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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)

Thermal management in die casting involves controlling heat transfer between the molten metal and the die surface. A cooling system integrated into the die facilitates the rate of heat extraction at the die-molten metal interface. However, non-uniformity of die surface temperature can occur due to the variation in the amount of heat that needs to be extracted from the casting leading to low casting quality. These variations are usually caused by differences in the casted part thicknesses. Therefore, effective die thermal management (DTM) is crucial, as it influences the quality of the final casted component in terms of its final shape, microstructure, and mechanical properties. The main objective of the present research work is to develop a new DTM algorithm that addresses the shortcomings of existing DTM techniques. Initially, the aim is to estimate the rate of heat transfer at the die-metal interface in order to identify locations experiencing the highest heat exposures (i.e., hot spots). Subsequently, a heat balance is used to determine the necessary adjustments to the cooling water flow rates fed into each cooling channel to mange the hot spot and to achieve a more uniform temperature distribution along the die interface. Ultimately, the goal is to develop a die thermal management model (DTMM) that can be used to vary the water flow rate in each cooling channel based on the rate of heat extraction required based on the casted part geometry. The DTMM has developed using inverse heat transfer techniques and validated using data obtained for a set of virtual and real experiments. The data of the virtual experiments were generated using numerical simulations carried out using the computer software Flow3D Cast. The numerical and real experiments were carried out for a gravity-fed die casting process of pure Aluminum in a wedge-shaped mold, which was intentionally selected to reproduce some non-uniformity in the thickness of the casted part. Such non-uniformity was used to assess the effectiveness of the developed DTMM. Simulation results obtained using Flow-3D have been compared with the experimental results in order to assess the predictive capabilities of Flow3D. The DTMM demonstrated a significant reduction in the maximum temperature difference along the die surface, achieving up to 92 % improvement. As a result, the die interface experienced a more uniform heat distribution when variable cooling flow rates were applied, in contrast to constant cooling flow rates. / Thesis / Doctor of Engineering (DEng) / A die thermal management model has been developed to predict the heat transfer rate at the die-metal interface and to determine the required changes to the rate of heat extraction by the cooling channels at different die sections to minimize temperature non-uniformity of the produced casting. The effectiveness of the developed thermal management model has been evaluated using both numerical and experimental data obtained for a wedge-shaped casting. The used casting shape was intended to mimic significant variations of the casting cross sections in order to create significant temperature non-uniformity along the die surface. The results obtained using the developed thermal management model showed the model’s effectiveness in reducing the temperature non-uniformity along the die-metal interface, hence within the produced casting.

Diploma thesis deals with optimization of technological process casting a die cast, which is part of vacuum pump. The die cast is made from alloy AlSi9Cu3(Fe) in foundry KOVOLIT, a. s. There is a problem with inner defects at this cast. Solution of this thesis is to suggest suitable actions to minimize of incidence the defects in the cast. According to analysis of the defects in the cast these defects were classified as combination of shrinkages and gas holes. According to analysis causes of the defects are high temperature of die mould and closed air in die mould. As a result suitable actions were suggested – a change of the die mould tempering and a design adjustment of the cast. In case of implementing a new die mould in the manufacture a new gating system was designed. Suitability of the new gating system was assessed according to simulation of filling die cavity.

Published Article / This paper is based on tests performed on die component specimens manufactured by EOS-DMLS (direct metal laser sintering) and LENS (laser engineered net shape) RP (rapid prototyping) technology platforms, as well as manufactured specimens machined out of preferred standard hot work steel DIN 1.2344. These specimens resemble typical components used in metal high pressure die casting tool sets. The specimens were subjected to a programme of cyclic immersion in molten aluminium alloy and cooling in water-based die release medium. The heat checking and soldering phenomena were analyzed through periodic inspections, monitoring crack formation and evidence of surface washout. At the end of the thermal tests, mechanical strength and hardness tests were performed to assess toughness and core resistance variations in relation to the initial conditions. Finally metallographic investigations were performed through optical microscopy on all the specimens considered. The outcomes of this research will be presented and used by the CSIR for further development and application of the assessed EOS-DMLS and LENS rapid prototyping technologies in rapid die manufacturing techniques and die design principles, including time and economic feasibility criteria to be applied when considering rapid die manufacture.

Additive manufacturing has a great potential to benefit die manufacture by shortening the lead time considerably and lifting the limitations on design complexity imposed by conventional manufacturing techniques. However, AM has its own requirements that together are known as Design for Additive Manufacturing and account for the process limitations. One of the significant requirements is mass efficiency of the design (it should be as light as possible). If it’s not fulfilled, AM won’t be able to make an economical solution or substitution despite having outstanding benefits. The present investigation has been framed with respect to such concern. This investigation attempts to draw a comparison between the performance of two design variants. Additionally, it has been tried to study the employed method, document implementation of the approach, and identify the challenges in accordance with design for additive manufacturing. Simulation of thermal stresses generated in die inserts for a given component during one cycle of high pressure die casting is presented. Initial design of the die inserts is subjected to redesign with the intention of mass reduction by incorporating honeycomb structure. Temperature evolution and resultant thermal stresses are analyzed for redesign and compared to those of original design. Simulation of high pressure die casting was carried out in MagmaSoft to obtain temperature history of die inserts and cast. Implicit nonlinear elastic fully coupled thermal displacement model was setup in Abaqus in which Magma results were used as input for stress calculation. Results show that according to our specific design, HPDC die with thin walled feature cannot withstand the thermal and mechanical load. However, with iterative analysis and proper topology optimization, a lightweight complex geometry die can be successfully made.

In recent years there has been a growing demand to produce lightweight high pressure die cast (HPDC) parts for structural applications to decrease vehicle mass and to reduce manufacturing costs. Due to the coupled rapid heat flow and complex flow/deformation that occur in the process, the formation of microstructure and defects in HPDC are still not fully understood. Developing a better understanding of microstructure formation is essential to enable advances in die design and process optimisation, as well as alloy development, to improve the quality and productivity of HPDC components. Therefore, this thesis aims to enhance this understanding by conducting detailed microstructural analysis of samples produced in controlled HPDC experiments. In the first series of experiments, various microstructure characterisation techniques were used to study salient HPDC microstructural features. The microstructures of castings were characterised at different length scales, from the scale of the casting to the scale of the eutectic interlamellar spacing. The results show that the salient as-cast microstructural features, e.g. externally solidified crystals (ESCs), defect bands, surface layer, grain size distribution, porosity and hot tears were similar for both two HPDC-specific Al alloys used, AlSi4MgMn and AlMg5Si2Mn. The formation of these features has been explained by considering the influence of flow and solidification during each stage of the HPDC process. The formation of defect bands is further studied by investigating the ratio between band thickness ( ) and average grain size in the band ( ). Suitable methods for measuring w and dsb in HPDC have been developed. The w/dsb relationship of defect bands has been investigated in HPDC specimens from a range of alloys, casting geometries and band locations within castings. The bands were measured to be 7-18 mean grains wide. This is substantial evidence that defect bands form due to strain localisation in partially solidified alloys during cold-chamber and hot-chamber HPDC. At the end of solidification, dilatant shear bands contain a higher eutectic volume fraction and/or porosity content than adjacent material. In the cross-section of the AM50 Mg alloy, the centrally-located band contains a much higher volume fraction of concentrated porosity than the second-outermost band and insignificant porosity was found in the outermost band. The level of porosity in bands was attributed to the relative difficulty of feeding shrinkage for each band location. As the feeding of material during the intensification stage is important for the reduction of porosity, the influence of intensification pressure (IP) and gate thickness on the transport of material through the gate during the latter stages of HPDC were investigated. Microstructural characterisation of the gate region indicated a marked change in feeding mechanism with increasing IP and gate size. Castings produced with a high IP and/or thick gate contained a relatively low fraction of total porosity and shear band-like features existed through the gate, suggesting that semi-solid strain localisation in the gate is involved in feeding during the pressure intensification stage. When a low IP is combined with a thin gate, no shear band was observed in the gate and feeding was less effective, resulting in a higher level of porosity in the HPDC component. As equiaxed primary crystals are subjected to intense shear during HPDC, their agglomeration and bending behaviour were investigated in the last series of experiment. Samples produced by near-static cooling, HPDC and Thixomoulding®, where the solidifying crystals experience different levels of mechanical stresses, were characterised. The electron backscatter diffraction (EBSD) technique was used to acquire grain misorientation data which is linked to the crystal agglomeration and bending behaviour during solidification. The number fraction of low-energy grain boundaries in HPDC and Thixomoulded samples was substantially higher than in ‘statically cooled’ samples. This is attributed to the much higher shear stresses and pressure applied on the solidifying alloy in HPDC and Thixomoulding, which promote crystal collisions and agglomeration. In-grain misorientations were found to be significant only in branched dendritic crystals which were subjected to significant shear stresses. This is related to the increased bending moment acting on long protruding dendrite arms compared to more compact crystal morphologies.

Aluminum alloys are having more attention due to their high specific stiffness and processing advantages. 7075 aluminum alloy is a wrought composition aluminum alloy in the Al-Zn-Mg-Cu series. Due to the significant addition of these alloying elements, 7075 has higher strength compared to all other aluminum alloys and effective precipitation hardenability characteristic. On the other hand, aluminum alloys have some drawbacks, which hinder the widespread application of them. One of the most commonly encountered defects in aluminum alloys is the hydrogen porosity. Additionally, in case of 7075, another problem is the lack of fluidity. Magnesium addition is thought to be effective in compensating this deficiency. Accordingly, in this study, die cast 7075 aluminum alloy samples with hydrogen porosity and additional magnesium content were investigated. The aim was to determine the relationship between hydrogen content and hydrogen porosity, and the effects of hydrogen porosity, additional magnesium and T6 heat treatment on ultimate tensile and flexural strength properties of pressure die cast 7075 aluminum alloy. 7075 aluminum alloy returns were supplied from a local pressure die casting company. After spectral analysis, pressure die casting was conducted at two stages. In the first stage, 7075 aluminum alloy with an increase in magnesium concentration was melted and secondly 7075 aluminum alloy was cast directly without any alloying addition. While making those castings, hydrogen content was measured continuously before each casting operation. As a final operation T6 heat treatment is carried out for certain samples. Finally, in order to accomplish our aim, mechanical and microstructural examination tests were conducted.

The aim of the present study was to investigate the effects of different levels of Saffil alumina fiber addition, magnesium content in aluminum alloy matrix and casting temperature on the mechanical behavior, microstructure and physical properties of short fiber reinforced aluminum matrix composites. The main alloying element silicon was kept constant at 10 wt%. Magnesium contents were selected as 0.3 wt% and 1 wt%. Saffil alumina fiber preforms varied from 10 to 30 vol%. The casting temperatures were fixed at 750 &deg / C and 800 &deg / C. Micro porosity was present at the fiber-fiber interactions. Closed porosity of the composites increased when fiber vol% increased, however, variation in casting temperature and magnesium content in matrix did not have influence on porosity. Hardness of the composites was enhanced with increasing fiber vol%, magnesium content in matrix and decreasing casting temperature. Alignment of fibers within the composite had an influence on hardness / when fibers were aligned perpendicular to the surface, composites exhibited higher hardness. The highest hardness values obtained from surfaces parallel and vertical to fiber orientation were 155.6 Brinell hardness and 180.2 Brinell hardness for AlSi10Mg1 matrix 30 vol% alumina fiber reinforced composite cast at 800 &deg / C and at 750 &deg / C, respectively. 30 vol% Saffil alumina fiber reinforced AlSi10Mg0.3 matrix composite cast at 750 &deg / C showed the highest flexural strength which is 548 MPa. Critical fiber content was found as 20 vol% for all composites.

Before beginning the experimental work of this study, a magnesium high pressure die casting facility is set up to manufacture magnesium cast parts for defence industry. In this thesis two components are cold chamber high pressure die casted using magnesium alloy AZ91 as raw material, and one component was manufactured using both aluminium alloy A.413, and magnesium alloy AZ91. Mechanical properties of high pressure die casting parts depend on various parameters such as, thickness of the cast part, position of the cast part in the cavity, molten metal temperature, die temperature, piston speeds, and injection pressure. The aim of this study is to investigate the effects of section thickness of the cast part, position of the cast part in the die cavity, piston speeds, and molten metal temperature on mechanical properties of magnesium die cast parts. Tensile properties of products from Al A.413 and Mg AZ91 alloys are also compared. Casting analysis software is used to simulate filling and temperature evolution of three different casting components. Piston speeds are first calculated from equations in the literature and then verified by using the software. Specimens for microstructural investigation, and mechanical tests are machined directly from the mass produced parts. Optical microscopy, and scanning electron microscopy investigations are carried out for grain size and porosity determination. Tensile tests are conducted for yield strength, ultimate tensile strength, and % elongation values. The results of casting analysis software simulations, grains size investigations, porosity investigations, and tensile tests are correlated to each other. Optimum piston speeds, optimum molten metal temperatures are observed, effect of grain size and porosity concentrations on the effect of mechanical properties are compared. Weight of cast parts produced from Mg AZ91 are 35 % lower than that of Al A.413 parts. However, ultimate tensile strength of the cast parts produced from Mg AZ91 are found to be similar to the aluminium parts.