface quality of the drilled specimen depends on the speed, feed, drill type and the thrust force. Thrust force plays the major role in drilling the specimen. In this experiment HMMCs are fabricated using two processes-called, sonication and casting. Sonication is the process of coating the carbon nanotubes over the silicon carbide particles (SiCp). Semisolid stir casting is used to reinforce the coated SiCp in the LM 25 alloy. A drilling process is performed on HMMC to analyse the extent to which the input parameters influence the thrust force and Ovality. The tools used for drilling are solid carbide tools of three different diameters. Taguchi’s experimental design is adopted for the drilling operation. A mathematical model is used to determine the influence of input parameters on the outputs thrust force and ovality. This paper proves the combination of N3, f1and d1of the carbide tool results in the lowest value of thrust force and ovality while drilling HMMCs. In this work the HMMC is prepared by coating the abrasive nature, silicon carbide particle and there is a good interfacial bonding between the reinforced particle and matrix and the drilling process becomes smoother. The new being of this article is the treated ceramics, SiCp with carbon nanotubes. This HMMC shows the improved mechanical properties compared to other metal matrix composites surveyed in the literatures.

Microstructures and tensile properties of nano-sized SiCp/Al-Cu composites fabricated by semisolid stirring assisted with hot extrusion

Al-Cu matrix composites containing nano-sized SiCp were successfully prepared by dispersing nano-sized SiCp/Al master alloy into the molten Al-Cu alloy with combined semi-solid stir casting and hot extrusion processes. Microstructures of nano-sized SiCp/Al-Cu composites and their tensile properties were investigated. Results show that the α-Al dendrites became finer and better formed and nano-sized SiCp was formed in the α-Al grains. With nano-sized SiCp adding to the Al-Cu matrix, the tensile strength of the described composites increased remarkably especially under the temperature of 453K, while their plasticity were still high. Nano-sized SiCp particles had been uniformly dispersed in the Al alloy, yielding composites with high strength at elevated temperatures. The strengthening mechanisms of nano-sized SiCp were also discussed. This will raise the probability of using Al matrix composites as lightweight materials for structural applications at elevated temperatures.

Effect of particle morphology of Ni on the mechanical behavior of AZ91E-Ni coated nano Al2O3 composites

The properties of any composite always depend on the bonding between the matrix and reinforcement phases. One way of improving the wettability of reinforcement in a matrix is to apply a layer of coating on reinforcing particles. The present study aims at developing Ni coating on nano Al2O3 ceramic particles and dispersing them in AZ91E magnesium matrix material. The electroless plating method has been employed to coat the particles and semi solid stir casting technique was adopted to prepare the composites. Several weight fractions of dispersed phase are considered to analyze the behavior of the fabricated composites. Field emission scanning electron microscopy (FESEM) and x-ray diffraction analysis has been carried out to investigate the distribution of particles and phase characteristics of the proposed material. The physical and mechanical behavior of the material was examined through density measurements, hardness, elastic modulus, ductility and tensile strength calculations. The metal coating on reinforcement aids to promote metal–metal bonding interface reactions which result in improved properties of the composite. Tensile fractography was carried out under FESEM and presented.

Investigation on the Mechanical Properties of A356 Alloy Reinforced AlTiB/SiCp Composite by Semi-Solid Stir Casting Method

Employing the semi-solid stir casting method to strengthen MMCs by SiCp particle was the simplest way in the casting process. The strength and toughness of a composite material can be obtained through a combination of the A356 / Al7Si composites and SiCp particle. The purpose of this study was to investigate the difference in the mechanical properties of Al7Si1Mg/SiCp and Al7Si1Mg1.5TiB/SiCp composites, as well as the changing effects on the extra level of SiCp particle. Al7Si was used as matrix strengthened by SiCp with the percentage variations of 10, 15, 20 wt%. The additional level of 1.5 wt% AlTiB aimed for increasing the matrix grain refinement. The semi-solid stir casting method was performed to spread the SiCp particles evenly in the liquid matrix. The results of the study were the tensile strength value of as much as 143 MPa or the increase of 22.16%. The biggest yield strength on the Al7Si1Mg1.5TiB/SiCp composite was averagely as much as 106 MPa. The highest impact toughness was averagely amounted to 4.74 J/mm2. The lowest porosity value was averagely 2.10%. The morphology of the composite between the reinforcing particle and the matrix was able to unite and to be dispersed evenly. The present study was conducted through density test, tensile test, impact test, microstructure test, and SEM.