The evolution of microstructure and coefficient of thermal expansion (CTE) of the Al–50Si (wt.%) alloy manufactured by spray deposition followed by hot isostatic pressing (HIP) are systematically investigated. The results indicate that the microstructure of the deposited alloy is composed of primary Si with average size of 12.5 ± 0.1 μm and α-Al. The CTE of the deposited alloy is higher than the corresponding alloy produced by casting due to the high solid solubility of Al in Si. After HIP, the CTE is lower than the parent as-deposited alloy owing to the high solid solubility of Si in Al. The residual thermal stress results in a higher CTE during the second heating as a result of the CTE mismatch between the Al matrix and the primary Si particles. Furthermore, the measured CTE value is in good agreement with the Turner model after complete densification by HIP at 843 K. 相似文献
The effect of stirring of melt on the behaviour of double oxide film (bifilm) defects in A356 melt was investigated using a reduced pressure test (RPT) technique. The melt was poured from a height into a crucible to introduce bifilms into the melt. The melt was then either remained stagnant or mechanically stirred, and RPT samples were taken from the melt at 8 min intervals. The RPT samples were then characterised by determination of their porosity parameters and examination of the internal surfaces of the pores using a scanning electron microscope. The results showed that stirring of the melt facilitated the diffusion of H in the melt into the atmosphere of the defects and hence accelerated the removal of the defects from the melt by floatation. This effect was attributed to the increase in the stress induced to the defects, which increased the rate of formation of cracks on their layers. 相似文献
The intermetallic compounds of the Ni–Al, Cu–Al and Cr–Al systems are characterised by the profitable set of mechanical and physical properties, such as good abrasion resistance, high temperature oxidation and sulfur corrosion resistance.
Alloy powders, among them intermetallic powders, are widely used and methods of their production are under development. The technology described here takes advantage of a natural phenomenon, i.e. self-disintegration which takes place in alloys containing Al4C3 carbide, e.g. in high aluminium cast iron. The result of chemical reaction between this carbide and moisture are products of bigger volume. It causes cracking of the matrix, i.e. self-disintegration into a powder. The physical–chemical principles of the powder production using self-disintegration are presented in this article.
In Ni–Al–C, Cu–Al–C and Cr–Al–C alloys, Al4C3 phase is not present in the liquid melt. Therefore, the presence of a catalysing component, increasing the chemical activity of carbon, is required. Iron can be one of such additions. The mechanism of the influence of the iron on the Al4C3 carbide crystallisation and the physical–chemical properties of the powders obtained by the self-disintegration process is presented in this work. Applications (plasma spraying, powder metallurgy) of the intermetallic powders obtained in this way are mentioned. 相似文献
The adherend surface topography has a dramatic effect on the durability of structural bonds formed between aluminium and an epoxy adhesive. Systematic changes in the micro-roughness of an aluminium adherend were achieved using an ultra-milling technique to prepare surfaces with topographies ranging from ultra-flat to a sawtooth profile with a base angle of approximately 60° and a peak-to-valley depth of 10 μm. The fracture toughness of double-cantilever beam specimens, stressed in the Mode 1 direction and exposed to a humid environment was found to change by a factor of approximately one hundred as the sawtooth profile angle was increased. These changes in fracture toughness may be accounted for through complex interrelationships between moisture diffusion and interphase mechanical properties, each with a strong dependence on the surface micro-topography. 相似文献
In order to investigate the coupled effects of heat treatments and anodizing processes on fatigue life of aluminium alloy 2017A, a series of fatigue tests were conducted at 25 Hz. The effect of different tempers, naturally and artificially ageing (T4 and T6) and overageing (T7) conditions before sulphuric anodization were studied. Additionally, information on the microstructure of the anodic films was acquired by Scanning Electron Microscopy (SEM) analyses. The image analysis yielded qualitative information on the evolution of the surface morphology as a function of the substrate microstructure. Hence measured mechanical properties were directly related to the corresponding microstructure, the result of fatigue tests showed a decrease in fatigue life of anodized specimens as compared to untreated ones. This phenomenon became more pronounced in the T6 and T7 states. The decrease in the fatigue life could mainly be attributed to the brittle nature of oxide layer and to the heterogeneous microstructure of the film. 相似文献
A disadvantage of selective laser melting (SLM) processes for the manufacture of large parts is their slow build time per unit volume. A hybrid route is to generate core simple shapes traditionally, for example by machining, followed by adding final features by SLM. Here the mechanical integrity of such hybrid parts is studied, choosing the building of AlSi10Mg by SLM on a machined AA6082 base, in the shape of a tensile test piece, as a simple example. These materials are chosen for their relevance to lightweight parts. As-built parts fail at the SLM/machined interface but standard heat treatments transfer failures to the machined material. Optimised SLM processing conditions and microstructures of the SLM and interfacial regions are reported. 相似文献