Shot Sleeve Research Articles

Formation mechanism of the microstructural heterogeneity in a die-cast Al-Mg-Si alloy and its effect on mechanical properties

Al-Mg-Si series alloys fabricated by high pressure die casting (HPDC) have a broad application prospect in the production of large-scale and thin-walled die-castings. However, the die-cast Al-Mg-Si series alloys usually exhibit obvious microstructural heterogeneity. This study investigated the microstructural heterogeneity of the die-cast Al-7 Mg-3Si alloy along the thickness direction, and the corresponding formation mechanism was verified. In this study, the die-cast sample can be divided into four distinct regions (R1 ∼ R4) from the surface to the center in turn according to the area fraction of the primary α-Al. Two aspects were considered to be the main reasons for the formation of microstructural heterogeneity. On the one hand, the externally solidified crystals (ESCs) preferentially formed in the shot sleeve and aggregated in the casting center. On the other hand, the cooling rates were quite different in each region, leading to different solidification behaviors. Based on the combination of the microstructural observation and calculated cooling rates, a physical model has been proposed to describe the formation mechanism of the microstructural heterogeneity. The heterogeneous microstructure of the die-cast sample resulted in the inhomogeneity of mechanical properties along the thickness direction. The R2 exhibited the highest micro-hardness than the other regions because of its highest amount of eutectics. Moreover, the casting surface with fine grains (R1) is conducive to improving the EL, whereas the center (R4) showed the lowest tensile properties due to the existence of ESCs and porosity band.

The characterization of porosity and externally solidified crystals in a high pressure die casting hypoeutectic Al-Si alloy using a newly developed ceramic shot sleeve

The effective methods to regulating porosity and externally solidified crystals (ESCs) have been remained as a challenging task for high pressure die casting (HPDC) automobile parts. In this work, a newly designed ceramic shot sleeve is proposed for reducing porosity and optimizing ESCs. As a result, both porosity and ESCs achieve an effective reduction after applying the ceramic shot sleeve. This study provides insights into regulating porosity and coarse ESCs of die castings and it is expected to expand its application in industrial manufacture.

Automatic Design of Overflow System for Preventing Gas Defects by Considering the Direction of Molten Metal Flow

In die casting, gas defects occur if the molten metal entrains the gas inside the shot sleeve and mold and remains inside the product after filling. Therefore, an exhaust system such as an exhaust runner or overflow is generally designed at the die casting mold to discharge the gas-entrained molten metal outside the mold completely. In addition, an overflow has a broader designable area than an exhaust runner has and can discharge the gas-entrained molten metal, which an exhaust runner cannot. Therefore, designing the overflows at appropriate positions and volumes in die casting is essential. In recent years, research regarding the design of the overflow positions has been conducted by combining optimization theory and computational fluid dynamics (CFD). However, optimizing the overflow positions only can cause gas defects in the product and the unnecessary discharge of molten metal due to the overflow volume excess. Moreover, applying those methods is difficult because the analysis to verify the exhaust system includes the entire mold as the analysis domain, which increases calculation time. In this research, we propose the automatic overflow design system to discharge the gas-entrained molten metal inside the product completely by estimating the direction of molten metal flow and evaluating the efficiency of overflow design positions. Finally, we verified the effectiveness of the proposed system by actual die casting experiments using the proposed overflow shape.

The microstructure characteristics and fracture behavior of the polyhedral primary iron-rich phase and plate-shaped eutectic iron-rich phase in a high-pressure die-cast AlSi10MnMg alloy

The characterization of multiple iron-rich phases in high-pressure die-cast AlSi10MnMg alloy was studied. Attention was focused on the formation and fracture behavior of the primary iron-rich phase ((P-IMC)I) formed in the shot sleeve and plate-shaped eutectic iron-rich phase in high-pressure die cast (HPDC) AlSi10MnMg alloy. Results show that multiple types of iron-rich phases with various morphologies, including primary iron-rich phases (polyhedral (P-IMC)I and (P-IMC)II) and eutectic iron-rich phases (plate-shaped, net shape, and fish-bone shape), were found in HPDC AlSi10MnMg. Coarse (P-IMC)I formed in the shot sleeve were distributed in the interface between primary α-Al and binary Al-Si eutectic. Small size (P-IMC)II and various eutectic iron-rich phases formed in the die cavity and they were distributed in Al-Si binary eutectic. The primary iron-rich phases belonged to a simple cubic crystal structure with a lattice constant a = 1.265 nmand they exhibited a lateral growth characteristic with a termination of {110} surface along a (P-IMC)II [1¯12¯] direction. β phase was surrounded by δ phase and they coexisted in a plate-shaped iron-rich phase. High-density stacking fault in β phase and δ/β interface provided an excellent nucleation site for δ phase. From mechanical behavior, the stress concentration caused by eutectic iron-rich phases was far less than (P-IMC)I and it would not cause crack initiation along the eutectic cluster boundary. In addition, (P-IMC)I showed the worst deformation coordination with primary α-Al while the plate-shaped eutectic iron-rich phase exhibited similar deformation characteristics with silicon particles.

Investigation of shot sleeve distortion and oil cooling in high pressure die casting

It is well known that thermomechanical distortion reduces the service life of shot sleeves in high pressure die casting (HPDC) processes. However, the underlying phenomenon which causes the distortion is still not well characterized. While finite element models (FEM) have been used to analyze shot sleeve distortion, these have typically used simplified 2D representations and do not consider the effect of transient molten metal flow on heat transfer. In the present study, a 3D finite element (FE) model based on ANSYS used a staggered approach to study the sources of shot sleeve distortion and the effect of active oil cooling. Transient flow behavior during pouring, settling, and slow shot phases was simulated using a computational fluid dynamics (CFD) based model after which the temperature field and internal pressure distribution were imported into a structural model which was used to predict shot sleeve distortion at selected instants during a representative steady-state cycle. The simulation results were validated using data obtained from an HPDC machine and demonstrated good agreement. A comparison of large and small internal diameter (ID) shot sleeves showed that the former distort the most and that cooling channels are only moderately effective at minimizing distortion. Based on the complex 3D nature of shot sleeve distortion, the use of total indicator runout (TIR) is also proposed as a metric for minimizing distortion in shot sleeve designs. In addition to distortion, the thermal gradient in the shot sleeve was analyzed and it was noted that the largest source of heat loss is through the mounting flange attached to the HPDC machine frame, which is not an area typically considered for thermal management.

Microstructural Characterization and Mechanical Properties Investigation of Nemalloy HE700 alloy: Effect of Pre-Solidified Grains

Structural plate castings of Nemalloy HE700 alloy, an Al-Fe eutectic alloy system with Zn and Mg as precipitation strengtheners were produced through high vacuum high pressure die casting (HVHPDC) and designed as an alternative to existing structural automotive materials. Cast materials are subject to the existence of pre-solidified grains (PSG) within the microstructure that originate from external solidification in the liquid melt and cause defects in the final cast components. In the case of HPDC, these PSG emerge in the shot sleeve and are injected through the gating system, influencing liquid metal flow behaviour and solidification characteristics. The extent of PSG and their distribution were manipulated through the altering of process route parameters such as shot delay intervals. Quantitative metallography and the effect of PSGs on the uniaxial tensile properties for the Nemalloy HE700 alloy are presented in this publication.

Optimization of Ladle Tilting Speed for Preventing Temperature Drops in the Die Casting Process

In die casting, molten metal poured into a shot sleeve is pressed into a mold by a plunger at high speed. The temperature of the metal drops significantly while it is being poured from the ladle to the shot sleeve, resulting in casting defects such as misrun flow lines. Although it is important to control the temperature at all stages of the process, a method for minimizing temperature loss has not yet been clarified to date. In this study, the cause of the temperature drop in the shot sleeve was clarified, and a method of optimizing the ladle tilting speed was proposed to prevent temperature drop. First, experiments were conducted to measure the decrease in metal temperature in the sleeve during pouring. These experiments revealed that the metal cools significantly from the moment it touches the shot sleeve. Therefore, the time from the first contact between the shot sleeve and the metal to the start of pouring was set as the objective function. A genetic algorithm was then used to derive the optimal ladle tilting speed pattern to suppress the temperature drop. This analysis confirmed that the metal was poured without flowing out or running ahead and that the immediate liquid level vibration after pouring was suppressed, thus ensuring stable pouring.

Improving the wear resistance of copper tools for pressure die casting by laser melt injection

Highly conductive copper alloys are used for various tools in casting and welding technology. In pressure die casting, copper alloys are used for pistons pressing the metal melt into a die. The high thermal conductivity of these alloys allows short process times as a result of high cooling rates. Due to a poor wear resistance, wear occurs on the running surface of the pistons causing the metal melt to spurt out of the shot sleeve. In order to improve the service life of the pistons, a new approach was taken: a reinforcement of the copper alloys with fused tungsten carbide (FTC) particles by laser melt injection (LMI) at high process velocities. FTC provides a hardness between 2700 HV 0.1 and 3500 HV 0.1. During LMI, a melt pool is induced on the substrate by a laser beam and a filler material is injected into this melt pool by a powder nozzle. In contrast to laser cladding, the filler material remains in the solid state and the substrate works as matrix material. Thereby, specific material properties of the substrate—e.g. a high thermal conductivity—can be preserved within the surface layer. It was shown that the FTC particle reinforcement reduced the wear by 69–75%. Abrasion and adhesion were identified as the dominant wear mechanisms. The run-in behavior of FTC particle reinforced and non-reinforced parts was determined.

High-Pressure Die Casting: A Review of Progress from the EPSRC Future LiME Hub

This article provides an overview of high-pressure die casting (HPDC)-related research undertaken at the EPSRC Future LiME Hub between 2015–2022. The project aimed to identify the cause of variability in the tensile ductility of die-cast structures, and to develop novel processing techniques to address this issue. Variability in tensile ductility was related to the size of large pores and non-metallic inclusions. It was proposed that these non-metallic inclusions formed during the pyrolysis of commercial plunger lubricants in the shot sleeve, and that these large pores derived from dilatational strains introduced during semi-solid deformation. Processing parameters and die design were found to significantly influence the microstructure of die-cast products, and the subsequent variability in tensile ductility. To close, recent progress on the application of intensive melt shearing to HPDC is reviewed. Intensive melt shearing was found to induce significant grain refinement in both Al and Mg alloys due to the effective dispersion of native oxide particles, and the use of these particles as heterogeneous nucleation substrates. The presence of native oxide particles also enabled the use of novel heat treatment procedures that avoided conventional issues such as surface blistering and geometrical distortion.

Enhanced mechanical properties and thermal conductivity of high-pressure die-cast AlMg6Si2MnZr alloy by controlling the externally solidified crystals

In this work, better mechanical properties and thermal conductivity of the high-pressure die-cast AlMg6Si2MnZr alloy were reported by replacing the conventional H13 steel shot sleeve with a new ceramic type shot sleeve (named LX shot sleeve). The work mainly concentrated on the effect of microstructure on the mechanical properties and thermal conductivity of two die-cast samples of AlMg6Si2MnZr alloy by different shot sleeves. The results showed that the LX shot sleeve produced smaller and fewer externally solidified crystals of α-Al (ESCs-α) as it dissipated heat more slowly than the H13 shot sleeve. Meanwhile, ESCs-α in the die-cast sample by the LX shot sleeve had lower dendritic branching extent. Due to the decrease in ESCs-α, the eutectic content and the number of the porosities, particularly shrinkage porosities, of the die-cast sample by the LX shot sleeve decreased. The mechanical properties of the die-cast sample by the LX shot sleeve were increased greatly, particularly the elongation, which was increased from 6.64% to 9.06% due to the decrease in the shrinkage porosities. The thermal conductivity of the die-cast sample by the LX shot sleeve was also increased from 112.2 W m −1 K −1 to 120.6 W m −1 K −1 . In the die-cast sample by the LX shot sleeve, the decrease in the Mg solute concentration in α-Al solidified in the cavity (α) was the main factor to distinctly increase the electrical thermal conductivity while the reduction of the eutectic phase resulted in a slight decrease in the phonon thermal conductivity. • The difference in the microstructure of samples of HPDC AlMg6Si2MnZr alloy by different shot sleeves is studied. • Mechanical properties and thermal conductivity are improved using a new LX shot sleeve. • Large-size shrinkage porosity in the center is the crack source and reduces the elongation. • Electrical thermal conductivity increases sharply and phonon thermal conductivity decreases slightly using the LX sleeve. • Higher Mg solute concentration in the sample using the H13 shot sleeve is the main factor to reduce thermal conductivity.

The effect of different high pressure die casting parameters on 3D microstructure and mechanical properties of AE44 magnesium alloy

To understand the relationship between the process-microstructure-mechanical properties of the high-pressure die-casting (HPDC) AE44 magnesium alloy, 3D reconstruction and 2D characterization were carried out on the HPDC castings produced with different process parameters (low slow-shot speed, fast slow-shot speed, solidification pressure). Microstructural characterization revealed that the formation of shrinkage pores are closely related to ESCs, which were mainly controlled by the low slow-shot speed in shot sleeve (ESCs growth time) and fast slow-shot speed into the die cavity (distribution of ESCs). In addition, solidification pressure can significantly reduce the shrinkage porosity in the center by improving the feeding capacity of liquid metal. Tensile fracture revealed that the tearing ridge is mainly evolved from the slip band of ESCs. The quantity and distribution of ESCs determine the fracture mode of castings. The relationship between mechanical properties of castings and the morphology of ESCs and porosity is also statistically discussed.

Failure analysis of shot-piston used in squeeze casting process equipment

The failure investigation has been conducted on shot-piston used in injection system of squeeze casting equipment to clarify its failure mechanism. The macroscopic morphology of failed shot-piston showed there were many network cracks on its upper-end surface while the cylindrical surface was seriously worn. Further studies were carried out on the two surfaces respectively. Firstly, the shot-piston upper-end surface was sampled. And the crack distribution and depth were observed. Then, the crack micromorphology was investigated by scanning electron microscope (SEM), and the sampling points inside cracks were analyzed by energy dispersive spectrometer (EDS). The results show the shot-piston upper-end surface produces thermal stress cracks due to the high-temperature thermal cycle, and oxidation occurs in the cracks. The same method was also used for the cylindrical surface failure mechanism analysis. Above all, the cylindrical surface was sampled and the wear morphology was measured. Afterward, the material composition of the bulge on the cylinder surface and the micromorphology were confirmed by SEM and EDS. The results demonstrate the main failure forms are abrasive wear and adhesive wear. The inconsistent thermal deformation of the shot-piston and shot sleeve caused changes in the fit clearance and resulted in friction and wear. Simultaneously, the metal solution and oxygen erode the shot-piston matrix through the furrow, accelerating wear and failure. According to the failure mechanism of different surfaces, shot-piston service life can be extended by optimizing the squeeze casting process, controlling the temperature gradient, and selecting the appropriate fit clearance, which has important engineering significance.

Al-Mn Intermetallics in High Pressure Die Cast AZ91 and Direct Chill Cast AZ80

Manganese-bearing intermetallic compounds (IMCs) are important for ensuring adequate corrosion performance of magnesium-aluminium alloys and can be deleterious to mechanical performance if they are large and/or form clusters. Here, we explore the formation of Al-Mn IMCs in Mg-9Al-0.7Zn-0.2Mn produced by two industrial casting processes, high-pressure die casting (HPDC) and direct chill (DC) casting. As Al8Mn5 starts forming above the α-Mg liquidus temperature in this alloy, we consider its formation during melt handling as well as during casting and heat treatment. In HPDC, we focus on sludge formation in the holding pot, partial solidification of IMCs in the shot chamber, and Al-Mn IMC solidification in the die cavity. In DC casting, we focus on interactions between Al-Mn IMCs and oxide films in the launder system, Al-Mn IMC solidification in the billet, and the partial transformation of Al8Mn5 into Al11Mn4 during solution heat treatment. The results show that minimising pre-solidification in the shot sleeve of HPDC and controlling pouring and filtration in DC casting are important for ensuring small Al-Mn intermetallic particles in these casting processes.

The formation mechanism of the chill fine-grain layer with high supersaturation and its influence on the mechanical properties of die casting Al-7Si-0.5Mg alloy

In this study, the chill layer with high supersaturation was observed on the surface of the Al-7Si-0.5Mg die casting tensile samples. The optional microstructure and electron backscatter diffraction (EBSD) results show that the chill layer has fine α-Al grains (≈5 μm). There is a solution gradient in die-casting aluminum alloy and the chill fine-grain layer is in a supersaturated state. The pre-solidified dendrites (PSDs) formed in the shot sleeve and the nonuniform velocity distribution of the melt are responsible for the formation mechanism of the chill fine-grain layer with high supersaturation. Under high pressure and high injection speed, the PSDs will aggregate in the core of the samples due to the Magnus effect. Moreover, the chill layer with solute enrichment can be obtained as a result of rapid cooling and incoordinate solute distribution. Consequently, the tiny Mg2Si phase could precipitate spontaneously from the supersaturated α-Al grains in the chill layer, simultaneously improving the of strength and ductility.

On Determining the Critical Velocity in the Shot Sleeve of a High-Pressure Die Casting Machine Using Open Source CFD

This paper investigates the critical plunger velocity in high-pressure die casting during the slow phase of the piston motion and how it can be determined with computational fluid dynamics (CFD) in open source software. The melt-air system is modelled via an Eulerian volume-of-fluid approach, treating the air as a compressible perfect gas. The turbulence is treated via a Reynolds-averaged Navier Stokes (RANS) approach that uses the Menter SST k-ω model. Two different strategies for mesh motion are presented and compared against each other. The solver is validated via analytical models and empirical data. A method is then presented to determine the optimal velocity using a two-dimensional (2D) mesh. As a second step, it is then discussed how the results are in line with those obtained for an actual, industrially relevant, three-dimensional (3D) geometry that also includes the ingate system of the die.

Thermal Fatigue Life Prediction under Temperature Uncertainty for Shot Sleeve of Squeeze Casting Machine

To quantify the influence of temperature uncertainty on thermal fatigue life prediction of a shot sleeve in an injection mechanism, an uncertainty analysis method based on a Kriging surrogate model and Monte Carlo simulation (MCS) was proposed. The training samples of the surrogate model were obtained by a finite element simulation, and the response relationships between input variables, such as pouring and preheating temperature, and target variables, such as strain and stress, were constructed by the Kriging surrogate model. The input variables were sampled by the MCS, and the predicted stress and strain parameters were combined with the modified universal slope equation to predict the thermal fatigue life of the shot sleeve. The statistical characteristics of the predicted life were obtained. The comparative analysis results indicate that the predicted life considering temperature uncertainty is more accurate than the deterministically predicted value.

Characteristics of Fe-rich intermetallics compounds and their influence on the cracking behavior of a newly developed high-pressure die cast Al–4Mg–2Fe alloy

Microstructure and mechanical properties of a newly developed Al–4Mg–2Fe alloy prepared via high pressure die casting (HPDC) were studied. Attention was focused on the characteristics of the iron-rich intermetallic compounds (IMCs) and their influence on crack initiation and propagation. Result shows three types of iron-rich IMCs (Al13Fe4) existed in the alloy. The first is the primary iron-rich IMCs (P-IMCs) precipitating prior to the α-Al phase. These IMCs comprised external solidified iron-rich IMCs (P-IMC)I forming inside the shot sleeve and secondary iron-rich IMCs (P-IMCs)II inside the cavity. The second is fine ternary eutectic iron-rich IMCs (TE-IMCs), one of the phases of the ternary Al–Al8Mg5–Al13Fe4 eutectic. The third is binary eutectic iron-rich IMCs (BE-IMCs), which formed between P-IMCs and TE-IMCs via binary eutectic reaction: L→Al + Al13Fe4. Accordingly, the (P-IMCs)I acted as crack initiation sources regardless of the orientation due to the extremely large size and aspect ratio. The (P-IMCs)II exhibiting a large aspect ratio but small size accelerated the crack propagation. The BE-IMC and TE-IMCs, due to the tiny small size and aspect ratio, barely exhibited any effect on the final failure.

Correlation of 3D defect-band morphologies and mechanical properties in high pressure die casting magnesium alloy

For understanding the processing-microstructure-properties correlation of high pressure die casting (HPDC) AZ91D alloy, 3D reconstruction was carried out to characterize the microstructural morphologies of castings produced by four designed HPDC processes. The influence of different parameters (vacuum, slow-shot speed, fast-shot speed) on porosity volume and morphology, defect band width and average externally solidified crystals (ESCs) size of castings were systematically studied. Microstructural characterization revealed that the defect band width was strongly related with the size and quantity of ESCs, rather than the porosity volume. Meanwhile, ESCs were mainly influenced by the slow-shot speed in shot sleeve (ESCs growth time) and fast-shot speed into the die cavity (shear stress of melt flow). Tensile fracture revealed that cracks easily propagated within the defect bands due to the accumulated ESCs and connected irregular pores, while the cracks were restrained in center zone. The mechanical properties of HPDC castings was inversely proportional to the defect band width, and is not dependent on the average volume fraction porosity.

Fluidity of Alloys Under High-Pressure Die Casting Conditions: Flow-Choking Mechanisms

Theories on fluidity of alloys based on the solidification mode are not satisfactory in describing fluidity of alloys under high-pressure die casting (HPDC) conditions. To understand the flow-choking mechanisms under HPDC conditions, microstructure in the fluidity test coupons made using a 125-ton HPDC machine was characterized. Pre-solidified dendrites (PSDs), or externally solidified crystals (ESCs), which were formed in the shot sleeve, were found in the runners as well as in the fluidity casting. Surprisingly, a large amount of PSDs are collected in the runner adjacent to the in-gate, forming a PSD core with a thin layer of PSD-less or PSD-free region near the surfaces of the runner due to Magnus effect. Analytical calculations were performed to estimate the pressure drop for molten aluminum flowing through the mushy PSD zone. The results indicate that the pressure drop is comparable to the maximum pressure that was used for injecting molten metal to fill the casting. When the pressure drop is equal to the pressure driving the mold filling, the metal ceases to flow. Thus, it is the PSDs that are responsible for the choking of mold filling either mechanically at the in-gate or providing a pressure drop high enough to resistant fluid flow.

Thermal Fatigue Testing of SiMoCr Compacted Graphite Cast Iron for HPDC Tooling Application

SiMoCr CGI (compacted graphite iron) has the potential to be a cost-effective replacement for some hot working tool steel parts like shot sleeve in HPDC (High-Pressure Die Casting) applications. Thermal fatigue testing of SiMoCr CGI cast alloy was performed on Gleeble 1500D machine. Cracks were evaluated on non-nitrided and nitrided samples at test temperatures of 400 and 600 °C, after 1000, 2000 and 4000 thermal cycles. Samples were heated to prescribed test temperature and afterward cooled in computer-guided cycles. After the test, all the samples were axially and radially sectioned and cracks on cross sections were evaluated. Length of all cracks which occurred was measured and statistically evaluated, i.e., the average length of cracks and distribution of crack lengths were determined. At nitrided samples, higher values for average crack lengths were obtained while density of cracks was lower in comparison with non-nitrided samples.