Cooling Slope Casting Research Articles

Impacts of T6 heat treatment on the microstructural, mechanical, and corrosion properties of thixoformed AA7075 alloy produced by cooling slope casting

Abstract Research into semi-solid metal forming techniques has been ongoing for an extended period with the aim of producing near-net shape products from aluminum alloys. The primary focus has traditionally been on casting alloys seeking to offer an alternative to the other processes such as high pressure die casting. Over the past twenty years, wrought aluminum alloys have also been explored for thixoforming operations as an alternative to traditional plastic deformation techniques. This research investigated the impacts of T6 heat treatment on the microstructural, mechanical, and corrosion properties of AA7075 alloy samples produced through cooling slope casting and subsequent thixoforming with different reheating durations. The selected alloy was chosen due to its widespread use in various industries, attributed to its excellent strength-to-density ratio achieved after T6 heat treatment. Building on optimized cooling slope casting parameters from a prior study, the standard solution treatment procedure following thixoforming with extended reheating times was found to be inadequate. Hardness and tensile tests revealed that specimens reheated for 120 min exhibited significantly reduced response to T6 treatment. Despite achieving the targeted hardness value of 154 HB with samples reheated for 20 min prior to thixoforming and T6 heat treatment, especially the elongation at break values were unsatisfactory. Potentiodynamic polarization tests indicated that corrosion primarily involved grain dissolution, with longer reheating times decreasing corrosion resistance due to increased amount of secondary phases and grain isolation. These findings highlight that while AA7075 alloy can be processed into semi-solid formable materials via cooling slope casting, issues such as hot tearing, micro-shrinkage, and physical defects post-thixoforming hinder the achievement of desired tensile properties.

Microstructure Evolution during Cooling Slope Rheoprocessing of Novel Al-15Mg<sub>2</sub>Si-4.5Si Composite

In this study, microstructure evolution during cooling slope casting of Al-15Mg2Si-4.5Si composite is studied considering a test case of melt pouring temperature of 650°C. The shear force exerted by the flowing melt on the evolving primary Mg2Si and α-Al grains facilitates their fragmentation and subsequent spherodisation. After leaving cooling slope, the composite slurry is kept isothermally within a holding furnace for different time duration i.e., 8, 16, 24 and 32 minutes. Increasing trend in grain size values is observed with the increasing slurry holding time, whereas sphericity value decreases after initial increase till 8 minutes of slurry holding. The slurry samples are scooped from chosen locations of the slope as well as from isothermal slurry holding bath and rapidly quenched in oil to study their microstructure and mechanical properties. Simultaneous spherodisation of both the primary phases i.e., primary Mg2Si and α-Al during cooling slope processing is evident from optical microscopy and Scanning electron microscopy of quenched slurry samples. Whereas increasing sphericity of P-Mg2Si and α-Al phases, along the melt flow direction over the slope, is found to accompany with the increasing micro hardness values.

Multiphase flow model of semi solid solidification of novel Al-15Mg2Si-Si composite

In this work, a volume averaging technique based Eulerian multiphase flow CFD (Computational Fluid Dynamics) model is developed to simulate the semi-solid solidification of the cooling slope generated Al-15Mg2Si-4.5Si composite slurry. The four phases considered here are liquid (l), primary solid (Mg2Si), secondary solid (α-Al) and air (a). Whereas latent heat release during solidification is tackled via a temperature correction scheme. The effect of recalescence is also observed in the present solidification model. The simulation findings include shape and size of the α-Al and primary Mg2Si grains, solid fraction, temperature, melt viscosity etc. The developed multiphase flow model of cooling slope casting (semi solid solidification) is applied to a test case having melt pouring temperature (into the slope) of 650°C (923K). The simulation findings are then validated with the help of measurements of microstructural features observed in the experimental (optical) micrographs of the solidified samples.

Influence of slurry delivery rate and height from cooling slope outlet on solidification and structural behaviors of molded AZ91 magnesium alloy

AZ91 magnesium alloy melt experiences partial solidification while flowing on cooling slope with counter flowing water channel underside. It results in continuous production of semisolid slurry available at cooling slope outlet. Current experimental investigations pertain to the influence of slurry delivery rate and slurry delivery height from cooling slope outlet on solidification and structural behaviors (microstructure along with mechanical properties) of AZ91 magnesium alloy intended for semisolid casting. Slurry delivery rate along with slurry delivery height warrant necessary solidification and shear for grain growth and globularization within metal mold for producing semisolid casting. Moderate slurry delivery rate of 0.025 kg/s along with slurry delivery height of 150 mm results fairly modest solidification that would greatly contribute toward enhanced structural behaviors. As, quite smaller/bigger slurry delivery rate/height generate low shear due to slurry flow inertia or accelerated slurry flow resulting stick-slip flow/motion of alloy slurry on cooling slope. It results poorer structural behaviors amid extremely unwanted casting issues. As, throughout the course escape/retain of metal with gas arise. Since, lesser slurry delivery rate/height allows metal to escape thereby reduces strength and vice-versa. Additionally, lesser slurry delivery rate/height allows gas to escape thereby enhances strength and vice-versa. Therefore, moderate cooling slope casting parameter magnitudes guarantee solution to bewilderment.

Microstructural characterization and mechanical behavior of Al-4 wt% Mg2Si in-situ metal matrix composite synthesis via cooling slope casting technique

In the present steady, A319-4 wt%Mg2Si metal matrix composite is cast by cooling slope casting technique with an objective to develop globalized fine microstructure and compare the results with conventional gravity cast specimen of same composition. The casting was subjected to microstructural characterization by optical microscopy and scanning electron microscopy. The in-situ generated Mg2Si particles are observed to be remarkably refined and uniformly dispersed in the matrix. Mechanical properties like hardness and tensile strength of the cooling slope cast in-situ composite are enhanced because of globalization of matrix structure and refined and uniform distribution of Mg2Si particles as compare to gravity cast sample.

Producing non-dendritic A356 and A380 feedstocks: Evaluation of the effects of cooling slope casting parameters

Abstract In this study, low superheat casting and cooling slope casting processes were carried out with A356 and A380 aluminum alloys in order to obtain feedstocks with near globular microstructures. Castings were conducted at 20 °C above of the liquidus temperature for both processes and molten alloys were cast through a copper cooling slope with two different lengths (350 mm and 650 mm) and two different tilt angles (30° and 60°). In order to evaluate the significance of boron nitride coating on cooling slope, castings in short slope were carried out under both coated and uncoated conditions. Microstructural examinations and hardness measurements were carried out. According to obtained results, cooling slope casting caused superior microstructural properties as compared to low superheat casting, especially for A356 alloy. 30° tilt angle was found more efficient in order to obtain a more globular microstructure for A356, while, on the other hand, the tilt angle of 60° was detected more favorable in that manner for A380. Obtained grain size measurements were slightly improved with the employment of short slope and coating was found beneficial especially for A356 alloy. The measured hardness values did not display any significant difference in the same alloy type except in the low superheat cast A356 specimen, which was obtained with coarser microstructure.

Producing non-dendritic A356 and A380 feedstocks: Evaluation of the effects of cooling slope casting parameters

Abstract In this study, low superheat casting and cooling slope casting processes were carried out with A356 and A380 aluminum alloys in order to obtain feedstocks with near globular microstructures. Castings were conducted at 20 °C above of the liquidus temperature for both processes and molten alloys were cast through a copper cooling slope with two different lengths (350 mm and 650 mm) and two different tilt angles (30° and 60°). In order to evaluate the significance of boron nitride coating on cooling slope, castings in short slope were carried out under both coated and uncoated conditions. Microstructural examinations and hardness measurements were carried out. According to obtained results, cooling slope casting caused superior microstructural properties as compared to low superheat casting, especially for A356 alloy. 30° tilt angle was found more efficient in order to obtain a more globular microstructure for A356, while, on the other hand, the tilt angle of 60° was detected more favorable in that manner for A380. Obtained grain size measurements were slightly improved with the employment of short slope and coating was found beneficial especially for A356 alloy. The measured hardness values did not display any significant difference in the same alloy type except in the low superheat cast A356 specimen, which was obtained with coarser microstructure.

Effect of cooling slope casting and partial remelting treatment on microstructure and mechanical properties of A319-xMg2Si In-Situ composites

The present study is aimed at evaluating the effect of cooling slope casting and partial remelting on hypoeutectic A319- 8Mg2Si and hypereutectic A319- 16 Mg2Si in-situ composites on the microstructural evolution and mechanical and wear properties. The characteristics are compared with those of conventional gravity castings. The microstructural features have been characterized by optical and scanning electron microscopy and X-ray diffraction analysis. Mechanical properties viz. bulk hardness, tensile properties and dry sliding wear characteristics with change in applied normal loads have been evaluated. The fractographs and worn surfaces are examined under scanning electron microscope. From the experimental findings it is observed that, the cooling slope casting can effectively refine and globularize α-Al grains, primary and eutectic Mg2Si and promote non-dendritic structures. Partial remelting further globularizes the matrix structures but develops microporosities. Improved hardness, tensile strength and dry sliding wear properties are obtained in cooling slope castings and in combined cooling slope casting with partial remelting. The improved properties are attributed to refinement and globularization of microstructural constituents with non-dendritic structures. Positive effects of microstructural features overshadowed the negative effect of porosity to the improvement in properties.

Optimization of dry sliding wear parameters of thixoformed A356-5TiB2in-situ composites using RSM

The present investigation is primarily aimed to examine the dry sliding wear behavior of in-situ formed TiB2 composites fabricated by cooling slope casting and thixoforging thereafter. Design of Experiments using central composite design is adapted to optimize the dry sliding wear parameters such as applied load, sliding speed and sliding distance. The responses considered for the analysis are wear rate and coefficient of friction. The wear surface topography and wear debris were characterized by Scanning Electron Microscope and analyzed. The results show that wear rate is significantly influenced by TiB2 particles in the matrix A356 alloy. It is noted that the thixoformed composites show better wear resistance than gravity cast A356 alloy. Moreover, TiB2 particles lower the coefficient of friction when reinforced in A356 alloy, in both gravity cast and thixoformed conditions. The wear rate in the thixoformed composite is reduced by 48% as compared to gravity cast alloy. The improvement in wear resistance in the present composite is not only due to the presence of fine TiB2 particles but also due to thixoforging. Thus, this work is an attempt to optimize the wear parameters of thixoformed A356-5TiB2 in-situ composites.

Evaluation of the reheating behavior of the cooling slope cast A356 and A380 aluminum alloys

A356 and A380 alloys are two well-known hypoeutectic Al-Si casting alloys in the non-ferrous casting industry and drew significant attention for semi-solid applications. The cooling slope casting method for producing materials with non-dendritic microstructure is one of the simplest liquid route techniques. In the beginning, microstructural differences of both alloys produced with 30° and 60° tilt angles were examined. It was observed that the angle change has a limited effect on A380 and it is almost non-effective for A356 as-cast structures. The samples were then subjected to the reheating processes for different times and the effects were investigated by measuring the average shape factor and the grain size values. In addition to the natural grain growth, it is understood that the changes in the eutectic are also effective on the properties. The rapid solidification of the melted eutectic by quenching the reheated samples modified the eutectic structure and improved the hardness. On the other hand, grain growth reduces hardness naturally. Additionally, it was observed that the increase in sphericity was supported by the liquid phase formation and it was determined that A356 alloy was more sensitive to reheating and formed larger grains than A380 alloy for the same reheating periods.

Cooling slope casting of AA7075 alloy combined with reheating and thixoforging

Abstract Cooling slope casting has been applied to aluminium casting alloys for producing ingots with non-dendritic microstructure. Semi-solid forming of the AA7075 was studied via cooling slope casting, reheating and thixoforging processes in order to determine the effect of semi-solid casting on the microstructure of the alloy. AA7075 ingots with non-dendritic microstructure were produced with cooling slope pouring. Castings were characterized by light microscopy, image analysis, scanning electron microscopy and EDS analysis. The resulting structures are promising in terms of grain size and sphericity. It was realized that grain coarsening may occur very suddenly in the reheating process. Cooling slope castings were obtained with 30° and 60° inclination angles, and in comparison, 60° castings showed better results. Moreover, by using short reheating periods, semi-solid forging causes trace formation in the solid grains.

Kesan Proses Pembentukan Tuangan Reo terhadap Sifat Mikrostruktur dan Mekanikal Aloi Al-5.7Si-2Cu-0.3Mg

This study shows the results of an experimental investigation of semisolid rheocasting of Al-5.7Si-2Cu-0.3Mg alloy using a cooling slope (CS) casting technique. However, the challenge is to determine process parameters of the CS process to get a desirable microstructure in the semisolid feedstock material. cooling slope technique was employed to create feedstock material for thixoforming under an argon gas atmosphere, where on an inclined plate that was fixed at a 60° slope angle, molten alloy is poured at different temperatures of 640°C, 650°C and 660°C at lengths 300, 400 and 500 mm. Examination the microstructure with optical microscope observed that the microstructure of conventionally cast alloy presented coarse and dendritic primary α-Al phase, whereas rheocast alloy included fine and nondendritic primary α-Al phase with homogeneous distribution of eutectic phase. The best CS processing condition has been identified for optimum pouring temperature of 650°C and the slope length of 400 mm as average globular grain size of around 31.67 ± 3 μm and a shape factor of about 0.66 ± 0.09 were obtained. The mechanical properties of conventional cast alloy were enhanced by the CS casting process. The ultimate tensile strength, the yield strength and elongation of the rheocast alloy were increased by 10%, 12% and 22% respectively compared to the conventional cast alloy. due to a reduction in shrinkage and porosity of the microstructure of the CS alloy.

Effect of feedstock geometry on the semisolid processing of Al–Si–Cu–Mg alloy

Shaping a metal by thixoforming involves feedstock preparation and reheating. Proper procedure and accurate processing criteria for thixoforming are required to provide a quality product. Appropriate parameters are crucial in assessing the capabilities of this thixoforming process. In this study, the effect of different billet geometry of Al–Si–Cu–Mg alloy on microstructure and mechanical properties were investigated. The billet with different geometries of height-to-diameter ratio (h0/d0 = 3.2 and h0/d0 = 0.8) was utilized through the cooling slope casting technique and thixoformed after being heated into compression press. The results indicate that low h0/d0 ratio produced the finest grain size for the α Al solid phase (≈52.8 ± 5.1 μm), best shape factor and complete die filling. By contrast, high h0/d0 ratio produced coarser grain size for the α Al solid phase (≈62.2 ± 6.1 μm), insufficient die filling, cold shut and shrinkage porosity defect. Moreover, the thixoformed billets with the lower h0/d0 ratio exhibited higher tensile stresses. The ultimate tensile strength, yield strength, and elongation to fracture of the thixoformed h0/d0 ratio 3.2 improved at 183 MPa, 163 MPa, and 1.6%, respectively, whereas the values of the thixoformed h0/d0 ratio 1.25 alloy were 206 MPa, 193 MPa, and 2.5%, respectively

Microstructural Evaluation and Corrosion Resistance of Semisolid Cast A356 Alloy Processed by Equal Channel Angular Pressing

As-cast and semisolid casting using a cooling slope A356 alloy were processed by equal channel angular pressing (ECAP) for Si and grain refinement. The ECAP was conducted at room temperature in a mold, with a channel angle of 120°, and this resulted in a significant size reduction of grain and Si particles from 170.5 and 4.22 to 23.12 and 0.71 µm, respectively, after six passes of heat-treated cooling slope casting, using the ECAP process. The hardness increased with ECAP processing, from 61 HV, for the as-cast alloy, to 134 Hv, after six passes of heat-treated cooling slope casting. The corrosion resistance of the alloy improved, from 0.042 to 0.0012 mmy−1, after the ECAP process. In this work both the strength and corrosion resistance of the ECAPed A356 alloys were improved with the application of the cooling slope process than without (i.e., from the as-cast condition).

Dry Sliding Wear Behaviour of Rheocat Al-5.7si-2cu-0.3mg Alloy

In this study, the effect of improved microstructure of Al-5.7Si-2Cu-0.3Mg alloys by using semisolid process on hardness and dry sliding wear behaviour were investigated. The microstructures of conventional cast alloy were totally dendritic, while in rheocasting the dendritic transfer to fine globular microstructures after using cooling slope casting. Tribological tests were carried out by using a pin-on-disc apparatus in dry sliding conditions. Wear tests were at low sliding speed 1ms-1 ,applied load at 50N and three different sliding distance (i.e., 1.8Km, 5.4Km and 9Km) respectively. An optical microscope and a scanning electron microscope were used to examine the microstructure and to understand the wear mechanism on the worn surface of both samples. The results showed that, the wear resistance of rheocast alloy was improved and higher than that those produce by conventional casting. The volume loss of rheocast alloy show reduction more than 18% at 1.8Km and 10% at 9Km compared to as-cast alloy. Moderate wear regimes were appeared in both alloys, according to the range of wear rate. The friction coefficient had increased due to increase in the contact point between pin and disc materials. The dominant wear mechanism for conventional and rheocasting alloys was adhesion wear and abrasive wear respectively.

Microstructure and Wear Properties of T6 Heat Treated Semisolid A356-TiB2 composite

The aim of this study is to investigate the microstructure and wear properties of T6 heat treated semisolid A356 composite containing 1.5 wt.% and 2.63 wt.% TiB2. The semisolid A356-TiB2 composite was prepared using a cooling slope casting technique. The sample, then was solution treated at different temperatures (500°C, 520°C and 540°C) for 5 hours soaking time. Then, age hardening was conducted at different temperatures (120°C, 150°C and 180°C) for 8 hours. Semisolid A356 composite was characterized for microstructure, microhardness and wear properties. Microstructure of semisolid A356 composite was refined with a higher amount of TiB2. High solution treated temperature (540°C) resulted in the finer size of Si particles in the semisolid A356 alloy. Microhardness of solution treated semisolid A356 alloy achieved higher hardness at 540°C with a hardness value of 75.16 HV. Solution treated of semisolid A356 composite containing 1.5 wt.% TiB2 has the smallest Si particles and the highest hardness of 119.7 HV. Among the samples, A356-1.5 wt.% composite after aging at 180°C showed the highest hardness (129.7 HV). Wear resistance of semisolid A356 alloys was improved by the addition of TiB2. Wear surface morphology revealed that the adhesive and abrasive wear mechanism present.

Optimization of processing parameters of cooling slope process for semi-solid casting of ADC 12 Al alloy

In the present work, the effect of processing parameters of cooling slope techniques (pouring temperature, slope angle and slope length) of ADC 12 Al alloy on its microstructural evolution has been studied in detail. A series of cooling slope casting experiments were conducted by varying the pouring temperature (580, 585 and 590 °C), slope length (400, 500 and 600 mm) and slope angle (30°, 45° and 60°). The effect of processing parameters on the response factors, viz. degree of sphericity and particle size, has been investigated by applying analysis of variance (ANOVA), interaction graphs obtained using response surface methodology. The obtained results infer that optimum values of the degree of sphericity (0.865) and particle size (49.30) are observed for the following set of processing parameters, namely 585 °C pouring temperature, 500 mm slope length and 45° slope angle. ANOVA results show that the pouring temperature is the most significant input variables that influence degree of sphericity and particle size followed by slope length and slope angle. The values of output variables obtained from confirmation experiment, performed at 95% confidence level, ensure that they are well within the permissible limits.

Microstructure and mechanical properties of Al-Mg 2 Si composite fabricated in-situ by vibrating cooling slope

Abstract An innovative semisolid technique termed as vibrating cooling slope (VCS) has been applied to producing in-situ Al-25%Mg2Si (mass fraction) composite. The molten Al-16.5Mg-9.4%Si (mass fraction) alloy with 100 °C superheat was poured on the surface of an inclined copper plate (set at 45° inclined angle) while it was vibrated at a frequency of 40 Hz and an amplitude of 400 μm. After travelling the length of 40 cm on the slope, the resultant semisolid alloy was cast into a steel mold. For the purpose of comparison, reference composite samples were made by gravity casting (GC) and conventionally still cooling slope casting (CS) methods using the same alloy under identical conditions. The samples were hot extruded at 500 °C. It was concluded that the size of Mg2Si particles was decreased by about 50% and 70% for the CS and VCS produced samples respectively when compared to that of the GC produced sample. Despite of their higher porosity contents, both the as-cast and hot-extruded VCS processed samples exhibited higher hardness, shear yield stress (SYS) and ultimate shear strength (USS) values as compared with their GC produced counterparts. These results were attributed to the refined and modified microstructure obtained via this newly developed technique.

Cooling slope casting of cast iron

AbstractThe aim of the present work is to study the effect of semi‐solid processing using cooling slope method on the microstructure and mechanical properties of grey cast iron. A water cooled castable cement coated steel plate with a variable inclination angle is used to make a mechanical treatment on the semi‐solid flow of grey cast iron. The experiment is repeated for three different pouring temperatures and three inclination angles. The tensile test, hardness test and microstructure examination is used to compare the new properties of the new resulting grey cast irons. The results show that the sharp edged carbon flakes can be refined and the mechanical properties is enhanced. The carbon particles average circularity is increased followed with a decrease in carbon particle size due to the effect of the cooling plate.

MICROSTRUCTURAL INVESTIGATION AND MECHANICAL PROPERTIES OF THIXOFORMED AL-6SI-XCU-0.3MG ALLOYS

In this study, the effect of different amounts of copper (CU) on the microstructure and mechanical properties of thixoformed Al-6Si-xCu-0.3Mg (x= 3, 4 and 5, mass fraction, %) were investigated. The alloys were prepared via cooling slope casting technique, before there were thixoformed using compression press. All of the alloys were then characterized using optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray (EDX). The results obtained revealed that cooling slope casting produced a non-dendritic microstructure and the intermetallic phase in the thixoformed samples was refined and evenly distributed. The results also revealed that as the Cu content in the alloy increases, the hardness and tensile strength of the thixoformed alloys also increase. The hardness of thixoformed Al-6Si-3Cu was 104.1 HV while the hardness of Al-6Si-5Cu alloy was increased to 118.2 HV. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed alloy which contained 3wt.% Cu were 241 MPa, 176 MPa and 3.2% respectively. The ultimate tensile strength, yield strength and elongation to fracture of the alloy that contained 6wt.% of Cu were 280 MPa, 238 MPa and 1.2% respectively. The fracture surface of the tensile sample with lower Cu content exhibited dimple rupture while higher Cu content showed a cleavage fracture.