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.

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.

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 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)

The purpose of the thesis work given is to gain a better understanding of the degating process in high-pressure die casting components, as well as the effectiveness of the thermo-mechanical vibration technique for detaching cast components from the gating system. In addition, to evaluate and establish the most appropriate degating procedure in order to reduce labor, material costs, and processing time.In recent days, many investigators have been looking at an automated technique that can help optimize and streamline the casting process. VOLVO CE is also exploring on ways to assess and establish the most acceptable degating process in order to optimize cost towards labor, material expense, and processing time. To begin with, VOLVO CE wants to develop the full Finite Element Method (FEM) based approach prior to implementationThis thesis consists of a substantial amount of numerical work, demonstrating the effectiveness of thermo-mechanical vibration technique for degating the casting high-pressure die casting component. The dynamic behavior of the component was studied in ANSYS WB where the impact of thermal loading has been taken into consideration.The component studied in this thesis is a transmission component (oil distributor) from a Volvo construction equipment, VOLVO group. It is cast in Aluminum alloy with the material composition AlSi13Fe. A oil distributor is a component which is bolted on the back side (place where electric motor is connected to the casing through shaft) of the transmission casing.

A global shift towards reducing carbon (CO2) emissions in the automotive industry while increasing fuel efficiency and range security has triggered the exploration of new processing routes and material alternatives for automotive components. To achieve such goals, manufacturing processes such as high vacuum high pressure die casting (HV-HPDC) have gained attention in recent years to fabricate cast Al alloys for structural automotive components. HV-HPDC allows for increased and more economical production as compared to other manufacturing methods due to the minimal steps involved in the process. Higher degrees of tolerance and precision can be upheld with HV-HPDC, ceasing the need for secondary operations to form the component into desired complex shapes. In this research, the effect of pre-solidified grains (PSG) and heightened metal residence time on the microstructure and mechanical properties were investigated in a new heat-treatable casting alloy, (Al-1.1wt%Fe-4.7wt%Zn-0.95wt%Mg)-0.07wt%Ti, also known as Nemalloy HE700 alloy, manufactured via HV-HPDC. Developed at McMaster University in conjunction with Nemak USA/CAN and CanmetMATERIALS, Nemalloy HE700 alloy is intended for structural automotive applications with its higher strength and increased light weighting capabilities. Nemalloy HE700 serves as a suitable candidate to replace existing Al-Si alloys such as Aural-5 (Al-8wt%Si-Mg-Mn), currently used in the market today. As-cast test plate castings adhering to two geometries: a 3-step plate geometry (nominal plate thicknesses of 3 mm, 2.5 mm, and 2.3 mm) and a singular plate (2.5 mm) with increasing shot delay intervals of 3 additional seconds to a total of 10 seconds from normal operating conditions (i.e., 1, 4, 7, and 10 seconds) were fabricated with the intention of increasing PSG content within the final cast components to study the underlying effects. Experimental efforts through metallography revealed that, much like traditional high pressure die cast (HPDC) components, PSG gravitated toward the centers of the castings in all operating conditions with heightened agglomerations and potential abnormal grain growth in higher delay samples. Moreover, distributions of PSG became more dispersed through the cross-sections as the delay time was increased. Size distributions of PSG adhered to a standard characteristic grain of 100 µm to sizes of 1000+ µm. Larger sizes of PSG grew substantially in equivalent circular diameter (ECD) and extent in higher delay interval samples. Affected area percentage as a result of an increase in PSG content uncovered higher degrees of porosity presenting themselves as shrinkage and gas porosities in the microstructure. A rise in gas porosity size and quantity was realized with higher delay intervals. Uniaxial mechanical testing of tensile specimens from both geometries indicated a directional relationship of PSG where samples were increasingly more brittle and demonstrated adverse mechanical properties when testing was performed parallel to the metal flow direction as opposed to when performed perpendicularly. Moreover, Nemalloy HE700 alloy exhibited a lower propensity of formation of PSG than Aural-5 in higher levels of shot delay times, primarily due to compositional and differing solidification behaviours of the two alloys. The research presented characterizes the nature of PSG formation in HV-HPDC Al alloys with increased metal residence time and the resultant adverse effects on performance. As efforts shift toward manufacturing structural Al components using HV-HPDC, a greater understanding of such effects will aid in alloy development, die mould design, and disseminate information on HV-HPDC to produce components of heightened quality. Additionally, the resultant findings aim to address gaps in current literature as automotive manufacturers transition from non-structural HPDC components to structural HV-HPDC products for commercial use. / Thesis / Master of Applied Science (MASc)

The AM60 Mg alloy has been used in the automotive industry to help achieve higher fuel efficiency. However, its products, mostly fabricated via high pressure die casting process, are inherently plagued with porosity issues. The presence of porosity impairs mechanical properties, especially fatigue properties, and thus affects the product reliability. We have therefore studied the effect of porosity on the fatigue behavior of samples drawn from a prototype AM60 shock tower by conducting strain-controlled fatigue test along with X-ray computed tomography (XCT). The 3D analysis of porosity by XCT showed discrepancies from 2D metallographic characterization. Fatigue testing results showed the machined surface is the preferential site for crack initiation to occur, on which pores are revealed after specimen extraction. A large scatter in fatigue life was observed as crack initiating at a large pore situated on the surface will result in a significantly shorter fatigue life. SEM fractography showed fracture surfaces are generally flat and full of randomly orientated serration patterns but without fatigue striations. The observations and measurements of porosity and fatigue cracks made by XCT were confirmed by SEM, supporting it as a reliable characterization tool for 3D objects and has value in assisting the failure analysis by SEM. Fatigue life was found to decrease with the increase of fatigue-crack-initiating pore size. The same trend was also found between the fatigue life and the volume fraction of porosity. The pore shape and pore orientation should be taken into account when determining the pore size as they can result in the difference in pore size between 2D and 3D measurement. / Thesis / Master of Applied Science (MASc) / The AM60 Mg alloy has been used in the automotive industry to help achieve higher fuel efficiency. However, its products, mostly fabricated via high pressure die casting process, are inherently plagued with porosity issues. The presence of porosity impairs mechanical properties, especially fatigue properties, and thus affects the product reliability. We have therefore studied the effect of porosity on the fatigue behavior of samples drawn from a prototype AM60 shock tower by conducting strain-controlled fatigue test along with X-ray computed tomography (XCT). The 3D analysis of porosity by XCT showed discrepancies from 2D metallographic characterization. Fatigue testing results showed the machined surface is the preferential site for crack initiation to occur, on which pores are revealed after specimen extraction. A large scatter in fatigue life was observed as crack initiating at a large pore situated on the surface will result in a significantly shorter fatigue life. SEM fractography showed fracture surfaces are generally flat and full of randomly orientated serration patterns but without fatigue striations. The observations and measurements of porosity and fatigue cracks made by XCT were confirmed by SEM, supporting it as a reliable characterization tool for 3D objects and has value in assisting the failure analysis by SEM. Fatigue life was found to decrease with the increase of fatigue-crack-initiating pore size. The same trend was also found between the fatigue life and the volume fraction of porosity. The pore shape and pore orientation should be taken into account when determining the pore size as they can result in the difference in pore size between 2D and 3D measurement.

High pressure die casting (HPDC) is both a cost-efficient and high throughput method for making near-net shape castings. 7xxx series aluminum alloys are excellent candidates for manufacturing structural components for significant light-weighting opportunities in the automotive industry. This project explores the development of a new 7xxx series aluminum alloy with iron additions to improve castability. The main objective of this project is to develop an optimized heat treatment process for the new Al-Zn-Mg-Fe alloy to achieve solute homogenization in the primary Al grains. The rationale behind adding iron as an alloying element was presented, as well as an analysis of the Al-Fe intermetallic phases to show their mitigating effects on hot tearing. A detailed analysis of the casting quality was carried out, including detailed microstructural analyses of defects and defect-free castings, correlating process parameters, shot profiles, uniaxial tensile properties, and fractography. Improvements on casting conditions and parameters were suggested. Solution heat treatments were carried out between 0.25 and 24 hours and quenched with forced air. Bulk hardness measurements were obtained following solution heat treatment to determine the arrest times for the precipitation reactions during natural aging. The uniaxial tensile properties of the alloy in the F- and T4-tempers were presented. Microstructural analyses of the alloy were carried out by optical and electron microscopy (SEM), including phase identification, phase fraction, average grain size, and distribution. A predictive model for the homogenization of the solutes in the Al matrix was developed using a one-dimensional diffusion model with spherical geometry, and a MATLAB code was developed to time for complete homogenization. Electron-dispersive X-ray spectroscopy (EDX) line scans were carried out on the F and T4 samples (0.25-2h) and the concentration profiles of Zn and Mg (the diffusing solutes) were extracted and analyzed. The models were verified and validated with experiment data. / Thesis / Master of Applied Science (MASc)