Gravity Casting Process Research Articles

Tribological investigation of new self-fluxing nickel alloys for high temperature application: the effect of silicon distribution on glaze layer formation

The objective of this study is to investigate the tribological performance of new nickel-based self-fluxing alloys for replacing cobalt-based alloys in aircraft components. Two new NiCrSiFeB alloys, manufactured by gravity casting and laser metal deposition processes, having different microstructures, are submitted to fretting loadings and tested at temperatures ranging from ambient to 650 °C. Their wear behavior is compared to a reference Stellite 6 cobalt- based alloy. Although the two NiCrSiFeB alloys have the same chemical composition, the alloy having a coarse microstructure rich in silicates was able to form a protective glaze layer at high temperature as Stellite 6. On the other hand, the alloy having a fine microstructure underwent severe adhesive wear. This highlights the crucial effect of the microstructure and the silicon distribution in activating the formation of a protective glaze layer at high temperatures.

3D numerical simulation and experimental validation of resin-bonded sand gravity casting: Filling, cooling, and solidification with SPH and ProCAST approaches

This article provides a comprehensive investigation into the resin-bonded sand gravity casting process, with a focus on the filling, cooling, and solidification steps. The research combines numerical simulations and experimental validation in a three-dimensional (3D) configuration, utilizing a realistic filling system. The study employs three approaches—experimental tests, Smoothed Particle Hydrodynamics (SPH) simulations, and ProCAST simulations—to analyze the filling, cooling, and solidification steps. Two different molds were used in the experiments. The first mold has a transparent glass component in front of the plate, enabling observation and recording of the filling process, while the second mold, used solely for thermal analysis, did not incorporate any glass component. The SPH approach yields more accurate results for the filling time, liquid level height, and morphology when compared to ProCAST. The discrepancy in final filling time for the desired casting part between the experiment and SPH is 5.13 %, and the difference between the experiment and ProCAST is 15.38 %. Additionally, the cooling and solidification steps are investigated through an analysis of cooling curves. The numerical methods demonstrate slightly higher cooling rates and deviations in solidification times compared to the experimental data, mainly due to the thermal Neumann boundary condition. Furthermore, the average discrepancy in solidification time for five points of the intended casting component between the experiment and SPH is 8.60 %, whereas when compared with ProCAST, the discrepancy increases to 9.13 %.

Effect of variations in pouring temperature on tensile strength of CuZn cast alloys

The solidification rate of materials affects the properties of the cast product and the pouring temperature also influences the freezing conditions of cast-metal alloys. The propose of this study is to evaluate the tensile strength of cast samples by using five variations of pouring temperatures through permanent molds by a gravity casting process. The results showed that the tensile strength maximum was 443 MPa at 1210 °C, the freezing range affected the tensile properties of cast samples.

Microstructure and mechanical properties of LPSC AZ91-Sb magnesium alloy

ABSTRACT Microstructures and mechanical properties of AZ91-Sb magnesium alloy fabricated by low-pressure shell casting (LPSC) process in different conditions were investigated. The as-cast alloy exhibited a good internal quality and denser structure. The microstructure of α-Mg phases displayed dendritic feature and fine isolated β-Mg17Al12 particles phases uniformly distributed in the matrix. After the solution treatment at 415°C for 12 h, almost β-Mg17Al12 phases dissolved into the matrix. After ageing treatment at 200°C for 14 h, the LPSC alloy attained the peak hardness with restrained age-hardening kinetics. The discontinuous precipitates initiated at the grain boundaries and then continuous precipitates occurred in the grain interior. The LPSC alloy exhibits higher mechanical properties in both as-cast and heat-treated alloys compared with the gravity casting (GC) process alloy.

Microstructure evolution, mechanical properties and strengthening mechanisms in the hot extruded Si3N4 particle reinforced Al–Cu–Mg composite

Si3N4 particles, with high modulus, hardness and thermal stability, are important reinforced phase candidates in Al matrix composite. In this work, Si3N4 particles were introduced into the 2026 Al alloy by a novel Al–Si–N master alloy and the Si3N4/2026 Al composite was successfully prepared via gravity casting and hot extrusion process. According to the SEM results, the Si3N4 particles tend to distribute at the grain boundary and coexist with the eutectic phases after solidification; however, a Si3N4 particles chain structure appears in the matrix after subsequent hot extrusion. The TEM results indicate that a nano-AlN particles transition layer is present on the surface of the Si3N4 particles, which has a good interfacial bonding with the Al matrix. The EBSD results show that the grains are refined significantly and the <111>Al fiber texture is improved in the Si3N4/2026 Al composite. At room temperature, the yield strength, ultimate tensile strength and Brinell hardness of composite are 454 MPa, 586 MPa and 143.5 HBW, respectively, which are increased by 15%, 12% and 11% than those of matrix alloy. The enhanced mechanical properties of the composite can be attributed to the load-bearing effect of the Si3N4 particles, grain boundary strengthening, dislocation strengthening and Orowan strengthening. This work will provide a new idea for the development of low cost and high strength Al matrix composites.

Quench sensitivity of A379 alloy under high-pressure die-casting and gravity-casting processes

Adding Cr to Al–Si–Mg alloys can eliminate the adverse effects of Fe, but can increase the quench sensitivity of the alloys. The influence of gravity-casting and high-pressure die-casting on the quench sensitivity of A379 (Al–7Si–0.5Mg–0.2Cr) alloys were studied using time–temperature–property curves. The nose temperatures of the gravity-casting- and high-pressure die-casting-fabricated specimens are near 350 °C and 355 °C, respectively. The temperature regions with high quench sensitivity characteristics of the former and latter occur from 310 °C to 390 °C and from 290 °C to 400 °C, respectively. The time–temperature–property curves of the high-pressure die-casting-fabricated samples are farther to the left than that of gravity-casting-fabricated samples, indicating that the high-pressure die-casting-fabricated specimens are more sensitive and are easier to generate precipitates than the gravity-casting-fabricated specimens during quenching because of the following reasons. For both specimens, the quench-induced precipitates (Mg xSi) nucleate on the Cr-containing dispersions in the grains, but the Cr-containing dispersions in the high-pressure die-casting-fabricated specimens are finer and more dispersible than in the gravity-casting-fabricated specimens. Meanwhile, the high-pressure die-casting-fabricated specimens exhibited finer grain sizes than the gravity-casting-fabricated specimens; thus, they can provide more grain boundary nucleation sites for forming the Mg xSi phase than the gravity-casting-fabricated specimens during isothermal treatment.

Microstructural Evolution as a Function of Increasing Aluminum Content in Novel Lightweight Cast Irons

In the context of the development of new lightweight materials, Al-alloyed cast irons have a great potential for reducing the weight of the different part of the vehicles in the transport industry. The correlation of the amount of Al and its effect in the microstructure of cast irons is not completely well established as it is affected by many factors such as chemical composition, cooling rate, etc. In this work, four novel lightweight cast irons were developed with different amounts of Al (from 0 wt. % to 15 wt. %). The alloys were manufactured by an easily scalable and affordable gravity casting process in an induction furnace, and casted in a resin-bonded sand mold. The microstructural evolution as a function of increasing Al content by different microstructural characterization techniques was studied. The hardness of the cast irons was measured by the Vickers indentation test and correlated with the previously characterized microstructures. In general, the microstructural evolution shows that the perlite content decrease with the increment of wt. % of Al. The opposite occurs with the ferrite content. In the case of graphite, a slight increment occurs with 2 wt. % of Al, but a great decrease occurs until 15 wt. % of Al. The addition of Al promotes the stabilization of ferrite in the studied alloys. The hardness obtained varied from 235 HV and 363 HV in function of the Al content. The addition of Al increases the hardness of the studied cast irons, but not gradually. The alloy with the highest hardness is the alloy containing 7 wt. % Al, which is correlated with the formation of kappa-carbides and finer perlite.

Comparison of the semisolid squeeze casting and gravity casting process on the precipitation behavior and mechanical properties of the Al-Si-Cu-Mg alloy

The differences in microstructure, ageing behavior and mechanical properties of the Al-17.8Si-4.3Cu-0.4Mg alloy formed by semisolid squeeze casting and gravity casting processes were investigated. It was found that a nearly equiaxed microstructure of α-Al, finer and denser Si phases, and a higher dislocation density exist in the semisolid extruded sample. In the peak ageing state, θ” and Q' phases are mainly observed under the two forming processes, while the precipitate increases and the size decreases after semisolid extrusion. According to the thermodynamics, the binding energy and enthalpy values of Q′ phase are lower than those of the θ' and θ″ phases. Therefore, among the three metastable phases, the Q′ phase precipitated before the θ″ and θ' phases. The semisolid extruded alloy exhibits higher strength and ductility in the as-cast state and T6 state. This might be caused due to more uniform microstructure and finer precipitating phase. Double ageing hardness peaks were found in the age-hardening curves of Al-17.8Si-4.3Cu-0.4Mg alloys under both processes, which were related to the influence of the precipitation sequence of the alloy. • Microstructure and properties of Al-Si -Cu-Mg alloy by semisolid extrusion and gravity casting was studied. • Better comprehensive mechanical properties were obtained after semisolid squeeze casting process. • There were two hardness peaks corresponding to the ageing time of 6 and 12 h under two forming processes. • Compared to gravity casting, the size of the precipitates in the semisolid extruded samples was smaller.

Composite Material of PDMS with Interchangeable Transmittance: Study of Optical, Mechanical Properties and Wettability

Polydimethylsiloxane (PDMS) is a polymer that has attracted the attention of researchers due to its unique properties such as transparency, biocompatibility, high flexibility, and physical and chemical stability. In addition, PDMS modification and combination with other materials can expand its range of applications. For instance, the ability to perform superhydrophobic coating allows for the manufacture of lenses. However, many of these processes are complex and expensive. One of the most promising modifications, which consists of the development of an interchangeable coating, capable of changing its optical characteristics according to some stimuli, has been underexplored. Thus, we report an experimental study of the mechanical and optical properties and wettability of pure PDMS and of two PDMS composites with the addition of 1% paraffin or beeswax using a gravity casting process. The composites’ tensile strength and hardness were lower when compared with pure PDMS. However, the contact angle was increased, reaching the highest values when using the paraffin additive. Additionally, these composites have shown interesting results for the spectrophotometry tests, i.e., the material changed its optical characteristics when heated, going from opaque at room temperature to transparent, with transmittance around 75%, at 70 °C. As a result, these materials have great potential for use in smart devices, such as sensors, due to its ability to change its transparency at high temperatures.

Tribological investigation of magnesium rare earth alloy for orthopedic application

Magnesium rare earth element (Mg-REE) alloys are actively used as bone implants in orthopedic applications due to their biocompatibility, strengthening ability and degradation rate. Pure Mg when casted has low strength and high rate of degradation. Properties of magnesium alloys can be strengthened and improved by using suitable alloying elements and processing conditions. When Magnesium, alloyed with elements like Al, Ca, Zn, Sr and rare earth elements (REE) used as reinforcing elements, gains high strength, better mechanical, metallurgical, and tribological property due to grain refinement and strong solution reinforcing mechanisms of the alloyed elements. This helps in developing Mg-REE alloy, which is a promising substitute for permanent bone implants due to biodegradability in the physiological environment i.e. inside the human body. In this research work using gravity casting process, by varying the elemental composition of Gadolinium (Gd) in Mg-2Sr, Mg-REE alloy of Mg-2Sr, Mg-2Sr-2Gd, Mg-2Sr-4Gd, Mg-2Sr-8Gd, Magnesium – Strontium – Gadolinium REE alloy is casted using gravity casting method and the tribological properties like wear rate, wear resistance, and coefficient of friction of Mg-REE alloy are investigated.

Interfacial microstructure formation in A356/steel compound castings using metal coating

Compound castings between aluminum and steel have great potential for applications in the automotive industry. However, due to large differences in thermal and mechanical properties between steel and aluminum, and the formation of stable aluminum oxides at the interface, it is difficult to form high strength metallic bonding between the two metals. In this work, A356/steel compound castings were produced through a gravity casting process. Various metal coatings, including galvanizing, aluminizing and brass-coating, were applied on the steel inserts to ensure that the A356 aluminum melt could react sufficiently with an oxide-free steel surface, resulting in a high-quality metallurgical bond. The reaction layer formed between the alloys was investigated using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). In addition, Vickers Micro-hardness was measured across the aluminum-steel interface. Results showed that metallurgical bonding could be achieved with all three coatings. However, for the brass-coated components only local bonding areas were found. In the aluminized and galvanized components, thick reaction layers consisting of binary Al-Fe and ternary Al-Fe-Si phases formed in the aluminum-steel interface. Between the A356 aluminum and aluminized layer, nearly no reaction layer formed. The mechanism for the formation of the various intermetallic phases at the reaction layers are discussed.

Effect of ladle outlet geometry on internal porosity in gravity casting automotive brackets: An experimental investigation

This study investigated whether the pouring ladle’s outlet shape could reduce the porosity of aluminum alloy casting products and whether it could be applied to mass production of automotive brackets based on computer simulations and experiment. The filling behaviors of the melt were simulated to compare the flow characteristics of the molten metal poured from the conventional ladle and the proposed ladle. Results show that for the conventional ladle, the pouring metal is V-shaped, while it is relatively circular and poured at a more constant rate in the proposed ladle. CT scans reveal that the proposed ladle reduces the porosity of the cast product. The proposed ladle resulted in an average of 30 fewer pores, a 299.56 mm3 smaller average total pore volume, and a 0.041% lower difference in average porosity. It is concludes that the proposed ladle can be used in the gravity casting process. By changing the ladle outlet shape can reduce the casting failure rate of mass-produced automobile bracket

Casting simulation and defect identification of geometry varied plates with experimental validation

This work mainly deals with the simulation of geometry varied plates subjected to permanent mold gravity casting process. There are extensive demands of Aluminum and its alloys in diverse industries owing to its better properties especially mechanical (good strength and stiffness with low density). Aluminum alloy AlSi5Cu3 was chosen and the behavior of metal filling and solidification was examined using AUTOCAST – XI software equipped with flow plus module. Three rectangular plates with variation in thickness were selected as casting geometry with equal length and width. Three feeders have been applied to each cavity at various locations with optimized dimensions. The casting yield and casting quality were calculated for all casting geometry. The values of casting yield for 8 mm, 12 mm and 16 mm thick plates were 91.20%, 91.5% and 92.05% while casting quality were 95.20%, 94.05% and 93.68%, respectively. The temperature difference, the velocity of melted metal and solidification time were analyzed for thickness varied plates. The front velocity of the liquid metal was calculated and having values of 1.02 m/sec, 0.91 m/sec and 0.39 m/sec and solidification time was 23.56 sec, 31.56 sec and 37.35 sec for 8 mm, 12 mm and 16 mm thick plates, respectively. The cooling curves for different geometry were obtained by placing virtual thermocouple at various locations. Shrinkage porosity defect identified and validated with actual experimentation. The depth of shrinkage porosity was measured by simulation results and calculated for actual casted plates. It showed a variation of shrinkage porosity depth by 10%, 5.88% and 4.34% for 8 mm, 12 mm and 16 mm thick plates, respectively.

Plastic deformation mechanism of MWCNTs/AZ91D nanocomposites with high ductility at room temperature

1.0 wt% MWCNTs/AZ91D magnesium matrix nanocomposites were prepared by metal mold gravity casting process assisted by high-intensity ultrasonic dispersion, and the ductility was further improved by T4 solid solution treatment. The tensile test results at room temperature revealed that the tensile strength and elongation of 1.0 wt% MWCNTs/AZ91D nanocomposites after T4 solid solution treatment reached up to 281.7 MPa and 15.4%, respectively. The ductility of magnesium matrix nanocomposites was significantly improved by the addition of Multiwalled carbon nanotubes (MWCNTs) and T4 solid solution treatment. SEM and TEM were used to observe the microstructure of 1.0 wt% MWCNTs/AZ91D-T4 nanocomposites after the tensile plastic deformation at room temperature. A considerable number of slip bands and twins were found in the microstructure of the nanocomposites. High strain zones were formed around MWCNTs during the tensile process at room temperature. A large number of dislocations and stacking faults were generated in the high strain zones, which could be used as the origin of slip bands and twins, so MWCNTs can promote slip and twining. MWCNTs can further activate non-basal slip and cross slip, and improve the ductility of 1.0 wt% MWCNTs/AZ91D-T4 nanocomposites.

Temperature field model and control strategy in gravity casting process.

Temperature control is one of the most important processes during aluminum (Al) alloy engine cylinder head product casting. An improper temperature control may result in no uniformity and microstructure defects in casting parts and give rise to high defect ratio. In this paper, a mathematical model with high nonlinearity, strong coupling, and less uncertainty is developed for the solidification process in Al alloy casting. The interfacial heat transfer coefficient is combined with the mold structure comprehensively to build the temperature-structure model, and the characteristics of the uncertainty conversion are also used in order to achieve optimal temperature control during the solidification process. The cloud model integrated with Proportion-Integral-Differential (PID) temperature control system enables evaluation of the uncertainty conversion quantitatively. By inputting the temperature error and the temperature error rate, the PID inference is output through the cloud inference engine to achieve the optimal temperature curve. The superiority of the control algorithm was verified on a customized experimental platform with the temperature control system. Compared with manual operation and traditional PID control, the result shows that the error of the cloud model control is lower than the manual operation and traditional PID control. The experimental results also suggest that the performance of our cloud model is better than that of the manual operation model and the traditional PID control model regarding to stability and controllability.

Microstructure Evolution and Mechanical Properties of the T6 Heat Treated AA6063 Alloy Produced by Squeeze Casting

The influence of T6 heat treatment on the microstructure, hardness and tensile properties of cast AA6063 aluminum alloy was investigated as a function of squeeze casting pressure. The specimens elaborated were solution treated at 500°C for 8 hours and then were subjected to aging at 140°C. Various test techniques, including optical microscopy, scanning electron microscope, X-ray diffraction, tensile tests, and hardness were used to examine the effect of this alloy produced by the gravity and squeeze casting processes. The experimental results showed that Mg2Si and Al15Si2(FeMn)3 were the primary particles observed in the α-Al matrix. The effect of precipitation on the mechanical properties was investigated. The changes in mechanical properties were correlated with changes in microstructure evolution and Mg–Si precipitation. Furthermore, hardness and tensile properties increased with both heat treatment and squeeze pressure.

Microstructure in A356/AA6xxx after bimetallic casting with flux coating

This work focuses on bimetallic casting between A356 alloy melt and profiles of AA6xxx wrought aluminum alloys through a gravity casting process, with the aim to improve the component’s mechanical properties. However, combining two aluminum alloys is difficult due to the stable aluminum oxide present on the surface of the aluminum inserts and the advancing liquid melt front. The oxide layer strongly reduces the wettability between aluminum melt and solid metal. It will also prevent diffusion and formation of a metallurgical bond. In order to obtain sound metallic bonding between the two alloys, different surface treatments, including flux coating and chemical treatments of the profiles have been tested. The influences of preheating temperature and melt flow modes on the quality of the bimetallic casting have been addressed. Based on a detailed microstructure characterization of the bonding layer in the casting, by using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), the solidification structure development at the interface has been discussed. Results showed that when flux coating was applied, magnesium diffused to the insert surface and prevented formation of a metallurgical bond. Without flux coating, a metallurgical bond was achieved due to slight melting of the insert surface.

Spatial interfacial heat transfer and surface characteristics during gravity casting of A356 alloy

Abstract As one of the key boundary conditions during casting solidification process, the interfacial heat transfer coefficient (IHTC) affects the temperature variation and distribution. Based on the improved nonlinear estimation method (NEM), thermal measurements near both bottom and lateral metal-mold interfaces throughout A356 gravity casting process were carried out and applied to solving the inverse heat conduction problem (IHCP). Finite element method (FEM) is employed for modeling transient thermal fields implementing a developed NEM interface program to quantify transient IHTCs. It is found that IHTCs at the lateral interface become stable after the volumetric shrinkage of casting while those of the bottom interface reach the steady period once a surface layer has solidified. The stable value of bottom IHTCs is 750 W/(m2·°C), which is approximately 3 times that at the lateral interface. Further analysis of the interplay between spatial IHTCs and observed surface morphology reveals that spatial heat transfer across casting-mold interfaces is the direct result of different interface evolution during solidification process.

Optimal design of a bio-inspired self-healing metal matrix composite reinforced with NiTi shape memory alloy strips

Utilizing smart materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to bio-mimic self-healing. This study aims to investigate the influence of design factors of a self-healing metal matrix composite by employing the Taguchi method for designing of the experimental procedure. Three design factors, each in three levels, were studied simultaneously according to L-9 standard Taguchi orthogonal array to determine the optimal level of each factor in mechanical properties enhancement with a reduced number of experiments. Composite specimens were fabricated from Sn-13 wt.% Bi alloy as matrix and nickel–titanium shape memory alloy strips as reinforcement with gravity casting process. Matrix alloy was melted and casted in a preheated metallic mold in which SMA strips were installed in various quantities (one, two, or three strips) and different pre-strains (0%, 2%, or 6%). After fabrication of the specimens, a tensile test was conducted until fracture to specify mechanical properties. Then, specimens were placed in a furnace in three different temperatures (170°C, 180°C, and 190°C) to activate the shape memory effect of strips and achieve crack closure and healing. Specimens were tensile tested again after healing to calculate the amount of healed properties and healing efficiency. Results show that using three strips with 6% of pre-strain and applying 190°C healing temperature can maximize the ultimate tensile strength efficiency. Also, the existence of one strip, 0% pre-strain, and 190°C healing temperature creates the best circumstances for healing ductility.

Numerical simulation for the investment casting process of a large-size titanium alloy thin-wall casing

To optimize the investment casting process when producing high quality large-size titanium alloy thin-wall components is a time-consuming job due to the complicated metallurgical process. Numerical simulation is a high-efficiency method compared with trial and error, and therefore is introduced to the investment casting process optimization to shorten the new product development cycle and reduce the production cost. In this study, weakly compressible model (WCM) and ununiformed finite difference mesh (UFDM) was developed to reduce the memory consumption and ensure the simulation efficiency. The precision of the WCM and UFDM were verified by numerical simulation of cavity heat convection in a square cavity and hydraulics simulation of centrifugal filling in a transparent cavity. The numerical simulation of the investment casting process of a titanium alloy thin-wall casing under different process conditions was accomplished using a self-developed software, and the distribution characteristics of potential shrinkage defects were predicted. It was found that the predicted defects in the titanium alloy casing matched well with the actual X-ray experimental results. For the components investigated in this paper, more numerical simulation results show that the centrifugal casting process with respect to gravity casting had no obvious improvements in the concentrated shrinkage defects, and the gravity casting process can be more reasonable from the engineering point of view.