This is the key publication for professionals and students in the metallurgy and foundry field. Fully revised and expanded, Castings Second Edition covers the latest developments in the understanding ...of the role of the liquid metal in controlling the properties of cast materials, and indeed, of all metallic materials that have started in the cast form. Practising foundry engineers, designers, and students will find the revealing insights into the behaviour of castings essential in developing their inderstanding and practice. John Campbell OBE is a leading international figure in the castings industry, with over four decades of experience. He is the originator of the Cosworth Casting Process, the pre-eminent production process for automobile cylinder heads and blocks. He is also co-inventor of both the Baxi Casting Process (now owned by Alcoa) developed in the UK, and the newly emerging Alotech Casting Process in the USA. He is Professor of Casting Technology at the University of Birmingham, UK. * New edition of this internationally respected reference and textbook for engineers and students * Develops understanding of the concepts and practice of casting operations * Castings' is the key work on castings technology and process metallurgy, and an essential resource on contemporary developments and thinking on the new metallurgy of cast alloys * Revised and updated throughout, with new material on subjects including surface turbulence, the new theory of entrainment defects including folded film defects, plus the latest concepts of alloy theory
A novel method named low frequency electro-magnetic stirring assisted near-liquidus squeeze casting (LFEMS-NSC) was developed for preparing Mg-RE alloy castings. The grain refining effect in ...commercially pure Mg (CP-Mg), peritectic Mg-Zr alloy and eutectic Mg-Gd alloy were comparatively analyzed among conventional gravity cast, squeeze cast and LFEMS-NSC. The results showed that the LFEMS-NSC exhibited effective grain refining efficiency in CP-Mg and Mg-Gd alloys. With changing conventional gravity casting or squeeze casting to LFEMS-NSC, the grain morphologies of CP-Mg were transformed from coarse columnar into fine equiaxed grains. The average grain size of CP-Mg was refined from ~10 mm to ~232 µm, where the grain refinement efficiency was comparable to that of adding Mg-Zr master alloy. The application of LFEMS-NSC to Mg-Zr and Mg-Gd alloy systems also show considerable grain refining effect, and it show different effectiveness when the solute content varies. The grain refinement mechanism of LFEMS-NSC is mainly because of the enhanced survival rate of free chill crystals and enhanced heterogeneous nucleation rate through melt pre-treatment by LFEMS and applied pressures during solidification.
Porosity plays an important role in determining the ductility in magnesium alloy high pressure die castings. In this work, X-ray Tomography (XRT), fractographic analysis and Digital Image ...Correlation(DIC) have been implemented to understand the inter-relation between various pore characteristics, specifically porosity spatial distribution and morphology, and the ductility in thin-wall AM60 alloy high pressure die casting. The results show that a great amount of porosity was detected in the 20 studied samples. The pore size follows the three-parameter lognormal distribution. Among the detected porosity, small porosity (equivalent diameter ≤90 μm) is numerically dominant and the proportion in number reaches up to ~80%, which constitutes ~50% of the volume of porosity. In comparison, the large porosity (equivalent diameter >425 μm) accounts for a very low percent of the porosity population, namely ~1%, and only occupies ~5% of the volume of porosity. For through-thickness distribution of porosity, two defect bands were observed consisting of concentrated porosity. A great amount of pores randomly distributed pores in the skin and core, and some large pores (equivalent diameter >425 μm) are presented in the core. In addition, along tensile axis, heterogeneous porosity distribution is displayed in terms of local porosity and pore size. Tensile test coupled with DIC measurement has been conducted for the twenty samples with XRT data and the influences of various parameters of pore, including local porosity, size and position of pore, on the ductility have been analyzed. It can be seen that the local porosity in the fracture segment plays the primary role in determining the ductility, although the location and size of pore have effect on deformation heterogeneity and thereby affect the ductility. Therefore, the ductility can be considered as a function of the local porosity in the fracture segment. Moreover, though it's difficult to obtain the local porosity in the fracture segment prior to tensile test and the ductility can't be predicted based on it, there is a clear correlation between the elongation and the highest local porosity in the gauge, which can be got before tensile test, and thus ductility can be estimated accordingly.
•A simple and efficient DCC process to prepare semisolid slurry was developed.•The semisolid viscosity model of A356 alloy was fitted.•The microstructure of the DCC Rheo-HPDC alloy was greatly ...refined compared to its HPDC analog.•DCC Rheo-HPDC alloy showed better mechanical properties than the HPDC alloy.•The nucleation mechanism and growth law of primary grain in DCC were clarified.
A simple and efficient semisolid slurry preparation technique, called distributary-confluence channel (DCC), was developed to prepare high-quality semisolid slurries of aluminum and magnesium alloys. The DCC process was coupled with the use of a high pressure die-casting (HPDC) machine to successfully achieve near-net forming and implement production applications with rheological high pressure die-casting (Rheo-HPDC) for various Al and Mg alloy castings. The changes in the flow state and in the physical field of the melt during the slurry preparation via the DCC technique were investigated by numerical simulations. The nucleation mechanism and the growth law of the primary grain during the DCC process were discussed. The microstructures, porosities, and mechanical properties of the aluminum and magnesium alloys prepared via DCC Rheo-HPDC were studied. The results show that semisolid slurries containing a large amount of primary grains with an average size < 50 μm, a shape factor >0.8, and uniformly dispersed in the liquid matrix can be prepared via DCC. The simulation results indicate that the melt exhibits opposite velocity vectors on the upper part and on the lower part of the DCC. Moreover, it encounters and collides at the confluence to generate convection, which is beneficial to obtain uniform melt temperature, composition fields, nuclei exfoliation, and spherical growth. The random particle tracking simulation results show that the DCC process improves the composition field of the slurry. The DCC process facilitates the melt nucleation by using multi-channel chilling and increasing the nucleation area. The self-stirring generated during the flow of the melt produces a large amount of free nuclei inside the melt. There exist two main mechanisms behind the formation of the spherical primary grains. The one is the mechanism of explosive nucleation and spheroidal growth, the other is the dendrite arm necking, fusing, grain ripening, and rounding. Furthermore, by comparing identical alloy castings produced via traditional HPDC and other Rheo-HPDC processes, the DCC Rheo-HPDC castings present finer and rounder grains, a lower porosity, and more performant mechanical properties.
As an important manufacturing process for Mg-alloy components, high pressure die casting (HPDC) has attracted considerable attention. However, the application of magnesium alloy high pressure die ...castings is limited by variations in the mechanical properties, which can be ascribed to a heterogeneous distribution of microstructure. In this work, the through-thickness distribution of the microstructure features (i.e. grain size, β-phase and porosity) of HPDC AM60 alloy and their effects on the strain heterogeneity and the microhardness variation were carefully investigated. The results show that the HPDC AM60 alloy exhibited a gradient structured microstructure, i.e., two skin layers sandwiching a core layer. The skin was mainly comprised of fine grains (diameter ≤10 μm), whereas the core predominately consisted of externally solidified crystals (ESCs). Furthermore, the skin shows higher number and area fractions of β-Mg17Al12 particles. Heterogeneous through-thickness distribution of microhardness was observed in the as-cast sample, and the skin showed higher the microhardness than the core. β-Phase was the primary factor accounting for heterogeneous distribution of microhardness. In the as-cast sample, strain heterogeneity was measured at strain of 3% using digital image correlation (DIC) method. The strain in the skin regions was homogeneous, whereas significant strain heterogeneity was presented in the core. After T4 treatment, remarkable strain heterogeneity was still observed, indicating that β-phase did not have profound effect on deformation heterogeneity. Strain localized at the interdendritic regions of ESCs and the vicinity of grain boundaries in fine-grained regions, where porosity occurred. This illustrates that porosity was the primary factor inducing strain localization.
The manufacturing of extra-large thin-wall castings using high pressure die casting is one of the most significant challenges for structural applications requiring excellent ductility. The present ...study aims to understand the effect of process parameters on the castability, defect formation and mechanical properties of aluminium alloys in extra-large thin-wall castings with a maximum flow length of 1230 mm in the 2.8 mm thick channel. Numerical simulation and experimental verification were carried out to tailor the process parameters in high pressure die casting. It is found that the process parameters can significantly affect the castability and mechanical properties of as-cast components. For a complete casting, the yield strength is slightly increased but the elongation is significantly decreased at the locations further away from runners. A new concept of effective flow length (EFL) is proposed and used to assess the castability in extra-large thin-wall high pressure die castings. Under the optimum casting condition, the EFL can reach 525 mm, at which the ratio of EFL to wall thickness is 187 and the yield strength and elongation are greater than 120 MPa and 10%, respectively. Although the extra-large thin-wall castings can be geometrically filled under several conditions, the heterogeneity of mechanical properties is the most significant concern, in which the variation of elongation is overwhelmingly important for the structural applications requiring excellent ductility under as-cast conditions. Therefore, the criteria of casting quality should consider both geometrical soundness and the homogeneity of mechanical properties in the casting body.
•Insight into interaction between interfacial heat transfer and pressure transfer.•Direct experimental evidence of interfacial pressure and pressure transmission.•Effect of sensitivity to materials ...on pressure transfer, interfacial heat transfer.
The interfacial heat transfer and pressure transmission in squeeze casting was studied through experimental and numerical approaches, especially the sensitivity to cast materials was focused via a case study on an aluminum alloy, A356, and a magnesium alloy, GW103K. The interfacial heat transfer coefficient (IHTC) at the metal-die interface was determined by employing an inverse approach based on the temperature measured inside the die. The pressure at the metal-die interface was measured by using Kistler pressure transducer. The pressure transmission in the solidification process of squeeze casting was solved by using a numerical model based on ANSYS software. The experimental results showed that the peak value and the duration time of the pressure at the casting-die interface of the aluminum alloy were higher than those of the magnesium alloy. The peak value of the IHTC of the magnesium alloy was about half of that of the aluminum alloy and the IHTC of magnesium alloy decreased more rapidly to a lower level. The numerical simulation revealed the whole process of how the solidification and mechanical properties of the materials affected the pressure transmission and the interfacial heat transfer in the solidification process. The latent heat of the aluminum alloy was higher than that of the magnesium alloy thus leading to a longer solidification time in the aluminum alloy. On the other hand, the magnesium alloy has a higher deformation resistance than the aluminum alloy under same temperature and strain rate conditions. These are the major factors resulting in the differences in the interfacial heat transfer and pressure transmission. It was also showed that these factors resulted in a higher tendency to form shrinkage defects in the magnesium alloy castings, thus higher process pressure is required for magnesium alloy castings.
The water-soluble salt core material has been successfully used for manufacturing hollow aluminum and magnesium alloy castings. However, there is rare report about the water-soluble salt core being ...used for lower melting point and higher density hollow zinc alloy castings. In order to obtain a high-performance composite water-soluble salt core material (CWSSC) which is suitable for manufacturing hollow-structure zinc alloy castings via high pressure die casting process, the comparative study on performance and microstructure of the salt cores fabricated by gravity casting technology was investigated using KNO3 and KCl as the base salt material with the reinforcements of bauxite or glass-fiber powder. The results show that CWSSC strengthened by reinforcements possesses many advantages of good surface quality and water-solubility rate, high bending strength and impact toughness, low shrinkage and moisture-absorption rate, and CWSSC composed of KNO3-20 mol% KCl with 15 wt% bauxite powder and 15 wt% glass-fiber powder has the better comprehensive performance, whose surface roughness is 0.4758 μm, bending strength is 46.6 MPa, impact toughness is 21.72 kJ/m2, and water-solubility rate is 178.21 kg/(min·m2) in still water at 80 °C with relatively low shrinkage and 24 h moisture-absorption rate. The scanning electron microscope analysis shows that the strengthening-toughening mechanisms of CWSSC mainly include refinement of the grain and deflection of the crack caused by KCl dendritic crystal and the rigid enhanced powders. A practical casting test has been conducted to prove that the developed CWSSC can be used to manufacture hollow-structure zinc alloy castings.
Fig. 8 Schematic diagram of strengthening-toughening mechanisms: (a)KNC + BP and (b)KNC + GP. Display omitted
•A high-strength water-soluble composite KNO3-20 mol% KCl salt core material was successfully fabricated.•Bauxite and glass-fiber powder were added and acted as reinforcer.•The strengthening-toughening mechanisms of the salt core material was revealed.•A hollow-structure zinc alloy component was casting using the developed salt core material.
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