冷冻铸造A356铝合金微观组织分析

基于数字化无模冷冻铸造精密成形技术实现了冷冻砂型的快速成形,对其浇注A356高温铝合金获得冷冻铸造平板试件。采用电子探针显微分析技术对冷冻铸造和树脂砂型铸造铸件微量元素的分布进行了表征,同时对冷冻铸造和树脂砂型铸造铸件断裂形貌进行了分析。结果表明,冷冻铸造Si元素在铝基体相中的溶解度较树脂砂型铸造显著提高,冷冻铸造较树脂砂型铸造试件中Mg元素分布均匀,树脂砂型铸造试件中出现较多的Mg元素成分偏析区;冷冻铸造试件断裂方式为韧性和脆性的混合断裂模式,树脂砂型铸造试件的断裂形貌为解理台阶破坏形貌和长方状的撕裂结构形貌,合金偏向于脆性断裂。      

Development of the manufacture of billets based on high-strength aluminum alloys

When pressure is applied upon casting as a factor of external impact on melt, the problems related mainly to filling of molds are solved; however, some casting defects cannot be avoided. The experimental results demonstrate that complete compensation of shrinkage under pressure can be achieved by compressing of casting by 8–10% prior to beginning of solidification and by 2–3% during the transition of a metal from the liquid to the solid state. It is mentioned that the procedure based on compressing a liquid metal can be efficiently applied for manufacture of high-strength aluminum alloy castings. The selection of engineering parameters is substantiated. Examples of castings made of V95 alloy according to the developed procedure are given. In addition, the article discusses the problems related to designing of engineering and special-purpose equipment, software, and control automation.     

大型复杂薄壁Ti-6Al-4V合金熔模精密铸造工艺研究

根据复杂薄壁铸件的熔模铸造理论,对Ti-6Al-4V合金滑轨铸件结构及难点进行了全面的研究分析,针对型壳的制造、合金的熔炼和浇注以及铸件的热等静压三个方面开展了相关工艺研究。结果表明:采用氧化钇耐火材料和三醋酸锆粘结剂进行面层造型,料浆涂挂性好,有较好的润湿性和良好的工艺性能;采用真空自耗凝壳炉熔炼合金以及离心浇注,可保证钛合金熔液的质量和充填性能;采用热等静压工艺处理铸件,可提高铸件的质量和性能。最终确定熔模精密铸造最佳工艺参数,并据此生产出了合格的铸件。     

Production of Steel Castings in Cylindrical Molds

The continuous casting of steel is simulated by means of Sn–Pb alloy on two models of the mold. One of the models, which has been patented, has a closed loop for two-phase coolant circulation. The following characteristics are compared: the cooling of the two castings; the temperature of the models’ cylindrical walls; the thickness of the crust formed; the structure of the castings; and their surface quality. The results are used in simulation of the thermal processes in a model with the continuous supply of an increasing heat flux and the correction of the processes for steel casting.     

提高含铅铜合金半连铸圆锭质量的方法

通过对含铅铜合金半连续铸造工艺的研究，提出了半连续铸造的基本原理，分析探讨了影响半连续铸锭质量的主要因素，并提出了改进措施，效果理想。     

Influence of casting technique and hot isostatic pressing on the fatigue of an Al-7Si-Mg alloy

The influence of the casting filling technique and hot isostatic pressing (hipping) on the fatigue-life distribution of Al-7Si-Mg alloy castings has been studied. To vary the number density and size of oxide-film defects in the castings, test bars were cast using bottom-gated filling systems with and without filtration. Some unfiltered castings were subjected to a hipping treatment of 100 MPa at 500 °C for 6 hours. Test pieces were machined from the castings and were fatigue tested in pull-pull sinusoidal loading, at maximum stresses of 150 and 240 MPa under a stress ratio of R=+0.1. The fatigue lives at any probability of failure and Weibull statistical parameters of the filtered castings were higher than those of the unfiltered and nonhipped castings, illustrating the importance of the casting technique. However, the unfiltered but hipped castings exhibited higher performance. It is proposed that the significant improvement in fatigue life after hipping is due to the deactivation of entrained double oxide-film defects as fatigue-crack initiators.     

钛精铸高尔夫球头的现状及发展趋势

综述了钛精铸高尔夫球头和普通石墨型高尔夫球头的发展动态，以及国外普通钛及钛合金铸件的现状和发展趋势。对国内主要精铸钛合金高尔夫球头商家及其特点，市场现状进行了分析预测。     

Investigation of surface roughness of aluminium solid mould investment castings

Solid investment moulds are used for precious or non-precious metals and alloys castings, the most common application areas are dental prosthesis and jewellery fabrications. Investment casting is known for high dimensional accuracy and smooth surface finish. Casting of ultra-thin sections and small complex parts require vacuum assisted or centrifugal filling. In this study, solid investment casting of aluminium has been tried and surface quality of the castings was investigated. Specially designed steppedwedge surface roughness specimens were produced with A413 aluminium alloy casting into gypsum bonded solid moulds. Casting operations were carried out in two ways; the first only with gravitational force and the second with vacuum assistance. Surface roughness of as cast specimens were measured, effects of section thickness, vacuum assistance and location of the pattern on the wax tree were determined.     

Microstructure and Corrosion Characterization of Squeeze Cast AM50 Magnesium Alloys

Squeeze casting of magnesium alloys potentially can be used in lightweight chassis components such as control arms and knuckles. This study documents the microstructural analysis and corrosion behavior of AM50 alloys squeeze cast at different pressures between 40 and 120 MPa and compares them with high-pressure die cast (HPDC) AM50 alloy castings and an AM50 squeeze cast prototype control arm. Although the corrosion rates of the squeeze cast samples are slightly higher than those observed for the HPDC AM50 alloy, the former does produce virtually porosity-free castings that are required for structural applications like control arms and wheels. This outcome is extremely encouraging as it provides an opportunity for additional alloy and process development by squeeze casting that has remained relatively unexplored for magnesium alloys compared with aluminum. Among the microstructural parameters analyzed, it seems that the β-phase interfacial area, indicating a greater degree of β network, leads to a lower corrosion rate. Weight loss was the better method for determining corrosion behavior in these alloys that contain a large fraction of second phase, which can cause perturbations to an overall uniform surface corrosion behavior.     

Influence of temperatures of melt overheating and pouring on the quality of aluminum alloy lost foam castings

Lost foam casting (LFC) is currently one of the most efficient and promising methods of fabricating high-quality thin-wall castings possessing specified dimensional accuracy, required surface roughness, and other properties. This technology is widely used in the production of aluminum alloy products. To minimize costs in the fabrication of wares and to fabricate high-quality castings, it is reasonable to use an increased amount of secondary materials in the charge, herewith paying attention to the melt overheating temperature and holding time. The results of studying the temperature modes of smelting pouring aluminum alloys in the LFC are presented. The most efficient modes in manufacturing conditions under consideration which provide the best quality characteristics of leak-tight castings by dimensional accuracy and surface roughness were as follows: the melt overheating temperature is 880–890°C and the melt pouring temperature into the casting mold is 820–830°C. The influence of various variants of temperature parameters of smelting and pouring the melt of the AK7 composition during the LFC on the content of nonmetallic inclusions in the cast state is investigated. It is revealed that the minimal γ-Al₂O₃ content in the final alloy is provided by a melt overheating temperature of up to 880–890 or 940–950°C and a melt pouring temperature into the casting mold of 820–830°C.     

Study of casting and mechanical properties of the AK8L alloy in castings fabricated using printed molds made of the ZCAST mixture

Due to the lack of information about the casting and mechanical properties of the AK8l alloy during casting into printed molds made of the ZCast mixture, studies on determining its fluidity, shrinkage, and mechanical properties, as well as on increasing the relative elongation of this alloy by means of optimizing its chemical composition, have been performed. It is shown that the method of casting into a printed mold made of the ZCast mixture can be effectively used in obtaining castings for critical applications from the AK8l alloy, especially at the stage of preparing cast products for production.     

Mathematical modeling of porosity formation in solidification

Shrinkage porosity and gas porosity occur simultaneously and at the same location when conditions are such that both may exist in a solidifying casting. Porosity formation in a solidifying alloy is described numerically, including the possible evolution of dissolved gases. The calculated amount and size of the porosity formed in Al-4.5 pct Cu plate castings compares favorably with measured values. The calculated distribution of porosity in sand cast Al-4.5 pct Cu plates of 1.5 cm thickness matches experimental measurements. The decrease of the hydrogen content by strong degassing and the increase of mold chilling power are recommended to produce sound aluminum alloy castings. The calculated results for steel plate castings are in agreement with the experimental work of Pellini. The present modeling has clarified the basis of empirical rules for soundness and suggests that the simultaneous occurrence of shrinkage and gas evolution is an essential mechanism in the formation of porosity defects.     

Influence of melting conditions of aluminum alloys on the properties and quality of castings obtained by lost foam casting

The development of modern foundry production is characterized by a constant increase in requirements for the quality of fabricated casting and rational use of material resources, which determines the search for new technical and process solutions, making it possible to acquire the required properties of cast wares along with resource saving. Herewith, the question of revelation and investigation into the regularities of the influence of thermal-temporal parameters of smelting and pouring of aluminum alloys into the casting mold during the lost foam casting on tightness and mechanical and qualitative characteristics of thin-wall castings remain poorly known and complex for implementation, especially allowing for the performance of resourcesaving measures. In this publication, the influence of process parameters of smelting on the strength, tightness, and content of nonmetallic inclusions in castings of the gas-analyzer case made of AK7 alloy during the lost foam casting is considered. The data set acquired based on the experimental investigations has been subjected to statistical processing. The use of statistic models makes it possible to acquire the results of the influence of the holding time and content of secondary materials in the charge on strength and tightness of mentioned castings. The results of an investigation into the influence of holding the AK7 melt at the overheating temperature of 880–890°С on the content of nonmetallic inclusions in castings show that it can be regulated varying the holding time. This procedure decreases the melt microinhomogeneity and provides the acquisition of numerous castings with a minimal content of nonmetallic inclusions.     

Experimental Investigation for the Hardness of Castings Produced by Using ZCast Process

ZCast direct metal casting process is one of the important techniques of additive manufacturing which is used for printing the shell moulds for casting of non-ferrous materials. In the present work, an attempt was made to experimentally investigate the effect of different control factors on the hardness of castings produced using this ZCast process. Taguchi’s design of experimental method was used to perform the experimentation. Aluminium, brass and copper alloy castings were obtained in three different sizes using 3D printed shell moulds of different wall thicknesses. The obtained results were analysed using signal-to-noise ratio and analysis-of-variance. Analysis showed that the hardness depended on the casting material and 3D printed shell mould wall thickness. Cooling curve analysis and microstructure analysis of casting obtained with mould of different thickness were also performed. Paper revealed the potential suitability of copper, brass and aluminium for producing casting using ZCast process. The present research could provide valuable data of hardness of rapid castings of different material and might confirm the effectiveness and applicability of ZCast process in foundry industry.     

Influence of Grain Refinement on Slurry Formation and Surface Segregation in Semi-solid Al-7Si-0.3Mg Castings

This study aims to evaluate the effect of grain refinement on slurry formation and surface segregation in semi-solid castings produced by the Rheometal™ process. The effect of two grain refiners, Al-8B and Al-5Ti-1B, on the slurry α-Al grain size, shape factor and solid fraction was evaluated. The results suggest that the addition of a grain refiner can affect the solid fraction obtained in the Rheometal^TM process and, consequently, reduce the solute content near the casting surface. Grain refiner addition resulted in a larger fraction of α-Al grains ≤ 60 µm for the refined alloys compared with the unrefined alloy. Additionally, the growth of α-Al slurry globules was greater for the unrefined alloy compared with the refined alloy during solidification in the die-cavity. A more homogeneous and finer microstructure was observed near the surface in the grain-refined castings compared with the unrefined castings. Evidence of significant liquid penetration was identified in some α-Al globules, indicating that disintegration of α-Al globules may occur during the Rheometal™ casting process.

     

Two Parameter Weibull Analysis of the Effect of Chemical Modification of Al–7si–0.3 Mg Alloy on Ultimate Tensile Strength

Double oxide films are one of the primary reasons that cause casting defects particularly in dross forming alloys. It is not clear whether the beneficial effect of modification melt treatment in Al–Si alloys is entirely due to the transformation of acicular eutectic Si to fibrous morphology. In the present work, the effect of chemical modification of Al–7Si–0.3 Mg alloy on casting reliability was assessed from the Weibull analysis of tensile strengths. The findings show that the modification melt treatment of Al–Si alloy has a beneficial effect as indicated by consistently higher Weibull modulus. Apart from transformation in the silicon morphology, modifiers decrease the scatter present as a result of various defects, particularly the bi-film, resulting in higher reliability for the modified castings.     

Use of plastic bar molded casting in the modification of variably expanding investment to compensate for casting shrinkage of nickel-chromium alloy

Trial plastic bar molded castings were compared for accuracy with cast crowns by means of a nickel-chromium alloy, which was used to establish the liquid density of variably expanding investments. The plastic bars were invested to evaluate the change of expansion rate in a wide range of six liquid densities from 0% to 100%, and the distances between the sections were measured before and after casting. Wax crowns were cast to obtain a more detailed relation around 0% expansion at seven liquid densities, and the gaps between the base of the die and the margin of the crown were measured before and after casting. The expansion rates of both castings were calculated and thus were proportional to the liquid density; both regression curves indicated high correlation coefficients. As a result of the statistics of the Student's t-test, the difference between the two methods was not significant. The trial plastic bar was useful in establishing the variably expanding investment for precise casting of artificial crowns.     

Microstructural and Tribological Characteristics of Al–10Cu–Fe alloy Produced by Vertical Centrifugal Casting process

In this study, an attempt has been made to produce Al–10Cu–Fe alloy by vertical centrifugal casting at speeds ranging from 800 to 2850 rpm. The microstructural features, mechanical and wear properties have been investigated. The microstructure of Al–10Cu–Fe alloy consists of equiaxed grain morphology of the primary α-phase with eutectic phases in the interdendritic regions. It has been observed that there is a variation in the grain size from the inner surface of the casting to its outer surface. The speed also has a strong influence on the grain size and subsequent mechanical properties of the alloy. The wear properties of the alloy have been evaluated at a constant sliding velocity of 1 m/s for a range of applied load and sliding distance. The variations in the wear behavior are attributed to the size and solidification morphology of the castings.     

Development of new feeding-distance rules using casting simulation: Part II. The new rules

Based on a correlation between the Niyama criterion and radiographic casting soundness developed in Part I of this work, a new set of riser feeding-distance rules is developed for low-alloy steel castings. These rules are designed to produce radiographically sound castings at 2 pct sensitivity. Rules are provided for the riser-zone length, end-zone length, end-effect feeding distance and lateral feeding distance for top risers, and feeding distance for side risers. In addition, the relationships between the end-zone length, riser-zone length, and the various feeding distances are discussed. Multipliers are given to apply these rules with end chills and drag chills, and multipliers are also provided to tailor these rules to different steel alloy compositions, sand mold materials, and pouring superheats. In comparison with previously published rules, the present rules are shown to provide longer feeding distances in most casting situations.