Aluminium alloys have been seen a dramatic increase in transport manufacturing in past two decades. This is primarily driven by the achievement of effective weight-savings, increased vehicle fuel efficiency and reduced CO2 emissions in transport. One of the significant progresses in most recent years has been in the application of aluminium-intensive car body structure, in which the manufacturing of thin wall castings with improved ductility is one of the critical issues. High pressure die casting (HPDC) is a fast and economical near-net shape manufacturing method to produce thin wall components. Therefore the application of HPDC process to make thin wall structural components for aluminium-intensive car body structure is one of the most challenges in recent development. However, the currently available die cast aluminium alloys are unable to fulfil this requirement because of the insufficient ductility, which is essential for joining castings with sheets and extruded parts. This has become critical in further development and extensive acceptance in car manufacturing industry. Generally, the mechanical properties of die castings are determined by alloy composition, defect levels and microstructure in the castings. In the present study, the significant achievement is the development of Al-Mg-Si-Mn alloy for HPDC process to provide improved ductility in die castings in order to satisfy the requirement of mechanical properties, in particular ductility for the application in automotive body structure. Starting from the thermodynamic analysis and CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) modelling of Al-Mg-Si system for solidification and phase formation, the alloy composition was optimised using international standard tensile samples to review the effect of various alloying elements on the mechanical properties. Another achievement is the understanding of the solidification and microstructural evolution, the relationship between the microstructure and mechanical properties, and the strengthening mechanisms in the developed alloy. The solidification behaviour in the shot sleeve and in the die cavity was examined for the formation of the primary α-Al phase, eutectic Al-Mg2Si phases in the alloy. The morphology, size and size distribution of the primary α-Al phase were characterised under different solidification conditions. The growth morphology of the primary α-Al phase formed in the shot sleeve and in the die cavity was analysed using the Mullins-Sekerka instability theory and the growth rate of eutectic Al-Mg2Si phases during solidification was calculated using Jackson-Hunt theory. Still another achievement is the study of the effect of Mn and Fe on the morphology, size and distribution of various Fe-rich compounds in the Al-Mg-Si alloy produced by HPDC process. The assessment was associated with the mechanical properties of yield strength, ultimate tensile strength and elongation with different Fe and Mn contents. CALPHAD modelling of multi-component Al-Mg-Si-Mn-Fe and Al-Mg-Si-Fe systems was studied to find out the effect of Fe impurity in the Al-Mg-Si alloy. The precise accumulation of iron during HPDC using fully recycled materials was examined to predict the maximum cycles to produce castings with required mechanical properties. The strengthening mechanism and the relationship between the microstructure and mechanical properties are explored in the alloy made by secondary materials. Furthermore, the effect of nickel on the microstructure and mechanical properties of the die-cast Al-Mg-Si-Mn alloy was also studied in association with the formation of Ni-rich intermetallics during solidification in the die-cast Al-Mg-Si-Mn alloy containing different Ni contents. The final achievement is the understanding of the repeatability of die castings made by the new alloy with industrial scale components. The tensile properties of standard samples that were obtained directly from HPDC process and made by the machined die castings at different locations were further assessed for the reproducibility of casting components made by the Al-Mg-Si-Mn alloy. The distributions of yield strength, ultimate tensile strength and elongation of the tensile samples were analysed by the average values with standard deviations and by the Weibull statistical model with three parameters. The correlations between the mechanical properties and the microstructural features, porosity levels and fracture morphology were investigated for the different types of samples. It was found that three-parameter Weibull analysis was capable of analysing the reproducibility of die cast components and the scattering of tensile properties was mainly due to the presence of porosity and non-uniform microstructure in the die-castings.

This diploma thesis deals with the technology of high pressure die casting and especially influences having effect on their final quality. The aim of this thesis is to design the measures to convert casting of the cylinder for chainsaw into the serial production. The thesis contains a description of the production of castings by technology of high pressure die casting, theoretical analysis of the factors with effects on their final quality and practical description of the conversion casting of cylinder for chainsaw into the serial production. The problem of converting to serial production has been solved by several samplings and final test series. Part of each sampling is analysis of defects and design of measures leading to elimination or at least minimization of such defects. On the basis of the production process has been successfully optimized and casting of the cylinder for chainsaw was successfully converted into the serial production. The results of this work also allowed for a smooth conversion into the serial production of another type of cylinder, manufactured by company MOTOR JIKOV.

Published Article / Global issues such as energy and climate changes have impacted on both the automotive and aerospace industries, forcing them to adopt measures to produce products that consume fewer combustibles and emit less carbon dioxide. Making vehicles lighter is one of the logical ways of reducing fuel consumption. The need for light components, able to fulfil technical and quality specifications, led to market growth for tooling that is able to mass produce parts using manufacturing processes such as high pressure die casting. Competitive pressures to reduce the lead time required for tooling-up has also increased dramatically. For this reason research into various methods, techniques and approaches to tool manufacture is being undertaken globally. This paper highlights the work undertaken at the CSIR on the issue of rapid die manufacturing through the application and evaluation of a rapid prototyping technique and coating technologies applied to die components of a high pressure casting die for the production of aluminium components. Criteria for determining suitability were developed against which the technique was evaluated that included time, cost and life-expectancy. Results of accelerated testing procedures to evaluate the die material produced by the rapid prototyping technique and surface coatings and treatments of die materials for their resistance to washout, erosion, heat checking and corrosion in a high pressure die casting environment, are presented. The outcomes of this research will be used for further development and application of specific techniques, design principles and criteria for this approach.

Within industrial product development processes there is an increasing demand towards reliable predictions of the material behavior, which aims to promote a property driven development that can reduce the lead times. The implementation of simulation based product development with integrated casting simulation may enable the design engineers to gain an early understanding of the products with relation to castability, and orient the subsequent design refinement so as to achieve the desired mechanical properties. This work investigates the suitability of three commercial casting simulation softwares –MAGMA 5.2, NovaFlow & Solid 4.7.5 (NFS) and Click2Cast 3.0 (C2C)–, with respect to the needs of design engineers, such as prediction of shrinkage porosity and mechanical properties with relation to the design. Simplified solidification simulations suitable for this stage were thus performed for three high pressure die cast components with different geometrical constraints. The comparability between the solidification and cooling behaviour predicted by the three softwares was studied, and showed that a reasonably good agreement between predicted solidification times by MAGMA and NFS could be obtained, albeit not between predictions by MAGMA and C2C. Predictions by the three softwares of the hot spot/porosity areas showed to have a good agreement. The calculation times by each software were compared, and MAGMA was seen to have the best performance, yielding significantly shorter times than NFS and C2C. The results obtained were also compared to experimental investigations of porosity, microstructural coarseness, and mechanical properties. There was a good agreement between the predicted hot spot areas –i.e. areas in the geometry that solidify last– and the findings of porosities in the actual castings, meaning that solidification simulations might be able to provide important information for the prediction of most of shrinkage related porosity locations that are related to the casting geometry. However, the lack of a detailed knowledge at the design stage of the casting process limits the possibilities to predict all porosities. The predicted microstructure and mechanical properties by MAGMA non-ferrous were seen to have a good agreement in trend with the experimental data, albeit the predicted values showed large differences in magnitude with the experimental data. Although, the MAGMA non-ferrous module was not developed for HPDC components, it was interesting to study if it could be applied in this context. However, the models seem to need adoption to the HPDC process and alloys. In conclusion, with a limited knowledge of the manufacturing parameters, simplified solidification simulations may still be able to provide reasonably reliable and useful information during early development stages in order to optimise the design of castings.

Numerical simulation of mold filling in low pressure die casting is considered in this study. The physical model includes modeling of free surface flow, heat transfer with phase change, surface tension, natural convection together with effect of trapped air in the mold. The governing equations are discretized by control volume finite difference method. The pressure field is computed by two-step projection method and the free surface is tracked by PLIC-VOF method. Water analog model is used for the validation purpose. Good agreement between numerical and experimental results is observed which supports the feasibility of the presented method.

The central goal of this research is to quantitatively characterize the relationships between processing, microstructure, and mechanical properties of important high-pressure die-cast (HPDC) Mg-alloys. For this purpose, a new digital image processing technique for automatic detection and segmentation of gas and shrinkage pores in the cast microstructure is developed and it is applied to quantitatively characterize the effects of HPDC process parameters on the size distribution and spatial arrangement of porosity. To get better insights into detailed geometry and distribution of porosity and other microstructural features, an efficient and unbiased montage based serial sectioning technique is applied for reconstruction of three-dimensional microstructures. The quantitative microstructural data have been correlated to the HPDC process parameters and the mechanical properties. The analysis has led to hypothesis of formation of new type of shrinkage porosity called, gas induced shrinkage porosity that has been substantiated via simple heat transfer simulations. The presence of inverse surface macrosegregation has been also shown for the first time in the HPDC Mg-alloys. An image analysis based technique has been proposed for simulations of realistic virtual microstructures that have realistic complex pore morphologies. These virtual microstructures can be implemented in the object oriented finite elements framework to model the variability in the fracture sensitive mechanical properties of the HPDC alloys.

Soldering results from the interfacial interactions between the die and the casting alloy during high pressure die casting and is one of the major die failure modes. To prevent this occurring, lubricant layers and surface coatings are used to act as a barrier between the die and the casting alloy. The microstructures of a series of soldered layers on H13 tool steel core pins were examined after conducting high pressure die casting experiments with a specially designed die using removable core pins and Al-11Si-3Cu casting alloy. This showed that first, a casting alloy build-up layer formed, and then intermetallic phases nucleated at the die steel interface and grew to cover the entire surface in subsequent casting cycles. The structures of intermetallic layers formed during immersion of H13 tool steel into an Al-11Si-3Cu casting alloy melt were studied by X-ray diffraction and energy dispersive spectroscopy (EDS). A thick composite layer away from the H13 steel substrate consisted of irregular intermetallic phases and solidified casting alloy. A thin intermetallic layer was present between the composite layer and an inner compact layer next to the steel substrate. The irregular intermetallic phase in the thick composite layer away from the H13 steel substrate was identified to have a body centre cubic (bcc) structure, abcc-( FeSiAlCrMnCu). The thin and continuous intermetallic layer between the composite layer and the inner compact layer was found to be structurally isomorphous with aH-Fe2SiAl8. The compositional differences observed between aH and abcc phases indicated that the latter consisted of a higher amount of chromium, manganese, copper, and a lower amount of iron. It was likely that the presence of chromium, manganese and copper in the H13 tool steel caused the transformation of aH®abcc. The inner compact layer next to the steel substrate was identified to be orthorhombic h-Fe2Al5 containing silicon and chromium. An examination of lubricants to prevent soldering in high pressure die casting in conjunction with Nissan Casting Australia Pty Ltd. found that soldering was reduced by using a suitable lubricant. The chemistry of the lubricant, spray parameters, and die surface temperature were important factors in producing a protective lubricant layer. It was found that lubricant containing polypropylene waxes prevented soldering significantly better than lubricant containing polyethylene waxes. It was also found that the lubricant containing polypropylene waxes had lower surface tension. An examination of the use of iron oxide layers to prevent soldering in high pressure die casting was performed. H13 tool steel was oxidised in air and produced porous iron oxide with a mixture of haematite (Fe2O3) and magnetite (Fe3O4). These porous iron oxides did not completely prevent the H13 steel from soldering in immersion tests as intermetallic cones formed at the surface of the steel. Commercial steam tempering of H13 steel produced more compact iron oxide layers with magnetite (Fe3O4) and haematite (Fe2O3) structures. It was found that these compact iron oxide layers offered better protection against soldering than the porous layers created in air. Pure iron oxidised in a CO2/H2 gas mixture at a ratio of 95:5 at 550°C produced structurally pure, compact magnetite (Fe3O4) layers. H13 steel oxidised in a CO2/H2 gas mixture at a ratio of 95:5 at 550°C produced compact iron oxide layers that showed only magnetite (Fe3O4) structure. The magnetite (Fe3O4) layer containing chromium, manganese, silicon and vanadium formed next to the H13 substrate was found to be a very adherent layer and protected H13 steel from soldering in high pressure die casting experiments with a specially designed die using removable core pins and Al-11Si-3Cu casting alloy. An examination of aluminium oxide layers to prevent soldering in high pressure die casting was performed. Incoloy MA956 containing 4.5 wt.% aluminium, oxidised in air at 1100°C, produced a single, compact, adherent oxide layer with a-alumina (Al2O3) structure, that prevented the formation of intermetallic phases between aluminium alloy and Incoloy MA956 during high pressure die casting. However, non-reactive casting alloy build-up formed on the oxide coatings, similarly to physical vapour deposition (PVD) and vanadium carbide coatings. It was found that the thickness of the non-reactive casting alloy build-up was reduced by decreasing the roughness of the oxide coatings by lightly grinding of the surface of the coatings. The industrial application of these findings are discussed and directions for further research are presented.

This thesis examines the influence of the degassing process on hydrogen contend and on the quality of part casted by high pressure casting technologies. The type of defects occurring in the casting is analyzed based on macrostructure and microstructure observations. For the overall assessment is used the statistical observation of the evolution trend of scrapping during the experiment. The results show that shortening of the degassing time may affect the incidence of porosity defect.

The project elaborated in scope of engineering studies branch 2307. The project is submitting design of production technology of car emblem. Different manufacturing technologies have been compared based on study of technical literature. Most suitable technologies have been chosen such as pressure die casting, especially aluminum alloys and plastic injection molding. Plastic part is metal plated afterwards in order to get desired metal look. Part of this project is injection molding tool design inclusive technical, technological and economic analysis.

The increasing global demand for a substantial lightweighting of automobiles to enable a reduction in the greenhouse gas (GHG) emissions and fuel consumption has led to the adaptation of the high strength Al wrought alloys such as the 2xxx and 7xxx series in near net-shaped manufacturing using the high pressure die casting (HPDC) process. However, the obstacle for this adaptation is the high susceptibility to hot tearing during the solidification of these alloys. A new structural Al alloy for high pressure die casting application was developed from the single-phase Al-Zn-Mg family; a high strength and ductile alloy that could be adapted to manufacturing automotive structural components using HPDC and help with a significant reduction in the overall curb-weight of an automobile and thereby increasing the vehicle fuel efficiency. The objective of this study was to enable a better understanding of the hot tearing phenomenon during solidification of the Al-3.8 wt%Zn-1 wt%Mg alloy, the effect of adding 1.2 wt% Fe to the alloy to improve the castability in HPDC process and the effect of adding Ti as a grain refiner of the primary Al phase during solidification of the alloy using Al-5 wt%Ti-1 wt%B master alloy. The constrained rod solidification (CRS) experiments were carried out to measure transient stress, transient strain, and transient temperature during solidification of the alloy. Improvements to the CRS experiments were also developed to obtain a repeatability of the acquired data. The computerized Tomography (CT) imaging was used to visually characterize the hot tearing. Hypothesis on the factors promoting the hot tearing tendencies in single-phase alloys solidified using net-shaped casting processes has been presented with evidence-based on transient stress-strain and thermal data curves obtained during the solidification experiments. / Thesis / Master of Applied Science (MASc)