1,720,961 research outputs found
Effect of surface roughness and eutectic segregation on anodising of Al-Si-Cu alloys
No full textTo study the influence of the surface roughness and eutectic silicon segregation on the anodising of diecast Al-Si-Cu alloys, an AlSi11Cu2(Fe) alloy was high-pressure diecast and hard anodised. The microstructure and surface topography of milled and grit-blasted regions were investigated to analyse their effect on the growth of the anodic layer. The surface mechanical properties of the anodised surfaces were also studied. The results showed how high surface roughness and silicon segregation present in the grit-blasted surface hindered the thickening of the oxide layer. After anodising, the milled surface exhibited better mechanical properties than the grit-blasted one. The wear resistance was enhanced by a thicker anodic layer, while the scratch resistance was positively affected by a lower surface roughness
The Influence of Sealing Processes and Machining Operations on the Scratch and Wear Resistance of Anodized AlSi9Cu3(Fe) Diecasting Alloy
Full text linkThe effects of hydrothermal and cold sealing processes on the scratch and wear resistance of the anodic layer have been studied. High-pressure diecast AlSi9Cu3(Fe) alloy plates were anodized in a sulfuric acid electrolyte at 16°C and further sealed in boiled water or in a NiF2 solution at 25°C. To analyze the influence of pre-anodizing machining operations, the plates were studied in the as-diecast condition and after milling. Metallographic investigations and image analysis techniques were carried out to study the morphology and thickness of the anodic layer. Hardness, wear, and scratch measurements were also performed to characterize the surface mechanical properties. The results showed that the sealing processes enhanced the wear and scratch resistance of the anodized surfaces because of the precipitation of hydrates that sealed the surface porosity. The thicker oxide layer formed on the milled substrate led to a greater wear resistance compared to the as-diecast surface, owing to reduced wear of the underlying aluminum substrate. Finally, a cracked mechanically mixed layer, which was enriched with fragmented intermetallics and anodic layer debris, was formed on the anodized surfaces at the end of the wear tests
Influence of T6 and T7 Heat Treatments on the Mechanical Properties of Rheocast Secondary AlSi7Cu3Mg Alloy
No full textThe effects of T6 and T7 heat treatmentsHeat treatment on the mechanical propertiesMechanical properties of a rheocast secondary AlSi7Cu3Mg alloyAlloys are investigated. A lower arm automotiveAutomotive suspension was cast as a demonstrator. While the solution treatment was optimized in previous research, the quenching rate and the ageing treatment were here studied. The influence of the quenching process on the component’s distortionDistortion was analysed by a coordinate-measuring technique. The results indicated a significant effect of the quenching rate on the tensile properties as well as the distortionDistortion of the component. Water quenching led to a greater distortionDistortion of the component compared to still-air cooling. The elongation to fractureFracture seemed to be less affected by the quenching process. Higher ductility was obtained after the over-ageing T7 treatment, while the yieldYield and tensile strengths were similar to those obtained after a peak ageing T6 treatment
Anodizing Al–Si Foundry Alloys: A Critical Review
Full text linkCompared with pure aluminum and wrought aluminum alloys, Al foundry alloys are more difficult to be anodized. The high content of alloying elements prevents the uniform growth of the Al oxide layer and enhances the embedding of defects in the anodic film. The microstructure of the substrate and the anodizing parameters play a key role in the final quality of the oxide layer. Variations in the chemical composition, casting process, and pre- and post-anodizing treatments can significantly affect the anodizing response. This work aims to critically review the main factors influencing the growth and morphology of the anodic layer in Al–Si foundry alloys. In particular, the effects on the oxide thickness, surface mechanical properties, and corrosion resistance are discussed in detail
Experimental and numerical investigations of oxide-related defects in Al alloy gravity die castings
Full text linkThis research aimed to study the formation and distribution of oxide-related defects in the gravity die casting process of an AlSi7Cu0.5Mg alloy by using experimental and numerical investigations. Metallographic and image analysis techniques were conducted to map the distribution of oxide inclusions inside the casting at the microscopic level. Numerical simulations were used to analyse the filling and solidification stages, and to foresee the turbulence of the melt and the formation of the oxide defects. The results show that most of the defects were correlated with the oxide layers or bubbles entrained inside the liquid metal. The accuracy of the numerical code in simulating the metal fluid-dynamic behaviour and the heat transfer was verified, and the results were in agreement with the experimental findings. The numerical distribution of defects was consistent with the experimental results, proving that the model successfully predicted the formation of oxide-related defects
The Influence of Surface Segregation on the Anodizing of AlSi11Cu2(Fe) Diecastings
Full text linkA positive segregation is usually formed on the casting surfaces produced by high-pressure die casting (HPDC). In diecast Al-Si-Cu alloy components, this segregation shows a higher content of Si compared to the nominal composition of the alloy and it drastically affects the anodizing response of the casting surface. In the present work, HPDC components were produced by AlSi11Cu2(Fe) alloy, grit-blasted, and then anodized in a sulfuric acid electrolyte at the temperature of-4.5°C. Before the anodizing process, some regions of the casting were also milled, in order to completely remove the surface segregation. Microstructural investigations were carried out on grit-blasted and milled surfaces to characterize the initial substrates before anodizing, and to study their effect on the growth of the anodic layer. Scratch and wear tests were also performed to investigate the surface mechanical properties after anodizing. The results show that the surface segregation and the rough surface present on grit-blasted substrate leads to the formation of a thin and homogeneous anodic layer. On the contrary, a thicker and scalloped oxide film is formed on the milled surfaces. After anodizing, grit-blasted surfaces show lower wear and scratch resistance than milled substrates. The presence of surface segregation prevents the thickening of the anodic layer, negatively affecting the surface wear resistance due to the reduced oxide thickness
Formation and distribution of entrainment defects in gravity AISi7Cu0.5Mg alloy castings
Full text linkIn this study, the formation of entrainment defects in gravity permanent mould casting process was experimentally and numerically investigated. The distribution of oxide inclusions was mapped at the microscopic scale using metallographic and image analysis techniques. A fluid-dynamic simulation commercial software was used to predict the formation of defects and air entrapment during the casting process. The results showed that the typical casting defects detected throughout the castings were generated by the entrainment of bifilms. Moreover, the good agreement between the numerical results and the experimental findings proved that the numerical models had successfully predicted the entrainment phenomena, especially the formation of oxide inclusions and the entrapment of air bubbles
Effects of Casting Temperature and Iron Content on the Microstructure of Hypoeutectic A380 Aluminium Alloy
No full textCasting temperature and iron content are among the most important factors in obtaining superior mechanical properties in hypoeutectic Al–Si alloys. An A380 aluminium alloy that is one of the most widespread alloys used in high-pressure diecasting was selected for examining different iron contents and casting temperatures. The alloy with contents of about 0.7 and 1.2 wt% Fe was cast at different temperatures in the range between 680 and 960 °C with 70 °C interval from each other. The outcome indicates that dendrite arm spacing does not change significantly at different cast temperatures or iron contents. From 820 °C in low-Fe containing alloy and from 890 °C in high-Fe containing alloy, the precipitation of harmful β-phase is suppressed. Moreover, blocky or Chinese script α-Fe compounds become the dominant phase throughout the microstructure. The results suggest A380 with lower Fe content at casting superheat of 100 °C would result in uniform microstructure and removal of detrimental β-phase
An Investigation on Wear Properties of A390 Alloy by Rare Alloying Elements
No full textHypereutectic Al–Si alloys are good candidates for many applications including automotive industry and heavy wear environments. Among them, A390 is widely used for cylinder blocks, transmission pumps, and air compressor housings. Due to high silicon content, primary and eutectic Si size and their morphologies have a significant effect on wear resistance of this alloy. In this research, the effect of Sr and Sb addition on the cast A390 alloy is examined and compared with unmodified alloy. Results suggest an enhanced wear resistance in Sb addition, whereas the Sr improved the wear resistance moderately compared with unmodified alloy. The involved mechanism (at nano and micro scales) and the microstructural evolution in each condition were analyzed and discussed
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