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)

In this work, the Bauschinger effect is shown to be intimately tied not only to plasticity but to damage as well. The plasticity-damage effect on the Bauschinger effect is demonstrated by employing different definitions (Bauschinger Stress Parameter, Bauschinger Effect Parameter, the Ratio of Forward-to-Reverse Yield, and the Ratio of Kinematic-to-Isotropic Hardening) for two differently processed aluminum alloys (rolled and cast) in which specimens were tested to different prestrain levels under tension and compression. Damage progression from second phase particles and inclusions that were generally equiaxed for the cast A356-T6 aluminum alloy and elongated for the rolled 7075 aluminum alloy was quantified from interrupted experiments. Observations showed that the Bauschinger effect had larger values for compression prestrains when compared to tension. The Bauschinger effect was also found to be a function of damage to particles/inclusions, dislocation/particle interaction, the work hardening rate, and the Bauschinger effect definition.

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Industry 4.0 will pave the way to a new age of advanced manufacturing. Additive manufacturing (AM) is one of the leading sectors of the upcoming industrial revolution. The key advantage of AM is its ability to generate lightweight, robust, and complex shapes. AM can also customize the microstructure and mechanical properties of the components according to the selected technique and process parameters. AM of metals using selective laser melting (SLM) could significantly impact a variety of critical applications. SLM is the most common technique of processing high strength Aluminum alloys. SLM of these alloys promises to enhance the performance of lightweight critical components used in various aerospace and automotive applications such as metallic optics and optomechanical components. However, the surface and inside defects of the as-built parts present an obstacle to product quality requirements. Consequently, the post-processing of SLM produced Al alloy parts is an essential step for homogenizing their microstructure and reducing as-built defects. In the current research, various studies assess the optimal process mapping for high-quality SLM parts and the post-processing treatment of Al alloy parts. Ultra-precision machining with single point diamond turning or diamond micro fly-milling is also investigated for the as-built and post-processed Al parts to satisfy the optical mirror’s surface finish requirements. The influence of the SLM process parameters on the quality of the AlSi10Mg and Al6061 alloy parts is investigated. A design of experiment (DOE) is used to analyze relative density, porosity, surface roughness, dimensional accuracy, and mechanical properties according to the interaction effect between SLM process parameters. The microstructure of both materials was also characterized. A developed process map shows the range of energy densities and SLM process parameters for each material needed to achieve optimum quality of the as-built parts. This comprehensive study also strives to reduce the amount of post-processing needed. Thermal post-processing of AlSi10Mg parts is evaluated, using recycled powder, with the aim of improving the microstructure homogeneity of the as-built parts. This work is essential for the cost-effective additive manufacturing (AM) of metal optics and optomechanical systems. To achieve this goal, a full characterization of fresh and recycled powder was performed, in addition to a microstructure assessment of the as-built fabricated samples. Annealing, solution heat treatment (SHT) and T6 heat treatment (T6 HT) were applied under different processing conditions. The results demonstrated an improvement in microstructure homogeneity after thermal post-processing under specific conditions of SHT and T6 HT. A micro-hardness map was developed to help in the selection of optimal post-processing parameters for the part’s design requirements. A study is also presented, which aims to improve the surface characteristics of the as-built AlSi10Mg parts using shot peening (SP). Different SP intensities were applied to various surface textures of the as-built samples. The SP results showed a significant improvement in the as-built surface topography and a higher value of effective depth using 22.9A intensity and Gp165 glass beads. The area near the shot-peened surface showed a significant microstructure refinement up to a specific depth, due to the dynamic precipitation of nanoscale Si particles. Surface hardening and high compressive residual stresses were generated due to severe plastic deformation. Friction stir processing (FSP) was studied as a localized treatment on a large surface area of the as-built and hot isostatic pressed (HIPed) AlSi10Mg parts using multiple FSP tool passes. The influence of FSP on the microstructure, hardness, and residual stresses of parts was investigated. FSP transforms the microstructure of parts into an equiaxed grain structure. A consistent microstructure homogenization was achieved over the processed surface after applying a high ratio of tool pass overlap of ≥60%. A map of microstructure and hardness was prepared to assist in the selection of the optimal FSP parameters for attaining the required quality of the final processed parts. Micromachining to the mirror surface was performed using diamond micro fly-milling and single point diamond turning techniques, and the effect of the material properties on surface roughness after machining was investigated. The machining parameters were also tuned to meet IR mirror optical requirements. A novel mirror structure is developed using the design for additive manufacturing concept additive (DFAM). This design achieved weight reduction of 50% as compared to the typical mirror structure. Moreover, the developed design offers an improvement of the mirror cooling performance due to the embedded cooling channels directed to the mirror surface. A novel mirror structure is developed using the design for additive manufacturing concept additive (DFAM). This design achieved weight reduction of 50% as compared to the typical mirror structure. Moreover, the developed design offers an improvement of the mirror cooling performance due to the embedded cooling channels directed to the mirror surface. / Thesis / Doctor of Philosophy (PhD)

The design of any mechanical components requires an understanding of the general statical, dynamical and environmental conditions where the components will be operating to give a satisfactory results in terms of performance and endurance. The premature failure of any components is undesirable and potentially catastrophic, therefore predictions on performances and endurances of components to proceed with repair or substitution is vital to the stability of the structure where the component is inserted. The capability of a component of withstanding fatigue loading conditions during service is called fatigue life and the designed predictions can be conservative or non conservative. Improvements to a strain based approach to fatigue were obtained in this study, studying the effects of mean stresses on fatigue life and investigating cyclic mean stress relaxation of two aluminum alloys, 7075-T6511 and 7249-T76511, used in structural aircraft applications. The two aluminum alloys were tested and their fatigue behavior characterized. The project, entirely funded by NAVAIR, Naval Air Systems Command, and jointly coordinated with TDA, Technical Data Analysis Inc., was aimed to obtain fatigue data for both aluminum alloys, with particular interest in 7249 alloy because of its enhanced corrosion resistance, and to give guidelines for improving the performances of FAMS, Fatigue Analysis of Metallic Structures, a life prediction software from the point of view of both mean stress effects and mean stress relaxation. The sensitivity of engineering materials to mean stresses is of high relevance in a strain based fatigue approach. The performance of the most common models used to calculate mean stress correction factors was studied for the two aluminum alloys 7075 and 7249 to give guidelines in the use of those for life predictions. Not only mean stresses have a high influence on fatigue life, but they are also subjected to transient cyclic behaviors. The following study considered both an empirical approach and a plasticity theory approach to simulate and include these transient effects in life calculations. Results will give valid directions to a successful modification of FAMS like any other life calculation software to include in the picture transient phenomena. / Ph. D.

This thesis presents a comprehensive investigation into the feasibility and optimization of self-piercing riveting (SPR) for joining high-ductility die-cast aluminum alloy Nemalloy HE700 in F temper (as-cast) condition to dissimilar sheet materials, namely wrought aluminum alloy 6082-T6 and dual-phase steel DP600. The study demonstrates successful SPR joining of HE700 to these materials, with optimized process parameters and joint quality meeting automotive industry standards. Systematic experimental studies were conducted to investigate the effects of key SPR process parameters, including die geometry, ring groove depth, rivet hardness, and length, on joint quality and performance. Microstructural characterization revealed distinct patterns of grain flow and localized hardening in HE700 around the rivet and die features, providing insights into its deformation characteristics. Finite element simulations, incorporating advanced material models such as Johnson-Cook plasticity and failure for AA6082 and DP600, and Voce hardening with Gurson-Tvergaard-Needleman void damage model for HE700, were developed and extensively validated against experimental results. The simulations accurately predicted potential failure sites in HE700, aligning with experimental observations of crack initiation. Numerical parametric studies demonstrated the intricate effects of process parameters and material properties on the stress and strain distributions, material flow, and damage accumulation during SPR. The research contributes to the growing body of knowledge on advanced joining techniques for dissimilar materials, supporting vehicle lightweighting efforts. It establishes a comprehensive methodology integrating experiments, microstructural characterization, and simulations for studying and optimizing SPR processes for low ductility casting alloys, serving as a blueprint for future research and industrial implementation. The findings demonstrate the viability and potential of SPR technology for integrating high-ductility die-cast aluminum alloy HE700 into lightweight automotive body structures, paving the way for its wider industrial adoption. / Thesis / Master of Applied Science (MASc) / This research explores the potential of using a novel high-ductility aluminum alloy, Nemalloy HE700, in self-piercing riveting (SPR) - a modern joining technique for automotive manufacturing. The study aims to optimize the SPR process for joining HE700 to other commonly used automotive materials, such as aluminum alloys and high-strength steels, without compromising joint quality. By conducting practical experiments and computer simulations, the research identifies the best process parameters, such as rivet design and die shape, that result in strong, reliable joints meeting automotive industry standards. The findings demonstrate the successful use of HE700 in SPR, offering a promising solution for creating lighter, more fuel-efficient vehicles. This work contributes to the development of advanced joining technologies for sustainable transportation, making vehicles more environmentally friendly while maintaining high performance and safety standards.