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Mechanisms of Soldering Formation on Coated Core Pins
Abstract and Figures
Die soldering is one of the major casting defects during the high-pressure die casting (HPDC) process, causing dimensional
inaccuracy of the castings and increased downtimes of the HPDC machine. In this study, we analyzed actually failed core pins
to determine the mechanism of soldering and its procedures. The results show that the soldering process starts from a local
coating failure, involves a series of intermetallic phase formation from reactions between molten aluminum alloys and the
H13 steel pin, and accelerates when an aluminum-rich, face-centered cubic (fcc) phase is formed between the intermetallic
phases. It is the formation of the aluminum-rich fcc phase in the reaction region that joins the core pin with the casting,
resulting in the sticking of the casting to the core pin. When undercuts are formed on the core pin, the ejection of castings
from the die will lead to either a core pin failure or damages to the casting being ejected.
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... Han et al found that die soldering is caused by a reaction between the molten aluminum alloy and steel at the die surface, resulting in phases that are liquid at the reaction temperatures. The liquid acts as glue that joins the die with the casting upon solidification, and thus results in soldering on the die [5,7,9,[11][12]. Shankar and Apelian report that a pyramid shaped intermediate phase layer forms on the locations on the core pin where soldering starts to occur [6,8,10]. ...
... Shankar and Apelian report that a pyramid shaped intermediate phase layer forms on the locations on the core pin where soldering starts to occur [6,8,10]. Our previous papers propose the mechanism of soldering formation on coated core pins [2,12], and describe the soldering procedures into five steps. In the step one, local coating failure occurs. ...
... In the previous study [2,12], we have found that coating failure starts from the local coating failure. The ceramic coating can be fractured or detached from the H-13 matrix under severe casting conditions. ...
Soldering of core pins is one of the issues limiting the productivity of aluminum castings using high pressure die casting process. Ceramic coating is usually applied on the core pins to reduce die soldering. As a result, the coating lifetime governs the soldering process and the core pin lifetime. This study was designed to analyze the failure mechanisms of coatings on core pins under conditions similar to that of diecasting conditions. High intensity ultrasonic vibration was applied on the coated core pins to accelerate the experiments. The coated core pins were vibrated for certain times in water, oil salt bath, molten zinc, and molten A380 alloys at various temperatures. SEM and XRD were used to characterize coating failure of the tested core pins. Experimental results indicate that coating detachment from the steel matrix is the main failure mechanism of the coatings tested at low temperatures in water, oil, molten salt, and molten zinc. Coating failure accelerates as the temperature of the melt is increased. At high temperatures, coating fragmentation as well as detachment occurs on core pins tested in molten zinc and A380 alloy. The reactions between zinc or aluminum with steel at the coating failure locations cause coating fragmentation and accelerate coating failure at high temperatures.
... Figure 1 illustrates the coating failure process. Two typical modes for the local coating failure are identified as cracking and detaching of the coating [3]. Even if the coating is applied onto H-13 matrix with the best technologies and application methods, local coating failure still occurs because of micro variations in the application, the microstructure of the H13 steel containing martensite and carbides, and from the thermal cycles of the diecasting process [4]. ...
... After local failure on coating occurs, molten aluminum gets in contact with the H-13 steel matrix, forming small pits. Figure 1 shows a small pit or small soldered area with 20 to 30 microns in lateral length and 15 to 20 microns in depth [3][4]. The lateral growth of the pit leads to the further coating failure. ...
... The lateral growth of the pit leads to the further coating failure. Fragments of the failed coating can be observed in the aluminum side of the reaction area, outside of the pit, shown in Figure 2 [3][4]. ...
This work examines the effect of Hot Isostatic Pressing (HIP) technology on the adhesion of PVD ceramic coating on H-13 steel matrix and on the service life of the core pins under the accelerated soldering testing conditions. Samples with a ceramic coating were heated up to various temperatures for one hour under argon protection. These samples were then characterized using an accelerated testing method for their service life in molten A380 alloy. Experimental results obtained under the accelerated testing conditions suggest that the use of commercial coatings such as BALINIT® ALCRONA, and BALINIT®D extends the service life of core pins by 1-3 times with the Hot Isostatic Pressing treatment. New method to determine the quality of the coating by cracks analysis has been initially developed. The experimental results indicate that much less cracking is formed near the indentation on the coatings subject to HIPing. It is believed that HIPing of the coated core pins increases the adhesion between the ceramic coating and the H-13 core pins and is beneficial in extending the service life of the coating under die-casting conditions.
... None of the images showed any diffusion or intermetallic formation at the interface between the soldered aluminum and the H13 steel, at least at the magnifications used in this study. Yu et al. [28] and Song et al. [29] have reported the presence and growth of intermetallic is necessary for the total removal of the coating from protecting the steel surface. The results presented here support the mechanism proposed by Gulizia et al. [24], where first mechanical build-up can occur but does not always progress to chemical soldering by reaction. ...
... PVD hard coatings are normally brittle and this shearing stress could be the cause for crack initiation and failure of the coating. As described earlier by Song et al. [29], most of the proposed soldering mechanisms for PVD-coated dies start with defects and/or cracks in the coating creating a path for the molten aluminum to contact the underlying steel die. ...
Aluminum high pressure castings (HPDC) were successfully produced on two simple but slightly different H13 steel dies that had been coated with AlCrN physical vapor deposition (PVD) coatings and without the use of conventionally-sprayed die lubricants. Over 200 lube-free (no lubricant) castings were produced in both of the dies. Temperature simulations of the dies matched well with thermal camera measurements taken during the trials, and helped explain the positions where small amounts of soldering and aluminum marks developed. Aluminum build-up on the die surfaces was observed as an intermittent phenomenon and did not lead to soldering. Due to the high gate velocities used in these trials, a large fraction of the AlCrN coating was washed out or cracked. No chemical reaction or intermetallic formation was observed on the analyzed surfaces, suggesting that build-up of aluminum on the die surface occurred by mechanical keying rather than by chemical soldering. A mechanistic model was developed to understand the correlation between surface roughness, wetting angle and HPDC pressure, in an attempt to explain why lube-free aluminum HPDC was possible for these simple die geometries, and to shed light on why it is more challenging for more complex die geometries. This study has demonstrated that lube-free aluminum die casting is possible by coating simple geometry dies with duplex AlCrN PVD coatings and suggests that lube-free castings might extend die life.
... region "C" of "soldering on coating" where a lot of Al can be seen in the EDS maps, but the coating is still present underneath the soldered layer as evidenced by the Si and C maps. Also, these results were combined with minor erosion indicated by the Fe maps, which could indicate the positions where the aluminum soldering occurred with the steel substrate (Song et al., 2012). It is interesting to note that in these same regions, a concentration of Mg and O was observed, which suggests that Mg from the A380 alloy may be assisting coating oxidation and creating an easy path to the substrate; similar results have been reported previously (Vian, 2021). ...
... As can be seen in Fig. 12, there is a good correlation between wetting and COF ( Fig. 12 (a)), wetting and Δd/D parameter ( Fig. 12 (b)), and the soldering response, where the smaller the cos(ϴ) and the lower the COF or Δd/D, the lower the fraction of soldering observed on the core pins. This correlation involves two soldering mechanisms (Song et al., 2012), the chemical (wetting) and the mechanical (wear), where those coatings with lower wetting and higher wear resistance experience a decrease in the amount of soldering, resulting in better protection for the die in HPDC. No obvious trend was found when wetting was correlated against measured wear rates, as shown in Fig. 12 (c). ...
... Washout and erosion can be considered as dissolution of die metal under severe convection in molten metal. The soldering process involves dissolution of die steel as soon as pits are formed [2]. ...
... The equipment for accelerated testing is shown in Figure 3 [2,13]. The output of the unit was 1.5 kW and the frequency was 20 kHz. ...
Most die metals dissolve into molten aluminum to some extent. The dissolution of die material to molten aluminum is directly related to issues such as die washout, die soldering, shot tooling failure, and decreased toughness of the aluminum castings. It is well known that the dissolution rate of a die metal is affected by the compositions of die metal and the cast alloy, the temperature and the flow rate of the molten aluminum, and the surface conditions of the die (surface heat treatment, coatings, and die lube). However, limited experimental data are available in the open literature on the effect fo these parameters on the dissolution of H13 steel in molten aluminum alloy. This article describes experiments in measuring dissolution rate of H13 in molten A380 aluminum alloy. Microstructure formation at eh steel/aluminum interface is examined in order to understand the dissolution mechanism. Factors that affect the dissolution rate of die materials in molten aluminum are discussed.
... The structure of this intermetallic layer is the same as that shown in Figure 5 and Figure 6(b). With an increase in reaction times, more pits would form and ultimately grow sideways, breaking up the suspended coating until the neighboring pits are connected 12 . With an increased loss of the coating, the dissolution rate of the steel would increase. ...
When liquid aluminum is poured into the horizontal shot sleeve of a die-casting machine, the surface of the shot sleeve's steel chemically reacts with the molten aluminum, forming intermetallic phases and dissolving into the molten aluminum. This produces wash out at the pouring location and ultimately requires replacement of the sleeve. This paper investigates the effect of three different surface treatment methods in an attempt to reduce the wash-out effect due to the aluminum-steel chemical reactions. The methods were Ion Plasma diffusion, Thermo-reactive diffusion, and High Velocity Air Fuel Physical Vapor Deposition. Cylindrical pucks with the various treatments were tested in a spindle apparatus that was placed inside of a crucible of molten aluminum and rotated for given amounts of time. The weight loss of the samples was then examined once the soldered aluminum was dissolved away and SEM analysis was performed on the microstructure. It was observed that both Ion Plasma treatments showed almost 0% dissolution up to 40 minutes while the chromium carbide CVD showed excellent dissolution resistance to dissolution as well. The HVAF also showed excellent resistance on the surface that was coated. All of these heat treatments/surface modifications tested in this study reduced the dissolution of H13 steel in molten aluminum.
Soldering (sticking) to and erosion of steel die materials are common problems in commercial aluminum die casting operations. One approach for minimizing both of these issues is to place physical vapor deposition (PVD) coatings onto the surfaces of the die components. An alternate approach is the use of higher thermal conductivity die materials, such as tungsten-based alloys. While PVD coatings are becoming relatively widely used, there is little rigorous data to identify the best coating conditions to maximize life of the coatings. There is also little information on the life of alternate nonferrous die materials. This paper reports on a laboratory study that examined the effect of PVD coating conditions and alternate die materials on die component life. The test involves rotating pins fabricated from different die materials and PVD coated H13 tool steel in a crucible of molten aluminum alloy held at a temperature of 680±10 °C. The pins were periodically removed from the melt (typically every 1–2 h) to observe their condition. The effect of two aluminum alloy composition were evaluated, A380 and a binary Al–11%Si alloy. The results showing rates of dissolution of the pins are presented. Examination of failed pins showed that the molten aluminum did not appear to attack or dissolve the PVD coatings, but the coatings failed when the molten aluminum penetrated the coating though cracks, and dissolved the steel substrate, causing the cracked coating to flake off. Once the coatings were breached by the liquid aluminum, the samples quickly failed. A mechanism describing factors controlling chemical soldering of the aluminum to die casting dies is presented.
An accelerated method for testing die soldering has been developed. High intensity ultrasonic vibrations has been used to simulate the die casting conditions such as high pressure and high impingement speed of molten metal on the pin. Soldering tendency of steels and coated pins has been examined. The results indicate that in the low carbon steel/Al system, the onset of soldering is 60 times faster with ultrasonic vibration than that without ultrasonic vibration. In the H13/A380 system, the onset of soldering reaction is accelerated to 30-60 times. Coating significantly reduces the soldering tendency of the core pins.
A mechanism of soldering of an aluminum alloy die casting to a steel die is proposed. A soldering critical temperature is
postulated, at which iron begins to react with aluminum to form an aluminum-rich liquid phase and solid intermetallic compounds.
The liquid joins the die with the casting upon solidification. The critical temperature is determined by the elements in both
the casting alloy and the die material and is equal to the solidus temperature of the resulting alloy. The critical temperature
is used to predict the onset of die soldering, and the local liquid fraction is related to the soldering tendency. Experiments
have been carried out to validate the concept and to determine the critical temperature for die soldering in an iron-aluminum
system. Thermodynamic calculations are used to determine the critical temperature and soldering tendency for the cases of
pure aluminum and a 380 alloy in a steel mold. Factors affecting the soldering tendency are discussed, and methods for reducing
die soldering are suggested.
Die soldering has been a major cause for concern in the aluminium metal mould casting industry for the past few years. In recent times, this defect has posed a major concern because of the notable decrease in productivity and efficiency of casting operations. Due to the high affinity that aluminium has for iron, a vigorous physio-chemical reaction occurs at the die/molten metal interface when aluminium melt comes into direct contact with the ferrous die. This reaction results in the immediate formation of a series of iron-aluminium-silicon inter-metallic compounds over the die surface and eventually the cast metal sticks to this inter-metallic layer. The casting parameters, such as the temperature of the melt, the alloy chemistry and the die pre-heat play a significant role in causing soldering. In this study, the critical process parameters affecting soldering have been identified and studied. The effect of seven alloying elements in aluminium 300 series alloy, their interactions, cycle time and temperatures of melt and die have been quantified through various experiments. The experiments were performed in a laboratory environment on an apparatus designed to simulate the harsh casting conditions under which soldering occurs. All the results and conclusions have been verified and validated in several production facilities. Recommendations to mitigate soldering have been proposed based on our conclusions.
A study is conducted on soldering in the die casting industry. The interactions between the aluminum alloy and die steel substrates are also discussed. Coatings and surface treatments provide increased resistance against soldering and washout by providing a protective barrier between the die steel surface and the cast metal alloy.
This work provides a comprehensive understanding of the reactions at the ferrous die/molten metal interface in a metal mold
casting operation. The literature has shown that several important factors influence reactions at the ferrous die/molten aluminum
interface, including temperature of the melt, temperature of the die, alloy chemistry of the melt and die, die surface engineering,
topographical features, and coatings. This article discusses the effect of the more critical factors on soldering, based on
the authors’ investigations. Inaddition, based on a mechanistic understanding of the interface reactions between ferrous die
and molten aluminum, recommendations are given for specific processing issues to alleviate soldering during die casting of
aluminum alloys.
Die soldering is the result when molten aluminum sticks to the surface of the die material and remains there after the ejection
of the part; it results in considerable economic and production losses in the casting industry, and is a major quality detractor.
In order to alleviate or mitigate die soldering, one must have a thorough understanding of the mechanism by which the aluminum
sticks to the die material. A key question is whether the die soldering reaction is diffusion controlled or interface controlled.
A set of diffusion couple experiments between molten aluminum alloy and the ferrous die was carried out. The results of the
diffusion couple experiments showed that soldering is a diffusional process. When aluminum comes in contact with the ferrous
die material, the iron and the aluminum atoms diffuse into each other resulting in the formation of a series of intermetallic
phases over the die material. Initially iron and aluminum react with each other to form binary iron-aluminum intermetallic
phases. Subsequently, these phases react with the molten aluminum to further form ternary iron-aluminum-silicon intermetallic
phases. Iron and aluminum have a great affinity for each other and the root cause of die soldering is the high reaction kinetics,
which exists between iron and aluminum. Once the initial binary and ternary intermetallic phase layers are formed over the
die material, the aluminum sticks to the die due to the abnormally low thermal conductivity of the intermetallic phases, and
due to favorable interface energies between the intermetallic layers and aluminum. The experimental details, the results of
the interface reactions, and the analysis leading to the establishment of the mechanism giving rise to die soldering are reviewed
discussed.
The stability against reaction with aluminum of materials and coatings commonly used in aluminum die casting was investigated. The materials considered here were H13 tool steel and Anviloy® 1150, whereas the coatings were TiN and CrN. Special model, freestanding, multilayered thin film structures were used in this study, in association with complementary differential scanning calorimetry and X-ray diffraction. The nature of the reactions (endo or exothermic) and their onset temperatures up to 1273 K were determined. Based on of these results, some activation energies for the different reactions taking place between aluminum and die material or between aluminum and coatings could be established. Different intermetallic compounds were formed in these reactions, which were identified by post mortem X-ray diffraction analysis. Anviloy® 1150 showed superior stability as compared to H13 tool steel, whereas CrN was more inert than TiN coatings. CrN exhibited the best performance among all materials and coatings considered here, although its practical application relies also on adhesion of the CrN coating to the die bulk material. The results are discussed on the lights of two recent models for soldering in aluminum die casting.
Erosion of the die material during die filling has long been regarded as a possible damage mechanism of dies in high pressure die casting (HPDC) of aluminium alloys. Melt impingement and erosion have also been proposed to be an important step leading to die soldering. However, there is little information in the literature on the direct measurement of any kind of die erosion in HPDC. The present analysis, based on existing erosion theories, has shown that liquid impingement and solid particle erosion is not likely to occur in HPDC in the short-term while soldering does. There is a paucity of data indicating how cavitation erosion may occur in HPDC in the short-term. Pins were examined that were used as soldering targets in specially designed dies during soldering trails using a semi-industrial HPDC machine. Although these pins were subjected to severe melt impingement during the trails, very little erosion occurred before the formation of soldered layers.
The experiment of hot dip aluminizing had been carried out in order to study the interaction between die casting die and aluminum alloy as well as how Si affects the soldering tendency in die and aluminum alloy casting. The experimental results show that intermetallic alloy layer is formed when non-inoculation samples of die steel are dipped in A380 melt. However, no inactive diffusion layers appear when inoculation samples are dipped in A380 melt. The existence of Si decreases the activity coefficient of Al in the phase of Fe-Si-Al and prevents aluminum atoms moving from molten Al to the steel substrate. As a result, Si reduces the interaction between die steel and molten aluminum alloy and then effectively impedes the soldering tendency of aluminum die casting.
Light Metals The Minerals, Metals &
- Q Han
- E A Kenik
- S Viswanathan
- R D Peterson