Accelerated method for testing soldering tendency of core pins

Abstract

An accelerated method for testing die soldering has been proposed and tested. High intensity ultrasonic vibration has been applied through a core pin to molten aluminium in order to simulate service conditions under die casting. Such conditions include high pressure and high impingement speed of molten metal on the pin. Soldering tendency of H-13 steel pins with or without commercial coatings was tested using this accelerated method. The experimental results indicate that soldering occurs within a few minutes of testing using this new method, much faster than that using the conventional methods. The coating failure mechanism identified in this new method is identical to that observed in the conventional methods, suggesting that the new method is suitable for testing soldering tendency of core pins under die casting conditions.     

Mechanism and preventive measures for die soldering during Al casting in a ferrous mold

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.     

A study of erosion in die casting dies by a multiple pin accelerated erosion test

An accelerated erosion test was developed to evaluate the erosion resistance of die materials and coatings for die casting application. An acceleration in wear was achieved by selecting pyramid-shaped core pins, hypereutectic aluminum silicon casting alloy, high melt temperatures and high gate velocities. Multiple pin design was selected to enable multiple test sites for comparative evaluation. Apilot run was conducted on a 300 ton commercial die casting machine at various sites (pins) to verify the thermal and flow similarities. Subsequently, campaigns were run on two different 300 ton commercial die casting machines to evaluate H13 die material and different coatings for erosive resistance. Coatings and surface treatments evaluated included surface micropeening, titanium nitride, boron carbide, vanadium carbide, and metallic coatings—tungsten, molybdenum, and platinum. Recent campaigns with different melt temperatures have indicated a possible link between soldering phenomena and erosive wear. This paper presents the details of the test set up and the results of the pilot and evaluation tests.     

Mechanism of die soldering during aluminum die casting

Soldering is a unique casting defect associated with die casting or metal mold casting of aluminum alloys. It occurs when molten aluminum sticks or solders the surface of the die steel and remains there after the ejection of the casting, causing a surface defect and dimensional inaccuracy of the castings and increased machine downtime. Soldering occurs easily when a bare die steel mold is used for die casting of aluminum alloys. When molten aluminum comes in contact with the die steel at a temperature higher than a critical temperature, the iron and aluminum atoms diffuse into each other, forming a series of intermetallic phases and a liquid aluminum-rich fcc phase. This liquid phase exists between intermetallic phases. On cooling, the liquid fcc phase solidifi es on the intermetallic phases and grows into the casting, resulting in soldering. The critical temperature is the eutectic temperature near the aluminum corner of the phase diagram. If the die is protected using a nonreactive ceramic coating, soldering starts at locations where local coating failure occurs. Molten aluminum comes into contact with die steel through the coating failure locations and eats into the steel matrix, forming small pits. As these small pits grow, the coating is gradually removed and soldering becomes more severe. Details of die soldering step on a bare steel die and on a coated die material are discussed.     

铝合金压铸模的焊合熔损现象及其预防措施

铝合金压铸模承受炽热压铸合金与模具润滑剂的激冷激热反复作用，极易在表面发生失效。本文探讨了在铝合金压铸模中常见的焊合及熔损现象，比较了生成的金属间化合物的不同之处，提出了使用蒸汽氧化、离子渗氮、PVD／CVD表面镀覆和渗硼等表面处理手段以及使用合适的模具润滑剂来预防模具表面的焊合和熔损。     

Investigation of a black oxide layer on the surface of pressure-diecasting dies

Detailed experiments have been carried out to study the effectiveness of two methods of generating a black oxide layer on a pressure-diecasting die in order to prevent soldering of molten aluminium. Three types of steel surface were examined: bare, black oxidised with oil and black oxidised using an acidic anti-solder grease.

As a result of experiments involving the pressure- diecasting of aluminium alloys, it was determined that the black oxidised surface obtained with the acidic anti-solder grease increased the yield of an insert by three times compared to a similar insert oxidised with oil, and by six times when compared with a bare steel insert.

This effect was confirmed in laboratory tests. The strength of the interface between aluminium alloy and a steel surface oxidised with an acidic anti-solder grease was six times lower than that of the interface between the aluminium alloy and bare steel. The oxide layer obtained with an acidic anti-solder grease is, therefore, seen to provide effective protection from soldering. This fact was also confirmed by a special laboratory test designed to determine the tendency of various aluminium alloys to solder to a die surface.

The treated surfaces of the die cavity were examined by X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy. It was found that the blue-black oxide layer was twice as deep when oxidised using an acidic anti-solder grease than when oxidised in oil.     

镁合金铸造成形过程宏观／微观模拟

通过研究镁合金压铸过程中界面热,采用热传导反算法确定压铸过程的界面换热系数,研究镁合金压铸过程中工艺参数及凝固过程对铸件界面换热系数的影响规律,建立镁合金压铸过程界面换热边界条件的处理模型,以实现镁合金压铸过程中凝固过程的准确预测。通过实验研究镁合金压铸过程中凝固组织,建立了镁合金压铸过程中形核模型。采用CA方法,建立了镁合金枝晶生长模型,以实现镁合金凝固组织的预测。采用相场方法研究了镁合金枝晶生长形貌。     

Effects of Gd Addition on the Microstructure and Tensile Properties of Mg-4Al-5RE Alloy Produced by Three Different Casting Methods

This work deals with the effect of 0.67 wt％ Gd addition on the microstructure and tensile properties of Mg-4Al-5RE (where RE represents LaCe mischmetal) alloy produced by sand casting (SC),permanent mold casting (PMC),and high-pressure die casting (HPDC).The results show that Gd addition could refine the grains,but its efficiency decreases by increasing the cooling rate due to the shifting from SC to PMC and finally to the HPDC method.Meanwhile,the acicular Al11RE3 phase is modified into the short-rod or granular-like shape under the three casting conditions.Such refined and modified micro-structures are due to the Al2(Gd,RE) phases,which act as the nucleation sites in both the α-Mg matrix and Al11RE3 phase.Also,the weakening grain refinement effect in the increased cooling rates can be attributed to the narrow constitutional undercooling zone.After Gd addition,the 0.2％ proof strength of the SC and PMC alloys increases by about 16.9％ and 12.7％,respectively,while in the HPDC alloy,it decreases by about 5.9％.The main factor in the strength increment of the SC and PMC alloys is the grain boundary strengthening due to grain refinement which is proved by modeling the related mechanisms,whereas weak secondary phases and grain boundary strengthening mechanisms in the HPDC alloy lead to strength reduction.After Gd addition,the elongation to failure of the SC,PMC,and HPDC alloys is significantly enhanced by about 34.8％,20.2％,and 12.3％,respectively,due to the crack resistance nature of the modified short-rod/granular Al11(RE,Gd)3 phase compared to the acicular one.     

The effect of casting temperature on the properties of squeeze cast aluminium and zinc alloys

Gravity casting and squeeze casting were carried out on an aluminium alloy with 13.5% silicon and a zinc alloy with 4.6% aluminium with different temperatures, 660, 690 and 720 °C for the former and 440, 460 and 480 °C for the latter. A top-loading crucible furnace was used to melt the alloys. The die-preheat temperatures used were 200–220 °C for the aluminium alloy and 150–165 °C for the zinc alloy. A K-type thermocouples with digital indicator were used to measure the die surface temperature and the molten metal temperature; while a 25 t hydraulic press with a die-set containing a steel mould was used to perform the squeeze casting with a pressure of 62 MPa. Tensile, impact and density tests were carried out on the specimens. It was found that casting temperature had an effect on the mechanical properties of both gravity cast and squeeze cast aluminium and zinc alloys. The best temperatures to gravity cast the aluminium alloy and the zinc alloy were 720 and 460 °C, respectively. For the squeeze casting of the aluminium alloy, the best temperature to use was either 690 or 660 °C; the former would give a better property at the top of the casting while the latter, at the bottom of the casting. However, for the squeeze casting of the zinc alloy, the best temperature was again 460 °C.     

硅对压铸模与铝合金相互作用的影响

为了研究压铸模与铝合金的相互作用,探讨Ｓｉ对压铸模与铝铸件焊合倾向性的影响,进行了热浸铝试验。试验结果表明,模具钢在纯铝熔体中热浸时,主要形成Ｆｅ２Ａｌ５相层和针片状的ＦｅＡｌ３相,Ｆｅ２Ａｌ５相是反应扩散的主导相。模具钢在Ａ３８０合金中热浸时,主要形成ＦｅＳｉＡｌ３和Ｆｅ２Ａｌ５两种相层。由于Ｓｉ降低了Ａｌ在ＦｅＳｉＡｌ３相层中的活度,减少了从铝熔体向Ｆｅ２Ａｌ５相供应的铝原子数,从而抑制了Ｆｅ２Ａｌ５相的快速生长。因而,Ｓｉ减弱了铝合金熔体与模具钢间的相互作用,从而降低压铸合金的焊合倾向性。热浸温度降低,Ｓｉ对Ｆｅ２Ａｌ５相层生长的抑制作用减弱。     

硅对压铸模与铝合金相互作用的影响

为了研究压铸模与铝合金的相互作用 ,探讨Si对压铸模与铝铸件焊合倾向性的影响 ,进行了热浸铝试验。试验结果表明 ,模具钢在纯铝熔体中热浸时 ,主要形成Fe2 Al5相层和针片状的FeAl3 相 ,Fe2 Al5相是反应扩散的主导相。模具钢在A3 80合金中热浸时 ,主要形成FeSiAl3 和Fe2 Al5两种相层。由于Si降低了Al在FeSiAl3 相层中的活度 ,减少了从铝熔体向Fe2 Al5相供应的铝原子数 ,从而抑制了Fe2 Al5相的快速生长。因而 ,Si减弱了铝合金熔体与模具钢间的相互作用 ,从而降低压铸合金的焊合倾向性。热浸温度降低 ,Si对Fe2 Al5相层生长的抑制作用减弱     

Modeling of high temperature- and diffusion-controlled die soldering in aluminum high pressure die casting

Soldering of cast alloys to the dies has been a continuing source of die surface damage in the aluminum die-casting industry. To reduce the repair and maintenance costs, an approach to modeling the damage and predicting the die lifetime is required. The aim of the present study is the estimation of the die lifetime based on a quantitative analysis of die soldering in the framework of the numerical simulations of the die-casting process.Full 3D simulations of the process, including the filling, solidification, and the die cooling, are carried out using the casting simulation software MAGMAsoft. The resulting transient temperature fields on the die surface and in the casting are then post-processed to estimate the die soldering.The present work deals only with the metallurgical/chemical kind of soldering which occurs at high temperatures and involves formation and growth of intermetallic layers. The die-soldering model combines two approaches available in literature, describing the two aspects of die soldering: the growth of the intermetallic layer, and the thermal and metallurgical conditions in the layer that lead to the die soldering. The theoretical model is then extended with the treatment of the intermetallic layer growth controlled by the idealized effective diffusivity and with the treatment of solder strength dependent on the temperature and liquid fraction within the layer. The solder strength locally on the die surface is calculated as a function of the number of die-casting cycles. This also provides the estimation of the die lifetime defined as the number of cycles until the critical solder strength level is reached.Proper validation of the model is required, and the model parameters (the critical solder strength value, among others) need to be calibrated by measurements and data from the die-casting industry.As an example, the model is applied to several cases of high pressure die casting (HPDC) where A380 alloy parts are cast in the H13 steel die. The predicted locations of the higher strength of soldering appear in the “hot spot” areas of the die surface in agreement with the reports in literature. The influence of several casting process parameters such as cooling/spraying efficiency and other parameters that control the thermal history of the die and the casting is in agreement with the expected behavior.     

Development of cermet coatings by kinetic spray technology for the application of die-soldering and erosion resistance

Soldering and erosion of casting moulds and their components are one of the most prominent and persistent problems occurring in the die-casting industry. In this study, MoB- and Co-based cermets and alloy, respectively, were deposited on bond coated hard substrates (SKD61) using kinetic spray coating technique. Coating of hard powder materials on hard substrate using kinetic spray technique has also been considered a difficult phenomenon. Microstructural and mechanical characterization of the coatings was carried out by SEM, XRD, micro-hardness, bond strength and wear resistance tests. The results showed that Co-based alloy displayed the highest deposition efficiency along with microstructural properties. However, MoB/NiCr demonstrated the highest mechanical properties. The coatings were tested for soldering resistance by immersion of coated SKD61 cylinders in molten aluminium alloy (ADC-12) bath. MoB/NiCr displayed superior soldering resistance among the coatings. Among the candidate coatings, MoB/NiCr is considered as the one with the highest durability in a die-casting operation.     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Microstructure and mechanical properties of melt-conditioned high-pressure die-cast Mg-Al-Ca alloy

A new shape casting process, melt-conditioned high-pressure die-casting （MC-HPDC） was developed. In this process, liquid metal was conditioned under intensively forced convection provided by melt conditioning with advanced shear technology （MCAST） unit before being transferred to a conventional cold chamber high-pressure die-casting （HPDC） machine for shape casting. The effect of melt conditioning was investigated, which was carried out both above and below the liquidus of the alloy, on the microstructure and properties of a Mg-Al-Ca alloy （AZ91D＋2%Ca （mass fraction）, named as AZX912）. The results show that many coarse externally-solidified crystals （ESCs） can be observed in the centre of conventional HPDC samples, and hot tearing occurs at the inter-dendritic region because of the lack of feeding. With the melting conditioning, the MC-HPDC samples not only have considerably refined size of ESCs but also have significantly reduced cast defects, thus provide superior mechanical properties to conventional HPDC castings. The solidification behaviour of the alloy under different processing routes was also discussed.     

压铸模与铝铸件焊合区的特征及形成机理

模具焊合区的表面上 ,存在着一定数量的显微孔洞、显微凹陷及裂纹等表面缺陷 ,大大增加了模具与铸件间的真实接触面积 ,焊合区的截面主要由焊合的铝合金、过渡层、氮化层及钢基体组成。对模具与铸件不同的焊合模式及形成机理进行了分析 ,将焊合分为物理化学焊合、机械焊合和混合焊合 ,并分析了压铸生产中焊合的形成及扩展过程     

压铸模与铝铸件焊合区的特征及形成机理

模具焊合区的表面上,存在着一定数量的显微孔洞、显微凹陷及裂纹等表面缺陷,大大增加了模具与铸件间的真实接触面积,焊合区的截面主要由焊合的铝合金、过渡层、氮化层及钢基体组成。对模具与铸件不同的焊合模式及形成机理进行了分析,将焊合分为物理化学焊合、机械焊合和混合焊合,并分析了压铸生产中焊合的形成及扩展过程。     

On the Steel–Aluminum Hybrid Casting by Sand Casting

Hybrid casting is a well-known technology to join steel inserts and aluminum. In order to achieve a high-performance material-based joining between steel and aluminum, a new PVD Al-Si-(Fe) coating, which consists of two sub-layers, has been successfully developed for high-pressure die casting. This coating system has been investigated further in this work for the sand casting process. By extending the sand casting process to the plaster casting process with preheating possibilities for the coated steel inserts, a material-based connection between steel and aluminum with a tensile shear strength of 7.7 MPa could be created. The ductility of this connection is decreased comparing with the connection manufactured by die casting. SEM and EDS analysis and diffusion experiments show that the difference of mechanical properties between plaster and die casting is caused by the extensive diffusion and the corresponding layer growth at plaster casting. The edge separation in plaster casting is a result of the edge stresses due to the different thermal expansion of steel and aluminum which can be suppressed at high-pressure die casting. To improve the joining properties at sand casting, it is necessary to control the layer diffusion by adding other alloy elements such as Mn into the Al-Si-(Fe) coating layer.     

Soldering mechanisms in materials and coatings for aluminum die casting

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.     

超硬纳微米 PVD 涂层技术在刀具领域的应用及研究进展

介绍了物理气相沉积(PVD)技术的原理、特点和真空蒸镀、溅射镀和离子镀之间的优缺点,从二元涂层、多元涂层、多层涂层和纳米多层复合涂层等4种类别上介绍了PVD涂层技术在切削刀具上的广泛应用。在查阅和整理大量文献资料的基础上,也结合笔者多年从事PVD技术的研究与应用心得,从提高切削刀具的寿命这一重要角度出发,阐述了国内外超硬纳微米PVD涂层技术在切削刀具应用领域的研究进展,并对多元涂层、多层涂层及涂层的纳米化也进行了较为详细地论述。切削刀具表面采用物理气相沉积涂层技术能使刀具获得优异的综合性能,从而显著提高切削刀具的使用寿命,降低生产成本,大幅提高机械加工效率。最后展望了物理气相沉积涂层技术未来将在超硬切削(包括模具钢、淬硬钢等硬度超过HRC55以上的铣削加工)、难加工材料切削(包括高温合金、钛合金、不锈钢等)、石墨和碳纤维等复合材料加工和有色金属的高速切削加工(包括铝合金、铜合金、镍等)的广泛应用。