Thesis (M.S.)--University of Idaho.

In the automotive industry, Al-Si alloy is widely used for manufacturing of various engine parts. Machinability of die-cast Al-12Si alloy is challenging due to severe abrasion and adhesion wear of the tools. Form tapping is a common method for generating internal threads in engine blocks. It is usually a finishing process on a production line. An unexpected tap failure may lead to significant scrap and high rework costs. The objective of this research was to investigate the wear mechanisms of high-speed steel form taps when machining Al-12Si alloy. This research involved replicating the same process conditions as the industry partner to determine a feasible solution without changing the tap geometry or process parameters. A critical region of wear on the crest was identified where the aluminum adhesion was acute. Intense abrasion wear occurred on the crest and flanks due to hard silicon precipitates. In this study, two methods were proposed for measuring linear and volumetric wear on the chamfered threads. The second and third chamfered threads experienced the most significant wear on the tap. To improve wear-resistance of the form tap, PVD surface coatings were deposited on it. The preliminary tests of 12 surface coatings showed coating-delamination mostly on the critical region. A progressive wear study of the TiAlN coating showed an improvement in tap performance over the ZrN coating currently used. By the 4320th hole, the volumetric wear of the TiAlN coated tap was reduced by nearly 200% and 50% when compared against the uncoated and ZrN coated taps, respectively. / Thesis / Master of Applied Science (MASc)

For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system. The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features. The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components. / Ett sätt att nå målen med minskade koldioxidutsläpp inom industrin är att producera lättare komponenter. Aluminium-kisel (Al-Si) gjutna legeringar är därför ett bra alternativ då dessa legeringar har ett bra förhållande mellan hållfasthet och vikt, goda korrosionsegenskaper, utmärkt gjutbarhet och är ett återvinningsbart material. En av de största utmaningarna för att producera högpresterande komponenter för kritiska applikationer är variationerna i egenskaper inom dessa komponenter. Orsaken till att inte gjutna Al-Si legeringar andvänds i dessa applikationer är förståelsen av defekter och mikrostruktuella faser påverkar de mekaniska egenskaperna negativt. Koppar (Cu) tillsätts i Al-Si legeringar för att öka de mekaniska egenskaperna vilket ofta nyttjas inom bilindustrin. Hot isostatic pressing (HIP) prosessen är en annan möjlighet att förbättra de mekaniska egenskaperna genom att reducera porositeter i materialet. Studien syftar till att undersöka de mekaniska egenskaperna och sprickinitiering och spricktillväxt i en gjuten legering av Al-7Si-Mg med utmattningstestning i svepelektronmikroskop (SEM) i kombination med electron backscatter diffraction, digital image correlation och focused ion beam (FIB). Mängden Cu i Al-Si legeringen påverkade de statiska mekaniska egenskaperna genom att öka sträckgränsen och brottgränsen. Tillsats av Cu upp till 1.5 vikt.% påverkar inte spricktillväxten märkbart. Däremot förändras beteendet markant vid tillsatser av Cu på mer än 3.0 vikt.% som resulterade i en markant reducering i duktilitet. I det värmebehandlade materialet påverkades de mekaniska egenskaperna av Al-matrisen och mängden intermetalliska faser. Avståndet mellan Cu faserna och Si faserna används för att beskriva spricktillväxten i Al-Si legeringarna. Detta tillsammans med tredimensionell tomografi visade att legeringen med 3.2 vikt.% Cu hade en ökad mängd sprickor i området framför den avancerande sprickan, vilket inte den Cu fria legeringen visade. Al-Si legeringen som utsattes för HIP-processen och värmebehandlingen visade att materialets mikrostruktur i gjutet tillstånd påverkade resultatet. HIP processen slöt porositerena i alla undersökta prover och förbättrade de mekaniska egenskaperna. Dessa resultat kommer kunna användas för att konstruera mer högpresterande komponenter.

Made available in DSpace on 2016-12-08T17:19:17Z (GMT). No. of bitstreams: 1 introducao 1.pdf: 60637 bytes, checksum: 290595bc9c94456b344557782acd7d97 (MD5) Previous issue date: 2012-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The properties of aluminum-silicon alloys are strongly dependent on the casting process used, the chemical additions made to control eutectic structure, primary silicon and grain structure, and molten metal treatment to reduce hydrogen gas content and to remove inclusions. Modification treatments transform the flake eutectic silicon into a fibrous form producing a structure with increased ultimate tensile strength, ductility, hardness, and machinability. Elements in groups I and II and the rare earths europium, lanthanum, cerium, praseodymium, and neodymium modify, but only sodium and strontium produce a strong modifying action at the low concentration required for commercial application. In this investigation, the effect of strontium concentration on the modification of the eutectic silicon in the 356 alloy was studied. For this porpoise the 356 alloy in as-cast and modified conditions using different Sr concentrations were examined. The results were accessed by tensile tests and metallographic examinations. As evaluated the effect of strontium in the formation temperature and the supercoiling of eutectic Al-Si through DTA. The results indicate that the Sr content of from 0 012% by weight resulted in total of Si modification with substantial increases in the toughness of the alloy 356, and supercoiling of 7.1 ° C temperature of the eutectic Al-Si. The indication of from 0.031% by weight mechanical properties, and temperature of the eutectic microstructure way similar to the alloys of the semi - modified but still higher than the same properties of the alloy without modification. / A resistência mecânica e a qualidade de ligas fundidas alumínio-silício são determinadas pela microestrutura e pela sanidade interna das peças fundidas. Tratamentos de refino de grão e de modificação do silício causam alterações microestruturais que resultam em melhorias nas propriedades mecânicas das ligas Al-Si de fundição. O tratamento de modificação altera a forma do silício do eutético da forma acicular para forma fibrosa interferindo sobre o comportamento mecânico da liga. Diversos tipos de modificadores são descritos na literatura, os mais utilizados são estrôncio e o sódio, pois apresentam efeitos de modificação adequados para as baixas concentrações requeridas. O estrôncio é o mais empregado em fundições, em função da maior facilidade no manuseio e uma maior resistência ao desvanecimento. Entretanto, adições de Sr estão associadas com a formação da porosidade em ligas modificadas. O principal objetivo deste estudo é avaliar a influência de diferentes percentuais de estrôncio sobre a morfologia e a distribuição das partículas de Si na matriz e os efeitos destas alterações sobre as propriedades mecânicas. Também foi avaliado o efeito do estrôncio na temperatura de formação e no superesfriamento do eutético Al-Si através de DTA. Os resultados obtidos indicam que teores de Sr a partir de 0, 012% em peso resultaram na modificação total do Si, com incrementos consideráveis na ductilidade da liga 356 e superesfriamento de 7,1 °C na temperatura do eutético Al-Si. Com valores a partir de 0,031% em peso as propriedades mecânicas, microestrutura e temperatura do eutético apresentavam semelhança com as das ligas semi-modificadas, porém superiores à condição sem modificação.